我刚刚开始开发Java应用程序并使用MySQL。该应用程序之前可以正常工作，但基本上在我重新启动计算机后，它就停止工作并显示“连接过多”。
我知道关闭连接时我做错了什么，但我无法弄清楚。如果可以的话请指出我做错的地方。
public class ProductFrame extends javax.swing.JFrame {
/**
* Creates new form ProductFrame
*/
public ProductFrame() {
initComponents();
Show_Products_In_JTable();
}
public Connection getConnection()
{
Connection con = null;
try {
con = DriverManager.getConnection("jdbc:mysql://localhost/smart-mart","root","");
return con;
} catch (SQLException ex) {
Logger.getLogger(ProductFrame.class.getName()).log(Level.SEVERE, null, ex);
return null;
}
}
public boolean checkInputs()
{
if(
txt_name.getText() == null
|| txt_price.getText() == null
|| txt_quantity.getText() == null
|| txt_arrdate.getText() == null
|| txt_minreq.getText() == null
|| txt_maxreq.getText() == null
|| txt_staff.getText() == null
){
return false;
}
else{
try{
Float.parseFloat(txt_price.getText());
return true;
}catch(Exception ex)
{
return false;
}
}
}
//** Display Date in the ItemTable ** //
//** Step 1- Create an arraylist and fill it with date **//
public ArrayList<Product> getProductList ()
{
ArrayList<Product> productList = new ArrayList<Product>();
Connection con = getConnection();
String query = "SELECT * FROM product";
Statement st;
ResultSet rs;
try {
st = con.createStatement();
rs = st.executeQuery(query);
Product product;
Show_Products_In_JTable();
while (rs.next())
{
product = new Product (rs.getInt("id"),rs.getString("name"), Float.parseFloat(rs.getString("price")),rs.getInt("quantity"), rs.getString("arrdate"), rs.getInt("minreq"),rs.getInt("maxreq"), rs.getString("staff"));
productList.add(product);
con.close();
}
} catch (SQLException ex) {
Logger.getLogger(ProductFrame.class.getName()).log(Level.SEVERE, null, ex);
}
return productList;
}
//** Stept 2- Populate the table ** //
public void Show_Products_In_JTable()
{
ArrayList<Product> list = getProductList();
DefaultTableModel model = (DefaultTableModel) J_Table_Products.getModel();
Object[] row = new Object [8];
for(int i = 0; i<list.size();i++)
{
row[0]=list.get(i).getId();
row[1]=list.get(i).getName();
row[2]=list.get(i).getPrice();
row[3]=list.get(i).getQuantity();
row[4]=list.get(i).getArrDate();
row[5]=list.get(i).getMinReq();
row[6]=list.get(i).getMaxReq();
row[7]=list.get(i).getStaff();
model.addRow(row);
}
}
// Show Data In Inputs
public void ShowItem(int index)
{
txt_id.setText(Integer.toString(getProductList().get(index).getId()));
txt_name.setText(getProductList().get(index).getName());
txt_price.setText(Float.toString(getProductList().get(index).getPrice()));
txt_quantity.setText(Integer.toString(getProductList().get(index).getQuantity()));
txt_arrdate.setText(getProductList().get(index).getArrDate());
txt_minreq.setText(Integer.toString(getProductList().get(index).getMinReq()));
txt_maxreq.setText(Integer.toString(getProductList().get(index).getMaxReq()));
txt_staff.setText(getProductList().get(index).getStaff());
}
private void btn_insertActionPerformed(java.awt.event.ActionEvent evt) {
if (checkInputs() && txt_name !=null){
try {
Connection con = getConnection();
PreparedStatement ps;
ps = con.prepareStatement("INSERT INTO product(name, price, quantity, arrdate, minreq, maxreq, staff)"+"values(?,?,?,?,?,?,?)");
ps.setString(1, txt_name.getText());
ps.setString(2, txt_price.getText());
ps.setString(3, txt_quantity.getText());
ps.setString(4, txt_arrdate.getText());
ps.setString(5 , txt_minreq.getText());
ps.setString(6 , txt_maxreq.getText());
ps.setString(7, txt_staff.getText());
ps.executeUpdate();
Show_Products_In_JTable();
JOptionPane.showMessageDialog(null, "Data Inserted");
ps.close();
} catch (SQLException ex) {
JOptionPane.showMessageDialog(null, ex.getMessage());
}
}
else{
JOptionPane.showMessageDialog(null, "One or more field empty");
}
System.out.println("Name=>" + txt_name.getText());
System.out.println("Price=>" + txt_price.getText());
System.out.println("Quantity=>" + txt_quantity.getText());
System.out.println("Arrdate=>" + txt_arrdate.getText());
System.out.println("MinReq=>" + txt_minreq.getText());
System.out.println("MaxReq=>" + txt_maxreq.getText());
System.out.println("Staff=>" + txt_staff.getText());
}
private void btn_updateActionPerformed(java.awt.event.ActionEvent evt) {
if (checkInputs() && txt_id.getText () !=null)
{
String UpdateQuery = null;
PreparedStatement ps = null;
Connection con = getConnection ();
try {
UpdateQuery = "UPDATE product SET name=?, price=?,quantity=?, arrdate=?, minreq=?,maxreq=?, staff=? WHERE id=?";
ps = con.prepareStatement(UpdateQuery);
ps.setString(1, txt_name.getText());
ps.setString(2, txt_price.getText());
ps.setString(3, txt_quantity.getText());
ps.setString(4, txt_arrdate.getText());
ps.setString(5 , txt_minreq.getText());
ps.setString(6 , txt_maxreq.getText());
ps.setString(7, txt_staff.getText());
ps.setInt(8, Integer.parseInt(txt_id.getText()));
ps.executeUpdate();
ps.close();
} catch (SQLException ex) {
Logger.getLogger(ProductFrame.class.getName()).log(Level.SEVERE, null, ex);
}
}else{
JOptionPane.showMessageDialog(null, "One or more fields are Empty");
}
}
private void btn_deleteActionPerformed(java.awt.event.ActionEvent evt) {
if (!txt_id.getText().equals(""))
{
try {
Connection con = getConnection();
PreparedStatement ps = con.prepareStatement("DELETE FROM product WHERE id = ?");
int id = Integer.parseInt(txt_id.getText());
ps.setInt(1, id);
ps.executeUpdate();
JOptionPane.showMessageDialog(null, "Item Deleted!");
ps.close();
} catch (SQLException ex) {
Logger.getLogger(ProductFrame.class.getName()).log(Level.SEVERE, null, ex);
JOptionPane.showMessageDialog(null, "Item Not Deleted!");
ex.printStackTrace();
} finally {
}
}
else{
JOptionPane.showMessageDialog(null, " Product not found. Please enter the product ID!");
}
}
private void J_Table_ProductsMouseClicked(java.awt.event.MouseEvent evt) {
int index = J_Table_Products.getSelectedRow();
ShowItem(index);
}
/**
* @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(ProductFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (InstantiationException ex) {
java.util.logging.Logger.getLogger(ProductFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (IllegalAccessException ex) {
java.util.logging.Logger.getLogger(ProductFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (javax.swing.UnsupportedLookAndFeelException ex) {
java.util.logging.Logger.getLogger(ProductFrame.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 ProductFrame().setVisible(true);
}
});
}
C.
最佳答案
每次调用方法 getConnection 时都会创建一个新连接，但不会关闭它，并且每次程序退出函数上下文时都会丢失引用，因此连接将打开，直到程序运行。这种情况会引发此问题(连接过多)。
关闭已使用过的连接，或仅保留对一个打开的连接的引用以重用它并避免“打开-使用-关闭”过程。
关于java - Mysql - 访问被拒绝 + "Too many connections"，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/47640640/