Hystrix请求命令 HystrixCommand、HystrixObservableCommand
Hystrix有两个请求命令 HystrixCommand、HystrixObservableCommand。
HystrixCommand用在依赖服务返回单个操作结果的时候。又两种执行方式
-execute():同步执行。从依赖的服务返回一个单一的结果对象，或是在发生错误的时候抛出异常。
-queue();异步执行。直接返回一个Future对象，其中包含了服务执行结束时要返回的单一结果对象。
HystrixObservableCommand 用在依赖服务返回多个操作结果的时候。它也实现了两种执行方式
-observe():返回Obervable对象，他代表了操作的多个结果，他是一个HotObservable
-toObservable():同样返回Observable对象，也代表了操作多个结果，但它返回的是一个Cold Observable。
HystrixCommand：
使用方式一：继承的方式
package org.hope.hystrix.example; import com.netflix.hystrix.HystrixCommand; import com.netflix.hystrix.HystrixCommandGroupKey; import com.netflix.hystrix.HystrixCommandKey; import com.netflix.hystrix.HystrixRequestCache; import com.netflix.hystrix.strategy.concurrency.HystrixConcurrencyStrategyDefault; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.web.client.RestTemplate; /** * Created by lisen on 2017/12/15. * HystrixCommand用在命令服务返回单个操作结果的时候 */ public class CommandHelloWorld extends HystrixCommand<String> { private final String name; public CommandHelloWorld(String name) { super(HystrixCommandGroupKey.Factory.asKey("ExampleGroup")); this.name = name; } @Override protected String run() throws Exception { int i = 1/0; return "Hello " + name + "!"; } /** * 降级。Hystrix会在run()执行过程中出现错误、超时、线程池拒绝、断路器熔断等情况时， * 执行getFallBack()方法内的逻辑 */ @Override protected String getFallback() { return "faild"; } }
单元测试：
package org.hope.hystrix.example; import org.junit.Test; import rx.Observable; import rx.Observer; import rx.Subscription; import rx.functions.Action1; import java.util.concurrent.ExecutionException; import java.util.concurrent.Future; import static org.junit.Assert.assertEquals; /** * Created by lisen on 2017/12/15. * */ public class CommandHelloWorldTest { /** * 测试同步执行 */ @Test public void testSynchronous() { System.out.println(new CommandHelloWorld("World").execute()); } /** * 测试异步执行 */ @Test public void testAsynchronous() throws ExecutionException, InterruptedException { Future<String> fWorld = new CommandHelloWorld("World").queue(); System.out.println(fWorld.get()); //一步执行用get()来获取结果 } /** * 虽然HystrixCommand具备了observe()和toObservable()的功能，但是它的实现有一定的局限性， * 它返回的Observable只能发射一次数据，所以Hystrix还提供了HystrixObservableCommand, * 通过它实现的命令可以获取能发多次的Observable */ @Test public void testObserve() { /** * 返回的是Hot Observable,HotObservable，不论 “事件源” 是否有“订阅者” * 都会在创建后对事件进行发布。所以对于Hot Observable的每一个“订阅者”都有 * 可能从“事件源”的中途开始的，并可能只是看到了整个操作的局部过程 */ //blocking Observable<String> ho = new CommandHelloWorld("World").observe(); // System.out.println(ho.toBlocking().single()); //non-blockking //- this is a verbose anonymous inner-class approach and doesn't do assertions ho.subscribe(new Observer<String>() { @Override public void onCompleted() { System.out.println("==============onCompleted"); } @Override public void onError(Throwable e) { e.printStackTrace(); } @Override public void onNext(String s) { System.out.println("=========onNext: " + s); } }); ho.subscribe(new Action1<String>() { @Override public void call(String s) { System.out.println("==================call:" + s); } }); } @Test public void testToObservable() { /** * Cold Observable在没有 “订阅者” 的时候并不会发布时间， * 而是进行等待，知道有 “订阅者” 之后才发布事件，所以对于 * Cold Observable的订阅者，它可以保证从一开始看到整个操作的全部过程。 */ Observable<String> co = new CommandHelloWorld("World").toObservable(); System.out.println(co.toBlocking().single()); } }
使用方式二：注解的方式；
package org.hope.hystrix.example.service; import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand; import com.netflix.hystrix.contrib.javanica.annotation.ObservableExecutionMode; import com.netflix.hystrix.contrib.javanica.command.AsyncResult; import org.springframework.stereotype.Service; import rx.Observable; import rx.Subscriber; import java.util.concurrent.Future; /** * 用@HystrixCommand的方式来实现 */ @Service public class UserService { /** * 同步的方式。 * fallbackMethod定义降级 */ @HystrixCommand(fallbackMethod = "helloFallback") public String getUserId(String name) { int i = 1/0; //此处抛异常，测试服务降级 return "你好:" + name; } public String helloFallback(String name) { return "error"; } //异步的执行 @HystrixCommand(fallbackMethod = "getUserNameError") public Future<String> getUserName(final Long id) { return new AsyncResult<String>() { @Override public String invoke() { int i = 1/0;//此处抛异常,测试服务降级 return "小明:" + id; } }; } public String getUserNameError(Long id) { return "faile"; } }
单元测试：
package org.hope.hystrix.example.service; import javafx.application.Application; import org.hope.hystrix.example.HystrixApplication; import org.hope.hystrix.example.model.User; import org.junit.Test; import org.junit.runner.RunWith; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.boot.test.context.SpringBootTest; import org.springframework.test.context.junit4.SpringJUnit4ClassRunner; import java.util.concurrent.ExecutionException; @RunWith(SpringJUnit4ClassRunner.class) @SpringBootTest(classes = HystrixApplication.class) public class UserServiceTest { @Autowired private UserService userService; /** * 测试同步 */ @Test public void testGetUserId() { System.out.println("=================" + userService.getUserId("lisi")); } /** * 测试异步 */ @Test public void testGetUserName() throws ExecutionException, InterruptedException { System.out.println("=================" + userService.getUserName(30L).get()); } }
HystrixObservableCommand：
使用方式一：继承的方式
HystrixObservable通过实现 protected Observable<String> construct() 方法来执行逻辑。通过 重写 resumeWithFallback方法来实现服务降级
package org.hope.hystrix.example; import com.netflix.hystrix.HystrixCommandGroupKey; import com.netflix.hystrix.HystrixObservableCommand; import rx.Observable; import rx.Subscriber; import rx.schedulers.Schedulers; public class ObservableCommandHelloWorld extends HystrixObservableCommand<String> { private final String name; public ObservableCommandHelloWorld(String name) { super(HystrixCommandGroupKey.Factory.asKey("ExampleGroup")); this.name = name; } @Override protected Observable<String> construct() { return Observable.create(new Observable.OnSubscribe<String>() { @Override public void call(Subscriber<? super String> subscriber) { try { if(!subscriber.isUnsubscribed()) { subscriber.onNext("Hello"); int i = 1 / 0; //模拟异常 subscriber.onNext(name + "!"); subscriber.onCompleted(); } } catch (Exception e) { subscriber.onError(e); } } }).subscribeOn(Schedulers.io()); } /** * 服务降级 */ @Override protected Observable<String> resumeWithFallback() { return Observable.create(new Observable.OnSubscribe<String>() { @Override public void call(Subscriber<? super String> subscriber) { try { if (!subscriber.isUnsubscribed()) { subscriber.onNext("失败了！"); subscriber.onNext("找大神来排查一下吧！"); subscriber.onCompleted(); } } catch (Exception e) { subscriber.onError(e); } } }).subscribeOn(Schedulers.io()); } }
单元测试：
package org.hope.hystrix.example; import org.junit.Test; import rx.Observable; import java.util.Iterator; public class ObservableCommandHelloWorldTest { @Test public void testObservable() { Observable<String> observable= new ObservableCommandHelloWorld("World").observe(); Iterator<String> iterator = observable.toBlocking().getIterator(); while(iterator.hasNext()) { System.out.println(iterator.next()); } } @Test public void testToObservable() { Observable<String> observable= new ObservableCommandHelloWorld("World").observe(); Iterator<String> iterator = observable.toBlocking().getIterator(); while(iterator.hasNext()) { System.out.println(iterator.next()); } } }
使用方式二：注解的方式；
package org.hope.hystrix.example.service; import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand; import com.netflix.hystrix.contrib.javanica.annotation.ObservableExecutionMode; import org.springframework.stereotype.Service; import rx.Observable; import rx.Subscriber; @Service public class ObservableUserService { /** * EAGER参数表示使用observe()方式执行 */ @HystrixCommand(observableExecutionMode = ObservableExecutionMode.EAGER, fallbackMethod = "observFailed") //使用observe()执行方式 public Observable<String> getUserById(final Long id) { return Observable.create(new Observable.OnSubscribe<String>() { @Override public void call(Subscriber<? super String> subscriber) { try { if(!subscriber.isUnsubscribed()) { subscriber.onNext("张三的ID:"); int i = 1 / 0; //抛异常，模拟服务降级 subscriber.onNext(String.valueOf(id)); subscriber.onCompleted(); } } catch (Exception e) { subscriber.onError(e); } } }); } private String observFailed(Long id) { return "observFailed---->" + id; } /** * LAZY参数表示使用toObservable()方式执行 */ @HystrixCommand(observableExecutionMode = ObservableExecutionMode.LAZY, fallbackMethod = "toObserbableError") //表示使用toObservable()执行方式 public Observable<String> getUserByName(final String name) { return Observable.create(new Observable.OnSubscribe<String>() { @Override public void call(Subscriber<? super String> subscriber) { try { if(!subscriber.isUnsubscribed()) { subscriber.onNext("找到"); subscriber.onNext(name); int i = 1/0; ////抛异常，模拟服务降级 subscriber.onNext("了"); subscriber.onCompleted(); } } catch (Exception e) { subscriber.onError(e); } } }); } private String toObserbableError(String name) { return "toObserbableError--->" + name; } }
单元测试：
package org.hope.hystrix.example.service; import org.hope.hystrix.example.HystrixApplication; import org.junit.Test; import org.junit.runner.RunWith; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.boot.test.context.SpringBootTest; import org.springframework.test.context.junit4.SpringJUnit4ClassRunner; import java.util.Iterator; @RunWith(SpringJUnit4ClassRunner.class) @SpringBootTest(classes = HystrixApplication.class) public class ObservableUserServiceTest { @Autowired private ObservableUserService observableUserService; @Test public void testObserve() { Iterator<String> iterator = observableUserService.getUserById(30L).toBlocking().getIterator(); while(iterator.hasNext()) { System.out.println("===============" + iterator.next()); } } @Test public void testToObservable() { Iterator<String> iterator = observableUserService.getUserByName("王五").toBlocking().getIterator(); while(iterator.hasNext()) { System.out.println("===============" + iterator.next()); } } }
总结：
在实际使用时，我们需要为大多数执行过程中可能会失败的Hystrix命令实现服务降级逻辑，但是也有一些情况可以不去实现降级逻辑，比如：
执行写操作的命令：
执行批处理或离线计算的命令：
https://gitee.com/huayicompany/Hystrix-learn/tree/master/hystrix-example
参考:
[1]Github，https://github.com/Netflix/Hystrix/wiki/How-it-Works
[2] 《SpringCloud微服务实战》，电子工业出版社，翟永超
