How do I send an HTTP POST request?

The following code snippet will show you how to send an HTTP post request using the Apache HttpComponents. We will send a post request to http://localhost:8080/register, with some parameters to the request using the NameValuePair object.

To pass this parameters to the HTTP post request we create an instance of UrlEncodedFormEntity and pass a list of NameValuePair as the arguments. And before executing the request we set this entity object to the HttpPost.setEntity() method.

Let’s see the code below:

package org.kodejava.example.httpclient;

import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.HttpClient;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.util.EntityUtils;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

public class HttpPostExample {
    public static void main(String[] args) {
        HttpClient client = HttpClientBuilder.create().build();
        HttpPost post = new HttpPost("http://localhost:8080/register");

        // Create some NameValuePair for HttpPost parameters
        List<NameValuePair> arguments = new ArrayList<>(3);
        arguments.add(new BasicNameValuePair("username", "admin"));
        arguments.add(new BasicNameValuePair("firstName", "System"));
        arguments.add(new BasicNameValuePair("lastName", "Administrator"));

        try {
            post.setEntity(new UrlEncodedFormEntity(arguments));
            HttpResponse response = client.execute(post);

            // Print out the response message
            System.out.println(EntityUtils.toString(response.getEntity()));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Maven Dependencies

<!-- http://repo1.maven.org/maven2/org/apache/httpcomponents/httpclient/4.5.3/httpclient-4.5.3.jar -->
<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.5.3</version>
</dependency>

How do I execute HTTP Get request?

Below is an example using HttpClient library to retrieve the content of a website using Http Get request. We start by creating an instance of DefaultHttpClient class. We then define an Http get request by create an instance of HttpGet class and specify the Url of a website we are going to retrieve.

To execute the request we call the HttpClient.execute() method and pass the HttpGet as the arguments. This execution return an HttpResponse object. From this response object we can read the content of the website by accessing the getEntity().getContent() which will give us an InputStream to the content.

For more detail let’s see the code snippet below:

package org.kodejava.example.httpclient;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.HttpClientBuilder;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;

public class HttpGetExample {
    public static void main(String[] args) {
        HttpClient client = HttpClientBuilder.create().build();
        HttpGet request = new HttpGet("https://kodejava.org");

        try {
            HttpResponse response = client.execute(request);
            HttpEntity entity = response.getEntity();
            if (entity != null) {
                try (InputStream stream = entity.getContent()) {
                    BufferedReader reader =
                            new BufferedReader(new InputStreamReader(stream));
                    String line;
                    while ((line = reader.readLine()) != null) {
                        System.out.println(line);
                    }
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Maven Dependencies

<!-- http://repo1.maven.org/maven2/org/apache/httpcomponents/httpclient/4.5.3/httpclient-4.5.3.jar -->
<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.5.3</version>
</dependency>