第九章 Spring Cloud Feign声明式调用服务

在Spring Cloud Netflix栈中，各个微服务都是以HTTP接口的形式暴露自身服务的，因此在调用远程服务时就必须使用HTTP客户端。我们可以使用JDK原生的

URLConnection

、Apache的

HttpClient

、Netty的异步HTTP
Client, Spring的

RestTemplate

。但是，用起来最方便、最优雅的还是要属Feign了。在实际项目中，都是使用声明式调用服务。而不会在客服端和服务端存储2份相同的model和api定义。Feign在RestTemplate的基础上对其封装，由它来帮助我们定义和实现依赖服务接口的定义。Spring
Cloud Feign基于Netflix Feign
实现的，整理Spring Cloud Ribbon
与 Spring CloudHystrix，并且实现了声明式的Web服务客户端定义方式。

项目结构如图：



OrderController类

package com.example.demo.controller;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;

import com.example.demo.entity.User;
import com.example.demo.feign.UserFeignClient;

//声明式服务
@RestController
public class OrderController {

@Autowired
private UserFeignClient userFeignClient;

@GetMapping("/order/{id}")
public User findById(@PathVariable Long id) {
return this.userFeignClient.findById(id);
}

@GetMapping("/testPost")
public User testPost(User user) {
return this.userFeignClient.postUser(user);
}

@GetMapping("/testGet")
public User testGet(User user) {
return this.userFeignClient.getUser(user);
}
}

User类

package com.example.demo.entity;

import java.math.BigDecimal;

public class User {
private Long id;

private String username;

private String name;

private Short age;

private BigDecimal balance;

public Long getId() {
return this.id;
}

public void setId(Long id) {
this.id = id;
}

public String getUsername() {
return this.username;
}

public void setUsername(String username) {
this.username = username;
}

public String getName() {
return this.name;
}

public void setName(String name) {
this.name = name;
}

public Short getAge() {
return this.age;
}

public void setAge(Short age) {
this.age = age;
}

public BigDecimal getBalance() {
return this.balance;
}

public void setBalance(BigDecimal balance) {
this.balance = balance;
}

}

UserFeignClient类

package com.example.demo.feign;

import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

import com.example.demo.entity.User;

////声明式服务
@FeignClient("spring-cloud-user") // 调用哪个服务的名称
public interface UserFeignClient {

@RequestMapping(value = "/user/{id}", method = RequestMethod.GET)
public User findById(@PathVariable("id") Long id); // 1. @GetMapping不支持 2.
// @PathVariable得设置value

@RequestMapping(value = "/testPost", method = RequestMethod.POST)
public User postUser(@RequestBody User user);

// 该请求不会成功，只要参数是复杂对象，即使指定了是GET方法，feign依然会以POST方法进行发送请求
@RequestMapping(value = "/getUser", method = RequestMethod.GET)
public User getUser(User user);
}

SpringCloudOrderApplication类

package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.cloud.netflix.feign.EnableFeignClients;

/**
* 声明式服务
*
*/

@SpringBootApplication
@EnableEurekaClient
@EnableFeignClients//表示为Fegin客户端
public class SpringCloudOrderApplication {

public static void main(String[] args) {
SpringApplication.run(SpringCloudOrderApplication.class, args);
}
}

application.yml配置

spring:
application:
name: spring-cloud-order-feign    #微服务的名称
server:
port: 7906  #微服务端口号
eureka:
client:
healthcheck:
enabled: true   # 开启健康检查
serviceUrl:
defaultZone: http://user:123456@localhost:8761/eureka   #服务eureka的URL地址
instance:
prefer-ip-address: true
# 解决第一次请求报超时异常的方案：
hystrix:
command:
default:
execution:
isolation:
thread:
timeoutInMilliseconds: 5000
# 或者：
# hystrix.command.default.execution.timeout.enabled: false
# 或者：

# 超时的issue：https://github.com/spring-cloud/spring-cloud-netflix/issues/768
# 超时的解决方案： http://stackoverflow.com/questions/27375557/hystrix-command-fails-with-timed-out-and-no-fallback-available # hystrix配置： https://github.com/Netflix/Hystrix/wiki/Configuration#execution.isolation.thread.timeoutInMilliseconds

pom.xml配置

<?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.example.demo</groupId>
<artifactId>spring-cloud-order_feign</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>war</packaging>

<name>spring-cloud-order_feign</name>
<description>spring-cloud-order_feign</description>

<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>1.4.1.RELEASE</version>
</parent>

<properties>
<!-- 文件拷贝时的编码 -->
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
<!-- 编译时的编码 -->
<maven.compiler.encoding>UTF-8</maven.compiler.encoding>
<!-- jdk版本 -->
<java.version>1.8</java.version>
</properties>

<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<!-- 注册中心 -->
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-eureka</artifactId>
</dependency>
<!-- 这个库让我们可以访问应用的很多信息,包括:/env、/info、/metrics、/health等 -->
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-actuator</artifactId>
</dependency>
<!-- 添加声明式feign依赖 -->
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-feign</artifactId>
</dependency>

<!-- 用于热部署 -->
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-devtools</artifactId>
</dependency>
</dependencies>
<dependencyManagement>
<dependencies>
<!-- 版本依赖管理，故之后添加依赖无需指定version -->
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-dependencies</artifactId>
<version>Camden.SR2</version>
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>
</dependencyManagement>

<build>
<plugins>
<!-- 用以为integration-test提供支持。 -->
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>