SpringCloud使用Feign实现服务调用

Spring Cloud Feign简介

Spring Cloud Feign也是一个基础工具类，它整合了Spring Cloud Ribbon和Spring Cloud Hystrix，除了提供这两者的强大功能以外，它还提供了一种声明式的Web服务客户端定义方式。使用它可以进行服务的消费，但是它的客户端负载平衡仍是通过Ribbon实现的

使用Spring Cloud Feign

创建一个SpringBoot工程，作为服务调用方

1.pom.xml

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-web</artifactId>
 </dependency>

 <dependency>
  <groupId>org.springframework.cloud</groupId>
  <artifactId>spring-cloud-starter-eureka</artifactId>
 </dependency>
 <dependency>
  <groupId>org.springframework.cloud</groupId>
  <artifactId>spring-cloud-starter-feign</artifactId>
 </dependency>

 <dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-test</artifactId>
  <scope>test</scope>
</dependency>

spring-cloud-starter-feign加入了feign的依赖

2.启动类

@EnableFeignClients
@EnableDiscoveryClient
@SpringBootApplication
public class FeignConsumerApplication {

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

@EnableFeignClients：开启Spring Cloud Feign的支持功能

3.服务层

@FeignClient("hello-service")
 public interface HelloService {

 @RequestMapping(value = "/hello", method = RequestMethod.GET)
 String hello();
}

@FeignClient(“hello-service”)：制定服务名来绑定服务

注：服务名不区分大小写

@RequestMapping：指定调用服务中的具体方法

4.Controller层

@Controller
public class ConsumerController {

 @Autowired
 private HelloService helloService;

 @RequestMapping(value = "/feign-consumer", method = RequestMethod.GET)
 @ResponseBody
 public String helloConsumer() {
  return helloService.hello();
 }
}

在方法中调用这个绑定了hello-service服务接口的客户端向该服务发起/hello接口的调用

5.配置类

server.port=9001

spring.application.name=feign-consumer
eureka.client.serviceUrl.defaultZone=http://localhost:1111/eureka/

启动程序以后，在浏览器中输入http://localhost:9001/feign-consumer出现下图：

- 提升使用，带参数的请求
在具体业务中的接口会比之前程序的复杂得多，这里介绍一下Feign对集中不同形式参数的绑定方法。有@RequestParam、@RequestHeader、@RequestBody

1.改造服务提供类的Service层，添加几个方法

@RequestMapping(value = "/hello1", method = RequestMethod.GET)
@ResponseBody
public String hello(@RequestParam String name) {
 return "hello " + name;
}

@RequestMapping(value = "/hello2", method = RequestMethod.GET)
@ResponseBody
public User hello(@RequestHeader String name, @RequestHeader Integer age) {
 return new User(name, age);
}

@RequestMapping(value = "/hello3", method = RequestMethod.POST)
@ResponseBody
public String hello(@RequestBody User user) {
 return "Hello " + user.getName() + ", " + user.getAge();
}

2.添加一个javabean

public class User {
 private String name;
 private Integer age;

 public User() {
 }

 public User(String name, Integer age) {
  this.name = name;
  this.age = 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;
 }

 @Override
 public String toString() {
  return "User{" +
    "name='" + name + '\'' +
    ", age=" + age +
    '}';
 }
}

3.修改服务调用类的接口

@RequestMapping(value = "/hello1", method = RequestMethod.GET)
String hello(@RequestParam("name") String name);

@RequestMapping(value = "/hello2", method = RequestMethod.GET)
User hello(@RequestHeader("name") String name, @RequestHeader("age") Integer age);

@RequestMapping(value = "/hello3", method = RequestMethod.POST)
String hello(@RequestBody User user);

这里在定义各参数绑定时@RequestParam、@RequestHeader等可以指定参数名称的注解，但它们的value不能少，否则会报错，这和SpringMVC中有一点不同

4.在服务调用类Controller层添加一个测试的接口

 @RequestMapping(value = "/feign-consumer2", method = RequestMethod.GET)
 @ResponseBody
 public String helloConsumer2() {
  String s2 = helloService.hello("dayday");
  return s2;
 }

启动以后访问浏览器：

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