从request.getParameter()获取Servlet上的空值

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

public class MyServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String parameterValue = request.getParameter("parameterName");
        
        if (parameterValue == null || parameterValue.isEmpty()) {
            // 参数值为空的处理逻辑
            // ...
        } else {
            // 参数值不为空的处理逻辑
            // ...
        }
    }
}