Sending HTTP POST Request In Java

A simple way using Apache HTTP Components is

Request.Post("http://www.example.com/page.php")
            .bodyForm(Form.form().add("id", "10").build())
            .execute()
            .returnContent();

Take a look at the Fluent API

I suggest using Postman to generate the request code. Simply make the request using Postman then hit the code tab:

Then you'll get the following window to choose in which language you want your request code to be:

Easy with java.net:

public void post(String uri, String data) throws Exception {
HttpClient client = HttpClient.newBuilder().build();
HttpRequest request = HttpRequest.newBuilder()
        .uri(URI.create(uri))
        .POST(BodyPublishers.ofString(data))
        .build();

HttpResponse<?> response = client.send(request, BodyHandlers.discarding());
System.out.println(response.statusCode());

Here is more information: https://openjdk.java.net/groups/net/httpclient/recipes.html#post

Using okhttp :

Source code for okhttp can be found here https://github.com/square/okhttp.

If you're writing a pom project, add this dependency

<dependency>
        <groupId>com.squareup.okhttp3</groupId>
        <artifactId>okhttp</artifactId>
        <version>4.2.2</version>
    </dependency>

If not simply search the internet for 'download okhttp'. Several results will appear where you can download a jar.

your code :

import okhttp3.*;
        
import java.io.IOException;

public class ClassName{
        private void sendPost() throws IOException {
        
                // form parameters
                RequestBody formBody = new FormBody.Builder()
                        .add("id", 10)
                        .build();
        
                Request request = new Request.Builder()
                        .url("http://www.example.com/page.php")
                        .post(formBody)
                        .build();


                OkHttpClient httpClient = new OkHttpClient();
        
                try (Response response = httpClient.newCall(request).execute()) {
        
                    if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);
        
                    // Get response body
                    System.out.println(response.body().string());
                }
        }
    }

Since java 11, HTTP requests can be made by using java.net.http.HttpClient with less code.

    var values = new HashMap<String, Integer>() {{
        put("id", 10);
    }};
    
    var objectMapper = new ObjectMapper();
    String requestBody = objectMapper
            .writeValueAsString(values);
    
    HttpClient client = HttpClient.newHttpClient();
    HttpRequest request = HttpRequest.newBuilder()
            .uri(URI.create("http://www.example.com/abc"))
            .POST(HttpRequest.BodyPublishers.ofString(requestBody))
            .build();
    
    HttpResponse<String> response = client.send(request,
            HttpResponse.BodyHandlers.ofString());
    
    System.out.println(response.body());