Question

我很想在一个将postgresql与glassfish一起使用的项目中眨眼。当我执行语句PreparedStatement pstmt = conn.prepareStatement(sql)时，它会给我java.lang.NullPointerException。

这是我的代码：

    String sql = "DELETE FROM blocklist WHERE ? >= time + ?;";

    try(Connection conn = this.connect(); 
            PreparedStatement pstmt = conn.prepareStatement(sql))
    {
        pstmt.setLong(1, System.currentTimeMillis());
        pstmt.setLong(2, blocktime);
        pstmt.executeUpdate();
    }
    catch(SQLException ex)
    {
        Logger.getLogger(RecordManager.class.getName()).log(Level.SEVERE, null, ex);
    }

connect（）函数在此处，它在Connection conn = this.connect();处被调用：

private Connection connect()
{
    Connection con = null;
    try
    {
        con = DriverManager.getConnection(Config.dburl, Config.dbusername, Config.dbpassword);
    }
    catch(SQLException ex)
    {
        Logger.getLogger(RecordManager.class.getName()).log(Level.SEVERE, null, ex);
    }
    return con;
}

这是异常日志：

Severe:   Exception in thread "AWT-EventQueue-0"
Severe:   java.lang.NullPointerException
    at urrsm.sng.RecordManager.unblockrun(RecordManager.java:91)
    at urrsm.sng.WebScocketEnd$1.actionPerformed(WebScocketEnd.java:45)
    at javax.swing.Timer.fireActionPerformed(Timer.java:313)
    at javax.swing.Timer$DoPostEvent.run(Timer.java:245)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:311)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
    at java.awt.EventQueue.access$500(EventQueue.java:97)
    at java.awt.EventQueue$3.run(EventQueue.java:709)
    at java.awt.EventQueue$3.run(EventQueue.java:703)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:74)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:205)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

Answer 1

不可能使用准备好的语句在查询中绑定实际的列名。只能绑定文字值。尝试重新定义您的删除查询，如下所示：

]]

conn.prepareStatement（sql）上的java.lang.NullPointerException

1 个答案: