如何Servlet中用post发送请求

在Servlet中发送POST请求可以使用以下步骤：

1. 创建一个URL对象，指定请求的目标地址。

   URL url = new URL("http://example.com/path/to/target");

2. 打开URL连接并设置请求方法为POST。

   HttpURLConnection connection = (HttpURLConnection) url.openConnection();
   connection.setRequestMethod("POST");

3. 设置请求头信息（可选）。

   connection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");

4. 设置请求体内容（如果有）。

   String requestBody = "param1=value1&param2=value2";
   connection.setDoOutput(true);
   OutputStream outputStream = connection.getOutputStream();
   outputStream.write(requestBody.getBytes());
   outputStream.flush();
   outputStream.close();

5. 获取响应结果。

   int responseCode = connection.getResponseCode();
   String responseBody = "";
   if (responseCode == HttpURLConnection.HTTP_OK) {
       InputStream inputStream = connection.getInputStream();
       BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
       String line;
       while ((line = reader.readLine()) != null) {
           responseBody += line;
       }
       reader.close();
       inputStream.close();
   }

完整的示例代码如下：

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    String targetUrl = "http://example.com/path/to/target";
    String requestBody = "param1=value1&param2=value2";

    URL url = new URL(targetUrl);
    HttpURLConnection connection = (HttpURLConnection) url.openConnection();
    connection.setRequestMethod("POST");
    connection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");

    connection.setDoOutput(true);
    OutputStream outputStream = connection.getOutputStream();
    outputStream.write(requestBody.getBytes());
    outputStream.flush();
    outputStream.close();

    int responseCode = connection.getResponseCode();
    String responseBody = "";
    if (responseCode == HttpURLConnection.HTTP_OK) {
        InputStream inputStream = connection.getInputStream();
        BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
        String line;
        while ((line = reader.readLine()) != null) {
            responseBody += line;
        }
        reader.close();
        inputStream.close();
    }
}