在Hystrix中實(shí)現(xiàn)了線程隔離、斷路器等一系列的服務(wù)保護(hù)功能，本文都沒有涉及，也沒有和spring cloud進(jìn)行整合卖局，本文內(nèi)容：

1. Hystrix命令的基本使用
2. 當(dāng)依賴的服務(wù)發(fā)生延遲時(shí)，對(duì)客戶端進(jìn)行保護(hù)
3. 回退方法的使用

1 服務(wù)提供端

首先需要明確一點(diǎn)双霍，Hystrix是在客戶端使用的砚偶，先創(chuàng)建一個(gè)服務(wù)端項(xiàng)目，提供服務(wù)洒闸，一個(gè)簡(jiǎn)單的spring boot項(xiàng)目即可染坯。
提供兩個(gè)服務(wù)，normalHello可以正常調(diào)用丘逸；errorHello至少10秒后才會(huì)返回結(jié)果单鹿，Hystrix處于對(duì)客戶端的保護(hù)，會(huì)認(rèn)為該服務(wù)超時(shí)深纲。

import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class MyController {

    @RequestMapping(value = "/normalHello", method = RequestMethod.GET)
    public String normalHello() {
        return "Hello World";
    }

    @RequestMapping(value = "/errorHello", method = RequestMethod.GET)
    public String errorHello() throws Exception {
        Thread.sleep(10000);
        return "Error Hello World";
    }
}

2 客戶端

再創(chuàng)建一個(gè)客戶端項(xiàng)目仲锄，在該項(xiàng)目中使用Hystrix，pom依賴如下：

<dependencies>
        <dependency>
            <groupId>com.netflix.hystrix</groupId>
            <artifactId>hystrix-core</artifactId>
            <version>1.5.12</version>
        </dependency>
        <dependency>
            <groupId>org.slf4j</groupId>
            <version>1.7.25</version>
            <artifactId>slf4j-log4j12</artifactId>
        </dependency>
        <dependency>
            <groupId>commons-logging</groupId>
            <artifactId>commons-logging</artifactId>
            <version>1.2</version>
        </dependency>
        <dependency>
            <groupId>org.apache.httpcomponents</groupId>
            <artifactId>httpclient</artifactId>
            <version>4.5.2</version>
        </dependency>
    </dependencies>

Hystrix是命令設(shè)計(jì)模式的實(shí)現(xiàn)者湃鹊，命令執(zhí)行者和命令調(diào)用者完全解耦儒喊，將服務(wù)的調(diào)用作為一個(gè)命令。如果想要調(diào)用服務(wù)器提供的normalHello服務(wù)币呵，創(chuàng)建一個(gè)實(shí)現(xiàn)HystrixCommand的類怀愧，并實(shí)現(xiàn)run方法，在run方法中實(shí)現(xiàn)對(duì)服務(wù)的調(diào)用余赢。

客戶端通過httpclient調(diào)用服務(wù)

public class HelloCommand extends HystrixCommand<String> {

    public HelloCommand() {
        super(HystrixCommandGroupKey.Factory.asKey("TestGroup"));
    }

    protected String run() throws Exception {
        String url = "http://localhost:8080/normalHello";
        HttpGet httpget = new HttpGet(url);     
        CloseableHttpClient httpclient = HttpClients.createDefault();
        HttpResponse response = httpclient.execute(httpget);
        return EntityUtils.toString(response.getEntity());
    }

}

當(dāng)調(diào)用延遲的服務(wù)時(shí)芯义，需要再實(shí)現(xiàn)一個(gè)getFallback方法，就是上篇文章中的回退方法妻柒，當(dāng)被調(diào)用的服務(wù)出現(xiàn)問題時(shí)扛拨，直接調(diào)用回退方法。

public class ErrorCommand extends HystrixCommand<String> {

    public ErrorCommand() {
        super(HystrixCommandGroupKey.Factory.asKey("TestGroup"));
    }

    protected String run() throws Exception {
        String url = "http://localhost:8080/errorHello";
        HttpGet httpget = new HttpGet(url);     
        CloseableHttpClient httpclient = HttpClients.createDefault();
        HttpResponse response = httpclient.execute(httpget);
        return EntityUtils.toString(response.getEntity());
    }

    protected String getFallback() {
        System.out.println("fall back method");
        return "fall back hello";
    }

}

3 服務(wù)調(diào)用

然后蛤奢，實(shí)例化一個(gè)調(diào)用服務(wù)的命令鬼癣，執(zhí)行命令即可陶贼。執(zhí)行ErrorCommand命令時(shí)啤贩，因?yàn)榉?wù)延遲待秃，會(huì)直接調(diào)用getFallback方法返回結(jié)果：

public class NormalMain {

    public static void main(String[] args) {
        HelloCommand command = new HelloCommand();
        String result = command.execute();
        System.out.println(result);
    }

}

public class ErrorMain {

    public static void main(String[] args) {
        ErrorCommand command = new ErrorCommand();
        String result = command.execute();
        System.out.println(result);
    }

}