Spring Boot Hystrix

Hystrix是Netflix的一個庫。 Hystrix隔離了服務之間的訪問點，阻止了它們之間的級聯故障並提供了後備選項。

例如，當調用第三方應用程序時，發送響應需要更多時間。所以在那個時候，控件轉到了回退方法並將自定義響應返回給你的應用程序。

在本章中，將看到如何在Spring Boot應用程序中實現Hystrix。

首先，需要在構建配置文件中添加Spring Cloud Starter Hystrix依賴項。

Maven用戶可以在pom.xml 文件中添加以下依賴項 -

<dependency>
   <groupId>org.springframework.cloud</groupId>
   <artifactId>spring-cloud-starter-hystrix</artifactId>
</dependency>

Gradle用戶可以在build.gradle 文件中添加以下依賴項 -

compile('org.springframework.cloud:spring-cloud-starter-hystrix')

現在，將[@EnableHystrix](https://github.com/EnableHystrix "@EnableHystrix")註釋添加到主Spring Boot應用程序類文件中。 [@EnableHystrix](https://github.com/EnableHystrix "@EnableHystrix")註釋用於將Hystrix功能啓用到Spring Boot應用程序中。

主 Spring Boot 應用程序類文件代碼如下 -

package com.yiibai.hystrixapp;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.hystrix.EnableHystrix;

@SpringBootApplication
@EnableHystrix
public class HystrixappApplication {
   public static void main(String[] args) {
      SpringApplication.run(HystrixappApplication.class, args);
   }
}

現在編寫一個簡單的Rest Controller，使其在請求的時間後3秒後返回String。

@RequestMapping(value = "/")
public String hello() throws InterruptedException {
   Thread.sleep(3000);
   return "Welcome Hystrix";
}

現在，爲Rest API添加[@Hystrix](https://github.com/Hystrix "@Hystrix")命令和[@HystrixProperty](https://github.com/HystrixProperty "@HystrixProperty")，並以毫秒爲單位定義超時值。

@HystrixCommand(fallbackMethod = "fallback_hello", commandProperties = {
   @HystrixProperty(name = "execution.isolation.thread.timeoutInMilliseconds", value = "1000")
})

接下來，如果請求需要很長時間來響應，請定義回退方法fallback_hello()。

private String fallback_hello() {
   return "Request fails. It takes long time to response";
}

此處顯示包含REST API和Hystrix屬性的完整Rest Controller類文件 -

@RequestMapping(value = "/")
@HystrixCommand(fallbackMethod = "fallback_hello", commandProperties = {
   @HystrixProperty(name = "execution.isolation.thread.timeoutInMilliseconds", value = "1000")
})
public String hello() throws InterruptedException {
   Thread.sleep(3000);
   return "Welcome Hystrix";
}
private String fallback_hello() {
   return "Request fails. It takes long time to response";
}

在此示例中，REST API編寫在主Spring Boot應用程序類文件本身中。

package com.yiibai.hystrixapp;

import org.springframework.boot.SpringApplication;
import com.netflix.hystrix.contrib.javanica.annotation.HystrixProperty;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.hystrix.EnableHystrix;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;

@SpringBootApplication
@EnableHystrix
@RestController
public class HystrixappApplication {
   public static void main(String[] args) {
      SpringApplication.run(HystrixappApplication.class, args);
   }
   @RequestMapping(value = "/")
   @HystrixCommand(fallbackMethod = "fallback_hello", commandProperties = {
      @HystrixProperty(name = "execution.isolation.thread.timeoutInMilliseconds", value = "1000")
   })
   public String hello() throws InterruptedException {
      Thread.sleep(3000);
      return "Welcome Hystrix";
   }
   private String fallback_hello() {
      return "Request fails. It takes long time to response";
   }
}

完整的構建配置文件如下所示。

Maven構建文件 - pom.xml 的內容：

<?xml version = "1.0" encoding = "UTF-8"?>
<project xmlns = "http://maven.apache.org/POM/4.0.0" 
   xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation = "http://maven.apache.org/POM/4.0.0 
   http://maven.apache.org/xsd/maven-4.0.0.xsd">

   <modelVersion>4.0.0</modelVersion>
   <groupId>com.yiibai</groupId>
   <artifactId>hystrixapp</artifactId>
   <version>0.0.1-SNAPSHOT</version>
   <packaging>jar</packaging>
   <name>hystrixapp</name>
   <description>Demo project for Spring Boot</description>

   <parent>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-parent</artifactId>
      <version>1.5.9.RELEASE</version>
      <relativePath/> <!-- lookup parent from repository -->
   </parent>

   <properties>
      <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
      <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
      <java.version>1.8</java.version>
      <spring-cloud.version>Edgware.RELEASE</spring-cloud.version>
   </properties>

   <dependencies>
      <dependency>
         <groupId>org.springframework.cloud</groupId>
         <artifactId>spring-cloud-starter-hystrix</artifactId>
      </dependency>
      <dependency>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-web</artifactId>
      </dependency>
      <dependency>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-test</artifactId>
         <scope>test</scope>
      </dependency>
   </dependencies>

   <dependencyManagement>
      <dependencies>
         <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-dependencies</artifactId>
            <version>${spring-cloud.version}</version>
            <type>pom</type>
            <scope>import</scope>
         </dependency>
      </dependencies>
   </dependencyManagement>

   <build>
      <plugins>
         <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
         </plugin>
      </plugins>
   </build>

</project>

Gradle構建文件 – build.gradle

buildscript {
   ext {
      springBootVersion = '1.5.9.RELEASE'
   }
   repositories {
      mavenCentral()
   }
   dependencies {
      classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}")
   }
}
apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'org.springframework.boot'

group = 'com.yiibai'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = 1.8

repositories {
   mavenCentral()
}
ext {
   springCloudVersion = 'Edgware.RELEASE'
}
dependencies {
   compile('org.springframework.cloud:spring-cloud-starter-hystrix')
   compile('org.springframework.boot:spring-boot-starter-web')
   testCompile('org.springframework.boot:spring-boot-starter-test')
}
dependencyManagement {
   imports {
      mavenBom "org.springframework.cloud:spring-cloud-dependencies:${springCloudVersion}"
   }
}

可以創建可執行的JAR文件，並使用以下Maven或Gradle命令運行Spring Boot應用程序 -

對於Maven，使用如下所示的命令 -

mvn clean install

在「BUILD SUCCESS」之後，可以在target目錄下找到JAR文件。

對於Gradle，使用如下所示的命令 -

gradle clean build

在「BUILD SUCCESSFUL」之後，可以在build/libs 目錄下找到JAR文件。現在，使用下面給出的命令運行JAR文件 -

java –jar <JARFILE>

這將在Tomcat端口8080上啓動應用程序。

現在，從Web瀏覽器中點擊URL => http://localhost:8080/，然後查看Hystrix響應。 API需要3秒鐘才能響應，但Hystrix超時爲1秒。