Apache Httpclient 简明教程

Apache HttpClient - Interceptors

拦截器是帮助阻塞或更改请求或响应的拦截器。协议拦截器通常作用于特定标头或一组相关标头。HttpClient 库提供对拦截器的支持。

Request interceptor

HttpRequestInterceptor 接口表示请求拦截器。此接口包含一个称为 process 的方法，您需要在其中编写代码块以拦截请求。

在客户端，此方法在将请求发送到服务器之前验证/处理请求，并且在服务器端，此方法在评估请求体之前执行。

Creating request interceptor

您可以按照以下步骤创建请求拦截器。

Step 1 - Create an object of HttpRequestInterceptor

通过实现其抽象方法 process 来创建 HttpRequestInterceptor 接口的对象。

HttpRequestInterceptor requestInterceptor = new HttpRequestInterceptor() {

@Override
 public void process(HttpRequest request, HttpContext context) throws
HttpException, IOException {
   //Method implementation . . . . .
};

Step 2 - Instantiate CloseableHttpClient object

通过将上述创建的拦截器添加到它来构建一个自定义 CloseableHttpClient 对象，如下所示 −

//Creating a CloseableHttpClient object
CloseableHttpClient httpclient =
HttpClients.custom().addInterceptorFirst(requestInterceptor).build();

使用此对象，您可以像往常一样执行请求执行。

Example

下面的示例演示了请求拦截器的用法。在此示例中，我们创建了一个 HTTP GET 请求对象，并向其中添加了三个标头：sample-header、demoheader 和 test-header。

在拦截器的 processor() 方法中，我们正在验证发送的请求的标头；如果其中任何标头为 sample-header ，我们将尝试将其删除并显示该特定请求的标头列表。

import java.io.IOException;
import org.apache.http.Header;
import org.apache.http.HttpException;
import org.apache.http.HttpRequest;
import org.apache.http.HttpRequestInterceptor;
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;
import org.apache.http.message.BasicHeader;
import org.apache.http.protocol.HttpContext;

public class InterceptorsExample {

   public static void main(String args[]) throws Exception{

      //Creating an HttpRequestInterceptor
      HttpRequestInterceptor requestInterceptor = new HttpRequestInterceptor() {
         @Override
         public void process(HttpRequest request, HttpContext context) throws
         HttpException, IOException {
            if(request.containsHeader("sample-header")) {
               System.out.println("Contains header sample-header, removing it..");
               request.removeHeaders("sample-header");
            }
            //Printing remaining list of headers
            Header[] headers= request.getAllHeaders();
            for (int i = 0; i<headers.length;i++) {
               System.out.println(headers[i].getName());
            }
         }
      };

      //Creating a CloseableHttpClient object
      CloseableHttpClient httpclient =
      HttpClients.custom().addInterceptorFirst(requestInterceptor).build();

      //Creating a request object
      HttpGet httpget1 = new HttpGet("https://www.tutorialspoint.com/");

      //Setting the header to it
      httpget1.setHeader(new BasicHeader("sample-header","My first header"));
      httpget1.setHeader(new BasicHeader("demo-header","My second header"));
      httpget1.setHeader(new BasicHeader("test-header","My third header"));

      //Executing the request
      HttpResponse httpresponse = httpclient.execute(httpget1);

      //Printing the status line
      System.out.println(httpresponse.getStatusLine());
   }
}

Output

在执行上述程序时，生成以下输出 −

Contains header sample-header, removing it..
demo-header
test-header
HTTP/1.1 200 OK

Response interceptor

HttpResponseInterceptor 接口表示响应拦截器。此接口包含一个称为 process() 的方法。在此方法中，您需要编写代码块以拦截响应。

在服务器端，此方法在将响应发送到客户端之前验证/处理响应，并且在客户端，此方法在评估响应体之前执行。

Creating response interceptor

您可以按照以下步骤创建响应拦截器 −

Step 1 - Create an object of HttpResponseInterceptor

通过实现其抽象方法 process 来创建 HttpResponseInterceptor 接口的对象。

HttpResponseInterceptor responseInterceptor = new HttpResponseInterceptor() {
   @Override
   public void process(HttpResponse response, HttpContext context) throws HttpException, IOException {
      //Method implementation . . . . . . . .
   }
};

Step 2: Instantiate CloseableHttpClient object

通过将上述创建的拦截器添加到它来构建一个自定义 CloseableHttpClient 对象，如下所示 −

//Creating a CloseableHttpClient object
CloseableHttpClient httpclient =
HttpClients.custom().addInterceptorFirst(responseInterceptor).build();

使用此对象，您可以像往常一样执行请求执行。

Example

以下示例演示了请求拦截器用法。在此示例中，已将三个标头添加到了处理器中的响应中：sample-header、demo-header 以及 test-header。

在执行请求和获取响应后，使用了 getAllHeaders() 方法打印了响应的所有标头的名称。

您可以在输出中观察到列表中的三个标头名称。

import java.io.IOException;
import org.apache.http.Header;
import org.apache.http.HttpException;
import org.apache.http.HttpResponse;
import org.apache.http.HttpResponseInterceptor;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.protocol.HttpContext;

public class ResponseInterceptorsExample {

   public static void main(String args[]) throws Exception{

      //Creating an HttpRequestInterceptor
      HttpResponseInterceptor responseInterceptor = new HttpResponseInterceptor() {
         @Override
         public void process(HttpResponse response, HttpContext context) throws
         HttpException, IOException {
            System.out.println("Adding header sample_header, demo-header, test_header to the response");
            response.setHeader("sample-header", "My first header");
            response.setHeader("demo-header", "My second header");
            response.setHeader("test-header", "My third header");
         }
      };

      //Creating a CloseableHttpClient object
      CloseableHttpClient httpclient = HttpClients.custom().addInterceptorFirst(responseInterceptor).build();

      //Creating a request object
      HttpGet httpget1 = new HttpGet("https://www.tutorialspoint.com/");

      //Executing the request
      HttpResponse httpresponse = httpclient.execute(httpget1);

      //Printing remaining list of headers
      Header[] headers = httpresponse.getAllHeaders();

      for (int i = 0; i<headers.length;i++) {
         System.out.println(headers[i].getName());
      }
   }
}

Output

在执行上述程序后，生成了以下结果 -

On executing the above program generates the following output.
Adding header sample_header, demo-header, test_header to the response
Accept-Ranges
Access-Control-Allow-Headers
Access-Control-Allow-Origin
Cache-Control
Content-Type
Date
Expires
Last-Modified
Server
Vary
X-Cache
sample-header
demo-header
test-header