如何在Java中构造并发送POST请求到包含参数的URL？

在Java中，你可以使用`java.net.HttpURLConnection`或第三方库如`org.apache.httpclient`或`org.springframework.web.client.RestTemplate`来构造并发送POST请求到包含参数的URL。这里我将展示一个基本的示例，使用HttpURLConnection：

import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;

public class PostRequestExample {

    public static void main(String[] args) {
        String url = "http://example.com/api?param1=value1&param2=value2";
        String requestBody = "key1=value1&key2=value2"; // POST body

        try {
            URL obj = new URL(url);
            HttpURLConnection con = (HttpURLConnection) obj.openConnection();

            // 设置连接为POST请求
            con.setRequestMethod("POST");
            con.setDoOutput(true);

            // 设置请求头，告诉服务器这是JSON数据
            con.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");

            // 获取输出流
            OutputStream os = con.getOutputStream();
            byte[] outputBytes = requestBody.getBytes();
            os.write(outputBytes); // 写入请求体
            os.flush();
            os.close();

            // 获取响应码
            int responseCode = con.getResponseCode();
            System.out.println("Response Code : " + responseCode);

            if (responseCode == HttpURLConnection.HTTP_OK) {
                // 读取响应内容
                BufferedReader in = new BufferedReader(
                        new InputStreamReader(con.getInputStream()));
                String inputLine;
                StringBuffer response = new StringBuffer();

                while ((inputLine = in.readLine()) != null) {
                    response.append(inputLine);
                }
                in.close();

                System.out.println(response.toString());
            } else {
                throw new RuntimeException("Failed : HTTP error code : "
                        + responseCode);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

这个例子中，我们首先创建URL对象，然后使用`HttpURLConnection`打开连接，并设置请求方法为POST。接着，我们将请求体作为字节数组写入输出流，最后接收服务器的响应。