How to Send Http Request in Java

How to send HTTP request in java?

You can use java.net.HttpUrlConnection.

Example (from here), with improvements. Included in case of link rot:

public static String executePost(String targetURL, String urlParameters) {
  HttpURLConnection connection = null;

  try {
    //Create connection
    URL url = new URL(targetURL);
    connection = (HttpURLConnection) url.openConnection();
    connection.setRequestMethod("POST");
    connection.setRequestProperty("Content-Type", 
        "application/x-www-form-urlencoded");

    connection.setRequestProperty("Content-Length", 
        Integer.toString(urlParameters.getBytes().length));
    connection.setRequestProperty("Content-Language", "en-US");  

    connection.setUseCaches(false);
    connection.setDoOutput(true);

    //Send request
    DataOutputStream wr = new DataOutputStream (
        connection.getOutputStream());
    wr.writeBytes(urlParameters);
    wr.close();

    //Get Response  
    InputStream is = connection.getInputStream();
    BufferedReader rd = new BufferedReader(new InputStreamReader(is));
    StringBuilder response = new StringBuilder(); // or StringBuffer if Java version 5+
    String line;
    while ((line = rd.readLine()) != null) {
      response.append(line);
      response.append('\r');
    }
    rd.close();
    return response.toString();
  } catch (Exception e) {
    e.printStackTrace();
    return null;
  } finally {
    if (connection != null) {
      connection.disconnect();
    }
  }
}

How do I send a java object in a HTTP Request?

Firstly you have to make your Place class serializable, by

implementing java.io.Serializable

Then the Place object needs to be converted to a json object, which can be done easily by using Jackson or GSON libraries.

Example using Gson:

Gson gson = new Gson();
String json = gson.toJson(placeObject);

Later while receiving the response you can deserialize it back to Place object using the same library.

Place placeObject = new Gson().fromJson(json, Place.class);

sending HTTP POST requests in Java

So I did some research and found this!

package com.*********.xyz;

        import java.io.IOException;
        import java.util.Scanner;
        import java.net.URI;
        import java.net.http.HttpClient;
        import java.net.http.HttpRequest;
        import java.net.http.HttpResponse;

public class Main {
    public static void main(String[] args) throws IOException, InterruptedException {
        String body = "this is the message you are going to post!";

        HttpClient client = HttpClient.newHttpClient();
        HttpRequest request = HttpRequest.newBuilder()
                .uri(URI.create("http://192.168.1.46:4046/authenticate"))
                .headers("Content-Type", "text/plain;charset=UTF-8")
                .POST(HttpRequest.BodyPublishers.ofString(body))
                .build();
        HttpResponse<String> response = client.send(request,
                HttpResponse.BodyHandlers.ofString());

        System.out.println(response);
        //Should print 200 after sending the response if the server is active
    }
}

This code works without any third-party libraries.

Java doesn't send HTTP POST Request

I tested this and it's working:

//Sender.java
String url = "http://localhost:8082/";
URL obj = new URL(url);
HttpURLConnection con = (HttpURLConnection) obj.openConnection();


con.setRequestMethod("POST");       
con.setDoOutput(true);

OutputStream os = con.getOutputStream();
os.write("Just Some Text".getBytes("UTF-8"));
os.flush();

int httpResult = con.getResponseCode(); 
con.disconnect();

As you can see, connect is not necessary. The key line is

int httpResult = con.getResponseCode();

What is the best way to make an HTTP request from a Java program?

https://square.github.io/okhttp/ is a good library for http interaction. Then you can use Jackson/Gson to parse the response to a typed object if you want

Usage

public static final MediaType JSON
    = MediaType.parse("application/json; charset=utf-8");

OkHttpClient client = new OkHttpClient();

String post(String url, String json) throws IOException {
  RequestBody body = RequestBody.create(JSON, json);
  Request request = new Request.Builder()
      .url(url)
      .post(body)
      .build();
  Response response = client.newCall(request).execute();
  return response.body().string();
}

Maven:

<dependency>
  <groupId>com.squareup.retrofit2</groupId>
  <artifactId>retrofit</artifactId>
  <version>2.4.0</version>
</dependency>

or Gradle:

implementation 'com.squareup.retrofit2:retrofit:2.4.0'

If you want to kill an ant with a Patton Tank, you have all sort of other options like spring, netflix OSS - feign client + ribbon etc

That being said, first, I would try out what Kayaman posted, https://www.baeldung.com/java-9-http-client as its one less dependency.

How to send a correct HTTP PUT request in Java

You are using the wrong URL for the PUT request.

A GET request to http://192.168.0.53/api/.../lights/1 will return the current state

But to modify you need a PUT request to http://192.168.0.53/api/.../lights/1/state

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