jdbc连接一定要关闭connection, resultset和preparedstatement

今天写了个程序往数据库插入100万条记录，代码如下

publicstaticvoid insertRecords() throws Exception {
 Connection conn = null;
 try {
 conn = DBUtil.getConnection();
 conn.setAutoCommit(false);

 while (count < TOTALNUM) {
 PreparedStatement ps = conn.prepareStatement("select * from custfund limit ?");
 ps.setInt(1, COPYNUM);
 ResultSet rs2 = ps.executeQuery();
 while (rs2.next() && count < TOTALNUM) {
 PreparedStatement ps2 = conn
 .prepareStatement("sql here...");
 ps2.setInt(1, ++maxCustId);
 ps2.setFloat(2, rs2.getFloat(2));
 ps2.setFloat(3, rs2.getFloat(3));
 ps2.setFloat(4, rs2.getFloat(4));
 ps2.setFloat(5, rs2.getFloat(5));
 ps2.setFloat(6, rs2.getFloat(6));
 ps2.setFloat(7, rs2.getFloat(7));
 ps2.setInt(8, rs2.getInt(8));

 ps2.executeUpdate();
 ps2.close();
 count++;
 if (count % 2000 == 0) {
 System.out.println(count);
 long curtime = new Date().getTime();
 long timeUsed = curtime - time;
 int remaincount = TOTALNUM - count;
 System.out.println("remaining time:" + (remaincount / 2000) * timeUsed / 1000 + "s");
 time = curtime;
 conn.commit();
 }
 }
 rs2.close();********
 ps.close();********
 }
 System.out.println("total time:" + (new Date().getTime() - starttime) / 1000 + "S");
 } finally {
 if (conn != null) {
 conn.close();
 }
 }
 }

public static void insertRecords() throws Exception {
        Connection conn = null;
        try {
            conn = DBUtil.getConnection();
            conn.setAutoCommit(false);
                      
            while (count < TOTALNUM) {
                PreparedStatement ps = conn.prepareStatement("select * from custfund limit ?");
                ps.setInt(1, COPYNUM);
                ResultSet rs2 = ps.executeQuery();
                while (rs2.next() && count < TOTALNUM) {
                    PreparedStatement ps2 = conn
                            .prepareStatement("sql here...");
                    ps2.setInt(1, ++maxCustId);
                    ps2.setFloat(2, rs2.getFloat(2));
                    ps2.setFloat(3, rs2.getFloat(3));
                    ps2.setFloat(4, rs2.getFloat(4));
                    ps2.setFloat(5, rs2.getFloat(5));
                    ps2.setFloat(6, rs2.getFloat(6));
                    ps2.setFloat(7, rs2.getFloat(7));
                    ps2.setInt(8, rs2.getInt(8));
                   
                    ps2.executeUpdate();
                    ps2.close();
                    count++;
                    if (count % 2000 == 0) {
                        System.out.println(count);
                        long curtime = new Date().getTime();
                        long timeUsed = curtime - time;
                        int remaincount = TOTALNUM - count;
                        System.out.println("remaining time:" + (remaincount / 2000) * timeUsed / 1000 + "s");
                        time = curtime;
                        conn.commit();
                    }
                }
                rs2.close();********
                ps.close();********
            }
            System.out.println("total time:" + (new Date().getTime() - starttime) / 1000 + "S");
        } finally {
            if (conn != null) {
                conn.close();
            }
        }
    }

 

在****处如果不对rs, ps close,就会有java虚拟机out of memory.

按理说java虚拟机会自动垃圾回收，但为什么这里会这样呢？

原因是rs, ps没有关闭，java虚拟机认为它还在被使用。很多循环以后，就内存满了。