即使我输入了正确的凭据，我仍然会收到错误showMessageDialog .. 我相信rs.next（）将返回一个高于0的值，然后如果用户的凭据与users_table中的凭据匹配，则必须进行限制，但我总是 获取错误消息，就好像凭据不匹配一样。
import java.sql.*;
import javax.swing.*;
public class System extends javax.swing.JFrame {
// variables needed for db connection
Connection conn;
Statement stmt;
ResultSet rs;
String sql;
String user;
char[] pass;
//for table row count
int ctr = 0;
//temporary variables needed in retrieving and inserting records in our db
int user_id;
String username;
String password;
public System() {
initComponents();
setLocationRelativeTo(null);
dbConnect();
}
public void dbConnect() {
conn = null;
String url = "jdbc:mysql://localhost:3306/item_db";
String driver = "com.mysql.jdbc.Driver";
String userName = "root";
String password = "";
try {
Class.forName(driver).newInstance();
conn = DriverManager.getConnection(url, userName, password);
stmt = conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_UPDATABLE);
sql = "Select * from users_table";
rs = stmt.executeQuery(sql);//rs - will hold the records from the databa sql = "Select * from item_table";se
} catch (Exception e) {
JOptionPane.showMessageDialog(this, e.getMessage());
}
}
private void login() {
try {
if (user != null && pass != null) {
sql = "Select * from users_table Where username='" + user + "' and password='" + pass + "'";
rs = stmt.executeQuery(sql);
rs.next();
if ((user.equals(username)) && (pass.equals(password))) {
JOptionPane.showMessageDialog(null, "You are now logon!");
}
else {
JOptionPane.showMessageDialog(null, "damn!", "alert", JOptionPane.ERROR_MESSAGE);
}
}
} catch (SQLException err) {
JOptionPane.showMessageDialog(this, err.getMessage());
}
}
@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">
private void initComponents() {
jLabel1 = new javax.swing.JLabel();
jLabel2 = new javax.swing.JLabel();
jTextField1 = new javax.swing.JTextField();
jButton1 = new javax.swing.JButton();
jButton2 = new javax.swing.JButton();
jPasswordField1 = new javax.swing.JPasswordField();
jLabel3 = new javax.swing.JLabel();
setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
jLabel1.setFont(new java.awt.Font("Calibri", 0, 18)); // NOI18N
jLabel1.setText("Username:");
jLabel2.setFont(new java.awt.Font("Calibri", 0, 18)); // NOI18N
jLabel2.setText("Password:");
jButton1.setText("Login");
jButton1.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
jButton1ActionPerformed(evt);
}
});
jButton2.setText("Cancel");
jLabel3.setIcon(new javax.swing.ImageIcon(getClass().getResource("/login.png"))); // NOI18N
javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
getContentPane().setLayout(layout);
layout.setHorizontalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addGap(46, 46, 46)
.addComponent(jLabel3))
.addGroup(layout.createSequentialGroup()
.addGap(82, 82, 82)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING)
.addComponent(jLabel2)
.addComponent(jLabel1))
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false)
.addComponent(jTextField1)
.addComponent(jPasswordField1, javax.swing.GroupLayout.PREFERRED_SIZE, 134, javax.swing.GroupLayout.PREFERRED_SIZE)))
.addGroup(layout.createSequentialGroup()
.addGap(51, 51, 51)
.addComponent(jButton1)
.addGap(28, 28, 28)
.addComponent(jButton2)))))
.addContainerGap(52, Short.MAX_VALUE))
);
layout.setVerticalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
.addComponent(jLabel3, javax.swing.GroupLayout.DEFAULT_SIZE, 100, Short.MAX_VALUE)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(jLabel1)
.addComponent(jTextField1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(jLabel2)
.addComponent(jPasswordField1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
.addGap(18, 18, 18)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(jButton1)
.addComponent(jButton2))
.addGap(29, 29, 29))
);
pack();
}// </editor-fold>
private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
// TODO add your handling code here:
//str = JOptionPane.showInputDialog(this, "Enter id number: ");
user = jTextField1.getText();
pass = jPasswordField1.getPassword();
login();
}
/**
* @param args the command line arguments
*/
public static void main(String args[]) {
/* Set the Nimbus look and feel */
//<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
/* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
* For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html
*/
try {
for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
if ("Nimbus".equals(info.getName())) {
javax.swing.UIManager.setLookAndFeel(info.getClassName());
break;
}
}
} catch (ClassNotFoundException ex) {
java.util.logging.Logger.getLogger(System.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (InstantiationException ex) {
java.util.logging.Logger.getLogger(System.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (IllegalAccessException ex) {
java.util.logging.Logger.getLogger(System.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (javax.swing.UnsupportedLookAndFeelException ex) {
java.util.logging.Logger.getLogger(System.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
}
//</editor-fold>
/* Create and display the form */
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
new System().setVisible(true);
}
});
}
// Variables declaration - do not modify
private javax.swing.JButton jButton1;
private javax.swing.JButton jButton2;
private javax.swing.JLabel jLabel1;
private javax.swing.JLabel jLabel2;
private javax.swing.JLabel jLabel3;
private javax.swing.JPasswordField jPasswordField1;
private javax.swing.JTextField jTextField1;
// End of variables declaration
}
答案 0 :(得分：1)
您没有检查rs.next（）
的返回值尝试：
if (rs.next()) {
JOptionPane.showMessageDialog(null, "You are now logon!");
} else {
JOptionPane.showMessageDialog(null, "damn!", "alert", JOptionPane.ERROR_MESSAGE);
}
请参阅： http://docs.oracle.com/javase/6/docs/api/java/sql/ResultSet.html#next%28%29
答案 1 :(得分：1)
您定义，但从不为以下内容指定值：
String username;
String password;
要使此检查有效。
if ((user.equals(username)) && (pass.equals(password))) {
您应该在设置username和password
this.username = rs.getString("username");
this.password = rs.getString("password");
无论如何都不需要它。由于这两个值都在您WHERE子句中，如果您得到任何结果，则意味着您获得了点击，因此您可以将if更改为
if (rs.next()) {
注意：您必须删除之前的rs.next()（查询只能获得一行）。
那说了几个提示：
1）不要存储未加密的密码。存储散列版本（MD-5，SHA-1）。如果重要，请使用盐。这样，可以读取表格的人将无法猜出密码。首先，您可以使用未编辑的表进行测试，当它工作时添加加密。
2）正如其他人所说，你最好使用PreparedStatement。
3）除非您经常使用它，否则不要将连接作为实例变量。使其成为使用它的方法的局部变量。并close()正确。这样你就不会占用你的服务器资源。
答案 2 :(得分：0)
你在真空中调用rs.next。您不测试结果或使用结果集数据。
答案 3 :(得分：-1)
我认为您的代码应该是类似的，
rs.next();
if ((user.equals(rs.getString("username"))) && (pass.equals(rs.getString("password")))) {
JOptionPane.showMessageDialog(null, "You are now logon!");
}