Java如何检查servlet请求中是否存在参数？
ServletRequest或HttpServletRequest对象具有用于映射参数名称及其值的映射对象。通过访问此映射，我们可以检查servlet请求中是否传递了参数。让我们看下面的例子。
package org.nhooo.example.servlet;
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 ParameterCheck extends HttpServlet {
protected void doGet(HttpServletRequest req, HttpServletResponse res)
throws ServletException, IOException {
//检查用户名参数是否存在
if (req.getParameterMap().containsKey("username")) {
String username = req.getParameter("username");
}
//检查密码参数是否存在
if (req.getParameterMap().containsKey("password")) {
String password = req.getParameter("password");
}
}
}