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谈到服务降级，Dubbo 本身就提供了服务降级的机制；而 Dubbo 的服务降级机制主要是利用服务消费者的 mock 属性。
服务消费者的 mock 属性有以下三种使用方式，下面将带着例子简单介绍一下。
例子：
mock=return+null，即当服务提供者出现异常（宕机或者业务异常），则返回null给服务消费者。
2021-01-26 09:39:54.631 [main] [INFO ] [o.a.d.r.z.ZookeeperRegistry] [] [] - [DUBBO] Notify urls for subscribe url consumer://127.0.0.1/com.winfun.service.DubboServiceOne?application=dubbo-service&category=providers,configurators,routers&check=false&dubbo=2.0.2&init=false&interface=com.winfun.service.DubboServiceOne&lazy=true&methods=sayHello&mock=return+null&pid=36270&qos.enable=false&reference.filter=default,dubboLogFilter&release=2.7.7&retries=1&side=consumer&sticky=false×tamp=1611625194544
例子：
mock="return null"，即当服务提供者出现异常（宕机或者业务异常），则返回null给服务消费者。
public class HelloController{
@DubboReference(check = false,lazy = true,retries = 1,mock = "return null")
private DubboServiceOne dubboServiceOne;
//.....
}
例子：
Mock实现类 为 Dubbo接口 的实现类，并且 Mock实现类 与 Dubbo接口 放同一个项目中。
/**
*
* DubboServiceTwo
* @author winfun
* @date 2020/10/29 5:00 下午
**/
public interface DubboServiceTwo {
/***
* say hi
* @author winfun
* @param name name
* @return {@link ApiResult<String> }
**/
ApiResult<String> sayHi(String name);
}
/**
* DubboServiceTwo 降级实现类
* @author winfun
* @date 2021/1/26 9:21 上午
**/
public class DubboServiceTwoMock implements DubboServiceTwo{
/***
* say hi
* @author winfun
* @param name name
* @return {@link ApiResult <String> }
**/
@Override
public ApiResult<String> sayHi(String name) {
return ApiResult.fail("Mock实现类-服务降级了");
}
}
下面将使用第二种方式来展示 Duboo 自身提供的服务降级机制。
/**
* Say Hello
* @author winfun
* @date 2020/10/29 5:12 下午
**/
@RestController
public class HelloController {
@DubboReference(check = false,lazy = true,retries = 1,mock="return {\"code\":1,\"message\":\"熔断限流了\"}")
private DubboServiceOne dubboServiceOne;
@GetMapping("/hello/{name}")
public ApiResult sayHello(@PathVariable("name") String name){
return this.dubboServiceOne.sayHello(name);
}
}
/**
* DubboServiceOneImpl
* @author winfun
* @date 2020/10/29 5:04 下午
**/
@DubboService(interfaceClass = DubboServiceOne.class)
public class DubboServiceOneImpl implements DubboServiceOne {
/***
* say hello
* @author winfun
* @param name name
* @return {@link ApiResult<String> }
**/
@SneakyThrows
@Override
public ApiResult<String> sayHello(String name) {
// dubbo 接口默认超时时间为1s，我们这里直接休眠5s
Thread.sleep(5000);
return ApiResult.success("hello "+name);
}
情况一：服务提供者没起来
这个时候服务消费者不会进行重试，只会直接进行服务降级，返回我们设定的 Mock 值。
2021-01-27 18:02:12.288 [http-nio-8081-exec-1] [WARN ] [o.a.d.r.c.s.w.MockClusterInvoker] [/hello/name] [16117417328056102141] - [DUBBO] fail-mock: sayHello fail-mock enabled , url : zookeeper://127.0.0.1:2181/org.apache.dubbo.registry.RegistryService?application=dubbo-service&check=false&dubbo=2.0.2&init=false&interface=com.winfun.service.DubboServiceOne&lazy=true&methods=sayHello&mock=return+%7B%22code%22%3A1%2C%22message%22%3A%22%E7%86%94%E6%96%AD%E9%99%90%E6%B5%81%E4%BA%86%22%7D&pid=51874&qos.enable=false&reference.filter=default,dubboLogFilter,-sentinel.dubbo.consumer.filter®ister.ip=172.26.144.16&release=2.7.7&retries=0&side=consumer&sticky=false×tamp=1611741716665, dubbo version: 2.7.7, current host: 172.26.144.16
org.apache.dubbo.rpc.RpcException: No provider available from registry 127.0.0.1:2181 for service com.winfun.service.DubboServiceOne on consumer 172.26.144.16 use dubbo version 2.7.7, please check status of providers(disabled, not registered or in blacklist).
//.....省略
2021-01-27 18:02:12.289 [http-nio-8081-exec-1] [INFO ] [o.a.d.r.c.s.w.MockClusterInvoker] [/hello/name] [16117417328056102141] - [DUBBO] Exception when try to invoke mock. Get mock invokers error for service:com.winfun.service.DubboServiceOne, method:sayHello, will construct a new mock with 'new MockInvoker()'., dubbo version: 2.7.7, current host: 172.26.144.16
org.apache.dubbo.rpc.RpcException: No provider available from registry 127.0.0.1:2181 for service com.winfun.service.DubboServiceOne on consumer 172.26.144.16 use dubbo version 2.7.7, please check status of providers(disabled, not registered or in blacklist).
//....省略
大家可能会存在一个质疑点：我上面说的是不会进行重试，但是控制台我们看到了两次异常；其实第二次异常，是获取 MockInvoker 导致的，所以大家可以先忽略，下面我会详细分析 MockClusterInvoker 的源码，就知道为啥会有两次异常了。
情况二：服务提供者超时
注意：Dubbo 提供的服务降级机制，不支持对服务提供者业务异常的情况。
这个时候消费者会进行 1+retries 次调用，然后再进行服务降级。
org.apache.dubbo.rpc.RpcException: Failed to invoke the method sayHello in the service com.winfun.service.DubboServiceOne. Tried 2 times of the providers [127.0.0.1:20881] (1/1) from the registry 127.0.0.1:2181 on the consumer 172.26.144.16 using the dubbo version 2.7.7. Last error is: Invoke remote method timeout. method: sayHello, provider: dubbo://127.0.0.1:20881/com.winfun.service.DubboServiceOne?anyhost=true&application=dubbo-service&check=false&deprecated=false&dubbo=2.0.2&dynamic=true&generic=false&init=false&interface=com.winfun.service.DubboServiceOne&lazy=true&methods=sayHello&mock=return+%7B%22code%22%3A1%2C%22message%22%3A%22%E7%86%94%E6%96%AD%E9%99%90%E6%B5%81%E4%BA%86%22%7D&pid=52020&qos.enable=false&reference.filter=default,dubboLogFilter,-sentinel.dubbo.consumer.filter®ister.ip=172.26.144.16&release=2.7.7&remote.application=dubbo-provider-one&retries=1&service.filter=default,dubboLogFilter&side=consumer&sticky=false×tamp=1611742232968, cause: org.apache.dubbo.remoting.TimeoutException: Waiting server-side response timeout by scan timer. start time: 2021-01-27 18:10:42.189, end time: 2021-01-27 18:10:43.204, client elapsed: 1 ms, server elapsed: 1014 ms, timeout: 1000 ms, request: Request [id=1, version=2.0.2, twoway=true, event=false, broken=false, data=null], channel: /172.26.144.16:56663 -> /172.26.144.16:20881
at org.apache.dubbo.rpc.cluster.support.FailoverClusterInvoker.doInvoke(FailoverClusterInvoker.java:113)
//....省略
关于服务降级的逻辑，主要在 Dubbo 提供的 MockClusterInvoker 类中。
下面我们直接看看 MockClusterInvoker 的源码：
public class MockClusterInvoker<T> implements Invoker<T> {
// ...省略
@Override
public Result invoke(Invocation invocation) throws RpcException {
Result result = null;
// 从 consumer 的注册url中获取方法的 mock 属性值
String value = getUrl().getMethodParameter(invocation.getMethodName(), MOCK_KEY, Boolean.FALSE.toString()).trim();
// mock 为空或者false，不进行服务降级处理
if (value.length() == 0 || "false".equalsIgnoreCase(value)) {
//no mock
result = this.invoker.invoke(invocation);
// 是否强行执行服务降级处理
} else if (value.startsWith("force")) {
if (logger.isWarnEnabled()) {
logger.warn("force-mock: " + invocation.getMethodName() + " force-mock enabled , url : " + getUrl());
}
//force:direct mock
result = doMockInvoke(invocation, null);
} else {
//fail-mock
try {
result = this.invoker.invoke(invocation);
//fix:#4585
if(result.getException() != null && result.getException() instanceof RpcException){
RpcException rpcException= (RpcException)result.getException();
// 如果是业务异常，直接抛出
if(rpcException.isBiz()){
throw rpcException;
}else {
// 服务降级处理
result = doMockInvoke(invocation, rpcException);
}
}
} catch (RpcException e) {
// 如果是业务异常，直接抛出
if (e.isBiz()) {
throw e;
}
if (logger.isWarnEnabled()) {
logger.warn("fail-mock: " + invocation.getMethodName() + " fail-mock enabled , url : " + getUrl(), e);
}
// 服务降级处理
result = doMockInvoke(invocation, e);
}
}
return result;
}
@SuppressWarnings({"unchecked", "rawtypes"})
private Result doMockInvoke(Invocation invocation, RpcException e) {
Result result = null;
Invoker<T> minvoker;
// 获取服务降级 Invoker 列表
List<Invoker<T>> mockInvokers = selectMockInvoker(invocation);
if (CollectionUtils.isEmpty(mockInvokers)) {
// 服务降级 Invoker 列表为空，默认使用 Dubbo 提供的 MockInvoker 类
minvoker = (Invoker<T>) new MockInvoker(getUrl(), directory.getInterface());
} else {
minvoker = mockInvokers.get(0);
}
try {
// 服务降级处理
result = minvoker.invoke(invocation);
} catch (RpcException me) {
if (me.isBiz()) {
result = AsyncRpcResult.newDefaultAsyncResult(me.getCause(), invocation);
} else {
throw new RpcException(me.getCode(), getMockExceptionMessage(e, me), me.getCause());
}
} catch (Throwable me) {
throw new RpcException(getMockExceptionMessage(e, me), me.getCause());
}
return result;
}
//...
}
从上面的源码分析可知：
在 MockClusterInvoker#invoke 方法里面，如果是业务异常是不会做 mock 做处理的。而其他关于 RPC 的异常，是会做 mock 处理的，例如我们这里拿来测试的服务提供者超时异常和服务提供者不存在；
在 doMockInvoke 方法中，首先会调用 selectMockInvoker 方法会尝试获取 MockInvoker，而默认情况下，都是没有的，所以最后会使用 Dubbo 提供的 MockInvoker。
这里也回答了情况一例子中，会抛出两次异常的原因，就是因为获取 MockInvoker 的时候，会调用 selectMockInvoker，而如果服务没启动，那么必须还会再抛一次 No provider 的异常啦～
最后，大家如果有兴趣，可以自行继续研究 MockInvoker 的源码，特别是里面的 invoke 和 parseMockValue 方法，分别是服务降级的逻辑和 Mock 属性内容的解析。
如果不是看了 MockInvoker#parseMockValue 方法，一开始我都不知道如何返回 Json 格式的结果，只会直接返回 null，哈哈哈。所以源码还是得多看！
到此，关于 Dubbo 提供的服务降级的 Mock 机制已经简单地过了一遍，但是我们可以发现有一个问题：
其实经过上面的例子分析和源码分析，我们会发现一个问题：由于 dubbo 不带熔断机制，所以尽管每次因为 RPC 异常而导致调用失败，也不会进行熔断处理；即不管调用失败多少次，消费者还是会继续进行调用。
其实这样会导致服务的资源浪费：
所以，为 dubbo 配一个熔断机制是非常有必要的了。
我个人对熔断的理解：
如果当调用失败达到指定的次数，则将熔断器打开一段时间，即将请求链路断开；在指定时间内，都不再让消费者向提供者发送请求；当熔断时间到了，就将熔断器设置为半打开的状态，此时消费者可以往提供者发送请求，并统计成功次数，如果达到指定的成功次数，熔断器则变为关闭状态，即将请求链路打开，否则熔断器又变回打开状态。
所以说，只要给dubbo加上熔断机制，不管是业务错误还是请求超时，只要时间内达到了一定的次数就做上述的熔断处理，这样就可以防止没有必要的调用。
熔断框架比较：https://www.icode9.com/content-4-620551.html
经过上面的对比，我个人是建议使用 Sentinel 的，因为它提供了更加灵活的使用方式，并且支持更多的规则，还提供了一个易用强大的控制台。
Sentinel 提供了三大接入方式：利用 sentinel-core 组件进行硬代码、利用 sentinel-annotation-aspectj 组件提供的注解功能、各种主流框架的接入方式。
下面我将分别使用三种方式为 Dubbo接口 接入限流和熔断的机制。
在接入之前，我们需要注意的一个点是：要为 Dubbo接口 接入熔断&限流等机制，必须要为 Dubbo接口 指定资源，并且为资源初始化规则；否则只是引入了组件，也无法使用 Sentinel 提供的限流&熔断功能。
引入依赖：
引入 sentinel-core 依赖，直接植入硬代码进行熔断限流。
<dependency>
<groupId>com.alibaba.csp</groupId>
<artifactId>sentinel-core</artifactId>
<version>1.8.0</version>
</dependency>
Controller 代码：
/**
* Say Hello
* @author winfun
* @date 2020/10/29 5:12 下午
**/
@Slf4j
@RequestMapping("/hello")
@RestController
public class HelloController {
public static final String RESOURCE_NAME = "dubboServiceOne";
@DubboReference(check = false,lazy = true,retries = 0)
private DubboServiceOne dubboServiceOne;
/**
* 初始化流控规则和熔断规则
* ps:因为我们没有接入 Sentinel Dashboard，所以得自己在代码里面设置好
*/
static{
// 初始化流控规则
final List<FlowRule> flowRules = new ArrayList<>();
final List<DegradeRule> degradeRules = new ArrayList<>();
// 限流规则
final FlowRule flowRule = new FlowRule();
flowRule.setResource(RESOURCE_NAME);
flowRule.setGrade(RuleConstant.FLOW_GRADE_QPS);
// 1 QPS
flowRule.setCount(1);
flowRules.add(flowRule);
// 熔断规则
final DegradeRule degradeRule = new DegradeRule();
degradeRule.setResource(RESOURCE_NAME);
degradeRule.setGrade(RuleConstant.DEGRADE_GRADE_EXCEPTION_COUNT);
// 2个异常数
degradeRule.setCount(2);
// 时间窗口长度，单位为秒
degradeRule.setTimeWindow(5);
// 最小请求数
degradeRule.setMinRequestAmount(5);
// 熔断时长：当5秒内，10个请求里面出现2个异常，则进行熔断，熔断时长为10s
degradeRule.setStatIntervalMs(10000);
degradeRules.add(degradeRule);
FlowRuleManager.loadRules(flowRules);
DegradeRuleManager.loadRules(degradeRules);
}
@GetMapping("/{name}")
public ApiResult sayHello(@PathVariable("name") final String name){
final String hello = this.sayHelloByDubbo2Code(name);
return ApiResult.success(hello);
}
/***
* 接入Sentinel方式：植入硬代码进行熔断限流
* @author winfun
* @param name name
* @return {@link ApiResult<String> }
**/
private ApiResult<String> sayHelloByDubbo2Code(final String name) {
ApiResult<String> result;
Entry entry = null;
try {
entry = SphU.entry(RESOURCE_NAME);
result = this.dubboServiceOne.sayHello(name);
} catch (BlockException e) {
if (e instanceof DegradeException){
log.error("资源：{} 被熔断了,message is {}",RESOURCE_NAME,e.getMessage());
result = ApiResult.fail("hello fallback");
}else {
log.error("资源：{} 被流控了",RESOURCE_NAME);
result = ApiResult.fail("hello block");
}
} catch (Exception e){
log.error("业务处理发生异常,exception is {}",e.getMessage());
// 若需要配置降级规则，需要通过这种方式记录业务异常
Tracer.traceEntry(e, entry);
result = ApiResult.fail("exception");
//throw new RuntimeException("业务处理发生异常");
} finally {
// 务必保证 exit，务必保证每个 entry 与 exit 配对
if (entry != null) {
entry.exit();
}
}
return result;
}
}
单元测试：
利用 MockMvc 来进行接口测试，循环调用。
@AutoConfigureMockMvc
@SpringBootTest(classes = DubboServiceApplication.class)
@RunWith(SpringRunner.class)
public class ServiceOneApplicationTests {
@Autowired
private MockMvc mockMvc;
@SneakyThrows
@Test
public void sayHello(){
for (int i = 0; i < 100; i++) {
// 休眠500毫秒，即1秒两次调用，可以触发流控规则
Thread.sleep(500);
MvcResult result = mockMvc.perform(MockMvcRequestBuilders.get("/hello/winfun"))
.andReturn();
System.out.println(result.getResponse().getContentAsString());
}
}
}
在看单元测试的结果前，我们先分析一下我们的流控&熔断配置：
单元测试中，我们是不会开启服务提供者的，先看看控制台打印的日志信息：
2021-01-27 11:42:18.568 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 发生异常,message is No provider available from registry 127.0.0.1:2181 for service com.winfun.service.DubboServiceOne on consumer 127.0.0.1 use dubbo version 2.7.7, please check status of providers(disabled, not registered or in blacklist).
{"code":1,"message":"exception","data":null,"traceId":null}
2021-01-27 11:42:19.147 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被流控了
{"code":1,"message":"hello block","data":null,"traceId":null}
2021-01-27 11:42:19.653 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 发生异常,message is No provider available from registry 127.0.0.1:2181 for service com.winfun.service.DubboServiceOne on consumer 127.0.0.1 use dubbo version 2.7.7, please check status of providers(disabled, not registered or in blacklist).
{"code":1,"message":"exception","data":null,"traceId":null}
2021-01-27 11:42:20.160 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被流控了
{"code":1,"message":"hello block","data":null,"traceId":null}
2021-01-27 11:42:20.666 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 发生异常,message is No provider available from registry 127.0.0.1:2181 for service com.winfun.service.DubboServiceOne on consumer 127.0.0.1 use dubbo version 2.7.7, please check status of providers(disabled, not registered or in blacklist).
{"code":1,"message":"exception","data":null,"traceId":null}
2021-01-27 11:42:21.172 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被流控了
{"code":1,"message":"hello block","data":null,"traceId":null}
2021-01-27 11:42:21.681 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 发生异常,message is No provider available from registry 127.0.0.1:2181 for service com.winfun.service.DubboServiceOne on consumer 127.0.0.1 use dubbo version 2.7.7, please check status of providers(disabled, not registered or in blacklist).
{"code":1,"message":"exception","data":null,"traceId":null}
2021-01-27 11:42:22.190 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被流控了
{"code":1,"message":"hello block","data":null,"traceId":null}
2021-01-27 11:42:22.695 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 发生异常,message is No provider available from registry 127.0.0.1:2181 for service com.winfun.service.DubboServiceOne on consumer 127.0.0.1 use dubbo version 2.7.7, please check status of providers(disabled, not registered or in blacklist).
{"code":1,"message":"exception","data":null,"traceId":null}
2021-01-27 11:42:23.202 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被流控了
{"code":1,"message":"hello block","data":null,"traceId":null}
2021-01-27 11:42:23.709 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 发生异常,message is No provider available from registry 127.0.0.1:2181 for service com.winfun.service.DubboServiceOne on consumer 127.0.0.1 use dubbo version 2.7.7, please check status of providers(disabled, not registered or in blacklist).
{"code":1,"message":"exception","data":null,"traceId":null}
2021-01-27 11:42:24.215 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被流控了
{"code":1,"message":"hello block","data":null,"traceId":null}
2021-01-27 11:42:24.724 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 发生异常,message is No provider available from registry 127.0.0.1:2181 for service com.winfun.service.DubboServiceOne on consumer 127.0.0.1 use dubbo version 2.7.7, please check status of providers(disabled, not registered or in blacklist).
{"code":1,"message":"exception","data":null,"traceId":null}
2021-01-27 11:42:25.232 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被流控了
{"code":1,"message":"hello block","data":null,"traceId":null}
2021-01-27 11:42:25.738 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被熔断了,message is null
{"code":1,"message":"hello fallback","data":null,"traceId":null}
2021-01-27 11:42:26.247 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被熔断了,message is null
{"code":1,"message":"hello fallback","data":null,"traceId":null}
2021-01-27 11:42:26.757 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被熔断了,message is null
{"code":1,"message":"hello fallback","data":null,"traceId":null}
2021-01-27 11:42:27.265 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被熔断了,message is null
{"code":1,"message":"hello fallback","data":null,"traceId":null}
2021-01-27 11:42:27.769 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被熔断了,message is null
{"code":1,"message":"hello fallback","data":null,"traceId":null}
2021-01-27 11:42:28.274 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被熔断了,message is null
{"code":1,"message":"hello fallback","data":null,"traceId":null}
2021-01-27 11:42:28.779 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被熔断了,message is null
{"code":1,"message":"hello fallback","data":null,"traceId":null}
2021-01-27 11:42:29.284 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被熔断了,message is null
{"code":1,"message":"hello fallback","data":null,"traceId":null}
2021-01-27 11:42:29.790 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 发生异常,message is No provider available from registry 127.0.0.1:2181 for service com.winfun.service.DubboServiceOne on consumer 127.0.0.1 use dubbo version 2.7.7, please check status of providers(disabled, not registered or in blacklist).
{"code":1,"message":"exception","data":null,"traceId":null}
2021-01-27 11:42:30.299 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被流控了
{"code":1,"message":"hello block","data":null,"traceId":null}
2021-01-27 11:42:30.803 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被熔断了,message is null
{"code":1,"message":"hello fallback","data":null,"traceId":null}
2021-01-27 11:42:31.309 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被熔断了,message is null
{"code":1,"message":"hello fallback","data":null,"traceId":null}
2021-01-27 11:42:31.814 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被熔断了,message is null
{"code":1,"message":"hello fallback","data":null,"traceId":null}
// .....
总结：
我们可以看到，控制台的日志打印是符合我们的预期的：
并且，流控规则的优先级优先于熔断规则。
引入依赖：
引入 sentinel-annotation-aspectj 依赖。
<dependency>
<groupId>com.alibaba.csp</groupId>
<artifactId>sentinel-transport-simple-http</artifactId>
<version>1.8.0</version>
</dependency>
注入切面：
手动注入 SentinelResourceAspect，因为 Sentinel 提供的这个切面，是没有 @Component 等注解的，所以还是得自己注入到 Spring 容器中。
/**
* 需要引入一下，因为 Sentile 提供的这个切面是没有加 @Component 注解的
* @return
*/
@Bean
public SentinelResourceAspect sentinelResourceAspect() {
return new SentinelResourceAspect();
}
我们使用这个 @SentinelResource 注解，可直接在 Controller 的方法加注解，也可以自己再弄一个 Service 来加注解，这两个都可以.
因为我们的 Controller 层就是只调用了 Dubbo 接口，所以就直接在 Controller 的方法上面加注解了，而如果业务是非常多的，那就可以考虑单独弄个 Service 来给 Dubbo 接口再包一层。
Spring AOP 同时支持 JDK 和 CGLIB 动态代理，SpringBoot 2.x 默认使用 CGLIB 动态代理。
Controller 代码：
/**
* Say Hello
* @author winfun
* @date 2020/10/29 5:12 下午
**/
@Slf4j
@RequestMapping("/hello")
@RestController
public class HelloController {
public static final String RESOURCE_NAME = "dubboServiceOne";
@DubboReference(check = false,lazy = true,retries = 0)
private DubboServiceOne dubboServiceOne;
/**
* 初始化流控规则和熔断规则
* ps:因为我们没有接入 Sentinel Dashboard，所以得自己在代码里面设置好
*/
static{
// 初始化流控规则
final List<FlowRule> flowRules = new ArrayList<>();
final List<DegradeRule> degradeRules = new ArrayList<>();
// 限流规则
final FlowRule flowRule = new FlowRule();
flowRule.setResource(RESOURCE_NAME);
flowRule.setGrade(RuleConstant.FLOW_GRADE_QPS);
// 1 QPS
flowRule.setCount(1);
flowRules.add(flowRule);
// 熔断规则
final DegradeRule degradeRule = new DegradeRule();
degradeRule.setResource(RESOURCE_NAME);
degradeRule.setGrade(RuleConstant.DEGRADE_GRADE_EXCEPTION_COUNT);
// 2个异常数
degradeRule.setCount(1);
// 时间窗口长度，单位为秒
degradeRule.setTimeWindow(5);
// 最小请求数
degradeRule.setMinRequestAmount(5);
// 熔断时长：当5秒内，10个请求里面出现2个异常，则进行熔断，熔断时长为10s
degradeRule.setStatIntervalMs(10000);
degradeRules.add(degradeRule);
FlowRuleManager.loadRules(flowRules);
DegradeRuleManager.loadRules(degradeRules);
}
@GetMapping("/{name}")
@SentinelResource(value=RESOURCE_NAME,fallback = "sayHelloFallback",blockHandler = "sayHelloBlock")
public ApiResult sayHello(@PathVariable("name") final String name){
String hello = this.dubboServiceOne.sayHello(name);
return ApiResult.success(hello);
}
/**
* Fallback 函数，函数签名与原函数一致或加一个 Throwable 类型的参数.
* @param name
* @param throwable
* @return {@link ApiResult<String> }
*/
public ApiResult<String> sayHelloFallback(final String name, final Throwable throwable){
log.error("资源：{} 发生异常,message is {}",RESOURCE_NAME,throwable.getMessage());
return ApiResult.fail("hello exception");
}
/**
* BlockHandler 函数
* blockHandler 函数访问范围需要是 public，返回类型需要与原方法相匹配，参数类型需要和原方法相匹配并且最后加一个额外的参数，类型为 BlockException
* @param name
* @param e
* @return {@link ApiResult<String> }
*/
public ApiResult<String> sayHelloBlock(final String name, final BlockException e){
ApiResult<String> result;
if (e instanceof DegradeException){
log.error("资源：{} 被熔断了,message is {}",RESOURCE_NAME,e.getMessage());
result = ApiResult.fail("hello fallback");
}else {
log.error("资源：{} 被流控了",RESOURCE_NAME);
result = ApiResult.fail("hello block");
}
return result;
}
}
bolckHandler 和 fallbackHandler 的返回值都要原方法一致。
单元测试：
@AutoConfigureMockMvc
@SpringBootTest(classes = DubboServiceApplication.class)
@RunWith(SpringRunner.class)
public class ServiceOneApplicationTests {
@Autowired
private MockMvc mockMvc;
@SneakyThrows
@Test
public void sayHello(){
for (int i = 0; i < 100; i++) {
// 休眠500毫秒，即1秒两次调用，可以出发流控规则
Thread.sleep(500);
MvcResult result = mockMvc.perform(MockMvcRequestBuilders.get("/hello/winfun"))
.andReturn();
System.out.println(result.getResponse().getContentAsString());
}
}
}
控制台打印：可以看到和上面使用 Sentinel-core 植入硬代码的打印是一样的
2021-01-27 11:43:36.995 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 发生异常,message is No provider available from registry 127.0.0.1:2181 for service com.winfun.service.DubboServiceOne on consumer 127.0.0.1 use dubbo version 2.7.7, please check status of providers(disabled, not registered or in blacklist).
{"code":1,"message":"hello exception","data":null,"traceId":null}
2021-01-27 11:43:37.560 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 发生异常,message is No provider available from registry 127.0.0.1:2181 for service com.winfun.service.DubboServiceOne on consumer 127.0.0.1 use dubbo version 2.7.7, please check status of providers(disabled, not registered or in blacklist).
{"code":1,"message":"hello exception","data":null,"traceId":null}
2021-01-27 11:43:38.098 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被流控了
{"code":1,"message":"hello block","data":null,"traceId":null}
2021-01-27 11:43:38.605 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 发生异常,message is No provider available from registry 127.0.0.1:2181 for service com.winfun.service.DubboServiceOne on consumer 127.0.0.1 use dubbo version 2.7.7, please check status of providers(disabled, not registered or in blacklist).
{"code":1,"message":"hello exception","data":null,"traceId":null}
2021-01-27 11:43:39.114 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被流控了
{"code":1,"message":"hello block","data":null,"traceId":null}
2021-01-27 11:43:39.620 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 发生异常,message is No provider available from registry 127.0.0.1:2181 for service com.winfun.service.DubboServiceOne on consumer 127.0.0.1 use dubbo version 2.7.7, please check status of providers(disabled, not registered or in blacklist).
{"code":1,"message":"hello exception","data":null,"traceId":null}
2021-01-27 11:43:40.129 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被流控了
{"code":1,"message":"hello block","data":null,"traceId":null}
2021-01-27 11:43:40.638 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 发生异常,message is No provider available from registry 127.0.0.1:2181 for service com.winfun.service.DubboServiceOne on consumer 127.0.0.1 use dubbo version 2.7.7, please check status of providers(disabled, not registered or in blacklist).
{"code":1,"message":"hello exception","data":null,"traceId":null}
2021-01-27 11:43:41.144 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被流控了
{"code":1,"message":"hello block","data":null,"traceId":null}
2021-01-27 11:43:41.651 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 发生异常,message is No provider available from registry 127.0.0.1:2181 for service com.winfun.service.DubboServiceOne on consumer 127.0.0.1 use dubbo version 2.7.7, please check status of providers(disabled, not registered or in blacklist).
{"code":1,"message":"hello exception","data":null,"traceId":null}
2021-01-27 11:43:42.160 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被流控了
{"code":1,"message":"hello block","data":null,"traceId":null}
2021-01-27 11:43:42.668 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 发生异常,message is No provider available from registry 127.0.0.1:2181 for service com.winfun.service.DubboServiceOne on consumer 127.0.0.1 use dubbo version 2.7.7, please check status of providers(disabled, not registered or in blacklist).
{"code":1,"message":"hello exception","data":null,"traceId":null}
2021-01-27 11:43:43.173 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被流控了
{"code":1,"message":"hello block","data":null,"traceId":null}
2021-01-27 11:43:43.679 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 发生异常,message is No provider available from registry 127.0.0.1:2181 for service com.winfun.service.DubboServiceOne on consumer 127.0.0.1 use dubbo version 2.7.7, please check status of providers(disabled, not registered or in blacklist).
{"code":1,"message":"hello exception","data":null,"traceId":null}
2021-01-27 11:43:44.185 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被流控了
{"code":1,"message":"hello block","data":null,"traceId":null}
2021-01-27 11:43:44.691 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 发生异常,message is No provider available from registry 127.0.0.1:2181 for service com.winfun.service.DubboServiceOne on consumer 127.0.0.1 use dubbo version 2.7.7, please check status of providers(disabled, not registered or in blacklist).
{"code":1,"message":"hello exception","data":null,"traceId":null}
2021-01-27 11:43:45.198 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被流控了
{"code":1,"message":"hello block","data":null,"traceId":null}
2021-01-27 11:43:45.704 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被熔断了,message is null
{"code":1,"message":"hello fallback","data":null,"traceId":null}
2021-01-27 11:43:46.208 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被熔断了,message is null
{"code":1,"message":"hello fallback","data":null,"traceId":null}
2021-01-27 11:43:46.714 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被熔断了,message is null
{"code":1,"message":"hello fallback","data":null,"traceId":null}
2021-01-27 11:43:47.222 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被熔断了,message is null
{"code":1,"message":"hello fallback","data":null,"traceId":null}
2021-01-27 11:43:47.729 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被熔断了,message is null
{"code":1,"message":"hello fallback","data":null,"traceId":null}
2021-01-27 11:43:48.233 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被熔断了,message is null
{"code":1,"message":"hello fallback","data":null,"traceId":null}
2021-01-27 11:43:48.736 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被熔断了,message is null
{"code":1,"message":"hello fallback","data":null,"traceId":null}
2021-01-27 11:43:49.247 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被熔断了,message is null
{"code":1,"message":"hello fallback","data":null,"traceId":null}
2021-01-27 11:43:49.758 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 发生异常,message is No provider available from registry 127.0.0.1:2181 for service com.winfun.service.DubboServiceOne on consumer 127.0.0.1 use dubbo version 2.7.7, please check status of providers(disabled, not registered or in blacklist).
{"code":1,"message":"hello exception","data":null,"traceId":null}
2021-01-27 11:43:50.266 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被流控了
{"code":1,"message":"hello block","data":null,"traceId":null}
2021-01-27 11:43:50.773 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被熔断了,message is null
{"code":1,"message":"hello fallback","data":null,"traceId":null}
2021-01-27 11:43:51.277 [main] [ERROR] [c.w.c.HelloController] [] [] - 资源：dubboServiceOne 被熔断了,message is null
{"code":1,"message":"hello fallback","data":null,"traceId":null}
// .....
