分布式环境中,可能会有一些被依赖的服务会失效,影响系统的稳定运行。
Hystrix通过添加延迟阈值以及容错的逻辑,以控制分布式系统间组件的交互。
Hystrix通过隔离服务间的访问点、停止它们之间的级联故障、提供可回退操作来实现容错。
下面例子为在Spring Cloud的使用。
开发工具:IntelliJ IDEA 2019.2.3
一、服务器端
1、创建项目
IDEA中创建一个新的SpringBoot项目,名称为“spring-hystrix-server”,SpringBoot版本选择2.1.10,在选择Dependencies(依赖)的界面勾选Spring Cloud Discovery ->
Eureka Server,创建完成后的pom.xml配置文件自动添加SpringCloud最新稳定版本依赖,当前为Greenwich.SR3。
pom.xml完整内容如下:
<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.1.10.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>com.example</groupId>
<artifactId>spring-hystrix-server</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>spring-hystrix-server</name>
<description>Demo project for Spring Boot</description>
<properties>
<java.version>1.8</java.version>
<spring-cloud.version>Greenwich.SR3</spring-cloud.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-netflix-eureka-server</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>
2、修改配置application.yml
修改端口号为8761;取消将自己信息注册到Eureka服务器,不从Eureka服务器抓取注册信息。
server:
port: 8761
eureka:
client:
register-with-eureka: false
fetch-registry: false
3、修改启动类代码
增加注解@EnableEurekaServer
二、服务提供者
1、创建项目
IDEA中创建一个新的SpringBoot项目,除了名称为“spring-hystrix-provider”,其它步骤和上面创建服务器端一样。
2、修改配置application.yml
server:
port: 8080
spring:
application:
name: spring-hystrix-provider
eureka:
instance:
hostname: localhost
client:
serviceUrl:
defaultZone: http://localhost:8761/eureka/
3、添加一个实体类User.java
package com.example.springhystrixprovider;
public class User {
String name;
Integer age;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
}
4、修改启动类代码
package com.example.springhystrixprovider;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.http.MediaType;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import javax.servlet.http.HttpServletRequest;
@SpringBootApplication
@EnableEurekaClient
@RestController
public class SpringHystrixProviderApplication {
public static void main(String[] args) {
SpringApplication.run(SpringHystrixProviderApplication.class, args);
}
@RequestMapping("/hello")
public String hello(HttpServletRequest request) {
return "hello world." + request.getServerPort();
}
@RequestMapping(value="/user/{name}", produces = MediaType.APPLICATION_JSON_VALUE)
public User user(@PathVariable String name) {
User u = new User();
u.setName(name);
u.setAge(30);
return u;
}
}
三、服务调用者
1、创建项目
IDEA中创建一个新的SpringBoot项目,名称为“spring-hystrix-invoker”,SpringBoot版本选择2.1.10,在选择Dependencies(依赖)的界面勾选Spring Cloud Discovery -> Eureka Server,Spring Cloud Circuit Breaker -> Hystrix。
pom.xml完整内容如下:
<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.1.10.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>com.example</groupId>
<artifactId>spring-hystrix-invoker</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>spring-hystrix-invoker</name>
<description>Demo project for Spring Boot</description>
<properties>
<java.version>1.8</java.version>
<spring-cloud.version>Greenwich.SR3</spring-cloud.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-netflix-hystrix</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>
2、修改配置application.yml
server:
port: 9000
spring:
application:
name: spring-hystrix-invoker
eureka:
instance:
hostname: localhost
client:
serviceUrl:
defaultZone: http://localhost:8761/eureka/
3、修改启动类代码
增加注解@EnableEurekaClient和@EnableCircuitBreaker。
package com.example.springhystrixinvoker;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.servlet.ServletComponentScan;
import org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;
@SpringBootApplication
@EnableEurekaClient
@EnableCircuitBreaker
public class SpringHystrixInvokerApplication {
@LoadBalanced
@Bean
public RestTemplate getRestTemplate(){
return new RestTemplate();
}
public static void main(String[] args) {
SpringApplication.run(SpringHystrixInvokerApplication.class, args);
}
}
4、添加一个实体类User.java
package com.example.springhystrixinvoker;
public class User {
String name;
Integer age;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
}
5、添加一个服务类,在服务方法中调用服务
服务方法用@HystrixCommand注解进行修饰,并配置了回退方法。package com.example.springhystrixinvoker;
import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import org.springframework.web.client.RestTemplate;
@Component
public class UserService {
@Autowired
private RestTemplate restTemplate;
@HystrixCommand(fallbackMethod = "getUserFallback")
public User getUser(String name){
User user = restTemplate.getForObject("http://spring-hystrix-provider/user/{name}", User.class, name);
return user;
}
public User getUserFallback(String name){
User user = new User();
user.setName("无名");
user.setAge(20);
return user;
}
}
6、添加控制器 InvokerController.java
package com.example.springhystrixinvoker;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.MediaType;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;
@RestController
public class InvokerController {
@Autowired
private UserService userService;
@RequestMapping(value = "/invokeUser/{name}", method = RequestMethod.GET, produces = MediaType.APPLICATION_JSON_VALUE)
public User invokeUser(@PathVariable String name){
User user = userService.getUser(name);
return user;
}
}
四、测试
1、启动服务器端。
浏览器访问http://localhost:8761/,正常
2、启动服务提供者
浏览器访问 http://localhost:8080/user/小明
页面输出:{"name":"小明","age":30}
3、启动服务调用者。
浏览器访问http://localhost:9000/invokeUser/小明
页面输出:{"name":"小明","age":30}
4、停止8080服务提供者,再访问9000地址
页面输出:{"name":"无名","age":20}
由此可见,由于调用失败,触发了回退方法。
五、缓存注解
Hystrix支持缓存功能,如果在一次请求过程中,多个地方调用同一个接口,可以考虑使用缓存。
缓存可以通过注解实现,缓存与合并请求功能需要先初始化请求上下文才能实现。
1、新建一个javax.servlet.Filter,用于创建与销毁Hystrix的请求上下文
package com.example.springhystrixinvoker;
import com.netflix.hystrix.strategy.concurrency.HystrixRequestContext;
import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import java.io.IOException;
@WebFilter(urlPatterns = "/*", filterName = "hystrixFilter")
public class HystrixFilter implements Filter {
public void init(FilterConfig filterConfig) throws ServletException {
}
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
HystrixRequestContext context = HystrixRequestContext.initializeContext();
try{
chain.doFilter(request,response);
}finally {
context.shutdown();
}
}
public void destroy() {
}
}
2、在启动类中加入注解@ServletComponentScan
3、编写服务方法,使用缓存注解
(1)@CacheResult 被修饰的方法返回结果会被缓存,和@HystrixCommand搭配
(2)@CacheRemove 让缓存失效
(3)@CacheKey 修饰方法参数,表示该参数作为缓存的key
package com.example.springhystrixinvoker;
import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
import com.netflix.hystrix.contrib.javanica.cache.annotation.CacheRemove;
import com.netflix.hystrix.contrib.javanica.cache.annotation.CacheResult;
import org.springframework.stereotype.Component;
@Component
public class CacheService {
@CacheResult
@HystrixCommand(commandKey = "removeKey")
public String cacheMethod(String name){
System.out.println("执行cacheMethod方法");
return "hello";
}
@CacheRemove(commandKey = "removeKey")
@HystrixCommand(commandKey = "removeKey")
public String updateMethod(String name){
System.out.println("执行updateMethod方法");
return "update";
}
}
4、控制器中调用
浏览器访问:http://localhost:9000/cacheMethod,IDEA控制台输出:控制器调用服务:0
执行cacheMethod方法
控制器调用服务:1
控制器调用服务:2
控制器调用服务:3
控制器调用服务:4
控制器调用服务:5
执行updateMethod方法
控制器调用服务:6
执行cacheMethod方法
控制器调用服务:7
控制器调用服务:8
控制器调用服务:9
六、Feign与Hystrix整合
修改服务调用者项目的代码
1、pom.xml加入Feign依赖
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-openfeign</artifactId>
</dependency>
2、修改配置application.yml
增加下面配置:打开Feign的Hystrix的配置
feign:
hystrix:
enabled: true
3、启动类加上注解@EnableFeignClients
4、新建Feign接口package com.example.springhystrixinvoker;
import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.stereotype.Component;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
//指定调用的服务名称
@FeignClient(name="spring-hystrix-provider", fallback = UserClient.UserClientFallback.class)
public interface UserClient {
@RequestMapping(method = RequestMethod.GET, value = "/user/{name}")
User getUser(@PathVariable("name") String name);
@Component
static class UserClientFallback implements UserClient{
public User getUser(String name){
User user = new User();
user.setName("无名");
user.setAge(20);
return user;
}
}
}
5、控制器InvokerController,添加代码
@Autowired
private UserClient userClient;
@RequestMapping(value = "/invokeUser2/{name}", method = RequestMethod.GET, produces = MediaType.APPLICATION_JSON_VALUE)
public User invokeUser2(@PathVariable String name){
User user = userClient.getUser(name);
return user;
}