5

我正在为一家酒吧编写一个库存补充系统作为我最后一年的项目。我可以从 MYSQL 数据库中检索信息，并且一次可以滚动浏览一个结果。

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这一点，但是在类别之间移动时出现以下错误：

线程“主”com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException 中的异常：数据源拒绝建立连接，来自服务器的消息：“连接太多”

两个独立文件的代码如下：

  • 中的 SQL 查询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());   
  }
}

  • 我的ViewStockGUI班级

      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，将不胜感激。

4

3 回答 3

7

当您有太多打开的连接时，您会收到此异常。
这是可配置的，但在您的情况下，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或者你在处理结果集的过程中关闭它！

在任何情况下，您都应该在完成后立即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(); 
}

通过将关闭放在 afinally中，您可以确定连接以正确的流程或异常关闭（为了清楚起见，我省略try-catch了）。

所以以这种方式修改代码以关闭连接。

为了获得更好的性能，您应该研究连接池

于 2012-04-16T15:27:44.460 回答
1

我想我在您的代码中看到了问题。您的代码非常奇怪，但这是我认为正在发生的事情：

在你的ViewStockQuery课堂上，你有retrieveStock()方法。然后，此方法创建您的 GUI 类的实例，ViewStockGUI. 除了这种不好的做法外，它还会导致一个问题，因为在 的构造函数中ViewStockGUI，您在这一行的方法中调用了retrieveStock()它：

stockGUI = new ViewStockGUI();

然后您再次retrieveStock()使用此行调用：

final ViewStockQuery stock = new ViewStockQuery();

comboGUI = stock.getComboBox();
stock.retrieveStock();

这会导致递归问题，因为您的ViewStockGUI()构造函数调用retrieveStock()创建连接的方法并再次调用ViewStockGUI()构造函数，该构造函数将再次调用retrieveStock()尚未关闭连接的方法并尝试打开不同的连接。希望你能得到图片。

解决它的一种方法是清理你的代码。不要在retrieveStock(). 找到一种不同的方式为您的查询传递所选类别。

编辑：

像这样写你ViewStockQuery：

private String mSelected;

public ViewStockQuery(String selectedCategory) {
    mSelected = selectedCategory;
}

...

public void retrieveStock() throws SQLException { 

    con = SQLConnect.getConnection();


    String viewStock = "SELECT * FROM Stock where categoryName = '" + "'" + mSelected + "'";
    System.out.println(viewStock);


     try {
...

然后以这样的方式编写您ViewStockGUI的方式，即选择类别时，即创建ViewStockQuery并传递选定的字符串时。

编辑：

就像我之前说的，你最终需要在代码中更改很多东西。但是，就本期而言，您可以在ViewStockGUI, 中执行以下操作：

String selected = (String)combo.getSelectedItem();
final ViewStockQuery stock = new ViewStockQuery(selected);

第一行从组合框中收集所选类别，第二行创建一个实例并将所选类别ViewStockQuery传递给构造函数。然后，这将初始化 mSelected，正如您在上面为ViewStockQuery.

于 2012-04-16T15:43:48.013 回答
0

如果您想使用 JDBC（而不是 JPA），那么我建议使用Spring 中的JdbcTemplate或 Java SE 7 的自动资源管理（ARM）。（我还没有尝试使用 ARM 的 JDBC，但它应该可以工作。 )

基本上，您需要在 try-catch 子句的 finally 块中关闭 Closeables。

于 2012-04-16T15:28:36.357 回答