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Apache HttpClient

i

Apache HttpClient

i Http client is a transfer library. It resides on the client side, sends and receives Http messages. It provides up to date, feature-rich, and an efficient implementation which meets the recent Http standards. This tutorial has been prepared for the beginners to help them understand the concepts of Apache HttpClient library. Before you start practicing various types of examples given in this reference, we assume that you already have knowledge in Java programming. And, having knowledge of Http protocol concepts helps in understanding this tutorial better.

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Apache HttpClient

ii

About the Tutorial ............................................................................................................................................ i

Audience ........................................................................................................................................................... i

Prerequisites ..................................................................................................................................................... i

Copyright & Disclaimer ..................................................................................................................................... i

Table of Contents ............................................................................................................................................ ii

What is Http Client? ........................................................................................................................................ 1

Features of Http Client .................................................................................................................................... 1

Step 1: Download the dependency JAR file ..................................................................................................... 2

Step 2: Create a project and set build path ..................................................................................................... 2

Step 1: Create a HttpClient object ................................................................................................................... 5

Step 2: Create an HttpGet Object .................................................................................................................... 5

Example ........................................................................................................................................................... 5

Output ............................................................................................................................................................. 6

Step 1: Create an HttpClient Object ................................................................................................................ 8

Step 2: Create HttpPost Object ....................................................................................................................... 8

Step 3: Execute the Get Request ..................................................................................................................... 8

Example ........................................................................................................................................................... 8

Output ............................................................................................................................................................. 9

Creating a response handler.......................................................................................................................... 11

Executing the request using response handler ............................................................................................. 11

Step 1: Create an HttpClient Object .............................................................................................................. 11

Apache HttpClient

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Step 2: Instantiate the Response Handler ..................................................................................................... 11

Step 3: Create a HttpGet Object .................................................................................................................... 11

Step 4: Execute the Get request using response handler ............................................................................. 12

Example ......................................................................................................................................................... 12

Output ........................................................................................................................................................... 13

Step 1: Create an HttpClient object ............................................................................................................... 15

Step 2: Start a try-finally block ...................................................................................................................... 15

Step 3: Create a HttpGet object .................................................................................................................... 15

Step 4: Execute the Get request .................................................................................................................... 16

Step 5: Start another (nested) try-finally ....................................................................................................... 16

Example ......................................................................................................................................................... 16

Output ........................................................................................................................................................... 17

Example ......................................................................................................................................................... 19

Output ........................................................................................................................................................... 20

Request interceptor....................................................................................................................................... 21

Example ......................................................................................................................................................... 22

Output ........................................................................................................................................................... 23

Response interceptor .................................................................................................................................... 24

Example ......................................................................................................................................................... 24

Output ........................................................................................................................................................... 26

Step 1: Create a CredentialsProvider object ................................................................................................. 27

Step 2: Set the Credentials ............................................................................................................................ 27

Step 3: Create a HttpClientBuilder Object ..................................................................................................... 27

Apache HttpClient

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Step 4: Set the credentialsPovider ................................................................................................................ 28

Step 5: Build the CloseableHttpClient ........................................................................................................... 28

Step 6: Create a HttpGet object and execute it ............................................................................................. 28

Example ......................................................................................................................................................... 28

Output ........................................................................................................................................................... 30

Step 1: Create a HttpHost object ................................................................................................................... 31

Step 2: Create an HttpRoutePlanner object .................................................................................................. 31

Step 3: Set the route planner to a client builder ........................................................................................... 31

Step 4: Build the CloseableHttpClient object ................................................................................................ 32

Step 5: Create a HttpGet object .................................................................................................................... 32

Step 6: Execute the request .......................................................................................................................... 32

Example ......................................................................................................................................................... 32

Output ........................................................................................................................................................... 34

Step 1: Create a CredentialsProvider object ................................................................................................. 35

Step 2: Set the credentials ............................................................................................................................. 35

Step 3: Create an HttpClientBuilder object ................................................................................................... 35

Step 4: Set the CredentialsProvider............................................................................................................... 35

Step 5: Build the CloseableHttpClient ........................................................................................................... 36

Step 6: Create the proxy and target hosts ..................................................................................................... 36

Step 7: Set the proxy and build a RequestConfig object ............................................................................... 36

Step 8: Create a HttpGet request object and set config object to it. ............................................................ 36

Step 9: Execute the request .......................................................................................................................... 36

Example ......................................................................................................................................................... 37

Output ........................................................................................................................................................... 38

Apache HttpClient

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Step 1: Create an HttpClient object ............................................................................................................... 39

Step 2: Create a RequestBuilder object ......................................................................................................... 39

Step 3: Set Uri and parameters to the RequestBuilder. ................................................................................ 39

Step 4: Build the HttpUriRequest object ....................................................................................................... 39

Step 5: Execute the request .......................................................................................................................... 40

Example ......................................................................................................................................................... 40

Output ........................................................................................................................................................... 41

Form Login with Cookies ............................................................................................................................... 42

Creating a cookie ........................................................................................................................................... 43

Example ......................................................................................................................................................... 44

Retrieving a cookie ........................................................................................................................................ 45

Example ......................................................................................................................................................... 45

Output ........................................................................................................................................................... 46

Step 1: Creating the Client Connection Pool Manager .................................................................................. 47

Step 2: Set the maximum number of connections ........................................................................................ 47

Step 3: Create a ClientBuilder Object ............................................................................................................ 47

Step 4: Create the HttpGet request objects .................................................................................................. 47

Step 5: Implementing the run method .......................................................................................................... 48

Step 6: Create Thread objects ....................................................................................................................... 48

Step 7: Start and join the threads .................................................................................................................. 48

Step 8: Run method implementation ............................................................................................................ 49

Example ......................................................................................................................................................... 49

Output ........................................................................................................................................................... 51

Step 1: Create SSLContextBuilder object ....................................................................................................... 52

Apache HttpClient

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Step 2: Load the Keystore .............................................................................................................................. 52

Step 3: build an SSLContext object ................................................................................................................ 52

Step 4: Creating SSLConnectionSocketFactory object ................................................................................... 52

Step 5: Create an HttpClientBuilder object ................................................................................................... 53

Step 6: Set the SSLConnectionSocketFactory object ..................................................................................... 53

Step 7: Build the CloseableHttpClient object ................................................................................................ 53

Step 8: Create an HttpGet object .................................................................................................................. 53

Step 9: Execute the request .......................................................................................................................... 54

Example ......................................................................................................................................................... 54

Output ........................................................................................................................................................... 56

Step 1: Create an HttpClient object ............................................................................................................... 57

Step 2: Create a FileBody object .................................................................................................................... 57

Step 3: Create a MultipartEntityBuilder ....................................................................................................... 58

Step 4: Set the mode ..................................................................................................................................... 58

Step 5: Add various the desired parts ........................................................................................................... 58

Step 6: Building single entity ......................................................................................................................... 58

Step 7: Create a RequestBuilder object ......................................................................................................... 58

Step 8: Set the entity object to the RequestBuilder ...................................................................................... 59

Step 9: Build the HttpUriRequest .................................................................................................................. 59

Step 10: Execute the request ........................................................................................................................ 59

Example ......................................................................................................................................................... 59

Output ........................................................................................................................................................... 61

Apache HttpClient

1 The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information systems. This is the foundation for data communication for the World Wide Web (i.e., Internet) since 1990. HTTP is a generic and stateless protocol which can be used for other purposes as well using extensions of its request methods, error codes, and headers. Basically, HTTP is a TCP/IP based communication protocol, that is used to deliver data (HTML files, image files, query results, etc.) on the World Wide Web. The default port is TCP 80, but other ports can be used as well. It provides a standardized way for computers to communicate with each other. HTTP specification defines how clients' request data will be constructed and sent to the server, and how the servers respond to these requests. Http client is a transfer library, it resides on the client side, sends and receives HTTP messages. It provides up to date, feature-rich and, efficient implementation which meets the recent HTTP standards. In addition to this using client library, one can build HTTP based applications such as web browsers, web service clients, etc. Following are the prominent features of Http client: HttpClient library implements all the available HTTP methods. HttpClient library provides APIs to secure the requests using the Secure Socket

Layer protocol.

Using HttpClient, you can establish connections using proxies. You can authenticate connections using authentication schemes such as Basic,

Digest, NTLMv1, NTLMv2, NTLM2 Session etc.

HttpClient library supports sending requests through multiple threads. It manages multiple connections established from various threads using

ClientConnectionPoolManager.

Using Apache HttpClient library, you can set connection timeouts.

Apache HttpClient

2 In this chapter, we will explain how to set an environment for HttpClient in Eclipse IDE. Before proceeding with the installation, make sure that you already have Eclipse installed in your system. If not, download and install Eclipse. For more information on Eclipse, please refer to our Eclipse Tutorial. Open the official homepage of the HttpClient (components) website and go to the download page. Then, download the latest stable version of HttpClient. Here, throughout the tutorial, we are using the version 4.5.6 hence download the file 4.5.6.zip. Within the downloaded folder, you will find a folder named lib and this contains the required Jar files that are to be added in the classpath of your project, to work with

HttpClient.

Open eclipse and create a sample project. Right click on the project select the option Build

Path -> Configure Build Path as shown below.

Apache HttpClient

3 In the Java Build Path frame in the Libraries tab, click on Add External JARs.

Apache HttpClient

4 And select all the jar files in the lib folder and, click on Apply and Close. You are all set to work with HttpClient library in eclipse.

Apache HttpClient

5 The GET method is used to retrieve information from the given server using a given URI. Requests using GET should only retrieve data and should have no other effect on the data. The HttpClient API provides a class named HttpGet which represents the get request method. Follow the steps given below to send a get request using HttpClient library. The createDefault() method of the HttpClients class returns a CloseableHttpClient object, which is the base implementation of the HttpClient interface. Using this method, create an HttpClient object as shown below: CloseableHttpClient httpclient = HttpClients.createDefault(); The HttpGet class represents the HTTPGET request. Which retrieves the information of the given server using a URI. Create a HTTP GET request by instantiating this class. The constructor of this class accepts a String value representing the URI. HttpGet httpget = new HttpGet("http://www.tutorialspoint.com/");

Step 3: Execute the Get Request

The execute() method of the CloseableHttpClient class accepts a HttpUriRequest (interface) object (i.e. HttpGet, HttpPost, HttpPut, HttpHead etc.) and returns a response object. Execute the request using this method as shown below: HttpResponse httpresponse = httpclient.execute(httpget); Following is an example which demonstrates the execution of the HTTP GET request using

HttpClient library.

import java.util.Scanner;

Apache HttpClient

6 import org.apache.http.HttpResponse; import org.apache.http.client.methods.HttpGet; import org.apache.http.impl.client.CloseableHttpClient; import org.apache.http.impl.client.HttpClients; public class HttpGetExample { public static void main(String args[]) throws Exception{ //Creating a HttpClient object CloseableHttpClient httpclient = HttpClients.createDefault(); //Creating a HttpGet object HttpGet httpget = new HttpGet("https://www.tutorialspoint.com/ "); //Printing the method used System.out.println("Request Type: "+httpget.getMethod()); //Executing the Get request HttpResponse httpresponse = httpclient.execute(httpget); Scanner sc = new Scanner(httpresponse.getEntity().getContent()); //Printing the status line while(sc.hasNext()){

System.out.println(sc.nextLine());

The above program generates the following output:

Apache HttpClient

7

Request Type: GET

Apache HttpClient

8 A POST request is used to send data to the server; for example, customer information, file upload, etc., using HTML forms. The HttpClient API provides a class named HttpPost which represents the POST request. Follow the steps given below to send a HTTP POST request using HttpClient library. The createDefault() method of the HttpClients class returns an object of the class CloseableHttpClient, which is the base implementation of the HttpClient interface.

Using this method, create an HttpClient object.

CloseableHttpClient httpClient = HttpClients.createDefault(); The HttpPost class represents the HTTP POST request. This sends required data and retrieves the information of the given server using a URI. Create this request by instantiating the HttpPost class and pass a string value representing the URI, as a parameter to its constructor. HttpGet httpGet = new HttpGet("http://www.tutorialspoint.com/"); The execute() method of the CloseableHttpClient object accepts a HttpUriRequest (interface) object (i.e. HttpGet, HttpPost, HttpPut, HttpHead etc.) and returns a responsequotesdbs_dbs17.pdfusesText_23