java类。forName在尝试连接到MySQL数据库时不起作用
我在使用mysql时遇到问题。似乎当程序运行到这个部分时，它不会继续[已解决]
try{
//Load the Driver Class
Class.forName("com.mysql.jdbc.Driver");
我认为这部分代码有问题。因为我尝试了这个，JOptionPane弹出：
try{
JOptionPane.showMessageDialog(null, "Ok!");
//Load the Driver Class
Class.forName("com.mysql.jdbc.Driver");
但是，当我这样编写代码时，什么都没有发生：
try{
//Load the Driver Class
Class.forName("com.mysql.jdbc.Driver");
JOptionPane.showMessageDialog(null, "Ok!");
有什么建议吗？谢谢
顺便说一句，这是我的全部计划
private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
// TODO add your handling code here:
String user = userName.getText();
final String URL = "jdbc:mysql://localhost:3306/videorental";
if(user.equals("")){
JOptionPane.showMessageDialog(null, "Fields should not be empty", "Error", JOptionPane.ERROR_MESSAGE);
}
else{
try{
//Load the Driver Class
Class.forName("com.mysql.jdbc.Driver");
//Create the connection using the static getConnection method
JOptionPane.showMessageDialog(null, "Connecting to database");
Connection con = DriverManager.getConnection(URL, "root", "");
//Create statement to execute the SQL statement
JOptionPane.showMessageDialog(null, "Creating a statement");
Statement stmt = con.createStatement();
//Check the username
ResultSet rs = stmt.executeQuery("select * from 'user_tbl' where user_id = '"+user+"' ");
if(rs.next()){
String uname = rs.getString("user_id");
if(user.equals(uname)){
JOptionPane.showMessageDialog(null, "Thank you!");
}
else{
JOptionPane.showMessageDialog (null, "You are not registered.");
}
}
}
catch (Exception e) {
e.printStackTrace();
}
}
}
所以我试着放e.printStackTrace（），对不起，我真的是一个使用mySQL的新手。这就是结果。。。[已解决]
java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:190)
at user.loginFrame.jButton1ActionPerformed(loginFrame.java:113)
at user.loginFrame.access$000(loginFrame.java:14)
at user.loginFrame$1.actionPerformed(loginFrame.java:48)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at 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)
at java.awt.Component.processEvent(Component.java:6270)
at java.awt.Container.processEvent(Container.java:2229)
at java.awt.Component.dispatchEventImpl(Component.java:4861)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4687)
at 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)
at java.awt.Window.dispatchEventImpl(Window.java:2719)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:735)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:694)
at java.awt.EventQueue$3.run(EventQueue.java:692)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.awt.EventQueue$4.run(EventQueue.java:708)
at java.awt.EventQueue$4.run(EventQueue.java:706)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:705)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)
我不知道这些错误是什么。有人能帮我吗？谢谢
顺便说一句，我正在使用netbeans作为IDE
感谢大家的帮助，但出现了一个新问题，它说我有MYSQLSYntaxError
com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ''user_tbl' where user_id = '12345678'' at line 1
# 1 楼答案
如果您有表格的一段代码：
而且
B没有被执行，这是一个相当安全的赌注，A会引发某种类型的异常，尤其是，如果B执行的是相反的顺序就你而言：
正在捕获异常，但完全不做任何修复或报告。至少，你应该用
System.out.println (e);或e.printStackTrace()这样你就能看到发生了什么# 2 楼答案
你应该添加MySQL。Netbeans IDE附带的jar
在您创建的项目中有一个Libraries文件夹
在文件夹上单击鼠标右键，然后单击“添加库”
从可用库中，单击MySQL JDBC驱动程序（如果使用MySQL）
# 3 楼答案
确保将
mysql.jar添加到项目中。正如评论中提到的，不要接受你的例外。如果你这样做，你就不知道错误或错误是什么。它可以是ClassNotFoundException或SQLException，这是完全不同的东西。一旦将ex.printStackTrace()添加到catch块中，如果得到一个ClassNotFoundException，您可能忘记了将mysql.jar导入到项目中。如果得到一个SQLExcpetion，则说明SQL语法或连接语法有问题编辑以包含jar
.zip.jar添加到库中mysqul-connector.java...jar，然后选择它Libraries文件夹图标Add Jar/Folder.jar，然后选择它.jar就足够了更新
我认为
MySQL.jar是随Netbeans IDE一起提供的Libraries文件夹图标