apache httpclient interceptors

Interceptors in Apache HttpClient are a powerful feature that allows you to modify the behavior of the HTTP client by intercepting and modifying requests and responses. Interceptors are essentially plug-ins that you can add to the HTTP client to intercept HTTP requests and responses at different stages of processing.

Apache HttpClient provides two types of interceptors:

1. Request Interceptors: These interceptors are executed before the request is sent to the server. Request interceptors are typically used to add or modify request headers or request parameters.

2. Response Interceptors: These interceptors are executed after the response is received from the server. Response interceptors are typically used to modify the response content or response headers.

Here's an example that shows how to use request and response interceptors in Apache HttpClient:

import org.apache.http.HttpHost;
import org.apache.http.HttpRequestInterceptor;
import org.apache.http.HttpResponseInterceptor;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.impl.conn.DefaultProxyRoutePlanner;
import org.apache.http.protocol.HTTP;
import org.apache.http.protocol.HttpContext;

public class HttpClientExample {
    public static void main(String[] args) throws Exception {
        HttpHost proxy = new HttpHost("proxy.example.com", 8080);
        HttpClient httpClient = HttpClientBuilder.create()
            .setRoutePlanner(new DefaultProxyRoutePlanner(proxy))
            .addInterceptorFirst(new HttpRequestInterceptor() {
                public void process(HttpRequest request, HttpContext context) {
                    request.setHeader(HTTP.USER_AGENT, "My Custom User Agent");
                }
            })
            .addInterceptorLast(new HttpResponseInterceptor() {
                public void process(HttpResponse response, HttpContext context) {
                    response.setHeader("X-Custom-Header", "Custom Header Value");
                }
            })
            .build();
        HttpGet httpGet = new HttpGet("http://www.example.com");
        httpClient.execute(httpGet);
    }
}

In this example, we create an instance of HttpClient and configure it with a proxy route planner and two interceptors - one request interceptor and one response interceptor. The request interceptor adds a custom User-Agent header to the HTTP request, while the response interceptor adds a custom X-Custom-Header header to the HTTP response. We use the addInterceptorFirst() method to add the request interceptor first in the interceptor chain, and addInterceptorLast() method to add the response interceptor last in the interceptor chain.

By using interceptors, you can modify the behavior of the HTTP client in a wide variety of ways, such as adding custom authentication headers, logging requests and responses, or modifying the response content.