大家帮忙看看我的程序，为什么总是出错啊？

Question

错误信息是这样的：exception org.apache.jasper.JasperException
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:358)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:301)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:248)
javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
root cause java.lang.NullPointerException
org.apache.jsp.login1_jsp._jspService(login1_jsp.java:72)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:133)
javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:311)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:301)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:248)
javax.servlet.http.HttpServlet.service(HttpServlet.java:856)

Answer 1

空指针啊，看看你的取值的时候判断了吗？
sql语句拿到后台执行看是否有数据产生？

Answer 2

String sql="select * from login where id='"+us+"' and password='"+ps+"';";写法有问题String sql="select * from login where id=\'"+us+"\' and password=\'"+ps+"\'";单引号用转移符，发送给数据库的sql语句最后不用加分号

Answer 3

这是DBconn.java的源码：package com.coolservlets.beans;import java.sql.*;
public class DBconn {
    //private String driverName = "org.gjt.mm.mysql.Driver";
    private String driverName = "com.microsoft.jdbc.sqlserver.SQLServerDriver";      //"oracle.jdbc.driver.OracleDriver";
    //private String url = "jdbc:mysql://localhost:3306/feedman"; 
    private String url = "jdbc:microsoft:sqlserver://localhost:1433;DatabaseName=temp";          //"jdbc:oracle:thin:@127.0.0.1:1521:oracle";
    private String user = "sa";
    private String password = "";
    private Connection conn = null;
    private Statement stmt = null;
    private ResultSet rs = null;
    public void setDriverName(String newDriverName) {
        driverName = newDriverName;
    }
    public String getDriverName() {
        return driverName;
    }

    public void setUrl(String newUrl) {
        url = newUrl;
    }
    public String getUrl() {
        return url;
    }
    public void setUser(String newUser) {
        user = newUser;
    }
    public String getUser() {
        return user;
    }
    public void setPassword(String newPassword) {
        password = newPassword;
    }
    public String getPassword() {
        return password;
    }    public ResultSet executeQuery(String sql) {
rs = null;
stmt = null;
        try {
            Class.forName(driverName).newInstance();
     conn = DriverManager.getConnection(url, user, password);
            stmt = conn.createStatement();
     rs = stmt.executeQuery(sql);
//      stmt.close();
     conn.close();
     return rs;
        }
        catch (Exception e) {
            e.printStackTrace();
            return null;
        }


    }    public void executeUpdate(String sql) {
rs = null;
stmt = null;
        try {
            Class.forName(driverName).newInstance();
     conn = DriverManager.getConnection(url, user, password);
            stmt = conn.createStatement();
     stmt.executeUpdate(sql);
     stmt.close();
     conn.close();
        }
        catch (Exception e) {
            e.printStackTrace();
        }

    }
}

Answer 4

String sql="select * from login where id='"+us+"' and password='"+ps+"';";
                                                                       ^^是不是这个问题!!

Answer 5

你的sql语句有问题的，不应该有那个;号的。再者你的rs怎么能够用equals来判断呢？

Answer 6

可是我都改了；rs我用rs.next()判断了，也不行啊！