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Apache HttpClient Response Handler

By Arvind Rai, October 13, 2018
On this page we will provide Apache HttpClient Response Handler example. Apache HttpClient provides HttpClientResponseHandler to process responses. It enables the caller to concentrate on digesting HTTP responses and delegating the task. HTTP response handler ensures that HTTP connection will be released to connection manger automatically in all cases. Apache provides BasicHttpClientResponseHandler and ContentResponseHandler as the implementations of HttpClientResponseHandler interface. We can also create custom response handler by implementing HttpClientResponseHandler and overriding its handleResponse method.

Technologies Used

Find the technologies being used in our example.
1. Java 9
2. HttpClient5 5.0-beta1
3. Jackson 2.9.4
4. Gradle 4.3.1
5. Eclipse Oxygen

Gradle File

Find the Gradle file used in the example.
build.gradle
apply plugin: 'java'
apply plugin: 'eclipse'
archivesBaseName = 'concretepage'
version = '1' 
repositories {
    mavenCentral()
}
dependencies {
    compile 'org.apache.httpcomponents.client5:httpclient5:5.0-beta1'
    compile 'org.apache.httpcomponents.client5:httpclient5-fluent:5.0-beta1'
    
    compile 'com.fasterxml.jackson.core:jackson-core:2.9.5'
    compile 'com.fasterxml.jackson.core:jackson-databind:2.9.5'
    compile 'com.fasterxml.jackson.core:jackson-annotations:2.9.5'    
} 

HttpClientResponseHandler

HttpClientResponseHandler handles the process of generating response object from ClassicHttpResponse which encloses HttpEntity. HttpEntity is an auto closable entity that can be sent or received with HTTP message.
Apache provides following implementations of HttpClientResponseHandler.

BasicHttpClientResponseHandler: It returns the response body as string for successful responses.
ContentResponseHandler: It converts response as Content instances.

HttpClientResponseHandler is an interface and declares handleResponse method. To create a custom HttpClient response handler, we need to implement HttpClientResponseHandler and override its handleResponse method.

BasicHttpClientResponseHandler for String

BasicHttpClientResponseHandler returns the response body as string for successful responses. If response code is 300 or greater, exception is thrown. Find the example.
BasicHCRespHandlerDemo.java
package com.concretepage;
import org.apache.hc.client5.http.classic.methods.HttpGet;
import org.apache.hc.client5.http.impl.classic.BasicHttpClientResponseHandler;
import org.apache.hc.client5.http.impl.classic.CloseableHttpClient;
import org.apache.hc.client5.http.impl.classic.HttpClients;
import org.apache.hc.core5.http.io.HttpClientResponseHandler;

public class BasicHCRespHandlerDemo {
    public final static void main(final String[] args) throws Exception {
    	final CloseableHttpClient httpClient = HttpClients.createDefault();
        try (httpClient) {
            final HttpGet httpGet = new HttpGet("http://httpbin.org/get");
        	
            HttpClientResponseHandler<String> responseHandler = new BasicHttpClientResponseHandler();
            final String responseBody = httpClient.execute(httpGet, responseHandler);

            System.out.println(responseBody);        	
        }
    }
} 

ContentResponseHandler for Content

ContentResponseHandler converts response as Content instances. Find the example.
package com.concretepage;
import org.apache.hc.client5.http.classic.methods.HttpGet;
import org.apache.hc.client5.http.fluent.Content;
import org.apache.hc.client5.http.fluent.ContentResponseHandler;
import org.apache.hc.client5.http.impl.classic.CloseableHttpClient;
import org.apache.hc.client5.http.impl.classic.HttpClients;
import org.apache.hc.core5.http.io.HttpClientResponseHandler;

public class ContentRespHandlerDemo {
    public final static void main(final String[] args) throws Exception {
    	final CloseableHttpClient httpClient = HttpClients.createDefault();
        try (httpClient) {
           final HttpGet httpGet = new HttpGet("http://httpbin.org/get");
        	
           HttpClientResponseHandler<Content> responseHandler = new ContentResponseHandler();
           final Content content = httpClient.execute(httpGet, responseHandler);
        	
           System.out.println(content.asString());        	
        }
    }
} 

Custom Response Handler for JSON

Here we will create custom response handler by implementing HttpClientResponseHandler and overriding its handleResponse method. For the demo we are using a sample URL that will return JSON response as following.
{
  "userId": 1,
  "id": 1,
  "title": "delectus aut autem",
  "completed": false
} 
Within handleResponse method, we will deserialize JSON data into User object using Jackson API. Find the example.
CustomResponseHandler.java
package com.concretepage;
import java.io.IOException;
import java.io.InputStream;
import org.apache.hc.client5.http.ClientProtocolException;
import org.apache.hc.core5.http.ClassicHttpResponse;
import org.apache.hc.core5.http.HttpEntity;
import org.apache.hc.core5.http.HttpException;
import org.apache.hc.core5.http.HttpStatus;
import org.apache.hc.core5.http.io.HttpClientResponseHandler;
import com.fasterxml.jackson.core.JsonFactory;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.databind.ObjectMapper;

public class CustomResponseHandler implements HttpClientResponseHandler<User> {
 @Override
 public User handleResponse(ClassicHttpResponse response) throws HttpException, IOException {
  final int status = response.getCode();
  if (status >= HttpStatus.SC_SUCCESS && status < HttpStatus.SC_REDIRECTION) {
   final JsonFactory jsonFactory = new JsonFactory();

   try (HttpEntity httpEntity = response.getEntity(); 
	InputStream inputStream = httpEntity.getContent()) {

    JsonParser jsonParser = jsonFactory.createParser(inputStream);
    jsonParser.setCodec(new ObjectMapper());
    User user = jsonParser.readValueAs(User.class);
    return user;
   }
  } else {
   throw new ClientProtocolException("Unexpected response status: " + status);
  }
 }
} 
User.java
package com.concretepage;

public class User {
 private String id;
 private String userId;
 private String title;
 private Boolean completed;

 public String getId() {
  return id;
 }
 public String getUserId() {
  return userId;
 }
 public String getTitle() {
  return title;
 }
 public Boolean getCompleted() {
  return completed;
 }
} 
ClientWithCustomRespHandler.java
package com.concretepage;
import org.apache.hc.client5.http.classic.methods.HttpGet;
import org.apache.hc.client5.http.impl.classic.CloseableHttpClient;
import org.apache.hc.client5.http.impl.classic.HttpClients;
import org.apache.hc.core5.http.io.HttpClientResponseHandler;

public class ClientWithCustomRespHandler {
 public final static void main(final String[] args) throws Exception {
  CloseableHttpClient httpClient = HttpClients.createDefault();
  try (httpClient) {
   final HttpGet httpGet = new HttpGet("https://jsonplaceholder.typicode.com/todos/1");

   HttpClientResponseHandler <User> responseHandler = new CustomResponseHandler();
   final User user = httpClient.execute(httpGet, responseHandler);

   System.out.println("UserId: " + user.getUserId());
   System.out.println("Title: " + user.getTitle());
  }
 }
} 
Output
UserId: 1
Title: delectus aut autem 

References

HttpComponents HttpClient Overview
Interface HttpClientResponseHandler

Download Source Code

POSTED BY
ARVIND RAI
ARVIND RAI
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