Question

在创建与Access的连接并尝试插入简单数据时，我收到以下错误：

 run:
 Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at javaapplication1.Authenticate.insertdata(Authenticate.java:49)
at javaapplication1.vendor.actionPerformed(vendor.java:74)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
at java.awt.Component.processMouseEvent(Component.java:6505)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
at java.awt.Component.processEvent(Component.java:6270)
at java.awt.Container.processEvent(Container.java:2229)
at java.awt.Component.dispatchEventImpl(Component.java:4861)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
at java.awt.Container.dispatchEventImpl(Container.java:2273)
at java.awt.Window.dispatchEventImpl(Window.java:2719)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:729)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:688)
at java.awt.EventQueue$3.run(EventQueue.java:686)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.awt.EventQueue$4.run(EventQueue.java:702)
at java.awt.EventQueue$4.run(EventQueue.java:700)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:699)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)

以下是代码片段，如果有人可以帮助一点并查看此内容。代码代码编译正常但在运行时出错：

package javaapplication1;
import java.sql.*;

public class Authenticate {

    final String fileName = "C:/Users/darksword/Desktopdb.accdb";
    Connection con = null;

    Authenticate()
    {
        try {
            Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
            String url = "jdbc:odbc:Driver={Microsoft Access Driver (*.mdb, *.accdb)};DBQ="+fileName;
            con = DriverManager.getConnection(url,"","");
        }
        catch (Exception e)
            {

            }
        finally
            {
                try { if(con!=null) {con.close();} } catch (Exception e) {}
            }
    }

    void insertdata(String Name,String Address,String ContactNumber,int y) throws SQLException
    {
        String str = Integer.toString(y);
        //Statement st=con.createStatement();
        PreparedStatement pstmt = (PreparedStatement) con.prepareStatement("insert into product(id,VName,VAddress,VContactNumber) values(?,?,?,?)");
        pstmt.setString(1, str);
        pstmt.setString(1, Name);
        pstmt.setString(1, Address);
        pstmt.setString(1, ContactNumber);
        pstmt.executeUpdate();
        pstmt.close();
    }
}

Answer 1

在建立数据库连接时，您正在静默捕获异常，如果发生异常，con为null。添加

e.printStackTrace();

到异常块。

此外，在构造函数

中指定变量后立即关闭Connection

con.close();

使用Netbeans将数据插入Access时出错

1 个答案: