Apache HttpClient Tutorial

In this quick article, we will discuss how to use Apache HttpClient 4.5+ to work with HTML forms.

Related Apache HttpClient useful articles:

Apache HttpClient GET HTTP Request Example

Apache HttpClient POST HTTP Request Example

Apache HttpClient PUT HTTP Request Example

Apache HttpClient DELETE HTTP Request Example

Working with HTML forms

Many applications need to simulate the process of submitting an HTML form, for instance, in order to log in to a web application or submit input data. HttpClient provides the entity class UrlEncodedFormEntity to facilitate the process.

List<NameValuePair> formparams = new ArrayList<NameValuePair>();
formparams.add(new BasicNameValuePair("param1", "value1"));
formparams.add(new BasicNameValuePair("param2", "value2"));
UrlEncodedFormEntity entity = new UrlEncodedFormEntity(formparams, Consts.UTF_8);
HttpPost httppost = new HttpPost("http://localhost/handler.do");
httppost.setEntity(entity);

The UrlEncodedFormEntity instance will use the so-called URL encoding to encode parameters and produce the following content:

param1=value1&param2=value2

HttpClient supports out of the box all HTTP methods defined in the HTTP/1.1 specification: GET, HEAD, POST, PUT, DELETE, TRACE, and OPTIONS. There is a specific class for each method type.: HttpGet, HttpHead, HttpPost, HttpPut, HttpDelete, HttpTrace, and HttpOptions.

In this example, we will use HttpPost class to handle the POST HTTP method.

Using the Apache HttpClient - Maven dependencies

The Apache HttpClient library allows handling HTTP requests. To use this library add a dependency to your Maven or Gradle build file. You find the latest version here: https://mvnrepository.com/artifact/org.apache.httpcomponents/httpclient

We use maven to manage our dependencies and are using Apache HttpClient version 4.5. Add the following dependency to your project.

<dependency>
 <groupId>org.apache.httpcomponents</groupId>
 <artifactId>httpclient</artifactId>
 <version>4.5</version>
</dependency>

Development Steps

1. Create instance of CloseableHttpClient using helper class HttpClients.

CloseableHttpClient httpclient = HttpClients.createDefault()

The HttpClients.createDefault() method creates CloseableHttpClient instance with default configuration.

2. Create a basic POST request

HttpPost httpPost = new HttpPost("http://httpbin.org/post");

3. Prepare Form Object

List<NameValuePair> form = new ArrayList<>();
form.add(new BasicNameValuePair("John", "Cena"));
form.add(new BasicNameValuePair("Tom", "Cruise"));
form.add(new BasicNameValuePair("tony", "stark"));
UrlEncodedFormEntity entity = new UrlEncodedFormEntity(form, Consts.UTF_8);

4. Create a custom response handler

ResponseHandler < String > responseHandler = response - > {
    int status = response.getStatusLine().getStatusCode();
    if (status >= 200 && status < 300) {
        HttpEntity entity = response.getEntity();
        return entity != null ? EntityUtils.toString(entity) : null;
    } else {
        throw new ClientProtocolException("Unexpected response status: " + status);
    }
};

6. Send basic POST request via execute() Method

String responseBody = httpclient.execute(httpPost, responseHandler);

Submitting HTML Form Parameters

In the following example, we post HTML Form parameters to the resource http://httpbin.org/post. This resources acknowledges the data and returns a JSON object which we’ll simply print to the console. When sending HTML Form parameters, you should normally set the content-type to application/x-www-form-urlencoded, but Apache HttpClient automatically detects the content type and will set it accordingly.

package com.javadevelopersguide.httpclient.examples;

import org.apache.http.Consts;
import org.apache.http.HttpEntity;
import org.apache.http.NameValuePair;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.ResponseHandler;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.util.EntityUtils;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

/**
 * This example demonstrates the use of {@link HttpPost} request method. And
 * sending HTML Form request parameters
 */
public class HttpClientHttpFormExample {

    public static void main(String...args) throws IOException {

        try (CloseableHttpClient httpclient = HttpClients.createDefault()) {

            List < NameValuePair > form = new ArrayList < > ();
            form.add(new BasicNameValuePair("John", "Cena"));
            form.add(new BasicNameValuePair("Tom", "Cruise"));
            form.add(new BasicNameValuePair("tony", "stark"));
            UrlEncodedFormEntity entity = new UrlEncodedFormEntity(form, Consts.UTF_8);

            HttpPost httpPost = new HttpPost("http://httpbin.org/post");
            httpPost.setEntity(entity);
            System.out.println("Executing request " + httpPost.getRequestLine());

            // Create a custom response handler
            ResponseHandler < String > responseHandler = response - > {
                int status = response.getStatusLine().getStatusCode();
                if (status >= 200 && status < 300) {
                    HttpEntity responseEntity = response.getEntity();
                    return responseEntity != null ? EntityUtils.toString(responseEntity) : null;
                } else {
                    throw new ClientProtocolException("Unexpected response status: " + status);
                }
            };
            String responseBody = httpclient.execute(httpPost, responseHandler);
            System.out.println("----------------------------------------");
            System.out.println(responseBody);
        }
    }
}

Output

Executing request POST http://httpbin.org/post HTTP/1.1
----------------------------------------
{
  "args": {}, 
  "data": "", 
  "files": {}, 
  "form": {
    "John": "Cena", 
    "Tom": "Cruise", 
    "tony": "stark"
  }, 
  "headers": {
    "Accept-Encoding": "gzip,deflate", 
    "Connection": "close", 
    "Content-Length": "31", 
    "Content-Type": "application/x-www-form-urlencoded; charset=UTF-8", 
    "Host": "httpbin.org", 
    "User-Agent": "Apache-HttpClient/4.5 (Java/1.8.0_172)"
  }, 
  "json": null, 
  "origin": "49.35.12.218", 
  "url": "http://httpbin.org/post"
}