Spring HTTP Client

Question

I am new to Spring and I need my Java app to connect to another API over HTTP (JSON, RESTful). Does the Spring Framework have anything like a JSON HTTP Rest Client? What do Spri

Answer 1

The simplest is to use the RestTemplate, check this article on the official Spring blog:

The RestTemplate is the central Spring class for client-side HTTP access.

This is an example of a GET:

String result = restTemplate.getForObject("http://example.com/hotels/{hotel}/bookings/{booking}", String.class, "42", "21");

Answer 2

i did it in following way :

import java.io.FileReader;
import java.util.HashMap;
import java.util.Map;

import org.json.simple.JSONObject;
import org.json.simple.parser.JSONParser;
import org.springframework.http.HttpEntity;
import org.springframework.http.ResponseEntity;
import org.springframework.http.converter.StringHttpMessageConverter;
import org.springframework.util.LinkedMultiValueMap;
import org.springframework.util.MultiValueMap;
import org.springframework.web.client.RestTemplate;

public class PostRequestMain {

    /**
     * POST with Headers call using Spring RestTemplate
     * 
     * 
     * @param args
     */

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        MultiValueMap<String, String> headers = new LinkedMultiValueMap<String, String>();
        Map map = new HashMap<String, String>();
        map.put("Content-Type", "application/json");
        headers.setAll(map);
        Map req_payload = new HashMap();
        req_payload.put("name", "piyush");

        HttpEntity<?> request = new HttpEntity<>(req_payload, headers);
        String url = "http://localhost:8080/portal-name/module-name/";

        // Create a new RestTemplate instance
        RestTemplate restTemplate = new RestTemplate();

        // Add the String message converter
        restTemplate.getMessageConverters().add(new StringHttpMessageConverter());


        ResponseEntity<String> response = restTemplate.postForEntity(url, request, String.class);


        System.out.println(response);

    }

    private static void getPayloadMap() {
        JSONParser parser = new JSONParser();

        try {

            Object obj = parser.parse(new FileReader("C:\\Piyush\\test.json"));
            JSONObject jsonObject = (JSONObject) obj;

            Map payLoadMap = new HashMap();
            payLoadMap.putAll(jsonObject);

            System.out.println(jsonObject);
        } catch (Exception e) {
        }
    }

}

Answer 3

I achieved what I needed with the following:

import org.springframework.http.HttpEntity;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpMethod;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.client.RestTemplate;

public class RestClient {

  private String server = "http://localhost:3000";
  private RestTemplate rest;
  private HttpHeaders headers;
  private HttpStatus status;

  public RestClient() {
    this.rest = new RestTemplate();
    this.headers = new HttpHeaders();
    headers.add("Content-Type", "application/json");
    headers.add("Accept", "*/*");
  }

  public String get(String uri) {
    HttpEntity<String> requestEntity = new HttpEntity<String>("", headers);
    ResponseEntity<String> responseEntity = rest.exchange(server + uri, HttpMethod.GET, requestEntity, String.class);
    this.setStatus(responseEntity.getStatusCode());
    return responseEntity.getBody();
  }

  public String post(String uri, String json) {   
    HttpEntity<String> requestEntity = new HttpEntity<String>(json, headers);
    ResponseEntity<String> responseEntity = rest.exchange(server + uri, HttpMethod.POST, requestEntity, String.class);
    this.setStatus(responseEntity.getStatusCode());
    return responseEntity.getBody();
  }

  public void put(String uri, String json) {
    HttpEntity<String> requestEntity = new HttpEntity<String>(json, headers);
    ResponseEntity<String> responseEntity = rest.exchange(server + uri, HttpMethod.PUT, requestEntity, null);
    this.setStatus(responseEntity.getStatusCode());   
  }

  public void delete(String uri) {
    HttpEntity<String> requestEntity = new HttpEntity<String>("", headers);
    ResponseEntity<String> responseEntity = rest.exchange(server + uri, HttpMethod.DELETE, requestEntity, null);
    this.setStatus(responseEntity.getStatusCode());
  }

  public HttpStatus getStatus() {
    return status;
  }

  public void setStatus(HttpStatus status) {
    this.status = status;
  } 
}