Typed flag classes

This reintroduces the non-generic flag classes:
 - a value() returns the primitive type for flags wrapping a primitive type
 - easier to use in testing
 - Serializer is moved to internals of typed class

Defines the flag backed by boolean BooleanFlag instead of FeatureFlag since not
all boolean flags are necessarily guarding a feature.

26 files changed, 513 insertions, 198 deletions

diff --git a/configserver/src/main/java/com/yahoo/vespa/config/server/application/Application.java b/configserver/src/main/java/com/yahoo/vespa/config/server/application/Application.java
index 2d5d5296762..2463cca190a 100644
--- a/configserver/src/main/java/com/yahoo/vespa/config/server/application/Application.java
+++ b/configserver/src/main/java/com/yahoo/vespa/config/server/application/Application.java
@@ -23,9 +23,9 @@ import com.yahoo.vespa.config.server.rpc.ConfigResponseFactory;
 import com.yahoo.vespa.config.server.rpc.UncompressedConfigResponseFactory;
 import com.yahoo.vespa.config.server.tenant.TenantRepository;
 import com.yahoo.vespa.config.util.ConfigUtils;
+import com.yahoo.vespa.flags.BooleanFlag;
 import com.yahoo.vespa.flags.FetchVector;
 import com.yahoo.vespa.flags.FileFlagSource;
-import com.yahoo.vespa.flags.Flag;
 import com.yahoo.vespa.flags.FlagSource;
 import com.yahoo.vespa.flags.Flags;
 
@@ -49,7 +49,7 @@ public class Application implements ModelResult {
     private final ServerCache cache;
     private final MetricUpdater metricUpdater;
     private final ApplicationId app;
-    private final Flag<Boolean> useConfigServerCache;
+    private final BooleanFlag useConfigServerCache;
 
     public Application(Model model, ServerCache cache, long appGeneration, boolean internalRedeploy,
                        Version vespaVersion, MetricUpdater metricUpdater, ApplicationId app) {
diff --git a/configserver/src/main/java/com/yahoo/vespa/config/server/http/flags/DefinedFlags.java b/configserver/src/main/java/com/yahoo/vespa/config/server/http/flags/DefinedFlags.java
index 9f0e39b7d43..6d5d0df8f1a 100644
--- a/configserver/src/main/java/com/yahoo/vespa/config/server/http/flags/DefinedFlags.java
+++ b/configserver/src/main/java/com/yahoo/vespa/config/server/http/flags/DefinedFlags.java
@@ -20,12 +20,12 @@ import java.util.List;
  */
 public class DefinedFlags extends HttpResponse {
     private static ObjectMapper mapper = new ObjectMapper();
-    private static final Comparator<FlagDefinition<?>> sortByFlagId =
+    private static final Comparator<FlagDefinition> sortByFlagId =
             (left, right) -> left.getUnboundFlag().id().compareTo(right.getUnboundFlag().id());
 
-    private final List<FlagDefinition<?>> flags;
+    private final List<FlagDefinition> flags;
 
-    public DefinedFlags(List<FlagDefinition<?>> flags) {
+    public DefinedFlags(List<FlagDefinition> flags) {
         super(Response.Status.OK);
         this.flags = flags;
     }
diff --git a/configserver/src/main/java/com/yahoo/vespa/config/server/http/flags/FlagsHandler.java b/configserver/src/main/java/com/yahoo/vespa/config/server/http/flags/FlagsHandler.java
index e64c356aa96..e5efc74fb75 100644
--- a/configserver/src/main/java/com/yahoo/vespa/config/server/http/flags/FlagsHandler.java
+++ b/configserver/src/main/java/com/yahoo/vespa/config/server/http/flags/FlagsHandler.java
@@ -6,13 +6,17 @@ import com.yahoo.container.jdisc.HttpRequest;
 import com.yahoo.container.jdisc.HttpResponse;
 import com.yahoo.container.jdisc.LoggingRequestHandler;
 import com.yahoo.restapi.Path;
+import com.yahoo.vespa.config.server.http.HttpErrorResponse;
 import com.yahoo.vespa.config.server.http.HttpHandler;
 import com.yahoo.vespa.config.server.http.NotFoundException;
 import com.yahoo.vespa.configserver.flags.FlagsDb;
+import com.yahoo.vespa.flags.FlagDefinition;
 import com.yahoo.vespa.flags.FlagId;
 import com.yahoo.vespa.flags.Flags;
 import com.yahoo.vespa.flags.json.FlagData;
+import com.yahoo.yolean.Exceptions;
 
+import java.io.UncheckedIOException;
 import java.net.URI;
 import java.util.Objects;
 
@@ -74,7 +78,19 @@ public class FlagsHandler extends HttpHandler {
     }
 
     private HttpResponse putFlagData(HttpRequest request, FlagId flagId) {
-        flagsDb.setValue(flagId, FlagData.deserialize(request.getData()));
+        FlagData data;
+        try {
+            data = FlagData.deserialize(request.getData());
+        } catch (UncheckedIOException e) {
+            return HttpErrorResponse.badRequest("Failed to deserialize request data: " + Exceptions.toMessageString(e));
+        }
+
+        if (!isForce(request)) {
+            FlagDefinition definition = Flags.getFlag(flagId).get(); // FlagId has been validated in findFlagId()
+            data.validate(definition.getUnboundFlag().serializer());
+        }
+
+        flagsDb.setValue(flagId, data);
         return new OKResponse();
     }
 
@@ -86,12 +102,15 @@ public class FlagsHandler extends HttpHandler {
     private FlagId findFlagId(HttpRequest request, Path path) {
         FlagId flagId = new FlagId(path.get("flagId"));
 
-        if (!Objects.equals(request.getProperty("force"), "true")) {
-            if (Flags.getAllFlags().stream().noneMatch(definition -> flagId.equals(definition.getUnboundFlag().id()))) {
-                throw new NotFoundException("There is no flag '" + flagId + "' (use ?force=true to override)");
-            }
+        if (!isForce(request)) {
+            Flags.getFlag(flagId).orElseThrow(() ->
+                    new NotFoundException("There is no flag '" + flagId + "' (use ?force=true to override)"));
         }
 
         return flagId;
     }
+
+    private boolean isForce(HttpRequest request) {
+        return Objects.equals(request.getProperty("force"), "true");
+    }
 }
diff --git a/configserver/src/test/java/com/yahoo/vespa/config/server/http/flags/FlagsHandlerTest.java b/configserver/src/test/java/com/yahoo/vespa/config/server/http/flags/FlagsHandlerTest.java
index 8781ec413d2..71caed77dbe 100644
--- a/configserver/src/test/java/com/yahoo/vespa/config/server/http/flags/FlagsHandlerTest.java
+++ b/configserver/src/test/java/com/yahoo/vespa/config/server/http/flags/FlagsHandlerTest.java
@@ -11,7 +11,7 @@ import com.yahoo.vespa.curator.mock.MockCurator;
 import com.yahoo.vespa.flags.FetchVector;
 import com.yahoo.vespa.flags.FlagId;
 import com.yahoo.vespa.flags.Flags;
-import com.yahoo.vespa.flags.UnboundFlag;
+import com.yahoo.vespa.flags.UnboundBooleanFlag;
 import org.junit.Test;
 
 import java.io.ByteArrayInputStream;
@@ -21,6 +21,7 @@ import java.util.stream.Stream;
 
 import static com.yahoo.yolean.Exceptions.uncheck;
 import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.is;
 import static org.junit.Assert.assertEquals;
 
@@ -28,11 +29,11 @@ import static org.junit.Assert.assertEquals;
  * @author hakonhall
  */
 public class FlagsHandlerTest {
-    private static final UnboundFlag<Boolean> FLAG1 =
-            Flags.defineBoolean("id1", false, "desc1", "mod1");
-    private static final UnboundFlag<Boolean> FLAG2 =
-            Flags.defineBoolean("id2", true, "desc2", "mod2",
-                    FetchVector.Dimension.HOSTNAME, FetchVector.Dimension.APPLICATION_ID);
+    private static final UnboundBooleanFlag FLAG1 = Flags.defineFeatureFlag(
+            "id1", false, "desc1", "mod1");
+    private static final UnboundBooleanFlag FLAG2 = Flags.defineFeatureFlag(
+            "id2", true, "desc2", "mod2",
+            FetchVector.Dimension.HOSTNAME, FetchVector.Dimension.APPLICATION_ID);
 
     private static final String FLAGS_V1_URL = "https://foo.com:4443/flags/v1";
 
@@ -54,7 +55,7 @@ public class FlagsHandlerTest {
     public void testDefined() {
         try (Flags.Replacer replacer = Flags.clearFlagsForTesting()) {
             fixUnusedWarning(replacer);
-            Flags.defineBoolean("id", false, "desc", "mod", FetchVector.Dimension.HOSTNAME);
+            Flags.defineFeatureFlag("id", false, "desc", "mod", FetchVector.Dimension.HOSTNAME);
             verifySuccessfulRequest(Method.GET, "/defined", "",
                     "{\"id\":{\"description\":\"desc\",\"modification-effect\":\"mod\",\"dimensions\":[\"hostname\"]}}");
         }
@@ -153,32 +154,33 @@ public class FlagsHandlerTest {
 
     @Test
     public void testForcing() {
-        FlagId undefinedFlagId = new FlagId("undef");
-        HttpResponse response = handle(Method.PUT, "/data/" + undefinedFlagId, "");
+        assertThat(handle(Method.PUT, "/data/" + new FlagId("undef"), "", 404),
+                containsString("There is no flag 'undef'"));
 
-        assertEquals(404, response.getStatus());
-        assertEquals("application/json", response.getContentType());
+        assertThat(handle(Method.PUT, "/data/" + new FlagId("undef") + "?force=true", "", 400),
+                containsString("No content to map due to end-of-input"));
 
-    }
+        assertThat(handle(Method.PUT, "/data/" + FLAG1.id(), "{}", 400),
+                containsString("Flag ID missing"));
 
-    private void verifySuccessfulRequest(Method method, String pathSuffix, String requestBody, String expectedResponseBody) {
-        HttpResponse response = handle(method, pathSuffix, requestBody);
+        assertThat(handle(Method.PUT, "/data/" + FLAG1.id(), "{\"id\": \"id1\",\"rules\": [{\"value\":\"string\"}]}", 400),
+                containsString("Wrong type of JsonNode: STRING"));
 
-        assertEquals(200, response.getStatus());
-        assertEquals("application/json", response.getContentType());
-        String actualResponse = uncheck(() -> SessionHandlerTest.getRenderedString(response));
+        assertThat(handle(Method.PUT, "/data/" + FLAG1.id() + "?force=true", "{\"id\": \"id1\",\"rules\": [{\"value\":\"string\"}]}", 200),
+                is(""));
+    }
 
-        assertThat(actualResponse, is(expectedResponseBody));
+    private void verifySuccessfulRequest(Method method, String pathSuffix, String requestBody, String expectedResponseBody) {
+        assertThat(handle(method, pathSuffix, requestBody, 200), is(expectedResponseBody));
     }
 
-    private HttpResponse handle(Method method, String pathSuffix, String requestBody) {
+    private String handle(Method method, String pathSuffix, String requestBody, int expectedStatus) {
         String uri = FLAGS_V1_URL + pathSuffix;
         HttpRequest request = HttpRequest.createTestRequest(uri, method, makeInputStream(requestBody));
-        return handler.handle(request);
-    }
-
-    private String makeUrl(String component) {
-        return FLAGS_V1_URL + "/" + component;
+        HttpResponse response = handler.handle(request);
+        assertEquals(expectedStatus, response.getStatus());
+        assertEquals("application/json", response.getContentType());
+        return uncheck(() -> SessionHandlerTest.getRenderedString(response));
     }
 
     private InputStream makeInputStream(String content) {
diff --git a/flags/src/main/java/com/yahoo/vespa/flags/BooleanFlag.java b/flags/src/main/java/com/yahoo/vespa/flags/BooleanFlag.java
new file mode 100644
index 00000000000..1245aca65b8
--- /dev/null
+++ b/flags/src/main/java/com/yahoo/vespa/flags/BooleanFlag.java
@@ -0,0 +1,18 @@
+// Copyright 2019 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.vespa.flags;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * @author hakonhall
+ */
+@Immutable
+public class BooleanFlag extends FlagImpl<Boolean, BooleanFlag> {
+    public BooleanFlag(FlagId id, boolean defaultValue, FetchVector vector, FlagSerializer<Boolean> serializer, FlagSource source) {
+        super(id, defaultValue, vector, serializer, source, BooleanFlag::new);
+    }
+
+    public boolean value() {
+        return boxedValue();
+    }
+}
diff --git a/flags/src/main/java/com/yahoo/vespa/flags/Flag.java b/flags/src/main/java/com/yahoo/vespa/flags/Flag.java
index 18c1db0d756..7bf491a39c7 100644
--- a/flags/src/main/java/com/yahoo/vespa/flags/Flag.java
+++ b/flags/src/main/java/com/yahoo/vespa/flags/Flag.java
@@ -1,44 +1,23 @@
 // Copyright 2018 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package com.yahoo.vespa.flags;
 
-import javax.annotation.concurrent.Immutable;
-
 /**
+ * Interface for flag.
+ *
+ * @param <T> The type of the flag value (boxed for primitives)
+ * @param <F> The concrete subclass type of the flag
  * @author hakonhall
  */
-@Immutable
-public class Flag<T> {
-    private final FlagId id;
-    private final T defaultValue;
-    private final FlagSource source;
-    private final Deserializer<T> deserializer;
-    private final FetchVector fetchVector;
-
-    public Flag(String flagId, T defaultValue, FlagSource source, Deserializer<T> deserializer) {
-        this(new FlagId(flagId), defaultValue, source, deserializer);
-    }
-
-    public Flag(FlagId id, T defaultValue, FlagSource source, Deserializer<T> deserializer) {
-        this(id, defaultValue, deserializer, new FetchVector(), source);
-    }
-
-    public Flag(FlagId id, T defaultValue, Deserializer<T> deserializer, FetchVector fetchVector, FlagSource source) {
-        this.id = id;
-        this.defaultValue = defaultValue;
-        this.source = source;
-        this.deserializer = deserializer;
-        this.fetchVector = fetchVector;
-    }
+public interface Flag<T, F> {
+    /** The flag ID. */
+    FlagId id();
 
-    public FlagId id() {
-        return id;
-    }
+    /** Returns the flag serializer. */
+    FlagSerializer<T> serializer();
 
-    public Flag<T> with(FetchVector.Dimension dimension, String value) {
-        return new Flag<>(id, defaultValue, deserializer, fetchVector.with(dimension, value), source);
-    }
+    /** Returns an immutable clone of the current object, except with the dimension set accordingly. */
+    F with(FetchVector.Dimension dimension, String dimensionValue);
 
-    public T value() {
-        return source.fetch(id, fetchVector).map(deserializer::deserialize).orElse(defaultValue);
-    }
+    /** Returns the value, boxed if the flag wraps a primitive type. */
+    T boxedValue();
 }
diff --git a/flags/src/main/java/com/yahoo/vespa/flags/FlagDefinition.java b/flags/src/main/java/com/yahoo/vespa/flags/FlagDefinition.java
index a3f490e2f96..0dce61cf0bb 100644
--- a/flags/src/main/java/com/yahoo/vespa/flags/FlagDefinition.java
+++ b/flags/src/main/java/com/yahoo/vespa/flags/FlagDefinition.java
@@ -1,7 +1,8 @@
-// Copyright 2018 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+// Copyright 2019 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package com.yahoo.vespa.flags;
 
 import javax.annotation.concurrent.Immutable;
+import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
 
@@ -9,21 +10,21 @@ import java.util.List;
  * @author hakonhall
  */
 @Immutable
-public class FlagDefinition<T> {
-    private final UnboundFlag<T> unboundFlag;
+public class FlagDefinition {
+    private final UnboundFlag<?, ?, ?> unboundFlag;
     private final String description;
     private final String modificationEffect;
     private final List<FetchVector.Dimension> dimensions;
 
-    public FlagDefinition(UnboundFlag<T> unboundFlag, String description, String modificationEffect,
-                          List<FetchVector.Dimension> dimensions) {
+    public FlagDefinition(UnboundFlag<?, ?, ?> unboundFlag, String description, String modificationEffect,
+                          FetchVector.Dimension... dimensions) {
         this.unboundFlag = unboundFlag;
         this.description = description;
         this.modificationEffect = modificationEffect;
-        this.dimensions = Collections.unmodifiableList(dimensions);
+        this.dimensions = Collections.unmodifiableList(Arrays.asList(dimensions));
     }
 
-    public UnboundFlag<T> getUnboundFlag() {
+    public UnboundFlag<?, ?, ?> getUnboundFlag() {
         return unboundFlag;
     }
 
diff --git a/flags/src/main/java/com/yahoo/vespa/flags/FlagImpl.java b/flags/src/main/java/com/yahoo/vespa/flags/FlagImpl.java
new file mode 100644
index 00000000000..79da03e4982
--- /dev/null
+++ b/flags/src/main/java/com/yahoo/vespa/flags/FlagImpl.java
@@ -0,0 +1,47 @@
+// Copyright 2019 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.vespa.flags;
+
+/**
+ * @author hakonhall
+ */
+public abstract class FlagImpl<T, F extends FlagImpl<T, F>> implements Flag<T, F> {
+    private final FlagId id;
+    private final T defaultValue;
+    private final FlagSerializer<T> serializer;
+    private final FetchVector fetchVector;
+    private final UnboundFlagImpl.FlagFactory<T, F> factory;
+    private final FlagSource source;
+
+    protected FlagImpl(FlagId id,
+                       T defaultValue,
+                       FetchVector fetchVector, FlagSerializer<T> serializer,
+                       FlagSource source,
+                       UnboundFlagImpl.FlagFactory<T, F> factory) {
+        this.id = id;
+        this.defaultValue = defaultValue;
+        this.serializer = serializer;
+        this.fetchVector = fetchVector;
+        this.factory = factory;
+        this.source = source;
+    }
+
+    @Override
+    public FlagId id() {
+        return id;
+    }
+
+    @Override
+    public F with(FetchVector.Dimension dimension, String dimensionValue) {
+        return factory.create(id, defaultValue, fetchVector.with(dimension, dimensionValue), serializer, source);
+    }
+
+    @Override
+    public T boxedValue() {
+        return source.fetch(id, fetchVector).map(serializer::deserialize).orElse(defaultValue);
+    }
+
+    @Override
+    public FlagSerializer<T> serializer() {
+        return serializer;
+    }
+}
diff --git a/flags/src/main/java/com/yahoo/vespa/flags/Flags.java b/flags/src/main/java/com/yahoo/vespa/flags/Flags.java
index 50cb5ffdf7c..50f65e5ce13 100644
--- a/flags/src/main/java/com/yahoo/vespa/flags/Flags.java
+++ b/flags/src/main/java/com/yahoo/vespa/flags/Flags.java
@@ -1,53 +1,33 @@
-// Copyright 2018 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+// Copyright 2019 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package com.yahoo.vespa.flags;
 
-import com.fasterxml.jackson.databind.JsonNode;
-import com.fasterxml.jackson.databind.node.BooleanNode;
-import com.fasterxml.jackson.databind.node.IntNode;
-import com.fasterxml.jackson.databind.node.LongNode;
-import com.fasterxml.jackson.databind.node.TextNode;
 import com.yahoo.vespa.defaults.Defaults;
 
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.List;
 import java.util.Optional;
 import java.util.concurrent.ConcurrentHashMap;
 
 /**
- * Definitions of most/all flags.
- *
- * <p>The flags are centrally defined in this module to allow 1. all code to access flags that may be used in
- * quite different modules and processes, and 2. in particular allow the config server to access all flags
- * so operators have a nicer UI for setting, modifying, or removing flag values.
- *
- * <p>This class should have been an enum, but unfortunately enums cannot be generic, which will eventually be
- * fixed with <a href="https://openjdk.java.net/jeps/301">JEP 301: Enhanced Enums</a>.
- *
  * @author hakonhall
  */
 public class Flags {
-    public static final FlagSerializer<Boolean> BOOLEAN_SERIALIZER = new SimpleFlagSerializer<>(BooleanNode::valueOf, JsonNode::isBoolean, JsonNode::asBoolean);
-    public static final FlagSerializer<String> STRING_SERIALIZER = new SimpleFlagSerializer<>(TextNode::new, JsonNode::isTextual, JsonNode::asText);
-    public static final FlagSerializer<Integer> INT_SERIALIZER = new SimpleFlagSerializer<>(IntNode::new, JsonNode::isIntegralNumber, JsonNode::asInt);
-    public static final FlagSerializer<Long> LONG_SERIALIZER = new SimpleFlagSerializer<>(LongNode::new, JsonNode::isIntegralNumber, JsonNode::asLong);
+    private static volatile ConcurrentHashMap<FlagId, FlagDefinition> flags = new ConcurrentHashMap<>();
 
-    private static volatile ConcurrentHashMap<FlagId, FlagDefinition<?>> flags = new ConcurrentHashMap<>();
-
-    public static final UnboundFlag<Boolean> HEALTHMONITOR_MONITOR_INFRA = defineBoolean(
+    public static final UnboundBooleanFlag HEALTHMONITOR_MONITOR_INFRA = defineFeatureFlag(
             "healthmonitor-monitorinfra", true,
-            "Whether the health monitor in service monitor monitors the health of infrastructure applications.",
-            "Affects all applications activated after the value is changed.",
+                    "Whether the health monitor in service monitor monitors the health of infrastructure applications.",
+                    "Affects all applications activated after the value is changed.",
             FetchVector.Dimension.HOSTNAME);
 
-    public static final UnboundFlag<Boolean> DUPERMODEL_CONTAINS_INFRA = defineBoolean(
+    public static final UnboundBooleanFlag DUPERMODEL_CONTAINS_INFRA = defineFeatureFlag(
             "dupermodel-contains-infra", true,
             "Whether the DuperModel in config server/controller includes active infrastructure applications " +
                     "(except from controller/config apps).",
             "Requires restart of config server/controller to take effect.",
             FetchVector.Dimension.HOSTNAME);
 
-    public static final UnboundFlag<Boolean> DUPERMODEL_USE_CONFIGSERVERCONFIG = defineBoolean(
+    public static final UnboundBooleanFlag DUPERMODEL_USE_CONFIGSERVERCONFIG = defineFeatureFlag(
             "dupermodel-use-configserverconfig", true,
             "For historical reasons, the ApplicationInfo in the DuperModel for controllers and config servers " +
                     "is based on the ConfigserverConfig (this flag is true). We want to transition to use the " +
@@ -55,75 +35,86 @@ public class Flags {
             "Requires restart of config server/controller to take effect.",
             FetchVector.Dimension.HOSTNAME);
 
-    public static final UnboundFlag<Boolean> USE_CONFIG_SERVER_CACHE = defineBoolean(
+    public static final UnboundBooleanFlag USE_CONFIG_SERVER_CACHE = defineFeatureFlag(
             "use-config-server-cache", true,
             "Whether config server will use cache to answer config requests.",
             "Takes effect immediately when changed.",
             FetchVector.Dimension.HOSTNAME, FetchVector.Dimension.APPLICATION_ID);
 
-    public static final UnboundFlag<Boolean> CONFIG_SERVER_BOOTSTRAP_IN_SEPARATE_THREAD = defineBoolean(
+    public static final UnboundBooleanFlag CONFIG_SERVER_BOOTSTRAP_IN_SEPARATE_THREAD = defineFeatureFlag(
             "config-server-bootstrap-in-separate-thread", true,
             "Whether to run config server/controller bootstrap in a separate thread.",
             "Takes effect only at bootstrap of config server/controller",
             FetchVector.Dimension.HOSTNAME);
 
-    public static final UnboundFlag<Boolean> PROXYHOST_USES_REAL_ORCHESTRATOR = defineBoolean(
+    public static final UnboundBooleanFlag PROXYHOST_USES_REAL_ORCHESTRATOR = defineFeatureFlag(
             "proxyhost-uses-real-orchestrator", true,
             "Whether proxy hosts uses the real Orchestrator when suspending/resuming, or a synthetic.",
             "Takes effect immediately when changed.",
             FetchVector.Dimension.HOSTNAME);
 
-    public static final UnboundFlag<Boolean> CONFIGHOST_USES_REAL_ORCHESTRATOR = defineBoolean(
+    public static final UnboundBooleanFlag CONFIGHOST_USES_REAL_ORCHESTRATOR = defineFeatureFlag(
             "confighost-uses-real-orchestrator", false,
             "Whether the config server hosts uses the real Orchestrator when suspending/resuming, or a synthetic.",
             "Takes effect immediately when changed.",
             FetchVector.Dimension.HOSTNAME);
 
-    public static final UnboundFlag<Boolean> ENABLE_DOCKER_1_13 = defineBoolean(
+    public static final UnboundBooleanFlag ENABLE_DOCKER_1_13 = defineFeatureFlag(
             "enable-docker-1.13", true,
             "Whether to upgrade to Docker version 1.13.",
             "Takes effect on next host admin tick.",
             FetchVector.Dimension.HOSTNAME);
 
-    public static final UnboundFlag<Boolean> ENABLE_CROWDSTRIKE = defineBoolean(
+    public static final UnboundBooleanFlag ENABLE_CROWDSTRIKE = defineFeatureFlag(
             "enable-crowdstrike", true,
             "Whether to enable CrowdStrike.", "Takes effect on next host admin tick");
 
-    public static final UnboundFlag<Boolean> ENABLE_NESSUS = defineBoolean(
+    public static final UnboundBooleanFlag ENABLE_NESSUS = defineFeatureFlag(
             "enable-nessus", true,
             "Whether to enable Nessus.", "Takes effect on next host admin tick");
 
-    public static UnboundFlag<Boolean> defineBoolean(String flagId, boolean defaultValue, String description,
+    /** WARNING: public for testing: All flags should be defined in {@link Flags}. */
+    public static UnboundBooleanFlag defineFeatureFlag(String flagId, boolean defaultValue, String description,
+                                                       String modificationEffect, FetchVector.Dimension... dimensions) {
+        return define(UnboundBooleanFlag::new, flagId, defaultValue, description, modificationEffect, dimensions);
+    }
+
+    /** WARNING: public for testing: All flags should be defined in {@link Flags}. */
+    public static UnboundStringFlag defineStringFlag(String flagId, String defaultValue, String description,
                                                      String modificationEffect, FetchVector.Dimension... dimensions) {
-        return define(flagId, defaultValue, BOOLEAN_SERIALIZER, description, modificationEffect, dimensions);
+        return define(UnboundStringFlag::new, flagId, defaultValue, description, modificationEffect, dimensions);
     }
 
-    public static UnboundFlag<String> defineString(String flagId, String defaultValue, String description,
-                                                   String modificationEffect, FetchVector.Dimension... dimensions) {
-        return define(flagId, defaultValue, STRING_SERIALIZER, description, modificationEffect, dimensions);
+    /** WARNING: public for testing: All flags should be defined in {@link Flags}. */
+    public static UnboundIntFlag defineIntFlag(String flagId, int defaultValue, String description,
+                                               String modificationEffect, FetchVector.Dimension... dimensions) {
+        return define(UnboundIntFlag::new, flagId, defaultValue, description, modificationEffect, dimensions);
     }
 
-    public static UnboundFlag<Integer> defineInt(String flagId, Integer defaultValue, String description,
+    /** WARNING: public for testing: All flags should be defined in {@link Flags}. */
+    public static UnboundLongFlag defineLongFlag(String flagId, long defaultValue, String description,
                                                  String modificationEffect, FetchVector.Dimension... dimensions) {
-        return define(flagId, defaultValue, INT_SERIALIZER, description, modificationEffect, dimensions);
+        return define(UnboundLongFlag::new, flagId, defaultValue, description, modificationEffect, dimensions);
     }
 
-    public static UnboundFlag<Long> defineLong(String flagId, Long defaultValue, String description,
-                                               String modificationEffect, FetchVector.Dimension... dimensions) {
-        return define(flagId, defaultValue, LONG_SERIALIZER, description, modificationEffect, dimensions);
+    /** WARNING: public for testing: All flags should be defined in {@link Flags}. */
+    public static <T> UnboundJacksonFlag<T> defineJacksonFlag(String flagId, T defaultValue, Class<T> jacksonClass, String description,
+                                                              String modificationEffect, FetchVector.Dimension... dimensions) {
+        return define((id2, defaultValue2, vector2) -> new UnboundJacksonFlag<>(id2, defaultValue2, vector2, jacksonClass),
+                flagId, defaultValue, description, modificationEffect, dimensions);
     }
 
-    public static <T> UnboundFlag<T> defineJackson(String flagId, Class<T> jacksonClass, T defaultValue, String description,
-                                                   String modificationEffect, FetchVector.Dimension... dimensions) {
-        return define(flagId, defaultValue, new JacksonSerializer<>(jacksonClass), description, modificationEffect, dimensions);
+    @FunctionalInterface
+    private interface TypedUnboundFlagFactory<T, U extends UnboundFlag<?, ?, ?>> {
+        U create(FlagId id, T defaultVale, FetchVector defaultFetchVector);
     }
 
     /**
      * Defines a Flag.
      *
+     * @param factory            Factory for creating unbound flag of type U
      * @param flagId             The globally unique FlagId.
      * @param defaultValue       The default value if none is present after resolution.
-     * @param deserializer       Deserialize JSON to value type.
      * @param description        Description of how the flag is used.
      * @param modificationEffect What is required for the flag to take effect? A restart of process? immediately? etc.
      * @param dimensions         What dimensions will be set in the {@link FetchVector} when fetching
@@ -132,34 +123,46 @@ public class Flags {
      *                           For instance, if APPLICATION is one of the dimensions here, you should make sure
      *                           APPLICATION is set to the ApplicationId in the fetch vector when fetching the RawFlag
      *                           from the FlagSource.
-     * @param <T>                The type of the flag value, typically Boolean for flags guarding features.
+     * @param <T>                The boxed type of the flag value, e.g. Boolean for flags guarding features.
+     * @param <U>                The type of the unbound flag, e.g. UnboundBooleanFlag.
      * @return An unbound flag with {@link FetchVector.Dimension#HOSTNAME HOSTNAME} environment. The ZONE environment
      *         is typically implicit.
      */
-    private static <T> UnboundFlag<T> define(String flagId, T defaultValue, Deserializer<T> deserializer,
-                                             String description, String modificationEffect,
-                                             FetchVector.Dimension... dimensions) {
-        UnboundFlag<T> flag = new UnboundFlag<>(flagId, defaultValue, deserializer)
-                .with(FetchVector.Dimension.HOSTNAME, Defaults.getDefaults().vespaHostname());
-        FlagDefinition<T> definition = new FlagDefinition<>(flag, description, modificationEffect, Arrays.asList(dimensions));
-        flags.put(flag.id(), definition);
-        return flag;
+    private static <T, U extends UnboundFlag<?, ?, ?>> U define(TypedUnboundFlagFactory<T, U> factory,
+                                                                String flagId,
+                                                                T defaultValue,
+                                                                String description,
+                                                                String modificationEffect,
+                                                                FetchVector.Dimension[] dimensions) {
+        FlagId id = new FlagId(flagId);
+        FetchVector vector = new FetchVector().with(FetchVector.Dimension.HOSTNAME, Defaults.getDefaults().vespaHostname());
+        U unboundFlag = factory.create(id, defaultValue, vector);
+        FlagDefinition definition = new FlagDefinition(unboundFlag, description, modificationEffect, dimensions);
+        flags.put(id, definition);
+        return unboundFlag;
     }
 
-    public static List<FlagDefinition<?>> getAllFlags() {
+    public static List<FlagDefinition> getAllFlags() {
         return new ArrayList<>(flags.values());
     }
 
-    public static Optional<FlagDefinition<?>> getFlag(FlagId flagId) {
+    public static Optional<FlagDefinition> getFlag(FlagId flagId) {
         return Optional.ofNullable(flags.get(flagId));
     }
 
+    /**
+     * Allows the statically defined flags to be controlled in a test.
+     *
+     * <p>Returns a Replacer instance to be used with e.g. a try-with-resources block. Within the block,
+     * the flags starts out as cleared. Flags can be defined, etc. When leaving the block, the flags from
+     * before the block is reinserted.
+     * */
     public static Replacer clearFlagsForTesting() {
         return new Replacer();
     }
 
     public static class Replacer implements AutoCloseable {
-        private final ConcurrentHashMap<FlagId, FlagDefinition<?>> savedFlags;
+        private final ConcurrentHashMap<FlagId, FlagDefinition> savedFlags;
 
         private Replacer() {
             this.savedFlags = Flags.flags;
diff --git a/flags/src/main/java/com/yahoo/vespa/flags/IntFlag.java b/flags/src/main/java/com/yahoo/vespa/flags/IntFlag.java
new file mode 100644
index 00000000000..4a59c34e8d0
--- /dev/null
+++ b/flags/src/main/java/com/yahoo/vespa/flags/IntFlag.java
@@ -0,0 +1,18 @@
+// Copyright 2019 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.vespa.flags;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * @author hakonhall
+ */
+@Immutable
+public class IntFlag extends FlagImpl<Integer, IntFlag> {
+    public IntFlag(FlagId id, int defaultValue, FetchVector vector, FlagSerializer<Integer> serializer, FlagSource source) {
+        super(id, defaultValue, vector, serializer, source, IntFlag::new);
+    }
+
+    public int value() {
+        return boxedValue();
+    }
+}
diff --git a/flags/src/main/java/com/yahoo/vespa/flags/JacksonFlag.java b/flags/src/main/java/com/yahoo/vespa/flags/JacksonFlag.java
new file mode 100644
index 00000000000..e4afbd231a1
--- /dev/null
+++ b/flags/src/main/java/com/yahoo/vespa/flags/JacksonFlag.java
@@ -0,0 +1,18 @@
+// Copyright 2019 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.vespa.flags;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * @author hakonhall
+ */
+@Immutable
+public class JacksonFlag<T> extends FlagImpl<T, JacksonFlag<T>> {
+    public JacksonFlag(FlagId id, T defaultValue, FetchVector vector, FlagSerializer<T> serializer, FlagSource source) {
+        super(id, defaultValue, vector, serializer, source, JacksonFlag::new);
+    }
+
+    public T value() {
+        return boxedValue();
+    }
+}
diff --git a/flags/src/main/java/com/yahoo/vespa/flags/LongFlag.java b/flags/src/main/java/com/yahoo/vespa/flags/LongFlag.java
new file mode 100644
index 00000000000..8a1707c9e6a
--- /dev/null
+++ b/flags/src/main/java/com/yahoo/vespa/flags/LongFlag.java
@@ -0,0 +1,18 @@
+// Copyright 2019 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.vespa.flags;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * @author hakonhall
+ */
+@Immutable
+public class LongFlag extends FlagImpl<Long, LongFlag> {
+    public LongFlag(FlagId id, Long defaultValue, FetchVector vector, FlagSerializer<Long> serializer, FlagSource source) {
+        super(id, defaultValue, vector, serializer, source, LongFlag::new);
+    }
+
+    public long value() {
+        return boxedValue();
+    }
+}
diff --git a/flags/src/main/java/com/yahoo/vespa/flags/OrderedFlagSource.java b/flags/src/main/java/com/yahoo/vespa/flags/OrderedFlagSource.java
index 6ca74715999..1c6e113f489 100644
--- a/flags/src/main/java/com/yahoo/vespa/flags/OrderedFlagSource.java
+++ b/flags/src/main/java/com/yahoo/vespa/flags/OrderedFlagSource.java
@@ -15,7 +15,6 @@ public class OrderedFlagSource implements FlagSource {
     private final List<FlagSource> sources;
 
     /**
-     *
      * @param sources Flag sources in descending priority order.
      */
     public OrderedFlagSource(FlagSource... sources) {
diff --git a/flags/src/main/java/com/yahoo/vespa/flags/StringFlag.java b/flags/src/main/java/com/yahoo/vespa/flags/StringFlag.java
new file mode 100644
index 00000000000..925af130b95
--- /dev/null
+++ b/flags/src/main/java/com/yahoo/vespa/flags/StringFlag.java
@@ -0,0 +1,18 @@
+// Copyright 2019 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.vespa.flags;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * @author hakonhall
+ */
+@Immutable
+public class StringFlag extends FlagImpl<String, StringFlag> {
+    public StringFlag(FlagId id, String defaultValue, FetchVector vector, FlagSerializer<String> serializer, FlagSource source) {
+        super(id, defaultValue, vector, serializer, source, StringFlag::new);
+    }
+
+    public String value() {
+        return boxedValue();
+    }
+}
diff --git a/flags/src/main/java/com/yahoo/vespa/flags/UnboundBooleanFlag.java b/flags/src/main/java/com/yahoo/vespa/flags/UnboundBooleanFlag.java
new file mode 100644
index 00000000000..c228364434c
--- /dev/null
+++ b/flags/src/main/java/com/yahoo/vespa/flags/UnboundBooleanFlag.java
@@ -0,0 +1,27 @@
+// Copyright 2019 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.vespa.flags;
+
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.node.BooleanNode;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * @author hakonhall
+ */
+@Immutable
+public class UnboundBooleanFlag extends UnboundFlagImpl<Boolean, BooleanFlag, UnboundBooleanFlag> {
+    public UnboundBooleanFlag(FlagId id) {
+        this(id, false);
+    }
+
+    public UnboundBooleanFlag(FlagId id, boolean defaultValue) {
+        this(id, defaultValue, new FetchVector());
+    }
+
+    public UnboundBooleanFlag(FlagId id, boolean defaultValue, FetchVector defaultFetchVector) {
+        super(id, defaultValue, defaultFetchVector,
+                new SimpleFlagSerializer<>(BooleanNode::valueOf, JsonNode::isBoolean, JsonNode::asBoolean),
+                UnboundBooleanFlag::new, BooleanFlag::new);
+    }
+}
diff --git a/flags/src/main/java/com/yahoo/vespa/flags/UnboundFlag.java b/flags/src/main/java/com/yahoo/vespa/flags/UnboundFlag.java
index 597e19080ab..28307536233 100644
--- a/flags/src/main/java/com/yahoo/vespa/flags/UnboundFlag.java
+++ b/flags/src/main/java/com/yahoo/vespa/flags/UnboundFlag.java
@@ -1,38 +1,27 @@
-// Copyright 2018 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+// Copyright 2019 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package com.yahoo.vespa.flags;
 
-import javax.annotation.concurrent.Immutable;
-
 /**
  * @author hakonhall
  */
-@Immutable
-public class UnboundFlag<T> {
-    private final FlagId id;
-    private final T defaultValue;
-    private final Deserializer<T> deserializer;
-    private final FetchVector fetchVector;
-
-    public UnboundFlag(String flagId, T defaultValue, Deserializer<T> deserializer) {
-        this(new FlagId(flagId), defaultValue, deserializer, new FetchVector());
-    }
 
-    public UnboundFlag(FlagId id, T defaultValue, Deserializer<T> deserializer, FetchVector fetchVector) {
-        this.id = id;
-        this.defaultValue = defaultValue;
-        this.deserializer = deserializer;
-        this.fetchVector = fetchVector;
-    }
+/**
+ * Interface of an unbound flag.
+ *
+ * @param <T> Type of boxed value, e.g. Integer
+ * @param <F> Type of flag, e.g. IntFlag
+ * @param <U> Type of unbound flag, e.g. UnboundIntFlag
+ */
+public interface UnboundFlag<T, F extends Flag<T, F>, U extends UnboundFlag<T, F, U>> {
+    /** The flag ID. */
+    FlagId id();
 
-    public FlagId id() {
-        return id;
-    }
+    /** Returns the flag serializer. */
+    FlagSerializer<T> serializer();
 
-    public UnboundFlag<T> with(FetchVector.Dimension dimension, String value) {
-        return new UnboundFlag<>(id, defaultValue, deserializer, fetchVector.with(dimension, value));
-    }
+    /** Returns a clone of the unbound flag, but with the dimension set accordingly. */
+    U with(FetchVector.Dimension dimension, String dimensionValue);
 
-    public Flag<T> bindTo(FlagSource source) {
-        return new Flag<>(id, defaultValue, deserializer, fetchVector, source);
-    }
+    /** Binds to a flag source, returning a (bound) flag. */
+    F bindTo(FlagSource source);
 }
diff --git a/flags/src/main/java/com/yahoo/vespa/flags/UnboundFlagImpl.java b/flags/src/main/java/com/yahoo/vespa/flags/UnboundFlagImpl.java
new file mode 100644
index 00000000000..513712d8753
--- /dev/null
+++ b/flags/src/main/java/com/yahoo/vespa/flags/UnboundFlagImpl.java
@@ -0,0 +1,58 @@
+// Copyright 2019 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.vespa.flags;
+
+/**
+ * @author hakonhall
+ */
+public abstract class UnboundFlagImpl<T, F extends Flag<T, F>, U extends UnboundFlag<T, F, U>>
+        implements UnboundFlag<T, F, U> {
+
+    private final FlagId id;
+    private final T defaultValue;
+    private final FlagSerializer<T> serializer;
+    private final FetchVector defaultFetchVector;
+    private final UnboundFlagFactory<T, F, U> unboundFlagFactory;
+    private final FlagFactory<T, F> flagFactory;
+
+    public interface UnboundFlagFactory<T1, F1 extends Flag<T1, F1>, U1 extends UnboundFlag<T1, F1, U1>> {
+        U1 create(FlagId id, T1 defaultValue, FetchVector fetchVector);
+    }
+
+    public interface FlagFactory<T2, F2 extends Flag<T2, F2>> {
+        F2 create(FlagId id, T2 defaultValue, FetchVector fetchVector, FlagSerializer<T2> serializer, FlagSource source);
+    }
+
+    protected UnboundFlagImpl(FlagId id,
+                              T defaultValue,
+                              FetchVector defaultFetchVector,
+                              FlagSerializer<T> serializer,
+                              UnboundFlagFactory<T, F, U> unboundFlagFactory,
+                              FlagFactory<T, F> flagFactory) {
+        this.id = id;
+        this.defaultValue = defaultValue;
+        this.serializer = serializer;
+        this.defaultFetchVector = defaultFetchVector;
+        this.unboundFlagFactory = unboundFlagFactory;
+        this.flagFactory = flagFactory;
+    }
+
+    @Override
+    public FlagId id() {
+        return id;
+    }
+
+    @Override
+    public U with(FetchVector.Dimension dimension, String dimensionValue) {
+        return unboundFlagFactory.create(id, defaultValue, defaultFetchVector.with(dimension, dimensionValue));
+    }
+
+    @Override
+    public F bindTo(FlagSource source) {
+        return flagFactory.create(id, defaultValue, defaultFetchVector, serializer, source);
+    }
+
+    @Override
+    public FlagSerializer<T> serializer() {
+        return serializer;
+    }
+}
diff --git a/flags/src/main/java/com/yahoo/vespa/flags/UnboundIntFlag.java b/flags/src/main/java/com/yahoo/vespa/flags/UnboundIntFlag.java
new file mode 100644
index 00000000000..01b660fe625
--- /dev/null
+++ b/flags/src/main/java/com/yahoo/vespa/flags/UnboundIntFlag.java
@@ -0,0 +1,23 @@
+// Copyright 2019 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.vespa.flags;
+
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.node.IntNode;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * @author hakonhall
+ */
+@Immutable
+public class UnboundIntFlag extends UnboundFlagImpl<Integer, IntFlag, UnboundIntFlag> {
+    public UnboundIntFlag(FlagId id, int defaultValue) {
+        this(id, defaultValue, new FetchVector());
+    }
+
+    public UnboundIntFlag(FlagId id, int defaultValue, FetchVector defaultFetchVector) {
+        super(id, defaultValue, defaultFetchVector,
+                new SimpleFlagSerializer<>(IntNode::new, JsonNode::isIntegralNumber, JsonNode::asInt),
+                UnboundIntFlag::new, IntFlag::new);
+    }
+}
diff --git a/flags/src/main/java/com/yahoo/vespa/flags/UnboundJacksonFlag.java b/flags/src/main/java/com/yahoo/vespa/flags/UnboundJacksonFlag.java
new file mode 100644
index 00000000000..1cd303d1ede
--- /dev/null
+++ b/flags/src/main/java/com/yahoo/vespa/flags/UnboundJacksonFlag.java
@@ -0,0 +1,21 @@
+// Copyright 2019 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.vespa.flags;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * @author hakonhall
+ */
+@Immutable
+public class UnboundJacksonFlag<T> extends UnboundFlagImpl<T, JacksonFlag<T>, UnboundJacksonFlag<T>> {
+    public UnboundJacksonFlag(FlagId id, T defaultValue, Class<T> jacksonClass) {
+        this(id, defaultValue, new FetchVector(), jacksonClass);
+    }
+
+    public UnboundJacksonFlag(FlagId id, T defaultValue, FetchVector defaultFetchVector, Class<T> jacksonClass) {
+        super(id, defaultValue, defaultFetchVector,
+                new JacksonSerializer<>(jacksonClass),
+                (id2, defaultValue2, vector2) -> new UnboundJacksonFlag<>(id2, defaultValue2, vector2, jacksonClass),
+                JacksonFlag::new);
+    }
+}
diff --git a/flags/src/main/java/com/yahoo/vespa/flags/UnboundLongFlag.java b/flags/src/main/java/com/yahoo/vespa/flags/UnboundLongFlag.java
new file mode 100644
index 00000000000..732a9073fc8
--- /dev/null
+++ b/flags/src/main/java/com/yahoo/vespa/flags/UnboundLongFlag.java
@@ -0,0 +1,23 @@
+// Copyright 2019 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.vespa.flags;
+
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.node.LongNode;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * @author hakonhall
+ */
+@Immutable
+public class UnboundLongFlag extends UnboundFlagImpl<Long, LongFlag, UnboundLongFlag> {
+    public UnboundLongFlag(FlagId id, long defaultValue) {
+        this(id, defaultValue, new FetchVector());
+    }
+
+    public UnboundLongFlag(FlagId id, Long defaultValue, FetchVector defaultFetchVector) {
+        super(id, defaultValue, defaultFetchVector,
+                new SimpleFlagSerializer<>(LongNode::new, JsonNode::isIntegralNumber, JsonNode::asLong),
+                UnboundLongFlag::new, LongFlag::new);
+    }
+}
diff --git a/flags/src/main/java/com/yahoo/vespa/flags/UnboundStringFlag.java b/flags/src/main/java/com/yahoo/vespa/flags/UnboundStringFlag.java
new file mode 100644
index 00000000000..67c4bceb3e9
--- /dev/null
+++ b/flags/src/main/java/com/yahoo/vespa/flags/UnboundStringFlag.java
@@ -0,0 +1,23 @@
+// Copyright 2019 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.vespa.flags;
+
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.node.TextNode;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * @author hakonhall
+ */
+@Immutable
+public class UnboundStringFlag extends UnboundFlagImpl<String, StringFlag, UnboundStringFlag> {
+    public UnboundStringFlag(FlagId id, String defaultValue) {
+        this(id, defaultValue, new FetchVector());
+    }
+
+    public UnboundStringFlag(FlagId id, String defaultValue, FetchVector defaultFetchVector) {
+        super(id, defaultValue, defaultFetchVector,
+                new SimpleFlagSerializer<>(TextNode::new, JsonNode::isTextual, JsonNode::asText),
+                UnboundStringFlag::new, StringFlag::new);
+    }
+}
diff --git a/flags/src/main/java/com/yahoo/vespa/flags/json/FlagData.java b/flags/src/main/java/com/yahoo/vespa/flags/json/FlagData.java
index bfd959e82f9..b5bc2032bae 100644
--- a/flags/src/main/java/com/yahoo/vespa/flags/json/FlagData.java
+++ b/flags/src/main/java/com/yahoo/vespa/flags/json/FlagData.java
@@ -2,6 +2,7 @@
 package com.yahoo.vespa.flags.json;
 
 import com.fasterxml.jackson.databind.JsonNode;
+import com.yahoo.vespa.flags.Deserializer;
 import com.yahoo.vespa.flags.FetchVector;
 import com.yahoo.vespa.flags.FlagId;
 import com.yahoo.vespa.flags.FlagSource;
@@ -16,9 +17,9 @@ import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
-import java.util.Objects;
 import java.util.Optional;
 import java.util.stream.Collectors;
+import java.util.stream.Stream;
 
 /**
  * A data structure containing all data for a single flag, that can be serialized to/from JSON,
@@ -100,8 +101,12 @@ public class FlagData {
     }
 
     private static FlagData fromWire(WireFlagData wireFlagData) {
+        if (wireFlagData.id == null) {
+            throw new IllegalArgumentException("Flag ID missing");
+        }
+
         return new FlagData(
-                new FlagId(Objects.requireNonNull(wireFlagData.id)),
+                new FlagId(wireFlagData.id),
                 FetchVectorHelper.fromWire(wireFlagData.defaultFetchVector),
                 rulesFromWire(wireFlagData.rules)
         );
@@ -111,5 +116,13 @@ public class FlagData {
         if (wireRules == null) return Collections.emptyList();
         return wireRules.stream().map(Rule::fromWire).collect(Collectors.toList());
     }
+
+    /** E.g. verify all RawFlag can be deserialized. */
+    public void validate(Deserializer<?> deserializer) {
+        rules.stream()
+                .flatMap(rule -> rule.getValueToApply().map(Stream::of).orElse(null))
+                .forEach(deserializer::deserialize);
+
+    }
 }
 
diff --git a/flags/src/test/java/com/yahoo/vespa/flags/FileFlagSourceTest.java b/flags/src/test/java/com/yahoo/vespa/flags/FileFlagSourceTest.java
index 7d9d7868308..e19436069b5 100644
--- a/flags/src/test/java/com/yahoo/vespa/flags/FileFlagSourceTest.java
+++ b/flags/src/test/java/com/yahoo/vespa/flags/FileFlagSourceTest.java
@@ -24,44 +24,44 @@ public class FileFlagSourceTest {
 
     @Test
     public void testFeatureLikeFlags() throws IOException {
-        Flag<Boolean> featureFlag = new Flag<>(id, false, source, Flags.BOOLEAN_SERIALIZER);
-        Flag<Boolean> byDefaultTrue = new Flag<>(id, true, source, Flags.BOOLEAN_SERIALIZER);
+        BooleanFlag booleanFlag = new UnboundBooleanFlag(id).bindTo(source);
+        BooleanFlag byDefaultTrue = new UnboundBooleanFlag(id, true).bindTo(source);
 
-        assertFalse(featureFlag.value());
+        assertFalse(booleanFlag.value());
         assertTrue(byDefaultTrue.value());
 
         writeFlag(id.toString(), "true\n");
 
-        assertTrue(featureFlag.value());
+        assertTrue(booleanFlag.value());
         assertTrue(byDefaultTrue.value());
 
         writeFlag(id.toString(), "false\n");
 
-        assertFalse(featureFlag.value());
+        assertFalse(booleanFlag.value());
         assertFalse(byDefaultTrue.value());
     }
 
     @Test
     public void testIntegerLikeFlags() throws IOException {
-        Flag<Integer> intFlag = new Flag<>(id, -1, source, Flags.INT_SERIALIZER);
-        Flag<Long> longFlag = new Flag<>(id, -2L, source, Flags.LONG_SERIALIZER);
+        IntFlag intFlag = new UnboundIntFlag(id, -1).bindTo(source);
+        LongFlag longFlag = new UnboundLongFlag(id, -2L).bindTo(source);
 
         assertFalse(fetch().isPresent());
         assertFalse(fetch().isPresent());
-        assertEquals(-1, (int) intFlag.value());
-        assertEquals(-2L, (long) longFlag.value());
+        assertEquals(-1, intFlag.value());
+        assertEquals(-2L, longFlag.value());
 
         writeFlag(id.toString(), "1\n");
 
         assertTrue(fetch().isPresent());
         assertTrue(fetch().isPresent());
-        assertEquals(1, (int) intFlag.value());
-        assertEquals(1L, (long) longFlag.value());
+        assertEquals(1, intFlag.value());
+        assertEquals(1L, longFlag.value());
     }
 
     @Test
     public void testStringFlag() throws IOException {
-        Flag<String> stringFlag = new Flag<>(id, "default", source, Flags.STRING_SERIALIZER);
+        StringFlag stringFlag = new UnboundStringFlag(id, "default").bindTo(source);
         assertFalse(fetch().isPresent());
         assertEquals("default", stringFlag.value());
 
@@ -71,11 +71,11 @@ public class FileFlagSourceTest {
 
     @Test
     public void parseFailure() throws IOException {
-        Flag<Boolean> featureFlag = new Flag<>(id, false, source, Flags.BOOLEAN_SERIALIZER);
-        writeFlag(featureFlag.id().toString(), "garbage");
+        BooleanFlag booleanFlag = new UnboundBooleanFlag(id).bindTo(source);
+        writeFlag(booleanFlag.id().toString(), "garbage");
 
         try {
-            featureFlag.value();
+            booleanFlag.value();
         } catch (UncheckedIOException e) {
             assertThat(e.getMessage(), containsString("garbage"));
         }
diff --git a/flags/src/test/java/com/yahoo/vespa/flags/FlagsTest.java b/flags/src/test/java/com/yahoo/vespa/flags/FlagsTest.java
index 4f7d797e07d..591198f5e50 100644
--- a/flags/src/test/java/com/yahoo/vespa/flags/FlagsTest.java
+++ b/flags/src/test/java/com/yahoo/vespa/flags/FlagsTest.java
@@ -31,7 +31,7 @@ public class FlagsTest {
     public void testBoolean() {
         final boolean defaultValue = false;
         FlagSource source = mock(FlagSource.class);
-        Flag<Boolean> booleanFlag = Flags.defineBoolean("id", defaultValue, "description",
+        BooleanFlag booleanFlag = Flags.defineFeatureFlag("id", defaultValue, "description",
                 "modification effect", FetchVector.Dimension.ZONE_ID, FetchVector.Dimension.HOSTNAME)
                 .with(FetchVector.Dimension.ZONE_ID, "a-zone")
                 .bindTo(source);
@@ -65,19 +65,19 @@ public class FlagsTest {
 
     @Test
     public void testString() {
-        testGeneric(Flags.defineString("string-id", "default value", "description",
+        testGeneric(Flags.defineStringFlag("string-id", "default value", "description",
                 "modification effect", FetchVector.Dimension.ZONE_ID, FetchVector.Dimension.HOSTNAME),
                 "default value", "other value");
     }
 
     @Test
     public void testInt() {
-        testGeneric(Flags.defineInt("int-id", 2, "desc", "mod"), 2, 3);
+        testGeneric(Flags.defineIntFlag("int-id", 2, "desc", "mod"), 2, 3);
     }
 
     @Test
     public void testLong() {
-        testGeneric(Flags.defineLong("long-id", 1L, "desc", "mod"), 1L, 2L);
+        testGeneric(Flags.defineLongFlag("long-id", 1L, "desc", "mod"), 1L, 2L);
     }
 
     @Test
@@ -87,25 +87,24 @@ public class FlagsTest {
         instance.integer = -2;
         instance.string = "foo";
 
-        testGeneric(Flags.defineJackson("jackson-id", ExampleJacksonClass.class, defaultInstance,
+        testGeneric(Flags.defineJacksonFlag("jackson-id", defaultInstance, ExampleJacksonClass.class,
                 "description", "modification effect", FetchVector.Dimension.HOSTNAME),
                 defaultInstance, instance);
     }
 
-    private <T> void testGeneric(UnboundFlag<T> unboundFlag, T defaultValue, T value) {
+    private <T> void testGeneric(UnboundFlag<?, ?, ?> unboundFlag, T defaultValue, T value) {
         FlagSource source = mock(FlagSource.class);
-        Flag<T> flag = unboundFlag.bindTo(source);
+        Flag<?, ?> flag = unboundFlag.bindTo(source);
 
         when(source.fetch(any(), any())).thenReturn(Optional.empty());
-        assertThat(flag.value(), equalTo(defaultValue));
+        assertThat(flag.boxedValue(), equalTo(defaultValue));
 
         when(source.fetch(any(), any())).thenReturn(Optional.of(JsonNodeRawFlag.fromJacksonClass(value)));
-        assertThat(flag.value(), equalTo(value));
+        assertThat(flag.boxedValue(), equalTo(value));
 
         assertTrue(Flags.getFlag(unboundFlag.id()).isPresent());
     }
 
-
     @JsonIgnoreProperties(ignoreUnknown = true)
     private static class ExampleJacksonClass {
         @JsonProperty("integer")
diff --git a/service-monitor/src/main/java/com/yahoo/vespa/service/health/HealthMonitorManager.java b/service-monitor/src/main/java/com/yahoo/vespa/service/health/HealthMonitorManager.java
index 340d30e9f41..682f677a626 100644
--- a/service-monitor/src/main/java/com/yahoo/vespa/service/health/HealthMonitorManager.java
+++ b/service-monitor/src/main/java/com/yahoo/vespa/service/health/HealthMonitorManager.java
@@ -8,7 +8,7 @@ import com.yahoo.vespa.applicationmodel.ClusterId;
 import com.yahoo.vespa.applicationmodel.ConfigId;
 import com.yahoo.vespa.applicationmodel.ServiceStatus;
 import com.yahoo.vespa.applicationmodel.ServiceType;
-import com.yahoo.vespa.flags.Flag;
+import com.yahoo.vespa.flags.BooleanFlag;
 import com.yahoo.vespa.flags.FlagSource;
 import com.yahoo.vespa.flags.Flags;
 import com.yahoo.vespa.service.duper.DuperModelManager;
@@ -50,7 +50,7 @@ public class HealthMonitorManager implements MonitorManager {
     private final ConcurrentHashMap<ApplicationId, ApplicationHealthMonitor> healthMonitors = new ConcurrentHashMap<>();
     private final DuperModelManager duperModel;
     private final ApplicationHealthMonitorFactory applicationHealthMonitorFactory;
-    private final Flag<Boolean> monitorInfra;
+    private final BooleanFlag monitorInfra;
 
     @Inject
     public HealthMonitorManager(DuperModelManager duperModel, FlagSource flagSource) {
@@ -60,13 +60,13 @@ public class HealthMonitorManager implements MonitorManager {
     }
 
     private HealthMonitorManager(DuperModelManager duperModel,
-                                 Flag<Boolean> monitorInfra,
+                                 BooleanFlag monitorInfra,
                                  StateV1HealthModel healthModel) {
         this(duperModel, monitorInfra, id -> new ApplicationHealthMonitor(id, healthModel));
     }
 
     HealthMonitorManager(DuperModelManager duperModel,
-                         Flag<Boolean> monitorInfra,
+                         BooleanFlag monitorInfra,
                          ApplicationHealthMonitorFactory applicationHealthMonitorFactory) {
         this.duperModel = duperModel;
         this.monitorInfra = monitorInfra;
diff --git a/service-monitor/src/test/java/com/yahoo/vespa/service/health/HealthMonitorManagerTest.java b/service-monitor/src/test/java/com/yahoo/vespa/service/health/HealthMonitorManagerTest.java
index 39147955d4c..78b0bed0e6f 100644
--- a/service-monitor/src/test/java/com/yahoo/vespa/service/health/HealthMonitorManagerTest.java
+++ b/service-monitor/src/test/java/com/yahoo/vespa/service/health/HealthMonitorManagerTest.java
@@ -7,7 +7,7 @@ import com.yahoo.vespa.applicationmodel.ClusterId;
 import com.yahoo.vespa.applicationmodel.ConfigId;
 import com.yahoo.vespa.applicationmodel.ServiceStatus;
 import com.yahoo.vespa.applicationmodel.ServiceType;
-import com.yahoo.vespa.flags.Flag;
+import com.yahoo.vespa.flags.BooleanFlag;
 import com.yahoo.vespa.service.duper.ConfigServerApplication;
 import com.yahoo.vespa.service.duper.ControllerHostApplication;
 import com.yahoo.vespa.service.duper.DuperModelManager;
@@ -33,8 +33,7 @@ import static org.mockito.Mockito.when;
 public class HealthMonitorManagerTest {
     private final ConfigServerApplication configServerApplication = new ConfigServerApplication();
     private final DuperModelManager duperModel = mock(DuperModelManager.class);
-    @SuppressWarnings("unchecked")
-    private final Flag<Boolean> monitorInfra = (Flag<Boolean>) mock(Flag.class);
+    private final BooleanFlag monitorInfra = mock(BooleanFlag.class);
     private final ApplicationHealthMonitor monitor = mock(ApplicationHealthMonitor.class);
     private final ApplicationHealthMonitorFactory monitorFactory = mock(ApplicationHealthMonitorFactory.class);
     private final HealthMonitorManager manager = new HealthMonitorManager(duperModel, monitorInfra, monitorFactory);