Question

我正在创建一个简单的java应用程序，在表单中有两个文本字段，用于在按下按钮后传递用户名和密码，它应该是错误的或正确的用户名和密码。它给出了异常

抓住了异常

执行查询中的

;

package myproject;

import java.sql.*;

public class connectionDB {

    String loadDriver = null;
    String url = null;
    String uName = null;
    String uPass = null;
    Connection con = null;
    Statement st = null;
    ResultSet rst = null;
    PreparedStatement pstmt;

    public connectionDB() {
        loadDriver = "com.mysql.jdbc.Driver";
        url = "jdbc:mysql://localhost/mydatabase";
        uName = "root";
        uPass = "water";
    }

    void Connect() {
        try {
            try {
                Class.forName(loadDriver);
                System.out.println("Successfully load");
            } catch (Exception e) {
                System.out.println("Fail to load");
            }
            con = DriverManager.getConnection(url, uName, uPass);

            System.out.println("Connect to mysql sucessfull");
            st = con.createStatement();
        } catch (SQLException e) {
            System.out.println("Something goes worng in Connection the mysql\n");

        }
    }

    boolean validateUserNamePassword(String uName, String uPass) {
        boolean isThere = false;
        int count = 0;
        try {


            pstmt = con.prepareStatement("select * from admin where "
                    + "Admin_Name= ? "
                   + "'and Admin_pass= ? ");


            pstmt.setString(1, uName);
            pstmt.setString(2, uPass);
            rst = pstmt.executeQuery();

            while (rst != null) {
                count = 1;
                isThere = true;
            }

        } catch (Exception e) {
            System.out.println("Exception caught in execution query");
        }
        if (isThere) {
            return isThere;
        } else {
            return isThere;
        }
    }

    void closeConnection() {
        try {
            st.close();
            con.close();
            System.out.println("Connection Sucessfully close with Database");
        } catch (Exception e) {
            System.out.println("Excepiotn caught");
        }
    }
}

编辑：这是错误的堆栈跟踪

运行：java.lang.NullPointerException在myproject.connectionDB.validateUserNamePassword（connectionDB.java:48）的myproject.loginPage $ Handler.actionPerformed（loginPage.java:96）at javax.swing.AbstractButton.fireActionPerformed（AbstractButton。 java：2018）at javax.swing.AbstractButton $ Handler.actionPerformed（AbstractButton.java:2341）at javax.swing.DefaultButtonModel.fireActionPerformed（DefaultButtonModel.java:402）at javax.swing.DefaultButtonModel.setPressed（DefaultButtonModel.java:259 ）javax.swing.plaf.basic.BasicButtonListener.mouseReleased（BasicButtonListener.java:252）at java.awt.Component.processMouseEvent（Component.java:6505）at javax.swing.JComponent.processMouseEvent（JComponent.java:3321）在java.awt.Component.processEvent（Component.java:6270）的java.awt.Container.processEvent（Container.java:2229），位于java.awt的java.awt.Component.dispatchEventImpl（Component.java:4861）。 java.awt.Component.dispatchEvent中的Container.dispatchEventImpl（Container.java:2287）（Component.java:46 87）java.awt.LightweightDispatcher.retargetMouseEvent（Container.java:4832）at java.awt.LightweightDispatcher.processMouseEvent（Container.java:4492）at java.awt.LightweightDispatcher.dispatchEvent（Container.java:4422）at java。 awt.Container.dispatchEventImpl（Container.java:2273）位于java.awt.Eind上的java.awt.Window.dispatchEventImpl（Window.java:2719），java.awt.EventQueue.dispatchEventImpl，java.awt.Component.dispatchEvent（Component.java:4687）（EventQueue.java:723）java.awt.EventQueue.access $ 200（EventQueue.java:103）java.awt.EventQueue $ 3.run（EventQueue.java:682）at java.awt.EventQueue $ 3.run（EventQueue） .java：680）java.security.ProtectionDomain上的java.security.AccessController.doPrivileged（Native Method），java.security.ProtectionDomain $ 1.doIntersectionPrivilege（ProtectionDomain.java:87）中的$ 1.doIntersectionPrivilege（ProtectionDomain.java:76）at Java.awt.EventQueue $ 4.run（EventQueue.java:696）java.awt.EventQueue $ 4.run（EventQueue.java:694）at java.security.AccessController.doPrivileged（Native Me） java.security.ProtectionDomain $ 1.doIntersectionPrivilege（ProtectionDomain.java:76）at java.awt.EventQueue.dispatchEvent（EventQueue.java:693）at java.awt.EventDispatchThread.pumpOneEventForFilters（EventDispatchThread.java:244）at java在java.awt.EventDispatchThread的java.awt.EventDispatchThread。 java.awt.EventDispatchThread.run中的pumpEvents（EventDispatchThread.java:139）（EventDispatchThread.java:97）BUILD SUCCESSFUL（总时间：6秒）

Answer 1

查看您的查询：问题出在'。它应该是这样的：

pstmt = con.prepareStatement("select * from admin where "
                + "Admin_Name= ? "
               + "and Admin_pass= ?");

另外还有validateUserNamePassword()方法：

if (isThere) {
        return isThere;
    } else {
        return isThere;
    }
}

这没有任何意义。

Answer 2

你应该输入mysql的端口号

试试这个

url = "jdbc:mysql://localhost:3306/mydatabase";

3306是mysql的默认端口号。如果您有不同的端口号，请相应地更改它。

您尝试检索的方式将是无限循环

 while (rst != null) {
                count = 1;
                isThere = true;
            }

使用这种方式

 while (rst.next()) {
                count = 1;
                isThere = true;
            }

你有一个' Vimal bera 指出，相应地改变

验证用户名和密码时出现异常

2 个答案: