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，当调用第三方应用程序时，发送响应需要更多时间。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，将看到如何在Spring Boot应用程序中实现Hystrix。

首先，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 Spring Boot 应用程序类文件代码如下 -

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); } }

现在编写一个简单的Rest Controller，使其在请求的时间后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.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"; } }

完整的构建配置文件如下所示。

Maven构建文件 - pom.xml 的内容：

<?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构建文件 – 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，可以在target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，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。

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。

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