Spring Boot 简明教程

Spring Boot - Hystrix

Hystrix 是 Netflix 的一个库。Hystrix 可隔离服务之间的接入点,阻止级联故障,并提供后备选项。

例如,当您调用第三方应用程序时,它需要更多时间来发送响应。因此,那时,控件就会进入后备方法,并向您的应用程序返回自定义响应。

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

首先,我们需要在我们的构建配置文件中添加 Spring Cloud Starter Hystrix 依赖关系。

Maven 用户可以在 pom.xml 文件中添加以下依赖关系 −

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

Gradle 用户可以在 build.gradle 文件中添加下列依赖 -

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

现在,在您的主 Spring Boot 应用程序类文件中添加 @EnableHystrix 注解。@EnableHystrix 注解用于在 Spring Boot 应用程序中启用 Hystrix 功能。

主要 Spring Boot 应用程序类文件代码如下所示:

package com.tutorialspoint.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,以便在从请求时间开始的 3 秒后返回字符串。

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

现在,为 Rest API 添加 @HystrixCommand 和 @HystrixProperty,并以毫秒值为单位定义超时时间。

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

接下来,如果请求响应时间较长,则定义后备方法 fallback_hello()。

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

下面显示了包含 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 本身以主 Spring Boot 应用程序类文件编写。

package com.tutorialspoint.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 file

<?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.tutorialspoint</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.tutorialspoint'
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}"
   }
}

您可以创建一个可执行 JAR 文件并使用以下 Maven 或 Gradle 命令运行 Spring Boot 应用程序 -

对于 Maven,使用命令,如所示 −

mvn clean install

“BUILD SUCCESS”之后,您可以在目标目录中找到 JAR 文件。

对于 Gradle,使用命令,如所示 −

gradle clean build

“BUILD SUCCESSFUL”之后,您可以在 build/libs 目录中找到 JAR 文件。

现在,运行 JAR 文件,使用如下所示命令 −

java –jar <JARFILE>

这将启动 8080 端口上的应用程序,如下所示 −

tomcat application command prompt

现在,从 Web 浏览器点击网址 http://localhost:8080/ ,然后查看 Hystrix 响应。API 响应时间为 3 秒,但 Hystrix 超时时间为 1 秒。

request fail hystrix timeout