Apache HttpClient - 拦截器
拦截器可以帮助阻断或更改请求或响应。协议拦截器通常作用于特定的头部或一组相关的头部。HttpClient 库提供了对拦截器的支持。
请求拦截器
HttpRequestInterceptor 接口表示请求拦截器。此接口包含一个名为 process 的方法，您需要在其中编写拦截请求的代码块。
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，而在服务器端，此方法在评估请求主体之前执行。
创建请求拦截器
您可以按照以下步骤创建请求拦截器。
步骤 1 - 创建 HttpRequestInterceptor 对象
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 . . . . .
};
步骤 2 - 实例化 CloseableHttpClient 对象
通过将上面创建的拦截器添加到自定义的CloseableHttpClient 对象中来构建它，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。
示例
以下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头部：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头部；如果其中任何一个头部是sample-header，我们尝试将其删除并显示该特定请求的头部列表。
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.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());
}
}
输出
执行上述程序后，将生成以下输出：
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。此接口包含一个名为process() 的方法。在此方法中，您需要编写拦截响应的代码块。
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，而在客户端，此方法在评估响应主体之前执行。
创建响应拦截器
您可以按照以下步骤创建响应拦截器：
步骤 1 - 创建 HttpResponseInterceptor 对象
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 . . . . . . . .
}
};
步骤 2：实例化 CloseableHttpClient 对象
通过将上面创建的拦截器添加到自定义的CloseableHttpClient 对象中来构建它，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。
示例
以下示例演示了响应拦截器的用法。在此示例中，我们在处理器中向响应添加了三个头部：sample-header、demo-header 和 test-header。
执行请求并获得响应后，我们使用getAllHeaders() 方法打印了响应中所有头部的名称。
并且在输出中，您可以观察到列表中三个头部的名称。
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("https://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());
}
}
}
输出
执行上述程序后，将生成以下结果：
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
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