Merge pull request #29 from code77se/then-resolve

Add Promise methods thenResolve, thenReject and tap

jq/src/main/java/se/code77/jq/JQ.java

@@ -139,6 +139,7 @@ public interface DeferredHandler<V> {
      * operation is complete.
      *
      * @param <V> Type of the promise you want to convert to an empty (value) value.
+     * @deprecated Use {@link Promise#thenResolve(Object)} instead
      */
     public static final class OnFulfilledVoidCallback<V> implements OnFulfilledCallback<V, Void> {
         @Override

jq/src/main/java/se/code77/jq/Promise.java

@@ -165,6 +165,19 @@ public interface OnProgressedCallback {
         void onProgressed(float progress);
     }
 
+    /**
+     * Callback interface used for {@link #tap(OnTapCallback)} used to observe fulfilled promises
+     * without modifying the next promise.
+     * @param <V> Type of value carried by the promise
+     */
+    public interface OnTapCallback<V> {
+        /**
+         * The promise has been fulfilled with the given value
+         * @param value Value
+         */
+        void onTap(V value);
+    }
+
     /**
      * An exception thrown by a promise which is terminated without any
      * rejection callback. A promise is terminated by calling
@@ -375,6 +388,32 @@ public <NV> Promise<NV> then(
      */
     public <NV> Promise<NV> then(OnFulfilledCallback<V, NV> onFulfilled);
 
+    /**
+     * Convenience method, equivalent to adding a fulfillment callback that merely returns the given value.
+     *
+     * @param nextValue Value to resolve the next promise with
+     * @param <NV> Type of the value carried by the next promise
+     * @return A new promise that, provided the current promise is resolved, will be resolved with the given value.
+     */
+    public <NV> Promise<NV> thenResolve(NV nextValue);
+
+    /**
+     * Convenience method, equivalent to adding a fulfillment callback that merely throws the given exception
+     * @param reason Exception to reject the next promise with
+     * @param <NV> Type of the value carried by the next promise
+     * @return A new promise that, provided the current promise is resolved, will be rejected with the given reason.
+     */
+    public <NV> Promise<NV> thenReject(Exception reason, Class<NV> nextValueClass);
+
+    /**
+     * Observe the state of this promise by adding a handler that will be invoked when the promise
+     * is fulfilled, but without modifying the next promise.
+     *
+     * @param onTap Simple, observe-only fulfillment handler
+     * @return A new promise which will inherit the state of the current promise
+     */
+    public Promise<V> tap(OnTapCallback<V> onTap);
+
     /**
      * Like {@link Promise#then(OnFulfilledCallback, OnRejectedCallback)} but only for promised List values. The
      * elements in the list will be spread as individual arguments on the supplied callback, which

jq/src/main/java/se/code77/jq/PromiseImpl.java

@@ -99,6 +99,41 @@ public <NV> Promise<NV> then(OnFulfilledCallback<V, NV> onFulfilled) {
         return then(onFulfilled, null);
     }
 
+    @Override
+    public <NV> Promise<NV> thenResolve(final NV nextValue) {
+        return then(new OnFulfilledCallback<V, NV>() {
+            @Override
+            public Future<NV> onFulfilled(V value) throws Exception {
+                return Value.wrap(nextValue);
+            }
+        });
+    }
+
+    @Override
+    public <NV> Promise<NV> thenReject(final Exception reason, Class<NV> nextValueClass) {
+        return then(new OnFulfilledCallback<V, NV>() {
+            @Override
+            public Future<NV> onFulfilled(V value) throws Exception {
+                throw reason;
+            }
+        });
+    }
+
+    @Override
+    public Promise<V> tap(final OnTapCallback<V> onTap) {
+        return then(new OnFulfilledCallback<V, V>() {
+            @Override
+            public Future<V> onFulfilled(V value) throws Exception {
+                try {
+                    onTap.onTap(value);
+                } catch (RuntimeException e) {
+                    // Swallow
+                }
+                return Value.wrap(value);
+            }
+        });
+    }
+
     @Override
     public <NV> Promise<NV> spread(final OnFulfilledSpreadCallback<V, NV> onFulfilled, OnRejectedCallback<NV> onRejected) {
         if (onFulfilled == null) {

jq/src/test/java/se/code77/jq/PromiseTests.java

@@ -1022,4 +1022,73 @@ public Future<Void> onFulfilled(Double e1, Integer e2) throws Exception {
         assertData(spread, 500);
     }
 
+    @Test
+    public void thenResolve() {
+        final Promise<String> p = JQ.resolve(1).thenResolve(TEST_VALUE1);
+        final BlockingDataHolder<String> then1 = new BlockingDataHolder<>();
+
+        p.then(new DataFulfilledCallback<String, Void>(then1));
+
+        assertData(then1, 2000, TEST_VALUE1);
+        assertResolved(p, TEST_VALUE1);
+    }
+
+    @Test
+    public void thenReject() {
+        final Promise<String> p = JQ.resolve(1).thenReject(TEST_REASON1, String.class);
+        final BlockingDataHolder<Exception> fail1 = new BlockingDataHolder<>();
+
+        p.fail(new DataRejectedCallback<String>(fail1));
+
+        assertData(fail1, 2000, TEST_REASON1);
+        assertRejected(p, TEST_REASON1);
+    }
+
+    @Test
+    public void tap_isResolved() {
+        final Promise<String> p = JQ.resolve(TEST_VALUE1);
+        final BlockingDataHolder<String> tap1 = new BlockingDataHolder<>();
+
+        p.tap(new Promise.OnTapCallback<String>() {
+            @Override
+            public void onTap(String value) {
+                tap1.set(value);
+            }
+        });
+
+        assertData(tap1, 2000, TEST_VALUE1);
+        assertResolved(p, TEST_VALUE1);
+    }
+
+    @Test
+    public void tap_isRejected() {
+        final Promise<String> p = JQ.reject(TEST_REASON1);
+        final BlockingDataHolder<String> tap1 = new BlockingDataHolder<>();
+
+        p.tap(new Promise.OnTapCallback<String>() {
+            @Override
+            public void onTap(String value) {
+                tap1.set(value);
+            }
+        });
+
+        assertNoData(tap1, 2000);
+        assertRejected(p, TEST_REASON1);
+    }
+
+    @Test
+    public void tap_isTapExceptionIgnored() {
+        final Promise<String> p = JQ.resolve(TEST_VALUE1);
+        final BlockingDataHolder<String> then1 = new BlockingDataHolder<>();
+
+        p.tap(new Promise.OnTapCallback<String>() {
+            @Override
+            public void onTap(String value) {
+                throw new RuntimeException("Should be ignored");
+            }
+        }).then(new DataFulfilledCallback<>(then1));
+
+        assertData(then1, 2000, TEST_VALUE1);
+        assertResolved(p, TEST_VALUE1);
+    }
 }