如何在Java中正确更改http请求的内容类型？

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

public class HttpRequestExample {
    public static void main(String[] args) {
        try {
            // 创建URL对象
            URL url = new URL("http://example.com/api/endpoint");

            // 建立连接
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();

            // 设置请求方法为POST
            connection.setRequestMethod("POST");

            // 设置请求头的Content-Type字段为application/json
            connection.setRequestProperty("Content-Type", "application/json");

            // 设置其他请求头字段，如授权信息等

            // 启用输出流，用于发送请求体
            connection.setDoOutput(true);

            // 构造请求体
            String requestBody = "{\"key\": \"value\"}";

            // 发送请求体
            OutputStream outputStream = connection.getOutputStream();
            outputStream.write(requestBody.getBytes());
            outputStream.flush();
            outputStream.close();

            // 获取响应
            int responseCode = connection.getResponseCode();
            BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
            String line;
            StringBuilder response = new StringBuilder();
            while ((line = reader.readLine()) != null) {
                response.append(line);
            }
            reader.close();

            // 处理响应
            System.out.println("Response Code: " + responseCode);
            System.out.println("Response Body: " + response.toString());

            // 关闭连接
            connection.disconnect();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}