使用JDBC的Java - 连接太多？

我正在写一个酒吧的库存补货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，并且可以一次滚动查看一个结果。使用JDBC的Java - 连接太多？

我试图根据所选类别更改结果。我已经成功地使用组合框，以达致这可是类别之间移动时，我收到以下错误：在线程

异常“主要” com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException：数据源拒绝建立连接，消息从服务器：“有太多的联系”

为两个单独的文件中的代码如下：

的SQL查询中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ViewStockGUI类

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); 
    } 
}

如果有人可以帮助我们将不胜感激。

来源

2012-04-16 Liam Bull

你能告诉我们'SQLConnect.getConnection（）;'的代码吗？ – dash1e 2012-04-16 15:24:50

可能的重复[数据源拒绝建立连接，来自服务器的消息：“连接太多”]（http://stackoverflow.com/questions/3203673/data-source-rejected-establishment-of-connection-message-from -server-too-many） – duffymo 2012-04-16 15:25:01

为什么连接在while循环内关闭？它应该在try catch的finally块中。 – 2012-04-16 15:26:51

当你有太多打开的连接时，你会得到这个异常。
这是可配置的，但在你的情况下，问题出现在你的代码中。

您发布的代码很奇怪（至少）。
除非得到SQLException或者在处理结果集期间关闭连接，否则您不要关闭连接！

在任何情况下，您应该重构您的代码，以便在完成后立即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(); 
}

通过投入finally收盘您确信该连接是无论是在正确的流量或异常关闭（我省略try-catch为清楚起见）。

所以用这种方法修改代码来关闭连接。

为了获得更好的性能，你应该看看连接池

来源

2012-04-16 15:27:44 Cratylus

如果你想使用JDBC（而不是JPA），那么我建议要么使用JdbcTemplate从春天或Java的自动资源管理（ARM）SE 7 （我还没有用ARM试过JDBC，但它应该可以工作。）

基本上，您需要关闭try-catch子句的finally块中的Closeables。

来源

2012-04-16 15:28:36 Puce

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

在你的ViewStockQuery类中，你有retrieveStock()方法。这个方法然后创建一个GUI类的实例，ViewStockGUI。除了这是不好的做法，它会导致一个问题就在这里，因为在ViewStockGUI的构造函数，你在retrieveStock()方法在这条线叫：

stockGUI = new ViewStockGUI();

你然后再调用retrieveStock()这一行：

final ViewStockQuery stock = new ViewStockQuery(); 

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

这导致递归问题，因为你的ViewStockGUI()构造函数调用retrieveStock()方法，它创建一个连接并再次调用ViewStockGUI()构造函数将再次调用已不是CL的retrieveStock()方法提出连接并尝试打开不同的连接。希望你得到的照片。

解决它的一种方法是清理你的代码。不要在retrieveStock()中调用构造函数。找到一种不同的方式为您的查询传递选定的类别。

编辑：

写你ViewStockQuery像这样：

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 { 
...

然后再编写ViewStockGUI中，当一个类已经选择这样一种方式，那就是当你创建ViewStockQuery并传入所选字符串。

编辑：

就像我之前说的，也有相当多的事情，你最终将需要在你的代码改变。但是，对于这个问题的目的，你可以做的是在你的ViewStockGUI，做到：

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

第一行从您的组合框中收集所选择的类别和第二行创建的ViewStockQuery一个实例，并将所选到构造函数。然后这将初始化mSelected，如您在上面为ViewStockQuery所提供的构造函数中所看到的那样。

来源

2012-04-16 15:43:48 ugo

好吧，看着这个。 – 2012-04-17 12:37:30

你把私人mSelected; 这是什么意思？一个字符串？有点困惑。 – 2012-04-17 14:46:06

@LiamBull，哎呀。对不起，它意味着是一个字符串。纠正。 – ugo 2012-04-18 17:26:25

使用JDBC的Java - 连接太多？

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