这是Servlet
中的简单登录Eclipse
的代码,该代码可从数据库的现有表中检查用户名和密码,并将其带到主页(如果存在)或发送到登录页面。当我在服务器上运行它并将信息放入登录页面时,它显示以下错误。你能帮忙吗?谢谢。
1.解决时出错
root cause
java.lang.Error: Unresolved compilation problem:
Unreachable catch block for ClassNotFoundException. This exception is never thrown from the try statement body
com.loginapps.servlets.LoginServlet.doGet(LoginServlet.java:90)
javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
javax.servlet.http.HttpServlet.service(HttpServlet.java:723)
编码
package com.loginapps.servlets;
import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.ResultSet;
import java.sql.PreparedStatement;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
/*** Servlet implementation class LoginServlet* @param <con>*/
public class LoginServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
Connection con;
PreparedStatement pst;
public void init(ServletConfig config) throws ServletException {
String dname = config.getInitParameter("drivername");
String uname = config.getInitParameter("username");
System.out.println(dname);
System.out.println(uname);
try{
Class.forName(dname);
con = DriverManager.getConnection("jdbc:mysql://localhost:3306/logindb",uname,"");
}
catch(SQLException e){
e.printStackTrace();
}
catch(ClassNotFoundException e){
e.printStackTrace();
}
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
HttpSession session = request.getSession();
String uname = request.getParameter("txtuname");
String pwd = request.getParameter("txtpwd");
session.setAttribute("username",uname);
try {
pst = con.prepareStatement("select * from users where username = ? and password = ?");
pst.setString(1,uname);
pst.setString(2,pwd);
ResultSet rs = pst.executeQuery();
if(rs.next()){
response.sendRedirect("home.jsp");
}
else {
response.sendRedirect("login.html");
}
}
catch(SQLException e){
e.printStackTrace();
}
catch(ClassNotFoundException e){
e.printStackTrace();
}
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}
}
最佳答案
您发布的错误:ClassNotFoundException
的不可用捕获块。永远不会从try语句主体中抛出此异常
您的catch
块是问题所在:
catch(ClassNotFoundException e){
e.printStackTrace();
}
ClassNotFoundException
是一个已检查的异常,不会被try
块中的代码抛出-请参阅this page