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。
