13.1 dubbo服务降级源码解析

从 9.1 客户端发起请求源码的客户端请求总体流程图中，截取部分如下：

//代理发出请求
proxy0.sayHello(String paramString)
-->InvokerInvocationHandler.invoke(Object proxy, Method method, Object[] args)
  -->new RpcInvocation(method, args)
  -->MockClusterInvoker.invoke(Invocation invocation)//服务降级的地方

dubbo就是通过MockClusterInvoker来实现服务降级的。

一、示例

1 public interface DemoService {
2 //    String sayHello(String name);
3     Car sayHello(String name);
4 }

将dubbo-demo中的服务接口定义一个返回模型Car。提供者实现如下：

1 public class DemoServiceImpl implements DemoService {
2     public Car sayHello(String name) {
3         Car car = new Car();
4         car.setCarNum("浙A10000");
5         car.setGoMile(100);
6         return car;
7     }
8 }

消费者使用如下：

 1 public class Consumer {
 2     public static void main(String[] args) {
 3         ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext(new String[]{"META-INF/spring/dubbo-demo-consumer.xml"});
 4         context.start();
 5         DemoService demoService = (DemoService) context.getBean("demoService"); // get remote service proxy
 6 
 7         while (true) {
 8             try {
 9                 Thread.sleep(1000);
10                 Car hello = demoService.sayHello("world"); // call remote method
11                 System.out.println(hello.getCarNum() + "-" + hello.getGoMile()); // get result
12             } catch (Throwable throwable) {
13                 throwable.printStackTrace();
14             }
15         }
16     }
17 }

二、使用方式

实际使用中，会通过直接在dubbo-admin中设置服务降级策略，这里使用dubbo用户手册中的方式来更清晰的看一下服务降级的配置（实际上就是进行配置覆盖）

配置规则：

1、使用自定义mock类（接口名+Mock）

mock = default => DemoServiceMock
mock = true => DemoServiceMock
mock = fail => DemoServiceMock
mock = force => DemoServiceMock

2、先普通执行，执行失败之后再执行相应的mock逻辑

mock = fail:throw => throw new RpcException(" mocked exception for Service degradation. ");
mock = fail:throw XxxException => throw new RpcException(RpcException.BIZ_EXCEPTION, XxxException);
mock = fail:return => return null
mock = fail:return xxx => return xxx
mock = fail:return empty => return new Car()

3、直接执行相应的mock逻辑

mock = force:throw => throw new RpcException(" mocked exception for Service degradation. ");
mock = force:throw XxxException => throw new RpcException(RpcException.BIZ_EXCEPTION, XxxException);
mock = force:return => return null
mock = force:return xxx => return xxx
mock = force:return empty => return new Car()

进行配置：

 1 public class DegradeTest {
 2     public static void main(String[] args) {
 3         RegistryFactory registryFactory = ExtensionLoader.getExtensionLoader(RegistryFactory.class).getAdaptiveExtension();
 4         Registry registry = registryFactory.getRegistry(URL.valueOf("zookeeper://10.211.55.5:2181"));
 5         // return null;
 6         registry.register(URL.valueOf("override://0.0.0.0/com.alibaba.dubbo.demo.DemoService?category=configurators&dynamic=false&application=demo-consumer&mock=force:return"));
 7         registry.register(URL.valueOf("override://0.0.0.0/com.alibaba.dubbo.demo.DemoService?category=configurators&dynamic=false&application=demo-consumer&mock=force:return+null"));
 8         // return 空对象;
 9         registry.register(URL.valueOf("override://0.0.0.0/com.alibaba.dubbo.demo.DemoService?category=configurators&dynamic=false&application=demo-consumer&mock=force:return+empty"));
10         // return value;
11         registry.register(URL.valueOf("override://0.0.0.0/com.alibaba.dubbo.demo.DemoService?category=configurators&dynamic=false&application=demo-consumer&mock=force:return+hello"));
12         // throw exception
13         registry.register(URL.valueOf("override://0.0.0.0/com.alibaba.dubbo.demo.DemoService?category=configurators&dynamic=false&application=demo-consumer&mock=force:throw"));
14         // throw custom-msg exception
15         registry.register(URL.valueOf("override://0.0.0.0/com.alibaba.dubbo.demo.DemoService?category=configurators&dynamic=false&application=demo-consumer&mock=force:throw+com.alibaba.dubbo.Test.MyRuntimeException"));
16         // 执行mock类
17         registry.register(URL.valueOf("override://0.0.0.0/com.alibaba.dubbo.demo.DemoService?category=configurators&dynamic=false&application=demo-consumer&mock=force:com.alibaba.dubbo.demo.DemoServiceMock"));
18     }
19 }

上述需要注意的是需要配置为“force:return+null”的格式而非“force:return null”。（实际上空格的url encode就是+号），上述代码的执行，实际上是在zk上创建configurators的子节点：

关于覆盖配置：http://dubbo.io/books/dubbo-user-book/demos/config-rule.html

override:// 表示数据采用覆盖方式，支持 override 和 absent，可扩展，必填。
0.0.0.0 表示对所有 IP 地址生效，如果只想覆盖某个 IP 的数据，请填入具体 IP，必填。
com.alibaba.dubbo.demo.DemoService表示只对指定服务生效，必填。
category=configurators 表示该数据为动态配置类型，必填。
dynamic=false 表示该数据为持久数据，当注册方退出时，数据依然保存在注册中心，必填。
enabled=true 覆盖规则是否生效，可不填，缺省生效。
application=demo-consumer 表示只对指定应用生效，可不填，表示对所有应用生效。
mock=force:return+null表示将满足以上条件的 mock 参数的值覆盖为 force:return+null。如果想覆盖其它参数，直接加在 override 的 URL 参数上。

三、源码分析

 1 public class MockClusterInvoker<T> implements Invoker<T> {
 2     private final Directory<T> directory; //RegistryDirectory：存储invoker列表
 3     private final Invoker<T> invoker; //FailoverClusterInvoker:容错策略
 4 
 5     public Result invoke(Invocation invocation) throws RpcException {
 6         Result result = null;
 7 
 8         String value = directory.getUrl().getMethodParameter(invocation.getMethodName(), Constants.MOCK_KEY, Boolean.FALSE.toString()).trim();
 9         if (value.length() == 0 || value.equalsIgnoreCase("false")) {
10             //no mock
11             result = this.invoker.invoke(invocation);
12         } else if (value.startsWith("force")) {
13             ...
14             //force:direct mock
15             result = doMockInvoke(invocation, null);
16         } else {
17             //fail-mock
18             try {
19                 result = this.invoker.invoke(invocation);
20             } catch (RpcException e) {
21                 if (e.isBiz()) {
22                     throw e;
23                 } else {
24                     ...
25                     result = doMockInvoke(invocation, e);
26                 }
27             }
28         }
29         return result;
30     }
31 }

首先去获取mock参数，

如果没有配置，则直接使用FailoverClusterInvoker去正常的向provider发出请求；
如果配置为以force开头的，则直接执行doMockInvoke(Invocation invocation, RpcException e)，不再向provider发送请求；
如果配置为以fail开头的，则先使用FailoverClusterInvoker去正常的向provider发出请求，如果失败抛出了非业务异常，则执行doMockInvoke(Invocation invocation, RpcException e)；

 1     private Result doMockInvoke(Invocation invocation, RpcException e) {
 2         Result result = null;
 3         Invoker<T> minvoker;
 4 
 5         List<Invoker<T>> mockInvokers = selectMockInvoker(invocation); //获取mock类型的Invoker
 6         if (mockInvokers == null || mockInvokers.size() == 0) {
 7             minvoker = (Invoker<T>) new MockInvoker(directory.getUrl()); //如果没有配置mock类型的Invoker，则自己创建一个MockInvoker
 8         } else {
 9             minvoker = mockInvokers.get(0);
10         }
11         try {
12             result = minvoker.invoke(invocation); //执行MockInvoker的invoke(Invocation invocation)方法
13         } catch (RpcException me) {
14             if (me.isBiz()) {
15                 result = new RpcResult(me.getCause());
16             } else { //非业务异常
17                 throw new RpcException(me.getCode(), getMockExceptionMessage(e, me), me.getCause());
18             }
19         } catch (Throwable me) {
20             throw new RpcException(getMockExceptionMessage(e, me), me.getCause());
21         }
22         return result;
23     }

从RegistryDirectory中获取MockInvoker：

 1     /**
 2      * Return MockInvoker
 3      * Contract：
 4      * directory.list() will return a list of normal invokers if Constants.INVOCATION_NEED_MOCK is present in invocation, otherwise, a list of mock invokers will return.
 5      * if directory.list() returns more than one mock invoker, only one of them will be used.
 6      *
 7      * @param invocation
 8      * @return
 9      */
10     private List<Invoker<T>> selectMockInvoker(Invocation invocation) {
11         List<Invoker<T>> invokers = null;
12         //TODO generic invoker？
13         if (invocation instanceof RpcInvocation) {
14             //Note the implicit contract (although the description is added to the interface declaration, but extensibility is a problem. The practice placed in the attachement needs to be improved)
15             ((RpcInvocation) invocation).setAttachment(Constants.INVOCATION_NEED_MOCK, Boolean.TRUE.toString());
16             //directory will return a list of normal invokers if Constants.INVOCATION_NEED_MOCK is present in invocation, otherwise, a list of mock invokers will return.
17             try {
18                 invokers = directory.list(invocation);
19             } catch (RpcException e) {
20                 if (logger.isInfoEnabled()) {
21                     logger.info("Exception when try to invoke mock. Get mock invokers error for service:"
22                             + directory.getUrl().getServiceInterface() + ", method:" + invocation.getMethodName()
23                             + ", will contruct a new mock with 'new MockInvoker()'.", e);
24                 }
25             }
26         }
27         return invokers;
28     }

首先使用RegistryDirectory获取出方法名为sayHello的Invoker列表，之后使用MockInvokersSelector（Router）选取出MockInvoker。

 1 public class MockInvokersSelector implements Router {
 2 
 3     public <T> List<Invoker<T>> route(final List<Invoker<T>> invokers,
 4                                       URL url, final Invocation invocation) throws RpcException {
 5         if (invocation.getAttachments() == null) {
 6             return getNormalInvokers(invokers);
 7         } else {
 8             String value = invocation.getAttachments().get(Constants.INVOCATION_NEED_MOCK);
 9             if (value == null)
10                 return getNormalInvokers(invokers);
11             else if (Boolean.TRUE.toString().equalsIgnoreCase(value)) {
12                 return getMockedInvokers(invokers);
13             }
14         }
15         return invokers;
16     }
17 
18     private <T> List<Invoker<T>> getMockedInvokers(final List<Invoker<T>> invokers) {
19         if (!hasMockProviders(invokers)) {
20             return null;
21         }
22         List<Invoker<T>> sInvokers = new ArrayList<Invoker<T>>(1);
23         for (Invoker<T> invoker : invokers) {
24             if (invoker.getUrl().getProtocol().equals(Constants.MOCK_PROTOCOL)) {
25                 sInvokers.add(invoker);
26             }
27         }
28         return sInvokers;
29     }
30 
31     private <T> boolean hasMockProviders(final List<Invoker<T>> invokers) {
32         boolean hasMockProvider = false;
33         for (Invoker<T> invoker : invokers) {
34             if (invoker.getUrl().getProtocol().equals(Constants.MOCK_PROTOCOL)) {
35                 hasMockProvider = true;
36                 break;
37             }
38         }
39         return hasMockProvider;
40     }
41 }

这里获取到的是空列表。

所以会先创建一个MockInvoker对象，之后执行其invoker方法。

MockInvoker：

 1     public Result invoke(Invocation invocation) throws RpcException {
 2         String mock = getUrl().getParameter(invocation.getMethodName() + "." + Constants.MOCK_KEY); //sayHello.mock
 3         if (invocation instanceof RpcInvocation) {
 4             ((RpcInvocation) invocation).setInvoker(this);
 5         }
 6         if (StringUtils.isBlank(mock)) {
 7             mock = getUrl().getParameter(Constants.MOCK_KEY); //mock
 8         }
 9 
10         if (StringUtils.isBlank(mock)) {
11             throw new RpcException(new IllegalAccessException("mock can not be null. url :" + url));
12         }
13         mock = normallizeMock(URL.decode(mock));
14         if (Constants.RETURN_PREFIX.trim().equalsIgnoreCase(mock.trim())) { // return
15             RpcResult result = new RpcResult();
16             result.setValue(null);
17             return result;
18         } else if (mock.startsWith(Constants.RETURN_PREFIX)) { // return value(包括return null)
19             mock = mock.substring(Constants.RETURN_PREFIX.length()).trim();
20             mock = mock.replace('`', '"');
21             try {
22                 Type[] returnTypes = RpcUtils.getReturnTypes(invocation);
23                 Object value = parseMockValue(mock, returnTypes);
24                 return new RpcResult(value);
25             } catch (Exception ew) {
26                 throw new RpcException("mock return invoke error. method :" + invocation.getMethodName() + ", mock:" + mock + ", url: " + url, ew);
27             }
28         } else if (mock.startsWith(Constants.THROW_PREFIX)) { // throw xxx
29             mock = mock.substring(Constants.THROW_PREFIX.length()).trim();
30             mock = mock.replace('`', '"');
31             if (StringUtils.isBlank(mock)) {// throw
32                 throw new RpcException(" mocked exception for Service degradation. ");
33             } else { // user customized class ： throw xxx
34                 Throwable t = getThrowable(mock);
35                 throw new RpcException(RpcException.BIZ_EXCEPTION, t);
36             }
37         } else { //impl mock: 自定义mock类
38             try {
39                 Invoker<T> invoker = getInvoker(mock);
40                 return invoker.invoke(invocation);
41             } catch (Throwable t) {
42                 throw new RpcException("Failed to create mock implemention class " + mock, t);
43             }
44         }
45     }

首先获取到mock配置，例如：mock=force:return+null，之后进行url解码为mock=force:return null，最后进行处理为mock=return null，然后根据规则走分支。

mock参数的处理函数：

 1     /**
 2      * 一、使用自定义mock类
 3      * mock = default => DemoServiceMock
 4      * mock = true => DemoServiceMock
 5      * mock = fail => DemoServiceMock
 6      * mock = force => DemoServiceMock
 7      *
 8      * 二、先普通执行，执行失败之后再执行相应的mock逻辑
 9      * mock = fail:throw => throw new RpcException(" mocked exception for Service degradation. ");
10      * mock = fail:throw XxxException => throw new RpcException(RpcException.BIZ_EXCEPTION, XxxException);
11      * mock = fail:return => return null
12      * mock = fail:return xxx => return xxx
13      *
14      * 三、直接执行相应的mock逻辑
15      * mock = force:throw => throw new RpcException(" mocked exception for Service degradation. ");
16      * mock = force:throw XxxException => throw new RpcException(RpcException.BIZ_EXCEPTION, XxxException);
17      * mock = force:return => return null
18      * mock = force:return xxx => return xxx
19      *
20      * @param mock
21      * @return
22      */
23     private String normallizeMock(String mock) {
24         if (mock == null || mock.trim().length() == 0) {
25             return mock;
26         } else if (ConfigUtils.isDefault(mock) || "fail".equalsIgnoreCase(mock.trim()) || "force".equalsIgnoreCase(mock.trim())) {
27             mock = url.getServiceInterface() + "Mock";
28         }
29         if (mock.startsWith(Constants.FAIL_PREFIX)) {
30             mock = mock.substring(Constants.FAIL_PREFIX.length()).trim();
31         } else if (mock.startsWith(Constants.FORCE_PREFIX)) {
32             mock = mock.substring(Constants.FORCE_PREFIX.length()).trim();
33         }
34         return mock;
35     }

我们这里来看一下自定义mock类。消费端编写：

 1 public class DemoServiceMock implements DemoService {
 2 
 3     @Override
 4     public Car sayHello(String name) {
 5         Car car = new Car();
 6         car.setCarNum("mock中");
 7         car.setGoMile(666);
 8         return car;
 9     }
10 }

配置覆盖：

1         registry.register(URL.valueOf("override://0.0.0.0/com.alibaba.dubbo.demo.DemoService?category=configurators&dynamic=false&application=demo-consumer&mock=force:com.alibaba.dubbo.demo.DemoServiceMock"));

MockInvoker.invoke

1             try {
2                 Invoker<T> invoker = getInvoker(mock);
3                 return invoker.invoke(invocation);
4             } catch (Throwable t) {
5                 throw new RpcException("Failed to create mock implemention class " + mock, t);
6             }

 1     private Invoker<T> getInvoker(String mockService) {
 2         Invoker<T> invoker = (Invoker<T>) mocks.get(mockService);
 3         if (invoker != null) {
 4             return invoker;
 5         } else {
 6             Class<T> serviceType = (Class<T>) ReflectUtils.forName(url.getServiceInterface());
 7             if (ConfigUtils.isDefault(mockService)) {
 8                 mockService = serviceType.getName() + "Mock";
 9             }
10 
11             Class<?> mockClass = ReflectUtils.forName(mockService);
12             if (!serviceType.isAssignableFrom(mockClass)) {
13                 throw new IllegalArgumentException("The mock implemention class " + mockClass.getName() + " not implement interface " + serviceType.getName());
14             }
15 
16             if (!serviceType.isAssignableFrom(mockClass)) {
17                 throw new IllegalArgumentException("The mock implemention class " + mockClass.getName() + " not implement interface " + serviceType.getName());
18             }
19             try {
20                 T mockObject = (T) mockClass.newInstance(); // 获取自定义mock类实例
21                 invoker = proxyFactory.getInvoker(mockObject, (Class<T>) serviceType, url); // 和普通类一样创建Invoker
22                 if (mocks.size() < 10000) {
23                     mocks.put(mockService, invoker);
24                 }
25                 return invoker;
26             } catch (InstantiationException e) {
27                 throw new IllegalStateException("No such empty constructor \"public " + mockClass.getSimpleName() + "()\" in mock implemention class " + mockClass.getName(), e);
28             } catch (IllegalAccessException e) {
29                 throw new IllegalStateException(e);
30             }
31         }
32     }

上边看了return和自定义mock类，最后来看一下throw异常。

默认抛出RpcException，异常信息：mocked exception for Service degradation. 也可以自定义异常，例如：

1 public class MyRuntimeException extends RuntimeException {
2     private String msg;
3 
4     public MyRuntimeException(String msg){
5         this.msg = msg;
6     }
7 }

自定义异常必须具有单参构造器且参数为String。

配置覆盖：

MockInvoker.invoke

1 registry.register(URL.valueOf("override://0.0.0.0/com.alibaba.dubbo.demo.DemoService?category=configurators&dynamic=false&application=demo-consumer&mock=force:throw+com.alibaba.dubbo.Test.MyRuntimeException"));

 1     private Throwable getThrowable(String throwstr) {
 2         Throwable throwable = (Throwable) throwables.get(throwstr);
 3         if (throwable != null) {
 4             return throwable;
 5         } else {
 6             Throwable t = null;
 7             try {
 8                 Class<?> bizException = ReflectUtils.forName(throwstr);
 9                 Constructor<?> constructor;
10                 constructor = ReflectUtils.findConstructor(bizException, String.class);
11                 t = (Throwable) constructor.newInstance(new Object[]{" mocked exception for Service degradation. "});
12                 if (throwables.size() < 1000) {
13                     throwables.put(throwstr, t);
14                 }
15             } catch (Exception e) {
16                 throw new RpcException("mock throw error :" + throwstr + " argument error.", e);
17             }
18             return t;
19         }
20     }

服务降级结束！！！

来源：https://www.cnblogs.com/java-zhao/p/8320519.html

标签

Dubbo

mock

源码

try

string