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Apache HttpClient Interceptor

By Arvind Rai, October 25, 2018
On this page we will provide Apache HttpClient interceptor example. Apache HttpClient adds HttpRequestInterceptor and HttpResponseInterceptor protocol interceptors to CloseableHttpClient using HttpClientBuilder class. HttpClientBuilder is used to build CloseableHttpClient custom configurations. To add interceptor, HttpClientBuilder provides methods such as addRequestInterceptorFirst, addResponseInterceptorLast, addExecInterceptorAfter, addExecInterceptorBefore etc. Here in our example we will add request id in header and according to that value we will change entity details.

Technologies Used

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

Gradle File

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

HttpRequestInterceptor and HttpResponseInterceptor

HttpRequestInterceptor and HttpResponseInterceptor protocol interceptors act upon one header or the group of related headers of the incoming messages or they can populate the one header or group of related headers of the outgoing messages. HttpRequestInterceptor and HttpResponseInterceptor are interfaces and both declare process method.
Find the code snippet to instantiate HttpRequestInterceptor.
new HttpRequestInterceptor() {
	  @Override
	  public void process(HttpRequest request, EntityDetails entity, HttpContext context)
		  throws HttpException, IOException {
             ------
	  }
	} 
Find the code snippet to instantiate HttpResponseInterceptor.
new HttpResponseInterceptor() {
	  @Override
	  public void process(HttpResponse response, EntityDetails entity, HttpContext context)
		  throws HttpException, IOException {
             ------
	  }
	} 

ExecChainHandler

ExecChainHandler is an element in HTTP request execution chain. ExecChainHandler is an interface and declares execute method. We can instantiate ExecChainHandler as following.
new ExecChainHandler() {
	  @Override
	  public ClassicHttpResponse execute(ClassicHttpRequest request, Scope scope, ExecChain chain)
		  throws IOException, HttpException {
             ------
	  }
	} 

Add Interceptors using HttpClientBuilder

HttpClientBuilder provides following methods to add interceptors.
addRequestInterceptorFirst: Adds the protocol interceptor to the head of the protocol processing list. It can accept HttpRequestInterceptor or HttpResponseInterceptor interceptor as an argument.
addResponseInterceptorLast: Adds the protocol interceptor to the tail of the protocol processing list. It can accept HttpRequestInterceptor or HttpResponseInterceptor interceptor as an argument.
addExecInterceptorAfter: It adds execution interceptor after the given interceptor. This method accepts (1) existing interceptor name after which this execution interceptor will be added, (2) name for this interceptor and (3) ExecChainHandler instance.
addExecInterceptorBefore: It adds execution interceptor before the given interceptor. This method accepts (1) existing interceptor name before which this execution interceptor will be added, (2) name for this interceptor and (3) ExecChainHandler instance.
addExecInterceptorFirst: Adds execution interceptor to the head of the processing list. It accepts interceptor name and ExecChainHandler instance.
addExecInterceptorLast: Adds execution interceptor to the tail of the processing list. It accepts interceptor name and ExecChainHandler instance.

Find the example.
MyClientInterceptors.java
package com.concretepage;
import java.io.IOException;
import java.util.concurrent.atomic.AtomicLong;
import org.apache.hc.client5.http.classic.ExecChain;
import org.apache.hc.client5.http.classic.ExecChain.Scope;
import org.apache.hc.client5.http.classic.ExecChainHandler;
import org.apache.hc.client5.http.classic.methods.HttpGet;
import org.apache.hc.client5.http.impl.ChainElements;
import org.apache.hc.client5.http.impl.classic.CloseableHttpClient;
import org.apache.hc.client5.http.impl.classic.CloseableHttpResponse;
import org.apache.hc.client5.http.impl.classic.HttpClientBuilder;
import org.apache.hc.client5.http.impl.classic.HttpClients;
import org.apache.hc.core5.http.ClassicHttpRequest;
import org.apache.hc.core5.http.ClassicHttpResponse;
import org.apache.hc.core5.http.ContentType;
import org.apache.hc.core5.http.EntityDetails;
import org.apache.hc.core5.http.Header;
import org.apache.hc.core5.http.HttpException;
import org.apache.hc.core5.http.HttpRequest;
import org.apache.hc.core5.http.HttpRequestInterceptor;
import org.apache.hc.core5.http.HttpResponse;
import org.apache.hc.core5.http.HttpResponseInterceptor;
import org.apache.hc.core5.http.HttpStatus;
import org.apache.hc.core5.http.ParseException;
import org.apache.hc.core5.http.io.entity.EntityUtils;
import org.apache.hc.core5.http.io.entity.StringEntity;
import org.apache.hc.core5.http.message.BasicClassicHttpResponse;
import org.apache.hc.core5.http.protocol.HttpContext;

public class MyClientInterceptors {
  public static void main(String[] args) throws IOException, ParseException {
	HttpClientBuilder builder = HttpClients.custom();

	// Add HttpRequestInterceptor
	builder.addResponseInterceptorLast(new HttpRequestInterceptor() {
	  @Override
	  public void process(HttpRequest request, EntityDetails entity, HttpContext context)
		  throws HttpException, IOException {
		System.out.println("addResponseInterceptorLast with HttpRequestInterceptor");
		context.setAttribute("name", "Mahesh");
	  }
	});
	builder.addRequestInterceptorFirst(new HttpRequestInterceptor() {
	  private final AtomicLong count = new AtomicLong(0);

	  @Override
	  public void process(final HttpRequest request, final EntityDetails entity, final HttpContext context)
		  throws HttpException, IOException {
		System.out.println("addRequestInterceptorFirst with HttpRequestInterceptor");
		request.setHeader("requestId", Long.toString(count.incrementAndGet()));
		System.out.println(context.getAttribute("name"));
	  }
	});

	// Execution Interceptors
	builder.addExecInterceptorAfter(ChainElements.PROTOCOL.name(), "AAA", new ExecChainHandler() {
	  @Override
	  public ClassicHttpResponse execute(ClassicHttpRequest request, Scope scope, ExecChain chain)
		  throws IOException, HttpException {
		System.out.println("--Execution Interceptor AAA--");
		Header header = request.getFirstHeader("requestId");
		if (header != null && "2".equalsIgnoreCase(header.getValue())) {
		  ClassicHttpResponse response = new BasicClassicHttpResponse(HttpStatus.SC_NOT_FOUND, "Not Found");
		  response.setEntity(new StringEntity("Data not available", ContentType.TEXT_PLAIN));
		  return response;
		} else {
		  return chain.proceed(request, scope);
		}
	  }
	});

	builder.addExecInterceptorBefore("AAA", "BBB", new ExecChainHandler() {
	  @Override
	  public ClassicHttpResponse execute(ClassicHttpRequest request, Scope scope, ExecChain chain)
		  throws IOException, HttpException {
		System.out.println("--Execution Interceptor before AAA--");
		return chain.proceed(request, scope);
	  }
	});

	builder.addExecInterceptorAfter("AAA", "CCC", new ExecChainHandler() {
	  @Override
	  public ClassicHttpResponse execute(ClassicHttpRequest request, Scope scope, ExecChain chain)
		  throws IOException, HttpException {
		System.out.println("--Execution Interceptor after AAA--");
		return chain.proceed(request, scope);
	  }
	});

	// Add HttpResponseInterceptor
	builder.addResponseInterceptorLast(new HttpResponseInterceptor() {
	  @Override
	  public void process(HttpResponse response, EntityDetails entity, HttpContext context)
		  throws HttpException, IOException {
		System.out.println("addResponseInterceptorLast with HttpResponseInterceptor");
		System.out.println(context.getAttribute("name"));
	  }
	});
	builder.addRequestInterceptorFirst(new HttpResponseInterceptor() {
	  @Override
	  public void process(HttpResponse response, EntityDetails entity, HttpContext context)
		  throws HttpException, IOException {

		System.out.println("addRequestInterceptorFirst with HttpResponseInterceptor");
		System.out.println(context.getAttribute("name"));

	  }
	});

	for (int i = 1; i <= 2; i++) {
	  System.out.println("-----------Request " + i + "-------------");
	  try (CloseableHttpClient httpClient = builder.build()) {
		final HttpGet httpGet = new HttpGet("http://httpbin.org/get");
		try (CloseableHttpResponse response = httpClient.execute(httpGet)) {
		  System.out.println("-------Output---------");
		  System.out.println(response.getCode() + " " + response.getReasonPhrase());
		  System.out.println(EntityUtils.toString(response.getEntity()));
		}
	  }
	}
  }
} 
Find the output.
Output
-----------Request 1-------------
addResponseInterceptorLast with HttpRequestInterceptor
addRequestInterceptorFirst with HttpRequestInterceptor
Mahesh
--Execution Interceptor before AAA--
--Execution Interceptor AAA--
--Execution Interceptor after AAA--
addResponseInterceptorLast with HttpResponseInterceptor
Mahesh
addRequestInterceptorFirst with HttpResponseInterceptor
Mahesh
-------Output---------
200 OK
{
  "args": {}, 
  "headers": {
    "Accept-Encoding": "deflate, gzip, x-gzip", 
    "Connection": "close", 
    "Host": "httpbin.org", 
    "Requestid": "1", 
    "User-Agent": "Apache-HttpClient/5.0-beta1 (Java/9)"
  }, 
  "origin": "157.38.199.122", 
  "url": "http://httpbin.org/get"
}

-----------Request 2-------------
addResponseInterceptorLast with HttpRequestInterceptor
addRequestInterceptorFirst with HttpRequestInterceptor
Mahesh
--Execution Interceptor before AAA--
--Execution Interceptor AAA--
addResponseInterceptorLast with HttpResponseInterceptor
Mahesh
addRequestInterceptorFirst with HttpResponseInterceptor
Mahesh
-------Output---------
404 Not Found
Data not available 

References

HttpComponents HttpClient Overview
HttpClientBuilder
HttpRequestInterceptor
HttpResponseInterceptor
POSTED BY
ARVIND RAI
ARVIND RAI
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