PreparedStatement的问题

idilent 2007-01-08 05:55:51

java的文档是这样写的

An object that represents a precompiled SQL statement.

A SQL statement is precompiled and stored in a PreparedStatement object. This object can then be used to efficiently execute this statement multiple times.

那么如果这个PreparedStatement对象回收之后，这个SQL是不是就不再是precompiled的了？从网上找了些资料，说SQL是被Cache在数据库的，但是自己也作了测试，好像有点问题。

测试代码如下：
try{
Connection conn = JdbcConnectionUtil.getConnection();
long l = System.currentTimeMillis();
long l1 = System.currentTimeMillis();
///*
for(int I = 0; I < 20; ++I){
PreparedStatement ps = conn.prepareStatement("select * from tablename where ID = " + (I) );
ResultSet rs = ps.executeQuery();
System.out.println("---------------"+(System.currentTimeMillis()-l));
l = System.currentTimeMillis();
}
System.out.println("-------------------------------------" + (System.currentTimeMillis()-l1));
long l2 = System.currentTimeMillis();
for(int I = 0; I < 20; ++I){
PreparedStatement ps = conn.prepareStatement("select * tablename where ID = ?");
ps.setInt(1,I);
ResultSet rs = ps.executeQuery();
System.out.println("---------------"+(System.currentTimeMillis()-l));
l = System.currentTimeMillis();
}
System.out.println("-------------------------------------" + (System.currentTimeMillis()-l2));

long l3 = System.currentTimeMillis();
PreparedStatement ps = conn.prepareStatement("select * tablename where ID = ?");
for(int I = 0; I < 20; ++I){
ps.setInt(1,I);
ResultSet rs = ps.executeQuery();
System.out.println("---------------"+(System.currentTimeMillis()-l));
l = System.currentTimeMillis();
}
System.out.println("-------------------------------------" + (System.currentTimeMillis()-l3));

}catch(Exception e){}
打印出来的结果如下：
---------------829
---------------375
---------------0
---------------1140
---------------1391
---------------3187
---------------1907
---------------4000
---------------62
---------------1156
---------------125
---------------1485
---------------0
---------------0
---------------0
---------------235
---------------468
---------------27485
---------------1844
---------------562
-------------------------------------46266
---------------875
---------------359
---------------0
---------------1219
---------------1344
---------------2750
---------------1969
---------------4000
---------------47
---------------1203
---------------93
---------------1469
---------------0
---------------0
---------------16
---------------219
---------------500
---------------27375
---------------3765
---------------938
-------------------------------------48141
---------------828
---------------359
---------------0
---------------1531
---------------1391
---------------2797
---------------2125
---------------3968
---------------47
---------------1141
---------------109
---------------1453
---------------0
---------------0
---------------0
---------------203
---------------500
---------------26813
---------------1797
---------------500
-------------------------------------45578

似乎没有什么影响呀？

参考文献：
http://www.theserverside.com/tt/articles/article.tss?l=Prepared-Statments

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