Merge pull request #3 from Nordstrom/pr/add-exception-unwrapper

Add ExceptionUnwrapper utility class

Author: sbabcoc

pom.xml

@@ -213,5 +213,5 @@
       </build>
     </profile>
   </profiles>
-  <version>1.5.1-SNAPSHOT</version>
+  <version>1.6.0-SNAPSHOT</version>
 </project>

src/main/java/com/nordstrom/common/base/ExceptionUnwrapper.java

@@ -0,0 +1,54 @@
+package com.nordstrom.common.base;
+
+import java.lang.reflect.InvocationTargetException;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Set;
+
+public class ExceptionUnwrapper {
+
+    private static final Set<Class<? extends Exception>> unwrappable = 
+            Collections.unmodifiableSet(new HashSet<>(Arrays.asList(RuntimeException.class, InvocationTargetException.class)));
+
+    private ExceptionUnwrapper() {
+        throw new AssertionError("ExceptionUnwrapper is a static utility class that cannot be instantiated.");
+    }
+
+    /**
+     * Unwrap the specified exception.<br>
+     * <br>
+     * <b>NOTE</b>: This method unwraps the exception chain until it encounters either a non-wrapper exception or an
+     * exception with no specified cause. The unwrapped exception is returned.
+     * 
+     * @param throwable exception to be unwrapped
+     * @return unwrapped exception
+     */
+    public static Throwable unwrap(Throwable throwable) {
+        return unwrap(throwable, null);
+    }
+
+    /**
+     * Unwrap the specified exception, optionally retaining wrapper messages.<br>
+     * <br>
+     * <b>NOTE</b>: This method unwraps the exception chain until it encounters either a non-wrapper exception or an
+     * exception with no specified cause. The unwrapped exception is returned.
+     * 
+     * @param throwable exception to be unwrapped
+     * @param string builder to compile wrapper messages (may be 'null')
+     * @return unwrapped exception
+     */
+    public static Throwable unwrap(Throwable throwable, StringBuilder builder) {
+        Throwable thrown = throwable;
+        if (thrown != null) {
+            while (unwrappable.contains(thrown.getClass())) {
+                Throwable unwrapped = thrown.getCause();
+                if (unwrapped == null) break;
+                if (builder != null) builder.append(thrown.getMessage()).append(" -> ");
+                thrown = unwrapped;
+            }
+        }
+        return thrown;
+    }
+
+}