[*急*]关于prepareStatement关闭的问题

[lanyi2003]

我程序中有以下连续的三种sql
--------------------------------------------------
stmt = dbConn.prepareStatement(select_sql);
...set参数
rs=stmt.executeQuery();

--------------------------------------------------
stmt = dbConn.prepareStatement(update_sql);
...set参数
execute();
--------------------------------------------------
stmt = dbConn.prepareStatement(insert_sql);
...set参数
execute();

在程序中我只申明了一个stmt,在执行下一个sql之前,我是否应该先stmt.close()一下呢,这样将出现3个close动作
还是只需要在最后执行一次stmt.close()就可用了呢 ??? 这里虽然对stmt进行了三次赋值,但它一直持有的都是
同一个句柄吧 ?

[rumlee]

需要三次，因为否则你一旦重新赋值，前面的对象引用已经丢失，将无法关闭了。

[goosman]

下面的代码是反编译得到的mysql的jdbc5.1.6的jar包中的PreparedStatement的实现中的close方法.

    public synchronized void close()
        throws SQLException
    {
        realClose(true, true);
    }

close调用了下面这个方法

    protected void realClose(boolean calledExplicitly, boolean closeOpenResults)
        throws SQLException
    {
        if(useUsageAdvisor && numberOfExecutions <= 1)
        {
            String message = Messages.getString("PreparedStatement.43");
            eventSink.consumeEvent(new ProfilerEvent((byte)0, "", currentCatalog, connectionId, getId(), -1, System.currentTimeMillis(), 0L, Constants.MILLIS_I18N, null, pointOfOrigin, message));
        }
        super.realClose(calledExplicitly, closeOpenResults); 
//上面一句调用了父类的realClose()方法, 父类StatementImpl的这个方法代码在下面..
//下面这些地方做了很多成员的释放...
        dbmd = null;
        originalSql = null;
        staticSqlStrings = (byte[][])null;
        parameterValues = (byte[][])null;
        parameterStreams = null;
        isStream = null;
        streamLengths = null;
        isNull = null;
        streamConvertBuf = null;
        parameterTypes = null;
    }

下面这就是父类StatementImpl中的realClose方法

    protected void realClose(boolean calledExplicitly, boolean closeOpenResults)
        throws SQLException
    {
        if(isClosed)
            return;
        if(useUsageAdvisor && !calledExplicitly)
        {
            String message = Messages.getString("Statement.63") + Messages.getString("Statement.64");
            eventSink.consumeEvent(new ProfilerEvent((byte)0, "", currentCatalog, connectionId, getId(), -1, System.currentTimeMillis(), 0L, Constants.MILLIS_I18N, null, pointOfOrigin, message));
        }
        if(closeOpenResults)
            closeOpenResults = !holdResultsOpenOverClose;
        if(closeOpenResults)
        {
            if(results != null)
                try
                {
                    results.close();
                }
                catch(Exception ex) { }
            closeAllOpenResults();
        }
        if(connection != null)
        {
            if(maxRowsChanged)
                connection.unsetMaxRows(this);
            if(!connection.getDontTrackOpenResources())
                connection.unregisterStatement(this);
        }
//同样,下面有很多的释放语句
        isClosed = true;
        results = null;
        connection = null;
        warningChain = null;
        openResults = null;
        batchedGeneratedKeys = null;
        localInfileInputStream = null;
        pingTarget = null;
    }

[冰思雨]

用一个，后面就要close一个。