Apache HttpClient - 攔截器
攔截器可以幫助阻斷或更改請求或響應。協議攔截器通常作用於特定的頭部或一組相關的頭部。HttpClient 庫提供了對攔截器的支援。
請求攔截器
HttpRequestInterceptor 介面表示請求攔截器。此介面包含一個名為 process 的方法，您需要在其中編寫攔截請求的程式碼塊。
在客戶端，此方法在將請求傳送到伺服器之前驗證/處理請求，而在伺服器端，此方法在評估請求主體之前執行。
建立請求攔截器
您可以按照以下步驟建立請求攔截器。
步驟 1 - 建立 HttpRequestInterceptor 物件
透過實現其抽象方法 process 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 . . . . .
};
步驟 2 - 例項化 CloseableHttpClient 物件
透過將上面建立的攔截器新增到自定義的CloseableHttpClient 物件中來構建它，如下所示：
//Creating a CloseableHttpClient object CloseableHttpClient httpclient = HttpClients.custom().addInterceptorFirst(requestInterceptor).build();
使用此物件，您可以像往常一樣執行請求。
示例
以下示例演示了請求攔截器的用法。在此示例中，我們建立了一個 HTTP GET 請求物件，並向其中添加了三個頭部：sample-header、demoheader 和 test-header。
在攔截器的processor() 方法中，我們正在驗證傳送的請求的頭部；如果其中任何一個頭部是sample-header，我們嘗試將其刪除並顯示該特定請求的頭部列表。
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://tutorialspoint.tw/");
//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());
}
}
輸出
執行上述程式後，將生成以下輸出：
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。此介面包含一個名為process() 的方法。在此方法中，您需要編寫攔截響應的程式碼塊。
在伺服器端，此方法在將響應傳送到客戶端之前驗證/處理響應，而在客戶端，此方法在評估響應主體之前執行。
建立響應攔截器
您可以按照以下步驟建立響應攔截器：
步驟 1 - 建立 HttpResponseInterceptor 物件
透過實現其抽象方法process 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 . . . . . . . .
}
};
步驟 2：例項化 CloseableHttpClient 物件
透過將上面建立的攔截器新增到自定義的CloseableHttpClient 物件中來構建它，如下所示：
//Creating a CloseableHttpClient object CloseableHttpClient httpclient = HttpClients.custom().addInterceptorFirst(responseInterceptor).build();
使用此物件，您可以像往常一樣執行請求。
示例
以下示例演示了響應攔截器的用法。在此示例中，我們在處理器中向響應添加了三個頭部：sample-header、demo-header 和 test-header。
執行請求並獲得響應後，我們使用getAllHeaders() 方法列印了響應中所有頭部的名稱。
並且在輸出中，您可以觀察到列表中三個頭部的名稱。
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://tutorialspoint.tw/");
//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());
}
}
}
輸出
執行上述程式後，將生成以下結果：
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
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