无法在servlet中获取JSON字符串

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.BufferedReader;
import java.io.IOException;

public class MyServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        StringBuilder jsonBuilder = new StringBuilder();
        BufferedReader reader = request.getReader();
        String line;
        while ((line = reader.readLine()) != null) {
            jsonBuilder.append(line);
        }
        String jsonString = jsonBuilder.toString();

        // 在这里可以对获取到的JSON字符串进行处理或解析
        // ...

        response.getWriter().write("JSON received successfully");
    }
}