Spring Boot - Hystrix

Hystrix是Netflix的一个库。Hystrix隔离了服务之间的访问点，阻止了它们之间的级联故障并提供了后备选项。

例如，当你调用一个3 次第三方应用程序，它需要更多的时间来发送响应。所以在那个时候，控件转到了回退方法并将自定义响应返回给你的应用程序。

在本章中，您将看到如何在Spring Boot应用程序中实现Hystrix。

首先，我们需要在构建配置文件中添加Spring Cloud Starter Hystrix依赖项。

Maven用户可以在pom.xml文件中添加以下依赖项

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

Gradle用户可以在build.gradle文件中添加以下依赖项

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

现在，将@EnableHystrix注释添加到主Spring Boot应用程序类文件中。@EnableHystrix注释用于将Hystrix功能启用到Spring Boot应用程序中。

主要的Spring Boot应用程序类文件代码如下

package com.codingdict.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);
   }
}

现在编写一个简单的Rest Controller，使其在请求的时间3秒后返回String。

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

现在，为Rest API添加@Hystrix命令和@HystrixProperty，并以毫秒为单位定义超时值。

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

接下来，如果请求需要很长时间来响应，请定义回退方法fallback_hello()。

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

此处显示包含REST API和Hystrix属性的完整Rest Controller类文件

@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编写在主Spring Boot应用程序类文件本身中。

package com.codingdict.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";
   }
}

完整的构建配置文件如下所示。

Maven - pom.xml文件

<?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.codingdict</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 - 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.codingdict'
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}"
   }
}

您可以创建可执行的JAR文件，并使用以下Maven或Gradle命令运行Spring Boot应用程序 -

对于Maven，使用如下所示的命令

mvn clean install

在“BUILD SUCCESS”之后，您可以在目标目录下找到JAR文件。

对于Gradle，使用如下所示的命令

gradle clean build

在“BUILD SUCCESSFUL”之后，您可以在build / libs目录下找到JAR文件。

现在，使用下面给出的命令运行JAR文件

java –jar <JARFILE>

这将在Tomcat端口8080上启动应用程序，如下所示

Hystrix

现在，从Web浏览器中点击URL http://localhost:8080/，然后查看Hystrix响应。API需要3秒钟才能响应，但Hystrix超时为1秒。

Hystrix