dubbo 服务降级
官网：https://dubbo.apache.org/zh/docs/advanced/local-mock/
服务降级
应用：消费端服务调用失败，不抛出异常，返回默认的数据
服务降级配置示例
# 同目录下查找服务降级类：com.foo.service.BarServiceMock# 指定本地服务降级类：com.foo.service.impl.BarServiceMock# 方法级别服务容错：方法名后面加".mock"
mock 可选值
true：开启服务降级false：不开启服务降级# return：返回一个字符串表示的对象empty：基本类型返回对应的默认值、集合类返回空值，如：return emptynull：返回nulltrue：返回truefalse：返回falseJSON字符串：返回json字符串反序列化后的对象# throw：抛出异常对象抛出rpcException： 抛出自定义异常：# force：强制使用mock，不发起服务调用，可与return、throw组合使用# fail：服务调用失败时，执行mock（默认行为），可与return、throw组合使用强制返回fake：强制抛出异常：
消费端应用启动时，在创建failoverClusterInvoker的过程中，会用MockClusterWrapper包装，调用栈如下：
# 创建FailoverClusterInvoker对象，默认创建该对象at org.apache.dubbo.rpc.cluster.support.FailoverClusterInvoker.(FailoverClusterInvoker.java:52) # join操作at org.apache.dubbo.rpc.cluster.support.FailoverCluster.doJoin(FailoverCluster.java:33)at org.apache.dubbo.rpc.cluster.support.wrapper.AbstractCluster.join(AbstractCluster.java:58)# MockClusterWrapper：服务降级包装类at org.apache.dubbo.rpc.cluster.support.wrapper.MockClusterWrapper.join(MockClusterWrapper.java:39) # 创建invokerat org.apache.dubbo.registry.integration.RegistryProtocol.doCreateInvoker(RegistryProtocol.java:564) # 获取invokerat org.apache.dubbo.registry.integration.InterfaceCompatibleRegistryProtocol.getInvoker(InterfaceCompatibleRegistryProtocol.java:58) # MigrationInvoker类at org.apache.dubbo.registry.client.migration.MigrationInvoker.refreshInterfaceInvoker(MigrationInvoker.java:448)at org.apache.dubbo.registry.client.migration.MigrationInvoker.migrateToApplicationFirstInvoker(MigrationInvoker.java:239) # MigrationRuleHandler类at org.apache.dubbo.registry.client.migration.MigrationRuleHandler.refreshInvoker(MigrationRuleHandler.java:73)at org.apache.dubbo.registry.client.migration.MigrationRuleHandler.doMigrate(MigrationRuleHandler.java:57) - locked <0x21db> (a org.apache.dubbo.registry.client.migration.MigrationRuleHandler)at org.apache.dubbo.registry.client.migration.MigrationRuleListener.onRefer(MigrationRuleListener.java:241) # RegistryProtocol类at org.apache.dubbo.registry.integration.RegistryProtocol.interceptInvoker(RegistryProtocol.java:531)at org.apache.dubbo.registry.integration.RegistryProtocol.doRefer(RegistryProtocol.java:500)at org.apache.dubbo.registry.integration.RegistryProtocol.refer(RegistryProtocol.java:485) # refer操作at org.apache.dubbo.rpc.protocol.ProtocolListenerWrapper.refer(ProtocolListenerWrapper.java:74)at org.apache.dubbo.qos.protocol.QosProtocolWrapper.refer(QosProtocolWrapper.java:83)at org.apache.dubbo.rpc.cluster.filter.ProtocolFilterWrapper.refer(ProtocolFilterWrapper.java:71)at org.apache.dubbo.rpc.protocol.ProtocolSerializationWrapper.refer(ProtocolSerializationWrapper.java:52)at org.apache.dubbo.rpc.Protocol$Adaptive.refer(Protocol$Adaptive.java:-1) # ReferenceConfig类at org.apache.dubbo.config.ReferenceConfig.createInvokerForRemote(ReferenceConfig.java:481)at org.apache.dubbo.config.ReferenceConfig.createProxy(ReferenceConfig.java:386)at org.apache.dubbo.config.ReferenceConfig.init(ReferenceConfig.java:275) - locked <0x21dc> (a org.apache.dubbo.config.ReferenceConfig)at org.apache.dubbo.config.ReferenceConfig.get(ReferenceConfig.java:216) # SimpleReferenceCache类at org.apache.dubbo.config.utils.SimpleReferenceCache.get(SimpleReferenceCache.java:110) # DefaultModuleDeployer类at org.apache.dubbo.config.deploy.DefaultModuleDeployer.lambda$referServices$6(DefaultModuleDeployer.java:384)at org.apache.dubbo.config.deploy.DefaultModuleDeployer$$Lambda$880/0x0000000801039dc8.accept(Unknown Source:-1) at java.util.concurrent.ConcurrentHashMap$ValuesView.forEach(ConcurrentHashMap.java:4780) # DefaultModuleDeployer类at org.apache.dubbo.config.deploy.DefaultModuleDeployer.referServices(DefaultModuleDeployer.java:364)at org.apache.dubbo.config.deploy.DefaultModuleDeployer.start(DefaultModuleDeployer.java:151) - locked <0x21dd> (a org.apache.dubbo.config.deploy.DefaultModuleDeployer) # DubboDeployApplicationListener类at org.apache.dubbo.config.spring.context.DubboDeployApplicationListener.onContextRefreshedEvent(DubboDeployApplicationListener.java:108)at org.apache.dubbo.config.spring.context.DubboDeployApplicationListener.onApplicationEvent(DubboDeployApplicationListener.java:98)at org.apache.dubbo.config.spring.context.DubboDeployApplicationListener.onApplicationEvent(DubboDeployApplicationListener.java:44) # SimpleApplicationEventMulticaster类at org.springframework.context.event.SimpleApplicationEventMulticaster.doInvokeListener(SimpleApplicationEventMulticaster.java:176)at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:169)at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:143) # AbstractApplicationContext类at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:421)at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:378)at org.springframework.context.support.AbstractApplicationContext.finishRefresh(AbstractApplicationContext.java:938)at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:586) - locked <0x21de> (a java.lang.Object) # ServletWebServerApplicationContext类at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:145) # SpringApplication类at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:730)at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:412)at org.springframework.boot.SpringApplication.run(SpringApplication.java:302)at org.springframework.boot.SpringApplication.run(SpringApplication.java:1301)at org.springframework.boot.SpringApplication.run(SpringApplication.java:1290) # 项目启动入口at com.example.demo.DemoApplication.main(DemoApplication.java:12)
MockClusterWrapper：服务降级包装类
public class MockClusterWrapper implements Cluster { private final Cluster cluster; public MockClusterWrapper(Cluster cluster) { this.cluster = cluster; } @Override public Invoker join(Directory directory, boolean buildFilterChain) throws RpcException { return new MockClusterInvoker(directory, this.cluster.join(directory, buildFilterChain)); } //返回MockClusterInvoker对象 public Cluster getCluster() { return cluster; }}
MockClusterInvoker：发起服务调用
public class MockClusterInvoker implements ClusterInvoker { private static final Logger logger = LoggerFactory.getLogger(MockClusterInvoker.class); private final Directory directory; private final Invoker invoker; public MockClusterInvoker(Directory directory, Invoker invoker) { this.directory = directory; this.invoker = invoker; } public URL getUrl() { public URL getRegistryUrl() { public Class getInterface() { public Directory getDirectory() { public void destroy() { public boolean isDestroyed() { public boolean isAvailable() { @Override public Result invoke(Invocation invocation) throws RpcException { //服务调用 Result result; String value = getUrl().getMethodParameter(invocation.getMethodName(), MOCK_KEY, Boolean.FALSE.toString()).trim(); //value：获取mock值，如果mock没有设置，默认为false if (value.length() == 0 || "false".equalsIgnoreCase(value)) { //no mock result = this.invoker.invoke(invocation); //value长度为0或者值为false，直接发起服务调用，不使用服务降级，如果调用失败会抛出异常 } else if (value.startsWith(FORCE_KEY)) { //如果value以force开头，不发起远程调用，直接服务降级 if (logger.isWarnEnabled()) { logger.warn("force-mock: " + invocation.getMethodName() + " force-mock enabled , url : " + getUrl()); } //force:direct mock result = doMockInvoke(invocation, null); //服务降级操作 } else { //fail-mock try { //其他先执行服务调用，调用失败则执行服务降级 result = this.invoker.invoke(invocation); //执行远程调用 //fix:#4585 if(result.getException() != null && result.getException() instanceof RpcException){ RpcException rpcException= (RpcException)result.getException(); if(rpcException.isBiz()){ throw rpcException; }else { result = doMockInvoke(invocation, rpcException); } } } catch (RpcException e) { if (e.isBiz()) { //如果是业务异常，直接抛出异常，不进行服务降级 throw e; } if (logger.isWarnEnabled()) { logger.warn("fail-mock: " + invocation.getMethodName() + " fail-mock enabled , url : " + getUrl(), e); } result = doMockInvoke(invocation, e); //服务调用失败，进行服务降级 } } return result; //返回正常结果或者服务降级结果 } @SuppressWarnings({"unchecked", "rawtypes"}) private Result doMockInvoke(Invocation invocation, RpcException e) { //服务降级 Result result; Invoker mockInvoker; List> mockInvokers = selectMockInvoker(invocation); //选择服务降级invoker if (CollectionUtils.isEmpty(mockInvokers)) { mockInvoker = (Invoker) new MockInvoker(getUrl(), directory.getInterface()); } else { mockInvoker = mockInvokers.get(0); } //有多个mockInvoker，选择第一个mockInvoker try { result = mockInvoker.invoke(invocation); //服务降级调用 } catch (RpcException mockException) { if (mockException.isBiz()) { result = AsyncRpcResult.newDefaultAsyncResult(mockException.getCause(), invocation); } else { throw new RpcException(mockException.getCode(), getMockExceptionMessage(e, mockException), mockException.getCause()); } } catch (Throwable me) { throw new RpcException(getMockExceptionMessage(e, me), me.getCause()); } return result; } private String getMockExceptionMessage(Throwable t, Throwable mt) { String msg = "mock error : " + mt.getMessage(); if (t != null) { msg = msg + ", invoke error is :" + StringUtils.toString(t); } return msg; } private List> selectMockInvoker(Invocation invocation) { List> invokers = null; //TODO generic invoker？ if (invocation instanceof RpcInvocation) { //Note the implicit contract (although the description is added to the interface declaration, but extensibility is a problem、The practice placed in the attachment needs to be improved) invocation.setAttachment(INVOCATION_NEED_MOCK, Boolean.TRUE.toString()); //directory will return a list of normal invokers if Constants.INVOCATION_NEED_MOCK is absent or not true in invocation, otherwise, a list of mock invokers will return. try { RpcContext.getServiceContext().setConsumerUrl(getUrl()); invokers = directory.list(invocation); } catch (RpcException e) { if (logger.isInfoEnabled()) { logger.info("Exception when try to invoke mock、Get mock invokers error for service:" + getUrl().getServiceInterface() + ", method:" + invocation.getMethodName() + ", will construct a new mock with 'new MockInvoker()'.", e); } } } return invokers; } @Override public String toString() { return "invoker :" + this.invoker + ",directory: " + this.directory; }}
使用示例
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provider
application.yml
dubbo: application: name: dubbo-provider register-mode: instance registry: address: zookeeper://localhost:2181 group: dubbo #register-mode: instance #register: false protocol: name: dubbo port: 20880
HelloService
public interface HelloService { String hello();}
HelloService2
public interface HelloService2 { String hello2();}
HelloServiceImpl
@DubboService //服务暴露public class HelloServiceImpl implements HelloService { @Override public String hello() { System.out.println("hello provider"); return "hello provider"; }}
HelloService2Impl
@DubboService //服务暴露public class HelloService2Impl implements HelloService2 { @Override public String hello2() { throw new RpcException("hello2 调用出错了"); } //抛出rpcException，消费端调用时执行服务降级操作}
DemoApplication
@EnableDubbo //扫描注册dubbo服务@SpringBootApplicationpublic class DemoApplication { public static void main(String[] args) { SpringApplication.run(DemoApplication.class, args); }}
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consumer
application.yml
dubbo: application: name: dubbo-consumer registry: address: zookeeper://localhost:2181 group: dubbo #register-mode: instance protocol: name: dubbo #port: 20880server: port: 8081
HelloService
public interface HelloService { String hello();}
HelloService2
public interface HelloService2 { String hello2();}
HelloService2Mock
public class HelloService2Mock implements HelloService2 { @Override public String hello2() { return "hello2 mock"; }}
HelloController
@RestControllerpublic class HelloController { @DubboReference(cluster = ClusterRules.FORKING, parameters = {"forks","3"}) private HelloService helloService; @DubboReference(mock = "true") private HelloService2 helloService2; @RequestMapping("/hello") public String hello(){ System.out.println(helloService.hello()); System.out.println(helloService2.hello2()); return "hello consumer 2"; }}
DemoApplication
@EnableDubbo //开启dubbo@SpringBootApplicationpublic class DemoApplication { public static void main(String[] args) { SpringApplication.run(DemoApplication.class, args); }}
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使用测试
localhost:8081/hello，控制台输出：
2022-02-11 12:26:18.615 INFO 1570 --- [nio-8081-exec-1] o.s.web.servlet.DispatcherServlet : Initializing Servlet 'dispatcherServlet'2022-02-11 12:26:18.615 INFO 1570 --- [nio-8081-exec-1] o.s.web.servlet.DispatcherServlet : Completed initialization in 0 mshello providerhello2 mock
helloService2服务调用失败，执行服务降级操作