HttpClient拦截器

HttpClient拦截器

拦截器(interceptor)是那些有助于阻止或改变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库为拦截器提供支持。

请求拦截器

HttpRequestInterceptor接口表示请求拦截器。此接口包含一个称为进程的方法，需要编写代码块来拦截请求。

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，此方法在评估请求的主体之前执行。

创建请求拦截器

可以按照以下步骤创建请求拦截器。

第1步 - 创建HttpRequestInterceptor的对象

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

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

第2步 - 实例化CloseableHttpClient对象

通过将以上创建的拦截器添加到它来构建自定义的CloseableHttpClient对象，如下所示 - 

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

使用此对象，可以照常执行请求执行。

示例

以下示例演示了请求拦截器的用法。在此示例中，创建了一个HTTP GET请求对象，并添加了三个标头：sample-header，demoheader和test-header。

在拦截器processor()方法中，验证发送请求的头部; 如果这些标头中的任何一个是sample-header，我们尝试删除它并显示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("http://www.zyiz.net/");

      //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());
   }
}

执行上面示例代码，得到以下结果:

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

响应拦截器

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

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，在客户端，此方法在评估响应主体之前执行。

创建响应拦截器

可以按照以下步骤创建响应拦截器 -

第1步 - 创建HttpResponseInterceptor的对象

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

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

第2步 - 实例化CloseableHttpClient对象
通过向其添加上面创建的拦截器来构建自定义的CloseableHttpClient对象，如下所示 - 

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

使用此对象，可以照常执行请求执行。

示例

以下示例演示了响应拦截器的用法。在此示例中，向处理器中的响应添加了三个标头：sample-header，demo-header和test-header。
执行请求并获得响应后，使用getAllHeaders()方法打印响应的所有标头的名称。
在输出中，可以观察列表中三个标题的名称。

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("http://www.zyiz.net/");

      //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());
      }
   }
}

执行上面示例代码，得到以下结果：

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

目录
HttpClient拦截器