feign 使用示例

这个例子是自己写的，当然也是参照官方的文档，没有spring, 也没有spring boot. 就是普通的main()函数执行。

既然feign是http client, 肯定要有一个server, server是普通的spring boot的 RestController:

server project 结构：

共三个文件： DemoApplication.java, DemoAPI.java, Demo.java

Demo.java

package ex.demo.domain;

public class Demo {
    private int id;
    private String name;
    
    public Demo(){}
    public Demo(int id, String name) {
        this.id   = id;
        this.name = name;
    }
    
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
}

DemoAPI.java

package ex.demo.api;

import java.util.ArrayList;
import java.util.List;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.RestController;

import ex.demo.domain.Demo;

@RestController
public class DemoAPI {
    
    @GetMapping("/demo/hello")
    public String hello() {
        return "hello, DEMO!";
    }
    
    @GetMapping("/get/{id}")
    @ResponseBody
    public Demo getDemo(@PathVariable("id") int id) {
        return new Demo(id, "demo " + id);
    }
    
    @GetMapping("/demo/list")
    @ResponseBody
    public List<Demo> getDemoList() {
        List<Demo> list = new ArrayList<>();
        Demo       d1   = new Demo(1, "demo1");
        Demo       d2   = new Demo(2, "demo2");
        list.add(d1);
        list.add(d2);
        return list;
    }
}

DemoApplication.java

package ex.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

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

pom.xml

  <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-web</artifactId>
      <version>1.5.10.RELEASE</version>
  </dependency>

demo-service是个很简单的restful服务，这里只例出三个常用的情况：

1. 返回String

2. 返回Object

3. 返回对象列表

feign project 结构：

也是三个文件，都放一个包里了。也就是个例子，不用那么讲究。

Demo.java

package ex.feign;

public class Demo {
    private int    id;
    private String name;
    
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
}

RemoteService.java

package ex.feign;

import java.util.List;

import feign.Param;
import feign.RequestLine;

// 这个例子使用 demo-service 作为服务端
public interface RemoteService {

    @RequestLine("GET /demo/hello")
    String hello();
    
    
    @RequestLine("GET /get/{id}")
    Demo getDemo(@Param("id") int id);
    

    @RequestLine("GET /demo/list")
    List<Demo> getList();
}

FeignApplication.java

package ex.feign;

import java.util.List;

import feign.Feign;
import feign.jackson.JacksonDecoder;

public class FeignApplication {
    private static String SERVER_ADDR = "http://127.0.0.1:8080";
    
    public static void main(String[] args) {
        RemoteService helloService = Feign.builder().target(RemoteService.class, SERVER_ADDR);
        System.out.println(helloService.hello());
        
        
        // 这个要将json转成Demo
        RemoteService demoService = Feign.builder()
                .decoder(new JacksonDecoder())
                .target(RemoteService.class, SERVER_ADDR);
        Demo demo = demoService.getDemo(5);
        System.out.println("id=" + demo.getId() + ", name=" + demo.getName());
        
        
        // Demo列表也用JscksonDecoder
        List<Demo> list = demoService.getList();
        for(Demo d : list) {
            System.out.println("id=" + d.getId() + ", name=" + d.getName());
        }

    }
}

pom.xml

<dependency>
    <groupId>com.netflix.feign</groupId>
    <artifactId>feign-core</artifactId>
    <version>8.18.0</version>
</dependency>

<dependency>
    <groupId>com.netflix.feign</groupId>
    <artifactId>feign-jackson</artifactId>
    <version>8.18.0</version>
</dependency>

运行：先启动demo-service, 然后运行FeignApplication.java

输出结果：

hello, DEMO!
id=5, name=demo 5
id=1, name=demo1
id=2, name=demo2

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