Spring Cloud Hystrix 断路器模式

项目源码下载：（访问密码：9987）
Spring-Cloud-Circuit-Breaker.zip

学习在调用底层微服务的同时利用调用的Spring Cloud Netflix堆栈组件之一Hystrix来实现断路器。在一些底层服务永久宕机/抛出错误的应用中，一般需要开启容错功能，我们需要自动回退到不同的程序执行路径。这与使用大量底层微服务的生态系统的分布式计算风格有关。这是断路器模式的帮助所在，也是构建此断路器的工具

Hystrix Example for real impatient

1. 添加 Hystrix 启动器和仪表板依赖项。

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

2. 添加@EnableCircuitBreaker注释
3. 添加@EnableHystrixDashboard注释
4. 添加注释 @HystrixCommand(fallbackMethod = "myFallbackMethod")

什么是断路器模式？

Hystrix 断路器示例

• 学生微服务- 这将提供Student实体的一些基本功能。这将是一个基于 REST 的服务。我们将从SchoolService调用此服务以了解断路器。它将8098在本地主机的端口上运行。
• School Microservice – 又是一个简单的基于 REST 的微服务，我们将使用Hystrix. Student将从这里调用服务，一旦学生服务不可用，我们将测试回退路径。它将在本地主机的 9098 端口上运行。

技术栈和演示运行时

技术栈和演示运行时

• Java 1.8
• Eclipse as IDE
• Maven as build tool
• Spring cloud Hystrix as circuit breaker framework
• Spring boot
• Spring Rest

创建学生服务

创建spring boot项目

服务器端口设置

server.port = 8098

创建 REST API

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
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;
import com.example.howtodoinjava.springhystrixstudentservice.domain.Student;
 
@RestController
public class StudentServiceController {
 
    private static Map<String, List<Student>> schooDB = new HashMap<String, List<Student>>();
 
    static {
        schooDB = new HashMap<String, List<Student>>();
 
        List<Student> lst = new ArrayList<Student>();
        Student std = new Student("Sajal", "Class IV");
        lst.add(std);
        std = new Student("Lokesh", "Class V");
        lst.add(std);
 
        schooDB.put("abcschool", lst);
 
        lst = new ArrayList<Student>();
        std = new Student("Kajal", "Class III");
        lst.add(std);
        std = new Student("Sukesh", "Class VI");
        lst.add(std);
 
        schooDB.put("xyzschool", lst);
 
    }
 
    @RequestMapping(value = "/getStudentDetailsForSchool/{schoolname}", method = RequestMethod.GET)
    public List<Student> getStudents(@PathVariable String schoolname) {
        System.out.println("Getting Student details for " + schoolname);
 
        List<Student> studentList = schooDB.get(schoolname);
        if (studentList == null) {
            studentList = new ArrayList<Student>();
            Student std = new Student("Not Found", "N/A");
            studentList.add(std);
        }
        return studentList;
    }
}

public class Student {
 
    private String name;
    private String className;
 
    public Student(String name, String className) {
        super();
        this.name = name;
        this.className = className;
    }
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public String getClassName() {
        return className;
    }
 
    public void setClassName(String className) {
        this.className = className;
    }
}

构建和测试学生服务

创建学校服务 – Hystrix 已启用

生成spring boot项目

• Web – REST 端点
• Actuator – 提供基本的管理 URL
• Hystrix – 启用断路器
• Hystrix Dashboard – 启用一个与断路器监控相关的仪表板屏幕

服务器端口设置

server.port = 9098

启用 Hystrix 设置

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker;
import org.springframework.cloud.netflix.hystrix.dashboard.EnableHystrixDashboard;
 
@SpringBootApplication
@EnableHystrixDashboard
@EnableCircuitBreaker
public class SpringHystrixSchoolServiceApplication {
 
    public static void main(String[] args) {
        SpringApplication.run(SpringHystrixSchoolServiceApplication.class, args);
    }
}

添加 REST 控制器

import org.springframework.beans.factory.annotation.Autowired;
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;
import com.example.howtodoinjava.springhystrixschoolservice.delegate.StudentServiceDelegate;
 
@RestController
public class SchoolServiceController {
     
    @Autowired
    StudentServiceDelegate studentServiceDelegate;
 
    @RequestMapping(value = "/getSchoolDetails/{schoolname}", method = RequestMethod.GET)
    public String getStudents(@PathVariable String schoolname) {
        System.out.println("Going to call student service to get data!");
        return studentServiceDelegate.callStudentServiceAndGetData(schoolname);
    }
}

• 通过提供的 spring 框架调用学生服务 RestTemplate
• 添加 Hystrix 命令以启用回退方法 – @HystrixCommand(fallbackMethod = "callStudentServiceAndGetData_Fallback")– 这意味着我们将不得不添加另一个callStudentServiceAndGetData_Fallback具有相同签名的方法，该方法将在实际学生服务关闭时调用。
• 添加回退方法——callStudentServiceAndGetData_Fallback它只会返回一些默认值。

import java.util.Date;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Bean;
import org.springframework.core.ParameterizedTypeReference;
import org.springframework.http.HttpMethod;
import org.springframework.stereotype.Service;
import org.springframework.web.client.RestTemplate;
import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
 
@Service
public class StudentServiceDelegate {
 
    @Autowired
    RestTemplate restTemplate;
     
    @HystrixCommand(fallbackMethod = "callStudentServiceAndGetData_Fallback")
    public String callStudentServiceAndGetData(String schoolname) {
 
        System.out.println("Getting School details for " + schoolname);
 
        String response = restTemplate
                .exchange("http://localhost:8098/getStudentDetailsForSchool/{schoolname}"
                , HttpMethod.GET
                , null
                , new ParameterizedTypeReference<String>() {
            }, schoolname).getBody();
 
        System.out.println("Response Received as " + response + " -  " + new Date());
 
        return "NORMAL FLOW !!! - School Name -  " + schoolname + " :::  " +
                    " Student Details " + response + " -  " + new Date();
    }
     
    @SuppressWarnings("unused")
    private String callStudentServiceAndGetData_Fallback(String schoolname) {
 
        System.out.println("Student Service is down!!! fallback route enabled...");
 
        return "CIRCUIT BREAKER ENABLED!!! No Response From Student Service at this moment. " +
                    " Service will be back shortly - " + new Date();
    }
 
    @Bean
    public RestTemplate restTemplate() {
        return new RestTemplate();
    }
}

学校服务的构建和测试

测试 Hystrix 断路器 - 演示

Hystrix 仪表板

• http://localhost:9098/hystrix.stream – Hystrix 生成的连续流。它只是一个健康检查结果以及 Hystrix 正在监视的所有服务调用。示例输出在浏览器中看起来像 -
• http://localhost:9098/hystrix – 这是可视化仪表板初始状态。
• 现在在仪表板中添加http://localhost:9098/hystrix.stream以获得由 Hystrix 组件监控的电路的有意义的动态视觉表示。在主页中提供 Stream 输入后的 Visual Dashboard –

总结

项目源码下载：（访问密码：9987）
Spring-Cloud-Circuit-Breaker.zip

标签： Spring Cloud Hystrix 断路器 Spring Cloud Hystrix Spring Cloud

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