Add Exceptions.findCause()

2 files changed, 25 insertions, 2 deletions

diff --git a/yolean/src/main/java/com/yahoo/yolean/Exceptions.java b/yolean/src/main/java/com/yahoo/yolean/Exceptions.java
index fa3eb412016..063ba70c75d 100644
--- a/yolean/src/main/java/com/yahoo/yolean/Exceptions.java
+++ b/yolean/src/main/java/com/yahoo/yolean/Exceptions.java
@@ -3,9 +3,7 @@ package com.yahoo.yolean;
 
 import java.io.IOException;
 import java.io.UncheckedIOException;
-import java.nio.file.NoSuchFileException;
 import java.util.Optional;
-import java.util.function.Supplier;
 
 /**
  * Helper methods for handling exceptions
@@ -51,6 +49,17 @@ public class Exceptions {
     }
 
     /**
+     * Returns the first cause or the given throwable that is an instance of {@code clazz}
+     */
+    public static <T extends Throwable> Optional<T> findCause(Throwable t, Class<T> clazz) {
+        for (; t != null; t = t.getCause()) {
+            if (clazz.isInstance(t))
+                return Optional.of(clazz.cast(t));
+        }
+        return Optional.empty();
+    }
+
+    /**
      * Wraps any IOException thrown from a runnable in an UncheckedIOException.
      */
     public static void uncheck(RunnableThrowingIOException runnable) {
diff --git a/yolean/src/test/java/com/yahoo/yolean/ExceptionsTestCase.java b/yolean/src/test/java/com/yahoo/yolean/ExceptionsTestCase.java
index 390018efdf7..cd06d14bb55 100644
--- a/yolean/src/test/java/com/yahoo/yolean/ExceptionsTestCase.java
+++ b/yolean/src/test/java/com/yahoo/yolean/ExceptionsTestCase.java
@@ -6,6 +6,7 @@ import org.junit.Test;
 import java.io.IOException;
 import java.io.UncheckedIOException;
 import java.nio.file.NoSuchFileException;
+import java.util.Optional;
 
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
@@ -17,6 +18,19 @@ import static org.junit.Assert.assertNull;
 public class ExceptionsTestCase {
 
     @Test
+    public void testFindCause() {
+        IllegalArgumentException e1 = new IllegalArgumentException();
+        IllegalStateException e2 = new IllegalStateException(e1);
+        RuntimeException e3 = new RuntimeException(e2);
+
+        assertEquals(Optional.of(e3), Exceptions.findCause(e3, RuntimeException.class));
+        assertEquals(Optional.of(e1), Exceptions.findCause(e3, IllegalArgumentException.class));
+        assertEquals(Optional.empty(), Exceptions.findCause(e3, NumberFormatException.class));
+
+        assertEquals(Optional.of(e2), Exceptions.findCause(e2, RuntimeException.class));
+    }
+
+    @Test
     public void testToMessageStrings() {
         assertEquals("Blah",Exceptions.toMessageString(new Exception("Blah")));
         assertEquals("Blah", Exceptions.toMessageString(new Exception(new Exception("Blah"))));