UriComponentsBuilder란?
여러개의 파라미터를 이용하여 URL를 작성할 때에 편하게 작성할 수 있게끔 해주며 서버단에서 동적으로 URI를 생성 가능한 클래스이다.

Json의 형태가 재사용된다면 제네릭을 활용한다.

Server(lombok 사용)

package com.example.server.controller;

import com.example.server.controller.dto.Req;
import com.example.server.controller.dto.User;
import lombok.extern.slf4j.Slf4j;
import org.springframework.http.HttpEntity;
import org.springframework.web.bind.annotation.*;

import javax.servlet.annotation.HttpMethodConstraint;

@Slf4j
@RestController
@RequestMapping("/api/server")
public class ServerApiController {

    @GetMapping("/hello")
    public User hello(@RequestParam String name, int age){
        User user= new User();
        user.setName(name);
        user.setAge(age);
        return user;
    }
    @PostMapping("/user/{userId}/name/{Username}")
    public Req<User> post(
                            //HttpEntity<String> entity,
                            @RequestBody Req<User> user,
                          @PathVariable int userId,
                          @PathVariable String Username,
                          @RequestHeader ("x-authorization") String authorization,
                          @RequestHeader("custom-header") String customheader
                     ){
//        log.info("req: {} ",entity.getBody());
        log.info("userId: {}, Username: {}",userId,Username);
        log.info("authorization: {}, custom: {}",authorization,customheader);
        log.info("Client req: {}", user);

        Req<User> response= new Req<>();
        response.setHeader(
                new Req.Header()
        );
        response.setResbody(user.getResbody());
        return response;
    }
}

package com.example.server.controller.dto;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@NoArgsConstructor
@AllArgsConstructor
public class Req<T> {

    private Header header;
    private T resbody;


    @Data
    @NoArgsConstructor
    @AllArgsConstructor
    public static class Header{
        private String responseCode;

    }
}

package com.example.server.controller.dto;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@NoArgsConstructor
@AllArgsConstructor
public class User {
    private String name;
    private int age;

}

Client(lombok 미사용)

package com.example.client.controller;

import com.example.client.dto.Req;
import com.example.client.dto.UserResponse;
import com.example.client.service.RestTemplateService;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping("/api/client")
public class ApiController {

    private final RestTemplateService restTemplateService;

    public ApiController(RestTemplateService restTemplateService) {
        this.restTemplateService = restTemplateService;
    }


    @GetMapping("/hello")
    public Req<UserResponse> getHello(){
        return restTemplateService.genericExchange();
    }
}

package com.example.client.service;

import com.example.client.dto.Req;
import com.example.client.dto.UserRequest;
import com.example.client.dto.UserResponse;
import org.springframework.core.ParameterizedTypeReference;
import org.springframework.http.MediaType;
import org.springframework.http.RequestEntity;
import org.springframework.http.ResponseEntity;
import org.springframework.stereotype.Service;
import org.springframework.web.client.RestTemplate;
import org.springframework.web.util.UriComponentsBuilder;

import java.net.URI;

@Service
public class RestTemplateService {
//    http://localhost/api/sever/hello
//    Response
    public UserResponse hello(){
        URI uri = UriComponentsBuilder
                .fromUriString("http://localhost:9090")
                .path("/api/server/hello")
                .queryParam("name","이호영")
                .queryParam("age","25")
                .encode() //파라미터 붙는 경우 대비
                .build()
                .toUri();
        System.out.println(uri.toString());

        RestTemplate restTemplate= new RestTemplate();
        ResponseEntity<UserResponse> result=restTemplate.getForEntity(uri, UserResponse.class);

        System.out.println(result.getStatusCode());
        System.out.println(result.getBody());

        return result.getBody();
    }

    public UserResponse post(){
// hhtp://localhost:9090/api/server/user/{userId}/name/{Username}

        URI uri=UriComponentsBuilder
                .fromUriString(("http://localhost:9090"))
                .path("/api/server/user/{userId}/name/{Username}")
                .encode()
                .build()
                .expand(100,"이호영")
                .toUri();
        System.out.println(uri);  //주소만들기

        //http body-> object-> objectMapper-> json-> Rest Template-> http body json
        UserRequest req= new UserRequest();
        req.setName("이호영");
        req.setAge(25); //object만들면 objectMapper가 자연적으로 json으로 바꿔줌

        RestTemplate restTemplate= new RestTemplate();
        ResponseEntity<UserResponse> response= restTemplate.postForEntity(uri,req,UserResponse.class); //응답 지정
        System.out.println(response.getStatusCode());
        System.out.println(response.getHeaders());
        System.out.println(response.getBody());

        return response.getBody();
    }
    public UserResponse exchange(){
        URI uri=UriComponentsBuilder
                .fromUriString(("http://localhost:9090"))
                .path("/api/server/user/{userId}/name/{Username}")
                .encode()
                .build()
                .expand(100,"이호영")
                .toUri();
        System.out.println(uri);  //주소만들기

        //http body-> object-> objectMapper-> json-> Rest Template-> http body json
        UserRequest req= new UserRequest();
        req.setName("이호영");
        req.setAge(25); //object만들면 objectMapper가 자연적으로 json으로 바꿔줌

        RequestEntity<UserRequest> requestEntity= RequestEntity
                .post(uri)
                .contentType(MediaType.APPLICATION_JSON)
                .header("x-authorization","abcd")
                .header("custom-header", "fffff")
                .body(req);


        RestTemplate restTemplate= new RestTemplate();
        ResponseEntity<UserResponse> response=restTemplate.exchange(requestEntity,UserResponse.class);
        return response.getBody();


    }

    public Req<UserResponse> genericExchange(){
        URI uri=UriComponentsBuilder
                .fromUriString(("http://localhost:9090"))
                .path("/api/server/user/{userId}/name/{Username}")
                .encode()
                .build()
                .expand(100,"이호영")
                .toUri();
        System.out.println(uri);  //주소만들기

        //http body-> object-> objectMapper-> json-> Rest Template-> http body json

        UserRequest UserRequest= new UserRequest();
        UserRequest.setName("이호영");
        UserRequest.setAge(25);

        Req<UserRequest> req=new Req();
        req.setHeader(
                new Req.Header()
        );
        req.setResbody(
                UserRequest
        );


        RequestEntity<Req<UserRequest>>requestEntity= RequestEntity
                .post(uri)
                .contentType(MediaType.APPLICATION_JSON)
                .header("x-authorization","abcd")
                .header("custom-header", "fffff")
                .body(req);

        RestTemplate restTemplate=new RestTemplate();

        ResponseEntity<Req<UserResponse>> response
                =restTemplate.exchange(requestEntity,new ParameterizedTypeReference<Req<UserResponse>>(){});

        return response.getBody();
    }
}

package com.example.client.dto;

public class Req<T> {

    private Header header;

    private T resbody; //제네릭 타입

    public static class Header{
        private String responseCode;

        public String getResponseCode() {
            return responseCode;
        }

        public void setResponseCode(String responseCode) {
            this.responseCode = responseCode;
        }

        @Override
        public String toString() {
            return "Header{" +
                    "responseCode='" + responseCode + '\'' +
                    '}';
        }
    }

    public Header getHeader() {
        return header;
    }

    public void setHeader(Header header) {
        this.header = header;
    }

    public T getResbody() {
        return resbody;
    }

    public void setResbody(T resbody) {
        this.resbody = resbody;
    }

    @Override
    public String toString() {
        return "Req{" +
                "header=" + header +
                ", body=" + resbody +
                '}';
    }
}

package com.example.client.dto;

public class UserRequest {

    private String name;
    private int age;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

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

package com.example.client.dto;

public class UserResponse {

    private String name;
    private int age;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

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