HttpClient攔截器 - tw511教學網

攔截器(interceptor)是那些有助於阻止或改變請求或響應的攔截器。協定攔截器通常作用於特定檔頭或一組相關檔頭。HttpClient庫為攔截器提供支援。

請求攔截器

HttpRequestInterceptor介面表示請求攔截器。此介面包含一個稱為進程的方法，需要編寫程式碼塊來攔截請求。

在用戶端，此方法在將請求傳送到伺服器之前驗證/處理請求，並且在伺服器端，此方法在評估請求的主體之前執行。

建立請求攔截器

可以按照以下步驟建立請求攔截器。

第1步 - 建立HttpRequestInterceptor的物件

通過實現其抽象方法過程來建立HttpRequestInterceptor介面的物件。

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

第2步 - 範例化CloseableHttpClient物件

通過將以上建立的攔截器新增到它來構建自定義的CloseableHttpClient物件，如下所示 -

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

使用此物件，可以照常執行請求執行。

範例

以下範例演示了請求攔截器的用法。在此範例中，建立了一個HTTP GET請求物件，並新增了三個檔頭：sample-header，demoheader和test-header。

在攔截器processor()方法中，驗證傳送請求的頭部; 如果這些檔頭中的任何一個是sample-header，我們嘗試刪除它並顯示特定請求的檔頭列表。

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.kaops.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());
   }
}

執行上面範例程式碼，得到以下結果:

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

響應攔截器

HttpResponseInterceptor介面表示響應攔截器。該介面包含一個稱為process()的方法。在此方法中，需要編寫程式碼塊來攔截響應。

在伺服器端，此方法在將響應傳送到用戶端之前驗證/處理響應，在用戶端，此方法在評估響應主體之前執行。

建立響應攔截器

可以按照以下步驟建立響應攔截器 -

第1步 - 建立HttpResponseInterceptor的物件

通過實現其抽象方法過程來建立HttpResponseInterceptor介面的物件。

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

第2步 - 範例化CloseableHttpClient物件
通過向其新增上面建立的攔截器來構建自定義的CloseableHttpClient物件，如下所示 -

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

使用此物件，可以照常執行請求執行。

範例

以下範例演示了響應攔截器的用法。在此範例中，向處理器中的響應新增了三個檔頭：sample-header，demo-header和test-header。
執行請求並獲得響應後，使用getAllHeaders()方法列印響應的所有檔頭的名稱。
在輸出中，可以觀察列表中三個標題的名稱。

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.kaops.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());
      }
   }
}

執行上面範例程式碼，得到以下結果：

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