SpringBoot的搭建可以看一下我之前寫的一篇部落格

準備工作

要使用RestTemplate需要引入依賴，web依賴也可以在建立專案時選擇Web -> Web

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

<!-- 遠端呼叫 httpclient -->
<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.5.5</version>
</dependency>

 注入RestTemplate

  首先需要在Application中加入一個RestTemplate

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;
import org.springframework.http.client.HttpComponentsClientHttpRequestFactory;
import org.springframework.web.client.RestTemplate;

@SpringBootApplication
public class RemoteApplication {
    @Bean //必須new 一個RestTemplate並放入spring容器當中,否則啟動時報錯
    public RestTemplate restTemplate() {
        HttpComponentsClientHttpRequestFactory httpRequestFactory = new HttpComponentsClientHttpRequestFactory();
        httpRequestFactory.setConnectionRequestTimeout(30 * 1000);
        httpRequestFactory.setConnectTimeout(30 * 3000);
        httpRequestFactory.setReadTimeout(30 * 3000);
        return new RestTemplate(httpRequestFactory);
    }
    public static void main(String[] args) {
        SpringApplication.run(RemoteApplication.class, args);
    }
}
 

 呼叫服務

  實體類

import com.fasterxml.jackson.annotation.JsonProperty;
import lombok.Data;

@Data
public class UserEntity {
    @JsonProperty("user_id")
    private Long userId;
    private String name;
    private String phone;
}

import lombok.Data;

@Data
public class Result {
    private Integer code;
    private String message;
}
 

  controller

import com.cwr.remote.model.db.UserEntity;
import com.cwr.remote.model.vo.Result;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.*;
import org.springframework.web.bind.annotation.*;
import org.springframework.web.client.RestTemplate;


@RequestMapping("/remote")
//允許跨域訪問
@CrossOrigin(origins = "*", maxAge = 3600)
@RestController
public class RemoteController {
    //自動注入RestTemplate 
    private final RestTemplate restTemplate;

    @Autowired
    public RemoteController(RestTemplate restTemplate) {
        this.restTemplate = restTemplate;
    }

    /**
     * 呼叫遠端服務新增使用者資訊
     *
     * @param userEntity 使用者實體
     * @return
     */
    @PostMapping("/add-user")
    public Result addUser(@RequestBody UserEntity userEntity) {
        HttpEntity<UserEntity> entity = new HttpEntity<>(userEntity);
        ResponseEntity<Result> resultResponseEntity = this.restTemplate.exchange(
                "http://xxx.xxx.xxx.xxx/user/add",
                HttpMethod.POST, entity, Result.class);
        if (resultResponseEntity.getStatusCode() == HttpStatus.OK) {
            return resultResponseEntity.getBody();
        }
        return null;
    }

    /**
     * 呼叫遠端服務查詢單個使用者資訊
     *
     * @param id 使用者id
     * @return
     */
    @GetMapping("/find-user-id/{id}")
    public UserEntity findOne(@PathVariable Long id) {
        ResponseEntity<UserEntity> resultResponseEntity = this.restTemplate.exchange(
                String.format("http://xxx.xxx.xxx.xxx/user/find-id/%s", id),
                HttpMethod.GET, null, UserEntity.class);
        if (resultResponseEntity.getStatusCode() == HttpStatus.OK) {
            return resultResponseEntity.getBody();
        }
        return null;
    }
}

這裡詳細講一下exchange( )方法

public <T> ResponseEntity<T>

           exchange(String url, HttpMethod method, @Nullable HttpEntity<?> requestEntity, Class<T> responseType) 

•     url:請求地址，如果需要在url中帶引數，使用String.format()，用%s拼接即可;
•     method:請求方式，HttpMethod是一個列舉型別，有GET、POST、DELETE等方法;
•     requestEntity:請求引數，這個主要是POST等有請求體的方法才需要，GET、DELETE等方法可以為null;
•     responseType:返回資料型別。

測試結果（我使用的是Postman）