Hystrix熔断机制就像家里的保险丝一样,若同时使用高功率的电器,就会烧坏电路,这时候保险丝自动断开就有效的保护了电路。而我们程序中也同样是这样。例如若此时数据库压力太大速度很慢,此时还有不断的请求访问后台,就会造成数据库崩溃。这时候hystrix容错机制,可以为客户端请求设置超时链接,添加回退的逻辑,减少集群压力。
1.1 导依赖
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>1.5.8.RELEASE</version>
<relativePath/>
</parent>
<!-- springCloud -->
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-dependencies</artifactId>
<version>Dalston.SR3</version>
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>
</dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<!-- eureka客户端依赖 -->
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-eureka</artifactId>
</dependency>
<!-- hystrix -->
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-hystrix</artifactId>
</dependency>
1.2 配置application.yml
# 指定端口
server:
port: 8085
context-path: /demo
# 服务名称
spring:
application:
name: hystrix
# eureka服务器地址
eureka:
client:
serviceUrl:
defaultZone: http://localhost:8761/eureka/
1.3 配置Hystrix过滤器
import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;
import com.netflix.hystrix.strategy.concurrency.HystrixRequestContext;
/**
* urlPatterns:拦截所有路径(拦截规则)
* filterName:过滤器名称
*/
@WebFilter(urlPatterns = "/*", filterName = "hystrixFilter")
public class HystrixFilterConf implements Filter{
public void destroy() { }
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
throws IOException, ServletException {
// 初始化Hystrix上下文
HystrixRequestContext ctx = HystrixRequestContext.initializeContext();
try {
chain.doFilter(request, response);
} catch (Exception e) {
} finally {
ctx.shutdown();
}
}
public void init(FilterConfig arg0) throws ServletException { }
}
1.4 主函数入口
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.builder.SpringApplicationBuilder;
import org.springframework.boot.web.servlet.ServletComponentScan;
import org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
@SpringBootApplication
@EnableEurekaClient //开启Eureka
@EnableCircuitBreaker//开启断路器
@ServletComponentScan//扫描servlet过滤器监听器
public class ServerMain {
public static void main(String[] args) {
new SpringApplicationBuilder(ServerMain.class).web(true).run(args);
}
}
二: hystrix 的 熔断,降级 机制。
2.1 回退机制案例
import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
import com.netflix.hystrix.contrib.javanica.annotation.HystrixProperty;
import org.springframework.stereotype.Service;
import org.springframework.web.bind.annotation.RequestMapping;
/**
* Hystrix回退机制(熔断,降级)
*/
@Service
public class RollbackService {
/**
* fallbackMethod: 指定回退方法
*
* coreSize: 线程池最大数量
* maxQueueSize: 线程池最大队列,默认-1通过SynchronousQueue来实现; 否则使用LinkedBlockingQueue实现
* queueSizeRejectionThreshold: 当maxQueueSize是LinkedBlockingQueue时,即使没有达到最大列队也会据绝请求。
*
* timeoutInMilliseconds: 超时时间
* requestVolumeThreshold: 单位时间内超过这个多个请求失败才执行熔断
*/
@RequestMapping(value = "/testRollback")
@HystrixCommand(fallbackMethod = "myRollback",
threadPoolProperties = {
@HystrixProperty(name = "coreSize", value = "30"),
@HystrixProperty(name = "maxQueueSize", value = "-1"),
@HystrixProperty(name = "queueSizeRejectionThreshold", value = "-1")
},
commandProperties = {
@HystrixProperty(name = "execution.isolation.thread.timeoutInMilliseconds", value = "3000"),
@HystrixProperty(name = "circuitBreaker.requestVolumeThreshold", value = "1")
})
public String testRollback() {
try {// 模拟请求阻塞
Thread.sleep(4000);
} catch (Exception e) {
}
return "恭喜你访问成功!";
}
/** 回退方法 */
public String myRollback() {
return "服务器压力过大,明年再来吧!";
}
}
2.2 编写接口, 调用测试。
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
@RestController
public class RollbackController {
@Autowired
private RollbackService rollbackService;
@RequestMapping("/testRollback")
public String testRollback() {
return rollbackService.testRollback();
}
}
三: hystrix 缓存机制:hystrix的缓存有点像mybatis默认开启的一级缓存:在session关闭之前(一次会话期间),使用同样的参数调用同一个方法,实际只查询一次。
3.1 缓存逻辑
import org.springframework.stereotype.Service;
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;
@Service
public class CacheService {
@CacheResult
@HystrixCommand
public void cacheMember(Integer id) {
System.out.println("调用 cacheMember 方法");
}
/**
* commandKey:缓存的key
* 获取和删除必须用同一个key,并必须是同一次请求。
*/
@CacheResult
@HystrixCommand(commandKey = "myCacheKey")
public void getCache(Integer id) {
System.out.println("执行查询方法");
}
@CacheRemove(commandKey = "myCacheKey")
@HystrixCommand
public void removeCache(Integer id) {
System.out.println("删除缓存方法");
}
}
3.2 缓存接口开发
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.MediaType;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;
@RestController
public class CacheController {
@Autowired
private CacheService cacheService;
@RequestMapping(value = "/cache", method = RequestMethod.GET,
produces = MediaType.APPLICATION_JSON_VALUE)
public String cache() {
for(int i = 0; i < 3; i++) {
/** 在同一次请求里面调用了3次同一方法,会发现,控制台只
* 输出了一次,说明后2次走的缓存没调方法的逻辑 */
cacheService.cacheMember(1);
}
System.out.println("测试完毕");
return "";
}
@RequestMapping(value = "/rc", method = RequestMethod.GET,
produces = MediaType.APPLICATION_JSON_VALUE)
public String testRemoveCache() {
cacheService.getCache(1);
cacheService.getCache(1);
cacheService.removeCache(1);
System.out.println("######### 分隔线 ###########");
cacheService.getCache(1);
System.out.println("测试完毕");
return "";
}
}