Add default fallback support for Dubbo

- Update test cases and demo

Signed-off-by: Eric Zhao <sczyh16@gmail.com>

sentinel-adapter/sentinel-dubbo-adapter/src/main/java/com/alibaba/csp/sentinel/adapter/dubbo/SentinelDubboConsumerFilter.java

@@ -19,10 +19,10 @@ import com.alibaba.csp.sentinel.Entry;
 import com.alibaba.csp.sentinel.EntryType;
 import com.alibaba.csp.sentinel.SphU;
 import com.alibaba.csp.sentinel.Tracer;
+import com.alibaba.csp.sentinel.adapter.dubbo.fallback.DubboFallbackRegistry;
 import com.alibaba.csp.sentinel.context.ContextUtil;
 import com.alibaba.csp.sentinel.log.RecordLog;
 import com.alibaba.csp.sentinel.slots.block.BlockException;
-import com.alibaba.csp.sentinel.slots.block.SentinelRpcException;
 import com.alibaba.dubbo.common.extension.Activate;
 import com.alibaba.dubbo.rpc.Filter;
 import com.alibaba.dubbo.rpc.Invocation;
@@ -39,6 +39,7 @@ import com.alibaba.dubbo.rpc.RpcException;
  * </pre>
  *
  * @author leyou
+ * @author Eric Zhao
  */
 @Activate(group = "consumer")
 public class SentinelDubboConsumerFilter extends AbstractDubboFilter implements Filter {
@@ -58,7 +59,7 @@ public class SentinelDubboConsumerFilter extends AbstractDubboFilter implements
             methodEntry = SphU.entry(resourceName, EntryType.OUT);
             return invoker.invoke(invocation);
         } catch (BlockException e) {
-            throw new SentinelRpcException(e);
+            return DubboFallbackRegistry.getConsumerFallback().handle(invoker, invocation, e);
         } catch (RpcException e) {
             Tracer.trace(e);
             throw e;

sentinel-adapter/sentinel-dubbo-adapter/src/main/java/com/alibaba/csp/sentinel/adapter/dubbo/SentinelDubboProviderFilter.java

@@ -19,6 +19,7 @@ import com.alibaba.csp.sentinel.Entry;
 import com.alibaba.csp.sentinel.EntryType;
 import com.alibaba.csp.sentinel.SphU;
 import com.alibaba.csp.sentinel.Tracer;
+import com.alibaba.csp.sentinel.adapter.dubbo.fallback.DubboFallbackRegistry;
 import com.alibaba.csp.sentinel.context.ContextUtil;
 import com.alibaba.csp.sentinel.log.RecordLog;
 import com.alibaba.csp.sentinel.slots.block.BlockException;
@@ -39,6 +40,7 @@ import com.alibaba.dubbo.rpc.RpcException;
  * </pre>
  *
  * @author leyou
+ * @author Eric Zhao
  */
 @Activate(group = "provider")
 public class SentinelDubboProviderFilter extends AbstractDubboFilter implements Filter {
@@ -63,7 +65,7 @@ public class SentinelDubboProviderFilter extends AbstractDubboFilter implements
 
             return invoker.invoke(invocation);
         } catch (BlockException e) {
-            throw new SentinelRpcException(e);
+            return DubboFallbackRegistry.getProviderFallback().handle(invoker, invocation, e);
         } catch (RpcException e) {
             Tracer.trace(e);
             throw e;

sentinel-adapter/sentinel-dubbo-adapter/src/main/java/com/alibaba/csp/sentinel/adapter/dubbo/fallback/DefaultDubboFallback.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright 1999-2018 Alibaba Group Holding Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.alibaba.csp.sentinel.adapter.dubbo.fallback;
+
+import com.alibaba.csp.sentinel.slots.block.BlockException;
+import com.alibaba.csp.sentinel.slots.block.SentinelRpcException;
+import com.alibaba.dubbo.rpc.Invocation;
+import com.alibaba.dubbo.rpc.Invoker;
+import com.alibaba.dubbo.rpc.Result;
+
+/**
+ * @author Eric Zhao
+ */
+public class DefaultDubboFallback implements DubboFallback {
+
+    @Override
+    public Result handle(Invoker<?> invoker, Invocation invocation, BlockException ex) {
+        // Just wrap and throw the exception.
+        throw new SentinelRpcException(ex);
+    }
+}

sentinel-adapter/sentinel-dubbo-adapter/src/main/java/com/alibaba/csp/sentinel/adapter/dubbo/fallback/DubboFallback.java

@@ -0,0 +1,39 @@
+/*
+ * Copyright 1999-2018 Alibaba Group Holding Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.alibaba.csp.sentinel.adapter.dubbo.fallback;
+
+import com.alibaba.csp.sentinel.slots.block.BlockException;
+import com.alibaba.dubbo.rpc.Invocation;
+import com.alibaba.dubbo.rpc.Invoker;
+import com.alibaba.dubbo.rpc.Result;
+
+/**
+ * Fallback handler for Dubbo services.
+ *
+ * @author Eric Zhao
+ */
+public interface DubboFallback {
+
+    /**
+     * Handle the block exception and provide fallback result.
+     *
+     * @param invoker Dubbo invoker
+     * @param invocation Dubbo invocation
+     * @param ex block exception
+     * @return fallback result
+     */
+    Result handle(Invoker<?> invoker, Invocation invocation, BlockException ex);
+}

sentinel-adapter/sentinel-dubbo-adapter/src/main/java/com/alibaba/csp/sentinel/adapter/dubbo/fallback/DubboFallbackRegistry.java

@@ -0,0 +1,48 @@
+/*
+ * Copyright 1999-2018 Alibaba Group Holding Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.alibaba.csp.sentinel.adapter.dubbo.fallback;
+
+/**
+ * Global fallback registry for Dubbo.
+ *
+ * Note: Degrading is mainly designed for consumer. The provider should not
+ * give fallback result in most circumstances.
+ *
+ * @author Eric Zhao
+ */
+public final class DubboFallbackRegistry {
+
+    private static volatile DubboFallback consumerFallback = new DefaultDubboFallback();
+    private static volatile DubboFallback providerFallback = new DefaultDubboFallback();
+
+    public static DubboFallback getConsumerFallback() {
+        return consumerFallback;
+    }
+
+    public static void setConsumerFallback(DubboFallback consumerFallback) {
+        DubboFallbackRegistry.consumerFallback = consumerFallback;
+    }
+
+    public static DubboFallback getProviderFallback() {
+        return providerFallback;
+    }
+
+    public static void setProviderFallback(DubboFallback providerFallback) {
+        DubboFallbackRegistry.providerFallback = providerFallback;
+    }
+
+    private DubboFallbackRegistry() {}
+}

sentinel-adapter/sentinel-dubbo-adapter/src/test/java/com/alibaba/csp/sentinel/adapter/dubbo/fallback/DubboFallbackRegistryTest.java

@@ -0,0 +1,56 @@
+/*
+ * Copyright 1999-2018 Alibaba Group Holding Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.alibaba.csp.sentinel.adapter.dubbo.fallback;
+
+import com.alibaba.csp.sentinel.slots.block.BlockException;
+import com.alibaba.csp.sentinel.slots.block.SentinelRpcException;
+import com.alibaba.csp.sentinel.slots.block.flow.FlowException;
+import com.alibaba.dubbo.rpc.Invocation;
+import com.alibaba.dubbo.rpc.Invoker;
+import com.alibaba.dubbo.rpc.Result;
+import com.alibaba.dubbo.rpc.RpcResult;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+/**
+ * @author Eric Zhao
+ */
+public class DubboFallbackRegistryTest {
+
+    @Test(expected = SentinelRpcException.class)
+    public void testDefaultFallback() {
+        // Test for default.
+        BlockException ex = new FlowException("xxx");
+        DubboFallbackRegistry.getConsumerFallback()
+            .handle(null, null, ex);
+    }
+
+    @Test
+    public void testCustomFallback() {
+        BlockException ex = new FlowException("xxx");
+        DubboFallbackRegistry.setConsumerFallback(new DubboFallback() {
+            @Override
+            public Result handle(Invoker<?> invoker, Invocation invocation, BlockException e) {
+                return new RpcResult("Error: " + e.getClass().getName());
+            }
+        });
+        Result result = DubboFallbackRegistry.getConsumerFallback()
+            .handle(null, null, ex);
+        Assert.assertFalse("The invocation should not fail", result.hasException());
+        Assert.assertEquals("Error: " + ex.getClass().getName(), result.getValue());
+    }
+}

sentinel-demo/sentinel-demo-dubbo/src/main/java/com/alibaba/csp/sentinel/demo/dubbo/demo1/FooConsumerBootstrap.java

@@ -15,10 +15,8 @@
  */
 package com.alibaba.csp.sentinel.demo.dubbo.demo1;
 
-
 import com.alibaba.csp.sentinel.demo.dubbo.consumer.ConsumerConfiguration;
 import com.alibaba.csp.sentinel.demo.dubbo.consumer.FooServiceConsumer;
-import com.alibaba.csp.sentinel.init.InitExecutor;
 import com.alibaba.csp.sentinel.slots.block.SentinelRpcException;
 
 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
@@ -36,8 +34,6 @@ import org.springframework.context.annotation.AnnotationConfigApplicationContext
 public class FooConsumerBootstrap {
 
     public static void main(String[] args) {
-        InitExecutor.doInit();
-
         AnnotationConfigApplicationContext consumerContext = new AnnotationConfigApplicationContext();
         consumerContext.register(ConsumerConfiguration.class);
         consumerContext.refresh();
@@ -45,14 +41,14 @@ public class FooConsumerBootstrap {
         FooServiceConsumer service = consumerContext.getBean(FooServiceConsumer.class);
 
         for (int i = 0; i < 15; i++) {
-           try {
-                    String message = service.sayHello("Eric");
-                    System.out.println("Success: " + message);
-                } catch (SentinelRpcException ex) {
-                    System.out.println("Blocked");
-                } catch (Exception ex) {
-                    ex.printStackTrace();
-                }
+            try {
+                String message = service.sayHello("Eric");
+                System.out.println("Success: " + message);
+            } catch (SentinelRpcException ex) {
+                System.out.println("Blocked");
+            } catch (Exception ex) {
+                ex.printStackTrace();
+            }
         }
     }
 }

sentinel-demo/sentinel-demo-dubbo/src/main/java/com/alibaba/csp/sentinel/demo/dubbo/demo1/FooProviderBootstrap.java

@@ -40,9 +40,11 @@ public class FooProviderBootstrap {
     private static final String INTERFACE_RES_KEY = "com.alibaba.csp.sentinel.demo.dubbo.FooService";
 
     public static void main(String[] args) {
-        initFlowRule();
+        // Users don't need to manually call this method.
         InitExecutor.doInit();
 
+        initFlowRule();
+
         AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
         context.register(ProviderConfiguration.class);
         context.refresh();

sentinel-demo/sentinel-demo-dubbo/src/main/java/com/alibaba/csp/sentinel/demo/dubbo/demo2/FooConsumerBootstrap.java

@@ -19,6 +19,7 @@ import java.util.Collections;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 
+import com.alibaba.csp.sentinel.adapter.dubbo.fallback.DubboFallbackRegistry;
 import com.alibaba.csp.sentinel.concurrent.NamedThreadFactory;
 import com.alibaba.csp.sentinel.demo.dubbo.consumer.ConsumerConfiguration;
 import com.alibaba.csp.sentinel.demo.dubbo.consumer.FooServiceConsumer;
@@ -27,6 +28,8 @@ import com.alibaba.csp.sentinel.slots.block.RuleConstant;
 import com.alibaba.csp.sentinel.slots.block.SentinelRpcException;
 import com.alibaba.csp.sentinel.slots.block.flow.FlowRule;
 import com.alibaba.csp.sentinel.slots.block.flow.FlowRuleManager;
+import com.alibaba.dubbo.rpc.Result;
+import com.alibaba.dubbo.rpc.RpcResult;
 
 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
 
@@ -50,7 +53,6 @@ public class FooConsumerBootstrap {
 
     public static void main(String[] args) {
         initFlowRule();
-        InitExecutor.doInit();
 
         AnnotationConfigApplicationContext consumerContext = new AnnotationConfigApplicationContext();
         consumerContext.register(ConsumerConfiguration.class);
@@ -68,9 +70,7 @@ public class FooConsumerBootstrap {
                     ex.printStackTrace();
                 }
             });
-            pool.submit(() -> {
-                System.out.println("Another: " + service.doAnother());
-            });
+            pool.submit(() -> System.out.println("Another: " + service.doAnother()));
         }
     }
 
@@ -82,4 +82,12 @@ public class FooConsumerBootstrap {
         flowRule.setLimitApp("default");
         FlowRuleManager.loadRules(Collections.singletonList(flowRule));
     }
+
+    private static void registerFallback() {
+        // Register fallback handler for consumer.
+        // If you only want to handle degrading, you need to
+        // check the type of BlockException.
+        DubboFallbackRegistry.setConsumerFallback((a, b, ex) ->
+            new RpcResult("Error: " + ex.getClass().getTypeName()));
+    }
 }

sentinel-demo/sentinel-demo-dubbo/src/main/java/com/alibaba/csp/sentinel/demo/dubbo/demo2/FooProviderBootstrap.java

@@ -32,6 +32,7 @@ import org.springframework.context.annotation.AnnotationConfigApplicationContext
 public class FooProviderBootstrap {
 
     public static void main(String[] args) {
+        // Users don't need to manually call this method.
         InitExecutor.doInit();
 
         AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();