现在我可以通过单击连接到数据库按钮来连接到我的数据库。不幸的是，除了在同一个 if 语句中，我无法从其他任何地方关闭数据库。它不会将“conn”识别为本地连接变量。我还需要其他按钮来访问“conn”以执行其他任务，因此这一障碍阻碍了多个战线。下面是我的代码：
import java.awt.*;
import java.awt.event.*;
import java.sql.*;
import javax.swing.*;
public class ConnectToDB implements ActionListener {
final String url = "jdbc:mysql://localhost/";
final String dbName = "project3";
final String DBdriver = "com.mysql.jdbc.Driver";
final String userName = "root";
final String password = "OMGnpw=-0";
//GUI STUFF
//constants
final int windowX = 640; //pixels
final int windowY = 655; //pixels
final int fieldX = 20; //characters
//window
JFrame window = new JFrame("Mike's MySQL GUI Client");
//Connection Details
JLabel enterInfo = new JLabel("Enter Connection Details: ");
JLabel driver = new JLabel("Database Driver: ");
JTextField driverText = new JTextField(fieldX);
JLabel dburl = new JLabel("Database URL: ");
JTextField dburlText = new JTextField(fieldX);
JLabel dbuser = new JLabel("Username: ");
JTextField dbuserText = new JTextField(fieldX);
JLabel dbpass = new JLabel("Password: ");
JTextField dbpassText = new JTextField(fieldX);
//Enter a SQL Command
JLabel enterSQL = new JLabel("Enter a SQL Command:");
JTextArea enterSQLText = new JTextArea(10, 30);
//Connection Status and Command Buttons
JLabel connectionStatus = new JLabel ("No Connection Now");
JButton connectButton = new JButton("Connect");
JButton executeButton = new JButton("Execute SQL Command");
JButton clearCommandButton = new JButton("Clear Command");
//SQL Execution Result
JLabel executionResult = new JLabel("SQL Execution Result:");
JButton clearResultsButton = new JButton("Clear Results");
JTextArea executionResultText = new JTextArea(20, 50);
public ConnectToDB() throws Exception{
//Configure GUI
window.setSize(windowX, windowY);
window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
driverText.setEditable(false);
dburlText.setEditable(false);
dbuserText.setEditable(false);
dbpassText.setEditable(false);
executionResultText.setEditable(false);
//Register Event Listeners
connectButton.addActionListener(this);
executeButton.addActionListener(this);
clearCommandButton.addActionListener(this);
clearResultsButton.addActionListener(this);
//Construct Container
Container c = window.getContentPane();
final BoxLayout LAYOUT_STYLE = new BoxLayout(c, BoxLayout.Y_AXIS);
JPanel panel1 = new JPanel();
panel1.setLayout(new FlowLayout());
JPanel panel2 = new JPanel();
panel1.setLayout(new FlowLayout());
JPanel panel3 = new JPanel();
panel1.setLayout(new FlowLayout());
JPanel panel4 = new JPanel();
panel1.setLayout(new FlowLayout());
JPanel panel5 = new JPanel();
panel1.setLayout(new FlowLayout());
JPanel panel6 = new JPanel();
panel1.setLayout(new FlowLayout());
JPanel panel7 = new JPanel();
panel1.setLayout(new FlowLayout());
JPanel panel8 = new JPanel();
panel1.setLayout(new FlowLayout());
driverText.setText(DBdriver);
dburlText.setText(url);
dbuserText.setText(userName);
dbpassText.setText(password);
c.setLayout(LAYOUT_STYLE);
panel5.add(enterInfo);
panel1.add(driver);
panel1.add(driverText);
panel2.add(dburl);
panel2.add(dburlText);
panel3.add(dbuser);
panel3.add(dbuserText);
panel4.add(dbpass);
panel4.add(dbpassText);
panel5.add(connectionStatus);
panel5.add(connectButton);
panel6.add(enterSQL);
panel6.add(enterSQLText);
panel7.add(executeButton);
panel7.add(clearCommandButton);
panel8.add(executionResult);
panel8.add(clearResultsButton);
panel8.add(executionResultText);
c.add(panel5);
c.add(panel1);
c.add(panel2);
c.add(panel3);
c.add(panel4);
c.add(panel6);
c.add(panel7);
c.add(panel8);
window.setVisible(true);//END GUI STUFF
}
public static void main(String[] args) throws Exception{
@SuppressWarnings("unused")
ConnectToDB gui = new ConnectToDB();
}
public void actionPerformed(ActionEvent e){
if (e.getSource() == connectButton){
try
{
//DB Connection details
System.out.println("Attempting to connect to database...");
//Connect to DB and notify user
Class.forName(DBdriver).newInstance();
Connection conn = DriverManager.getConnection(url+dbName,userName,password);
System.out.println("Connected to the database");
}
catch (Exception f) {
f.printStackTrace();
}
}
else {
try{
conn.close();
System.out.println("Disconnected from database");
System.out.println("Other Button Works!");
}
catch (Exception g){
g.printStackTrace();
}
}
}
}
具体来说，这是我的 actionEventPerformed 序列，由于“conn.close();”处的错误而失败
public void actionPerformed(ActionEvent e){
if (e.getSource() == connectButton){
try
{
//DB Connection details
System.out.println("Attempting to connect to database...");
//Connect to DB and notify user
Class.forName(DBdriver).newInstance();
Connection conn = DriverManager.getConnection(url+dbName,userName,password);
System.out.println("Connected to the database");
}
catch (Exception f) {
f.printStackTrace();
}
}
else {
try{
conn.close();
System.out.println("Disconnected from database");
System.out.println("Other Button Works!");
}
catch (Exception g){
g.printStackTrace();
}
}
}