SpringCloud使用Feign进行服务调用

- 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@SpringBootApplicationpublic 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

  @Controllerpublic 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=9001spring.application.name=feign-consumereureka.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)@ResponseBodypublic String hello(@RequestParam String name) {    return "hello " + name;}@RequestMapping(value = "/hello2", method = RequestMethod.GET)@ResponseBodypublic User hello(@RequestHeader String name, @RequestHeader Integer age) {    return new User(name, age);}@RequestMapping(value = "/hello3", method = RequestMethod.POST)@ResponseBodypublic 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：