Apache HttpClient

Language: Java

Networking/HTTP

HttpClient was created to simplify HTTP communication in Java applications. It abstracts the complexities of HTTP connections, supports synchronous and asynchronous operations, and provides utilities for headers, cookies, and authentication. Widely used in web services, REST clients, and integrations, it ensures reliable and maintainable HTTP communication.

Apache HttpClient is a robust and feature-rich HTTP client library for Java. It allows sending HTTP requests, handling responses, managing connections, cookies, authentication, and supporting advanced features like redirects and timeouts.

Installation

maven:

Add dependency in pom.xml:
<dependency>
  <groupId>org.apache.httpcomponents.client5</groupId>
  <artifactId>httpclient5</artifactId>
  <version>5.2</version>
</dependency>

gradle:

Add dependency in build.gradle:
implementation 'org.apache.httpcomponents.client5:httpclient5:5.2'

Usage

HttpClient allows creating HTTP requests (GET, POST, PUT, DELETE), handling responses, managing cookies, setting headers, handling timeouts, and supporting connection pooling. It supports both synchronous and asynchronous request execution.

Simple GET request

import org.apache.hc.client5.http.fluent.Request;

String response = Request.get("https://httpbin.org/get").execute().returnContent().asString();
System.out.println(response);

Performs a simple GET request and prints the response content.

Simple POST request

import org.apache.hc.client5.http.fluent.Request;
import org.apache.hc.core5.http.io.entity.StringEntity;

String json = "{\"key\": \"value\"}";
String response = Request.post("https://httpbin.org/post")
    .bodyString(json, org.apache.hc.core5.http.ContentType.APPLICATION_JSON)
    .execute().returnContent().asString();
System.out.println(response);

Sends a POST request with JSON payload and prints the response.

Custom headers

import org.apache.hc.client5.http.fluent.Request;

String response = Request.get("https://httpbin.org/headers")
    .addHeader("User-Agent", "MyHttpClient/1.0")
    .execute().returnContent().asString();
System.out.println(response);

Adds custom headers to the request.

Handling timeouts

import org.apache.hc.client5.http.config.RequestConfig;
import org.apache.hc.client5.http.impl.classic.CloseableHttpClient;
import org.apache.hc.client5.http.impl.classic.HttpClients;
import org.apache.hc.client5.http.classic.methods.HttpGet;

RequestConfig config = RequestConfig.custom().setResponseTimeout(5_000).build();
try (CloseableHttpClient client = HttpClients.custom().setDefaultRequestConfig(config).build()) {
    HttpGet request = new HttpGet("https://httpbin.org/delay/10");
    client.execute(request);
} catch (Exception e) {
    System.out.println("Request timed out");
}

Sets a timeout to prevent indefinite waiting.

Using connection pool

import org.apache.hc.client5.http.impl.io.PoolingHttpClientConnectionManager;
import org.apache.hc.client5.http.impl.classic.CloseableHttpClient;
import org.apache.hc.client5.http.impl.classic.HttpClients;

PoolingHttpClientConnectionManager cm = new PoolingHttpClientConnectionManager();
cm.setMaxTotal(50);
cm.setDefaultMaxPerRoute(10);
CloseableHttpClient client = HttpClients.custom().setConnectionManager(cm).build();

Manages multiple HTTP connections efficiently using a connection pool.

Basic authentication

import org.apache.hc.client5.http.auth.UsernamePasswordCredentials;
import org.apache.hc.client5.http.impl.auth.BasicCredentialsProvider;
import org.apache.hc.client5.http.impl.classic.CloseableHttpClient;
import org.apache.hc.client5.http.impl.classic.HttpClients;

BasicCredentialsProvider credsProvider = new BasicCredentialsProvider();
credsProvider.setCredentials(new UsernamePasswordCredentials("user", "password".toCharArray()));
CloseableHttpClient client = HttpClients.custom().setDefaultCredentialsProvider(credsProvider).build();

Sets up basic authentication for requests.

Error Handling

IOException: Occurs when there is a network error or server is unreachable. Handle exceptions appropriately.

HttpResponseException: Occurs when the response status code indicates an error. Check status code and handle accordingly.

ConnectionPoolTimeoutException: Occurs when connections cannot be acquired from the pool. Adjust pool size or release connections promptly.

Best Practices

Use connection pooling for high-performance applications.

Always set timeouts to avoid hanging requests.

Use fluent API for simpler code and readability.

Handle exceptions like IOExceptions to ensure reliability.

Close resources properly using try-with-resources or clients’ close() methods.

Official Docs Github