Spring Boot2发布调用REST服务实现方法

开发环境：IntelliJ IDEA 2019.2.2
Spring Boot版本：2.1.8

一、发布REST服务

1、IDEA新建一个名称为rest-server的Spring Boot项目

2、新建一个实体类User.java

package com.example.restserver.domain;

public class User {
  String name;
  Integer 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;
  }
}

3、新建一个控制器类 UserController.java

package com.example.restserver.web;

import com.example.restserver.domain.User;
import org.springframework.http.MediaType;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class UserController {

  @RequestMapping(value="/user/{name}", produces = MediaType.APPLICATION_JSON_VALUE)
  public User user(@PathVariable String name) {
    User u = new User();
    u.setName(name);
    u.setAge(30);
    return u;
  }
}

项目结构如下：

访问http://localhost:8080/user/lc，页面显示：

{"name":"lc","age":30}

二、使用RestTemplae调用服务

1、IDEA新建一个名称为rest-client的Spring Boot项目

2、新建一个含有main方法的普通类RestTemplateMain.java，调用服务

package com.example.restclient;

import com.example.restclient.domain.User;
import org.springframework.web.client.RestTemplate;

public class RestTemplateMain {
  public static void main(String[] args){
    RestTemplate tpl = new RestTemplate();
    User u = tpl.getForObject("http://localhost:8080/user/lc", User.class);
    System.out.println(u.getName() + "," + u.getAge());
  }
}

右键Run 'RestTemplateMain.main()'，控制台输出：lc,30

3、在bean里面使用RestTemplate，可使用RestTemplateBuilder，新建类UserService.java

package com.example.restclient.service;

import com.example.restclient.domain.User;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.web.client.RestTemplateBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.stereotype.Service;
import org.springframework.web.client.RestTemplate;

@Service
public class UserService {
  @Autowired
  private RestTemplateBuilder builder;

  @Bean
  public RestTemplate restTemplate(){
    return builder.rootUri("http://localhost:8080").build();
  }

  public User userBuilder(String name){
    User u = restTemplate().getForObject("/user/" + name, User.class);
    return u;
  }

}

4、编写一个单元测试类，来测试上面的UserService的bean。

package com.example.restclient.service;

import com.example.restclient.domain.User;
import org.junit.Assert;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.NONE)
public class UserServiceTest {
  @Autowired
  private UserService userService;

  @Test
  public void testUser(){
    User u = userService.userBuilder("lc");
    Assert.assertEquals("lc", u.getName());
  }
}

5、控制器类UserController.cs 中调用

配置在application.properties 配置端口和8080不一样，如server.port = 9001

@Autowired
  private UserService userService;

  @RequestMapping(value="/user/{name}", produces = MediaType.APPLICATION_JSON_VALUE)
  public User user(@PathVariable String name) {
    User u = userService.userBuilder(name);
    return u;
  }

三、使用Feign调用服务

继续在rest-client项目基础上修改代码。

1、pom.xml添加依赖

<dependency>
      <groupId>io.github.openfeign</groupId>
      <artifactId>feign-core</artifactId>
      <version>9.5.0</version>
    </dependency>

    <dependency>
      <groupId>io.github.openfeign</groupId>
      <artifactId>feign-gson</artifactId>
      <version>9.5.0</version>
    </dependency>

2、新建接口UserClient.java

package com.example.restclient.service;

import com.example.restclient.domain.User;
import feign.Param;
import feign.RequestLine;

public interface UserClient {

  @RequestLine("GET /user/{name}")
  User getUser(@Param("name")String name);

}

3、在控制器类UserController.java 中调用

decoder(new GsonDecoder()) 表示添加了解码器的配置，GsonDecoder会将返回的JSON字符串转换为接口方法返回的对象。
相反的，encoder(new GsonEncoder())则是编码器，将对象转换为JSON字符串。

@RequestMapping(value="/user2/{name}", produces = MediaType.APPLICATION_JSON_VALUE)
  public User user2(@PathVariable String name) {
    UserClient service = Feign.builder().decoder(new GsonDecoder())
                  .target(UserClient.class, "http://localhost:8080/");
    User u = service.getUser(name);
    return u;
  }

4、优化第3步代码，并把请求地址放到配置文件中。

（1）application.properties 添加配置

代码如下:

application.client.url = http://localhost:8080

（2）新建配置类ClientConfig.java

package com.example.restclient.config;

import com.example.restclient.service.UserClient;
import feign.Feign;
import feign.gson.GsonDecoder;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class ClientConfig {
  @Value("${application.client.url}")
  private String clientUrl;

  @Bean
  UserClient userClient(){
    UserClient client = Feign.builder()
        .decoder(new GsonDecoder())
        .target(UserClient.class, clientUrl);
    return client;
  }
}

（3）控制器 UserController.java 中调用

@Autowired
  private UserClient userClient;

  @RequestMapping(value="/user3/{name}", produces = MediaType.APPLICATION_JSON_VALUE)
  public User user3(@PathVariable String name) {
    User u = userClient.getUser(name);
    return u;
  }

UserController.java最终内容：

package com.example.restclient.web;

import com.example.restclient.domain.User;
import com.example.restclient.service.UserClient;
import com.example.restclient.service.UserService;
import feign.Feign;
import feign.gson.GsonDecoder;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.MediaType;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class UserController {
  @Autowired
  private UserService userService;
  @Autowired
  private UserClient userClient;

  @RequestMapping(value="/user/{name}", produces = MediaType.APPLICATION_JSON_VALUE)
  public User user(@PathVariable String name) {
    User u = userService.userBuilder(name);
    return u;
  }

  @RequestMapping(value="/user2/{name}", produces = MediaType.APPLICATION_JSON_VALUE)
  public User user2(@PathVariable String name) {
    UserClient service = Feign.builder().decoder(new GsonDecoder())
                  .target(UserClient.class, "http://localhost:8080/");
    User u = service.getUser(name);
    return u;
  }
  @RequestMapping(value="/user3/{name}", produces = MediaType.APPLICATION_JSON_VALUE)
  public User user3(@PathVariable String name) {
    User u = userClient.getUser(name);
    return u;
  }
}

项目结构

先后访问下面地址，可见到输出正常结果

http://localhost:9001/user/lc
http://localhost:9001/user2/lc2
http://localhost:9001/user3/lc3

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