我正在为一家酒吧编写一个库存补货系统，作为我的最后一年项目。我可以从 MYSQL 数据库检索信息，并且可以一次滚动浏览一个结果。
我正在尝试根据所选类别更改结果。我已经设法使用组合框来实现此目的，但在类别之间移动时出现以下错误：
线程“main”中出现异常 com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException：数据源拒绝建立连接，来自服务器的消息：“连接过多”
两个独立文件的代码如下：
-
SQL 查询在RetrieveStockQuery
public JComboBox getComboBox() throws SQLException {
con = SQLConnect.getConnection();
combo = new JComboBox();
combo.removeAllItems();
try {
stat = con.createStatement( ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_UPDATABLE );
rs = stat.executeQuery("SELECT categoryName FROM Category");
while (rs.next()) {
combo.addItem(rs.getString("categoryName"));
categoryName = rs.getString("categoryName");
}
}
catch (SQLException sqle) {
System.out.println(sqle);
stat.close();
con.close();
}
return combo;
}
//----------------------------------------------------------------
public void retrieveStock() throws SQLException {
con = SQLConnect.getConnection();
stockGUI = new ViewStockGUI(); // I THINK THIS IS WHAT IS CAUSING THE ERROR
String viewStock = "SELECT * FROM Stock where categoryName = '" + "'" + stockGUI.selected + "'";
System.out.println(viewStock);
try {
stat = con.createStatement( ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_UPDATABLE );
rs = stat.executeQuery(viewStock);
while(rs.next()){
stockID = rs.getInt("stockID");
stockName = rs.getString("stockName");
stockDescription = rs.getString("stockDescription");
stockPrice = rs.getFloat("stockPrice");
stockQuantity = rs.getInt("stockQuantity");
categoryName = rs.getString("categoryName");
ID = Integer.toString(stockID);
price = Float.toString(stockPrice);
quantity = Double.toString(stockQuantity);
stat.close();
con.close();
System.out.println( "Stock ID: " + stockID + " Stock Name: " + stockName + " Stock Description: " + stockDescription + " Stock Price: " + stockPrice + " Stock Quantity:" + stockQuantity + " Category: " + categoryName);
}
}
catch (SQLException err) {
System.out.println(err.getMessage());
}
}
-
My ViewStockGUI class
public class ViewStockGUI extends JPanel {
private static final long serialVersionUID = 1L;
final JFrame viewFrame;
ViewStockQuery stockQuery;
ViewStockQuery stockName;
JComboBox comboGUI;
String selected;
JComboBox combo;
public ViewStockGUI() throws SQLException {
final ViewStockQuery stock = new ViewStockQuery();
comboGUI = stock.getComboBox();
stock.retrieveStock();
viewFrame = new JFrame("View Stock");
JPanel p = new JPanel();
p.setBorder (new TitledBorder(new LineBorder(Color.black, 1, true)));
p.setPreferredSize(new Dimension(500,400));
JPanel p2 = new JPanel();
p2.setBorder (new TitledBorder(new LineBorder(Color.black, 1, true)));
p2.setPreferredSize(new Dimension(500, 50));
JPanel p3 = new JPanel();
JPanel p4 = new JPanel();
JPanel p5 = new JPanel();
JPanel p6 = new JPanel();
Box box = Box.createVerticalBox();
Box box2 = Box.createHorizontalBox();
Box box3 = Box.createHorizontalBox();
Box box4 = Box.createHorizontalBox();
final JTextField textfieldStockName;
final JTextField textfieldStockID;
final JTextField textfieldStockDescription;
final JTextField textfieldStockPrice;
final JTextField textfieldStockQuantity;
final JTextField textfieldStockCategory;
final JLabel stockName = new JLabel("Name:");
JLabel stockID = new JLabel("ID:");
JLabel stockDescription = new JLabel("Description:");
JLabel stockPrice = new JLabel("Price:");
JLabel stockQuantity = new JLabel("Quantity:");
JLabel categoryName = new JLabel("Category:");
box.add(Box.createVerticalGlue());
box.add(stockName);
box.add(textfieldStockName = new JTextField(""));
textfieldStockName.setText(stock.getStockName());
textfieldStockName.setEditable(false);
box.add(stockID);
box.add(textfieldStockID = new JTextField(""));
textfieldStockID.setText(stock.getStockID());
textfieldStockID.setEditable(false);
box.add(stockDescription);
box.add(textfieldStockDescription = new JTextField(""));
textfieldStockDescription.setText(stock.getStockDescription());
textfieldStockDescription.setEditable(false);
box.add(stockPrice);
box.add(textfieldStockPrice = new JTextField(""));
textfieldStockPrice.setText(stock.getStockPrice());
textfieldStockPrice.setEditable(false);
box.add(stockQuantity);
box.add(textfieldStockQuantity = new JTextField(""));
textfieldStockQuantity.setText(stock.getStockQuantity());
textfieldStockQuantity.setEditable(false);
box.add(categoryName);
box.add(textfieldStockCategory = new JTextField(""));
textfieldStockCategory.setText(stock.getStockCategory());
textfieldStockCategory.setEditable(false);
box.add(Box.createVerticalGlue());
JButton next = new JButton("Next");
next.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
stock.doNext();
textfieldStockName.setText(stock.getStockName());
textfieldStockID.setText(stock.getStockID());
textfieldStockDescription.setText(stock.getStockDescription());
textfieldStockPrice.setText(stock.getStockPrice());
textfieldStockQuantity.setText(stock.getStockQuantity());
textfieldStockCategory.setText(stock.getStockCategory());
}
});
JButton previous = new JButton("Previous");
previous.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
stock.doPrevious();
textfieldStockName.setText(stock.getStockName());
textfieldStockID.setText(stock.getStockID());
textfieldStockDescription.setText(stock.getStockDescription());
textfieldStockPrice.setText(stock.getStockPrice());
textfieldStockQuantity.setText(stock.getStockQuantity());
textfieldStockCategory.setText(stock.getStockCategory());
}
});
final Counter counter = new Counter();
final JLabel text = new JLabel(counter.getValue1());
JButton plus = new JButton("+");
plus.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
counter.increment();
text.setText(counter.getValue1());
}
});
JButton minus = new JButton("-");
minus.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
counter.decrease();
text.setText(counter.getValue1());
}
});
JButton update = new JButton("Update");
update.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
try {
stock.updateStock(counter.getValue1());
}
catch (SQLException e1) {
e1.printStackTrace();
}
finally { // doesn't update yet; will work on this later
textfieldStockQuantity.setText(stock.getStockQuantity());
}
}
});
comboGUI.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
try {
combo = (JComboBox) e.getSource();
selected = (String)combo.getSelectedItem();
textfieldStockName.setText(stock.getStockName());
textfieldStockID.setText(stock.getStockID());
textfieldStockDescription.setText(stock.getStockDescription());
textfieldStockPrice.setText(stock.getStockPrice());
textfieldStockQuantity.setText(stock.getStockQuantity());
textfieldStockCategory.setText(stock.getStockCategory());
stockQuery.con.close();
}
catch (SQLException e1) {
e1.printStackTrace();
}
}
});
box.add(comboGUI);
box2.add(previous);
box2.add(next);
box3.add(minus);
box3.add(text);
box3.add(plus);
box4.add(update);
p.add(box2);
p.add(box);
p.add(box3);
p.add(box4);
this.add(p, BorderLayout.SOUTH);
}
}
如果有人可以提供帮助，我们将不胜感激。
当您有太多打开的连接时，您会收到此异常。
这是可配置的，但就您而言，问题出在您的代码中。
您发布的代码很奇怪（至少）。
你要么不关闭连接，除非你得到一个SQLException或者在处理结果集期间关闭它！
无论如何，您应该在完成后重构代码以关闭连接和结果集等。
例子：
try {
stat = con.createStatement( ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_UPDATABLE );
rs = stat.executeQuery("SELECT categoryName FROM Category");
while (rs.next()) {
combo.addItem(rs.getString("categoryName"));
categoryName = rs.getString("categoryName");
}
} catch (SQLException sqle) {
System.out.println(sqle);
}
finally{
if(stat != null) stat.close();
if(con != null) con.close();
}
通过将收盘价放在finally您确定连接在正确的流程或异常情况下关闭（我省略了try-catch为了清楚起见）。
因此修改代码以关闭连接。
为了获得更好的性能，您应该考虑连接池
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