「DUBBO系列」服务降级源码分析
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1 文章概述
假设服务提供者提供A服务,但是A服务并不稳定,那么如果服务消费者无法正常消费A服务就需要做降级处理,不再消费A服务而是返回一个mock值,这就是所谓服务降级。我们通过分析源码讲解服务降级策略,首先看一个消费者代码实例。
public class Consumer {
public static void main(String[] args) throws Exception {
ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext(new String[] { "classpath*:META-INF/spring/dubbo-consumer.xml" });
context.start();
HelloService helloService = (HelloService) context.getBean("helloService");
String result = helloService.sayHello("IT徐胖子");
System.out.println("==========客户端收到结果==========" + result);
}
}
<beans>
<dubbo:application name="xpz-consumer" />
<dubbo:registry address="zookeeper://127.0.0.1:2181" />
<dubbo:reference id="helloService" interface="com.itxpz.dubbo.demo.provider.HelloService" />
</beans>
MockClusterInvoker正是服务降级核心
// 通过动态代理机制生成代理对象Proxy
// Proxy持有InvokerInvocationHandler
// InvokerInvocationHandler持有invoker = MockClusterInvoker(FailoverClusterInvoker)
HelloService helloService = (HelloService) context.getBean("helloService")
2 服务降级策略
2.1 不配置降级策略
<dubbo:reference id="helloService" interface="com.itxpz.dubbo.demo.provider.HelloService" />
2.2 强制降级策略
<dubbo:reference id="helloService" mock="force:return 1" interface="com.itxpz.dubbo.demo.provider.HelloService" />
2.3 异常降级策略
<dubbo:reference id="helloService" mock="throw com.itxpz.BizException" interface="com.itxpz.dubbo.demo.provider.HelloService" />
2.4 自定义降级策略
package com.itxpz.dubbo.demo.consumer;
import com.itxpz.dubbo.demo.provider.HelloService;
public class HelloServiceMock implements HelloService {
public String sayHello(String name) throws Exception {
return "mock";
}
}
<dubbo:reference id="helloService" mock="com.itxpz.dubbo.demo.consumer.HelloServiceMock" interface="com.itxpz.dubbo.demo.provider.HelloService" />
3 源码分析
public class MockClusterInvoker<T> implements Invoker<T> {
public Result invoke(Invocation invocation) throws RpcException {
Result result = null;
// 检查是否有mock属性
String value = directory.getUrl().getMethodParameter(invocation.getMethodName(), Constants.MOCK_KEY, Boolean.FALSE.toString()).trim();
// 没有mock属性直接执行消费逻辑
if (value.length() == 0 || value.equalsIgnoreCase("false")) {
// 服务消费默认执行FailoverClusterInvoker
result = this.invoker.invoke(invocation);
}
// 不执行消费逻辑直接返回
else if (value.startsWith("force")) {
if (logger.isWarnEnabled()) {
logger.warn("force-mock: " + invocation.getMethodName() + " force-mock enabled , url : " + directory.getUrl());
}
// 直接执行mock逻辑
result = doMockInvoke(invocation, null);
} else {
try {
// 服务消费默认执行FailoverClusterInvoker
result = this.invoker.invoke(invocation);
} catch (RpcException e) {
if (e.isBiz()) {
throw e;
}
if (logger.isWarnEnabled()) {
logger.warn("fail-mock: " + invocation.getMethodName() + " fail-mock enabled , url : " + directory.getUrl(), e);
}
// 服务消费失败执行mock逻辑
result = doMockInvoke(invocation, e);
}
}
return result;
}
}
public class MockInvoker<T> implements Invoker<T> {
public Result invoke(Invocation invocation) throws RpcException {
String mock = getUrl().getParameter(invocation.getMethodName() + "." + Constants.MOCK_KEY);
if (invocation instanceof RpcInvocation) {
((RpcInvocation) invocation).setInvoker(this);
}
if (StringUtils.isBlank(mock)) {
mock = getUrl().getParameter(Constants.MOCK_KEY);
}
if (StringUtils.isBlank(mock)) {
throw new RpcException(new IllegalAccessException("mock can not be null. url :" + url));
}
mock = normalizeMock(URL.decode(mock));
// <mock="force:return 1">直接包装返回结果
if (mock.startsWith(Constants.RETURN_PREFIX)) {
mock = mock.substring(Constants.RETURN_PREFIX.length()).trim();
try {
Type[] returnTypes = RpcUtils.getReturnTypes(invocation);
Object value = parseMockValue(mock, returnTypes);
return new RpcResult(value);
} catch (Exception ew) {
throw new RpcException("mock return invoke error. method :" + invocation.getMethodName() + ", mock:" + mock + ", url: " + url, ew);
}
}
// <mock="throw">抛出异常
else if (mock.startsWith(Constants.THROW_PREFIX)) {
mock = mock.substring(Constants.THROW_PREFIX.length()).trim();
if (StringUtils.isBlank(mock)) {
throw new RpcException("mocked exception for service degradation.");
} else {
// 获取自定义异常
Throwable t = getThrowable(mock);
throw new RpcException(RpcException.BIZ_EXCEPTION, t);
}
}
// <mock="com.itxpz.HelloServiceMock">自定义mock策略
else {
try {
Invoker<T> invoker = getInvoker(mock);
return invoker.invoke(invocation);
} catch (Throwable t) {
throw new RpcException("Failed to create mock implementation class " + mock, t);
}
}
}
}
4 文章总结
本文我们分析了服务消费者降级策略源码,服务降级是分布式系统的重要策略,可以有效防止系统雪崩从而保护系统。
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