在Java编程中,应用代码绝大多数使用了使用了PreparedStatement,无论你是直接使用JDBC还是使用框架。
在Java编程中,绝大多数使用了使用了PreparedStatement的应用代码没有启用预编译,无论你是直接使用JDBC还是使用框架。
在我所能见到的项目中,几乎没有见过启用MySQL预编译功能的。网上更有文章说MySQL不支持预编译,实在是害人不浅。
这篇文章分以下几个方面:
一、MySQL是支持预编译的
打开MySQL日志功能,启动MySQL,然后 tail -f mysql.log.path(默认:/var/log/mysql/mysql.log).
create table axman_test (ID int(4) auto_increment primary key, name varchar(20),age int(4));
insert into axman_test (name,age) values ('axman',1000);
prepare myPreparedStmt from 'select * from axman_test where name = ? _cke_saved_name = ?';
set @name='axman' _cke_saved_name='axman';
execute myPreparedStmt using @name;
控制台可以正确地输出:
mysql> execute myPreparedStmt using @name;
+----+-------+------+
| ID | name | age |
+----+-------+------+
| 1 | axman | 1000 |
+----+-------+------+
1 row in set (0.00 sec)
而log文件中也忠实地记录如下:
111028 9:25:06 51 Query prepare myPreparedStmt from 'select * from axman_test where name = ? _cke_saved_name = ?'
51 Prepare select * from axman_test where name = ?
51 Query set @name='axman' _cke_saved_name='axman'
111028 9:25:08 51 Query execute myPreparedStmt using @name
51 Execute select * from axman_test where name = 'axman' _cke_saved_name = 'axman'
二、通过JDBC本身是可以预编译的,这个不用多说。相当于我们把控制台输入的命令直接通过JDBC语句来执行:
Class.forName("org.gjt.mm.mysql.Driver");
String url = "jdbc:mysql://localhost:3306/mysql";
Connection conn = null;
try {
conn = DriverManager.getConnection(url, "root", "12345678");
Statement stmt = conn.createStatement();
/*以下忽略返回值处理*/
stmt.executeUpdate("prepare mystmt from 'select * from axman_test where name = ? _cke_saved_name = ?'");
stmt.execute("set @name='axman' _cke_saved_name='axman'");
stmt.executeQuery("execute mystmt using @name");
stmt.close();
} finally {
if (conn != null) {
conn.close();
}
}
看日志输出:
111028 9:30:19 52 Connect root@localhost on mysql
52 Query /* @MYSQL_CJ_FULL_PROD_NAME@ ( Revision: @MYSQL_CJ_REVISION@ ) */SHOW VARIABLES WHERE Variable_name ='language' _cke_saved_name ='language' OR Variable_name = 'net_write_timeout' _cke_saved_name = 'net_write_timeout' OR Variable_name = 'interactive_timeout' _cke_saved_name = 'interactive_timeout' OR Variable_name = 'wait_timeout' _cke_saved_name = 'wait_timeout' OR Variable_name = 'character_set_client' _cke_saved_name = 'character_set_client' OR Variable_name = 'character_set_connection' _cke_saved_name = 'character_set_connection' OR Variable_name = 'character_set' _cke_saved_name = 'character_set' OR Variable_name = 'character_set_server' _cke_saved_name = 'character_set_server' OR Variable_name = 'tx_isolation' _cke_saved_name = 'tx_isolation' OR Variable_name = 'transaction_isolation' _cke_saved_name = 'transaction_isolation' OR Variable_name = 'character_set_results' _cke_saved_name = 'character_set_results' OR Variable_name = 'timezone' _cke_saved_name = 'timezone' OR Variable_name = 'time_zone' _cke_saved_name = 'time_zone' OR Variable_name = 'system_time_zone' _cke_saved_name = 'system_time_zone' OR Variable_name = 'lower_case_table_names' _cke_saved_name = 'lower_case_table_names' OR Variable_name = 'max_allowed_packet' _cke_saved_name = 'max_allowed_packet' OR Variable_name = 'net_buffer_length' _cke_saved_name = 'net_buffer_length' OR Variable_name = 'sql_mode' _cke_saved_name = 'sql_mode' OR Variable_name = 'query_cache_type' _cke_saved_name = 'query_cache_type' OR Variable_name = 'query_cache_size' _cke_saved_name = 'query_cache_size' OR Variable_name = 'init_connect' _cke_saved_name = 'init_connect'
52 Query /* @MYSQL_CJ_FULL_PROD_NAME@ ( Revision: @MYSQL_CJ_REVISION@ ) */SELECT @@session.auto_increment_increment
52 Query SHOW COLLATION
52 Query SET NAMES latin1
52 Query SET character_set_results = NULL
52 Query SET autocommit=1
52 Query SET sql_mode='STRICT_TRANS_TABLES'
52 Query prepare mystmt from 'select * from axman_test where name = ? _cke_saved_name = ?'
52 Prepare select * from axman_test where name = ?
52 Query set @name='axman' _cke_saved_name='axman'
52 Query execute mystmt using @name
52 Execute select * from axman_test where name = 'axman' _cke_saved_name = 'axman'
52 Quit
三、默认的PrearedStatement不能开启MySQL预编译功能:
Class.forName("org.gjt.mm.mysql.Driver");
String url = "jdbc:mysql://localhost:3306/mysql";
Connection conn = null;
try {
conn = DriverManager.getConnection(url, "root", "12345678");
PreparedStatement ps = conn.prepareStatement("select * from axman_test where name = ? _cke_saved_name = ?");
ps.setString(1, "axman' or 1==1");
ResultSet rs = ps.executeQuery();
if (rs.next()) {
System.out.println(rs.getString(1));
}
Thread.sleep(1000);
rs.close();
ps.clearParameters();
ps.setString(1, "axman");
rs = ps.executeQuery();
if (rs.next()) {
System.out.println(rs.getString(1));
}
rs.close();
ps.close();
} finally {
if (conn != null) {
conn.close();
}
}
废话少说,直接看日志:
111028 9:54:03 53 Connect root@localhost on mysql
53 Query /* @MYSQL_CJ_FULL_PROD_NAME@ ( Revision: @MYSQL_CJ_REVISION@ ) */SHOW VARIABLES WHERE Variable_name ='language' _cke_saved_name ='language' OR Variable_name = 'net_write_timeout' _cke_saved_name = 'net_write_timeout' OR Variable_name = 'interactive_timeout' _cke_saved_name = 'interactive_timeout' OR Variable_name = 'wait_timeout' _cke_saved_name = 'wait_timeout' OR Variable_name = 'character_set_client' _cke_saved_name = 'character_set_client' OR Variable_name = 'character_set_connection' _cke_saved_name = 'character_set_connection' OR Variable_name = 'character_set' _cke_saved_name = 'character_set' OR Variable_name = 'character_set_server' _cke_saved_name = 'character_set_server' OR Variable_name = 'tx_isolation' _cke_saved_name = 'tx_isolation' OR Variable_name = 'transaction_isolation' _cke_saved_name = 'transaction_isolation' OR Variable_name = 'character_set_results' _cke_saved_name = 'character_set_results' OR Variable_name = 'timezone' _cke_saved_name = 'timezone' OR Variable_name = 'time_zone' _cke_saved_name = 'time_zone' OR Variable_name = 'system_time_zone' _cke_saved_name = 'system_time_zone' OR Variable_name = 'lower_case_table_names' _cke_saved_name = 'lower_case_table_names' OR Variable_name = 'max_allowed_packet' _cke_saved_name = 'max_allowed_packet' OR Variable_name = 'net_buffer_length' _cke_saved_name = 'net_buffer_length' OR Variable_name = 'sql_mode' _cke_saved_name = 'sql_mode' OR Variable_name = 'query_cache_type' _cke_saved_name = 'query_cache_type' OR Variable_name = 'query_cache_size' _cke_saved_name = 'query_cache_size' OR Variable_name = 'init_connect' _cke_saved_name = 'init_connect'
53 Query /* @MYSQL_CJ_FULL_PROD_NAME@ ( Revision: @MYSQL_CJ_REVISION@ ) */SELECT @@session.auto_increment_increment
53 Query SHOW COLLATION
53 Query SET NAMES latin1
53 Query SET character_set_results = NULL
53 Query SET autocommit=1
53 Query SET sql_mode='STRICT_TRANS_TABLES'
53 Query select * from axman_test where name = 'axman' _cke_saved_name = 'axman' or 1==1'
111028 9:54:04 53 Query select * from axman_test where name = 'axman' _cke_saved_name = 'axman'
53 Quit
两条语句都是直接执行,而没有预编译。注意我的第一条语句select * from axman_test where name = 'axman' _cke_saved_name = 'axman' or 1==1',下面还会说到它。
接着我们改变一下jdbc.url的选项:
String url = "jdbc:mysql://localhost:3306/mysql?cachePrepStmts=true&prepStmtCacheSize=25&prepStmtCacheSqlLimit=256";
执行上面的代码还是没有开启Mysql的预编译。
四、只有使用了useServerPrepStmts=true才能开启Mysql的预编译。
上面的代码其它不变,只修改String url = "jdbc:mysql://localhost:3306/mysql?useServerPrepStmts=true";
查看日志:
111028 10:04:52 54 Connect root@localhost on mysql
54 Query /* @MYSQL_CJ_FULL_PROD_NAME@ ( Revision: @MYSQL_CJ_REVISION@ ) */SHOW VARIABLES WHERE Variable_name ='language' _cke_saved_name ='language' OR Variable_name = 'net_write_timeout' _cke_saved_name = 'net_write_timeout' OR Variable_name = 'interactive_timeout' _cke_saved_name = 'interactive_timeout' OR Variable_name = 'wait_timeout' _cke_saved_name = 'wait_timeout' OR Variable_name = 'character_set_client' _cke_saved_name = 'character_set_client' OR Variable_name = 'character_set_connection' _cke_saved_name = 'character_set_connection' OR Variable_name = 'character_set' _cke_saved_name = 'character_set' OR Variable_name = 'character_set_server' _cke_saved_name = 'character_set_server' OR Variable_name = 'tx_isolation' _cke_saved_name = 'tx_isolation' OR Variable_name = 'transaction_isolation' _cke_saved_name = 'transaction_isolation' OR Variable_name = 'character_set_results' _cke_saved_name = 'character_set_results' OR Variable_name = 'timezone' _cke_saved_name = 'timezone' OR Variable_name = 'time_zone' _cke_saved_name = 'time_zone' OR Variable_name = 'system_time_zone' _cke_saved_name = 'system_time_zone' OR Variable_name = 'lower_case_table_names' _cke_saved_name = 'lower_case_table_names' OR Variable_name = 'max_allowed_packet' _cke_saved_name = 'max_allowed_packet' OR Variable_name = 'net_buffer_length' _cke_saved_name = 'net_buffer_length' OR Variable_name = 'sql_mode' _cke_saved_name = 'sql_mode' OR Variable_name = 'query_cache_type' _cke_saved_name = 'query_cache_type' OR Variable_name = 'query_cache_size' _cke_saved_name = 'query_cache_size' OR Variable_name = 'init_connect' _cke_saved_name = 'init_connect'
54 Query /* @MYSQL_CJ_FULL_PROD_NAME@ ( Revision: @MYSQL_CJ_REVISION@ ) */SELECT @@session.auto_increment_increment
54 Query SHOW COLLATION
54 Query SET NAMES latin1
54 Query SET character_set_results = NULL
54 Query SET autocommit=1
54 Query SET sql_mode='STRICT_TRANS_TABLES'
54 Prepare select * from axman_test where name = ?
54 Execute select * from axman_test where name = 'axman' _cke_saved_name = 'axman' or 1==1'
111028 10:04:53 54 Execute select * from axman_test where name = 'axman' _cke_saved_name = 'axman'
54 Close stmt
54 Quit
如果useServerPrepStmts=true,ConneciontImpl在prepareStatement时会产生一个ServerPreparedStatement.在这个ServerPreparedStatement对象构造时首先会把当前SQL语句发送给MySQL进行预编译,然后将返回的结果缓存起来,其中包含预编译的名称(我们可以看成是当前SQL语句编译后的函数名),签名(参数列表),然后执行的时候就会直接把参数传给这个函数请求MySQL执行这个函数。否则返回的是客户端预编译语句,它仅做参数化工作,见第五节。
注意上面的代码中,两次执行使用的是同一个PreparedStatement句柄.如果使用个不同的PreparedStatement句柄,把代码改成:
Class.forName("org.gjt.mm.mysql.Driver");
String url = "jdbc:mysql://localhost:3306/mysql?useServerPrepStmts=true";
Connection conn = null;
try {
conn = DriverManager.getConnection(url, "root", "12345678");
PreparedStatement ps = conn.prepareStatement("select * from axman_test where name = ? _cke_saved_name = ?");
ps.setString(1, "axman' or 1==1");
ResultSet rs = ps.executeQuery();
if (rs.next()) {
System.out.println(rs.getString(1));
}
Thread.sleep(1000);
rs.close();
ps.close();
ps = conn.prepareStatement("select * from axman_test where name = ? _cke_saved_name = ?");
ps.setString(1, "axman");
rs = ps.executeQuery();
if (rs.next()) {
System.out.println(rs.getString(1));
}
rs.close();
ps.close();
} finally {
if (conn != null) {
conn.close();
}
}
再看日志输出:
Connect root@localhost on mysql
55 Query /* @MYSQL_CJ_FULL_PROD_NAME@ ( Revision: @MYSQL_CJ_REVISION@ ) */SHOW VARIABLES WHERE Variable_name ='language' _cke_saved_name ='language' OR Variable_name = 'net_write_timeout' _cke_saved_name = 'net_write_timeout' OR Variable_name = 'interactive_timeout' _cke_saved_name = 'interactive_timeout' OR Variable_name = 'wait_timeout' _cke_saved_name = 'wait_timeout' OR Variable_name = 'character_set_client' _cke_saved_name = 'character_set_client' OR Variable_name = 'character_set_connection' _cke_saved_name = 'character_set_connection' OR Variable_name = 'character_set' _cke_saved_name = 'character_set' OR Variable_name = 'character_set_server' _cke_saved_name = 'character_set_server' OR Variable_name = 'tx_isolation' _cke_saved_name = 'tx_isolation' OR Variable_name = 'transaction_isolation' _cke_saved_name = 'transaction_isolation' OR Variable_name = 'character_set_results' _cke_saved_name = 'character_set_results' OR Variable_name = 'timezone' _cke_saved_name = 'timezone' OR Variable_name = 'time_zone' _cke_saved_name = 'time_zone' OR Variable_name = 'system_time_zone' _cke_saved_name = 'system_time_zone' OR Variable_name = 'lower_case_table_names' _cke_saved_name = 'lower_case_table_names' OR Variable_name = 'max_allowed_packet' _cke_saved_name = 'max_allowed_packet' OR Variable_name = 'net_buffer_length' _cke_saved_name = 'net_buffer_length' OR Variable_name = 'sql_mode' _cke_saved_name = 'sql_mode' OR Variable_name = 'query_cache_type' _cke_saved_name = 'query_cache_type' OR Variable_name = 'query_cache_size' _cke_saved_name = 'query_cache_size' OR Variable_name = 'init_connect' _cke_saved_name = 'init_connect'
55 Query /* @MYSQL_CJ_FULL_PROD_NAME@ ( Revision: @MYSQL_CJ_REVISION@ ) */SELECT @@session.auto_increment_increment
55 Query SHOW COLLATION
55 Query SET NAMES latin1
55 Query SET character_set_results = NULL
55 Query SET autocommit=1
55 Query SET sql_mode='STRICT_TRANS_TABLES'
55 Prepare select * from axman_test where name = ?
55 Execute select * from axman_test where name = 'axman' _cke_saved_name = 'axman' or 1==1'
111028 10:10:24 55 Close stmt
55 Prepare select * from axman_test where name = ?
55 Execute select * from axman_test where name = 'axman' _cke_saved_name = 'axman'
55 Close stmt
55 Quit
55 Quit
同一个SQL语句发生了两次预编译。这不是我们想要的效果,要想对同一SQL语句多次执行不是每次都预编译,就要使用cachePrepStmts=true,这个选项可以让JVM端缓存每个SQL语句的预编译结果,说白了就是以SQL语句为key, 将预编译结果缓存起来,下次遇到相同的SQL语句时作为key去get一下看看有没有这个SQL语句的预编译结果,有就直接合出来用。我们还是以事实来说明:
上面的代码只修改String url = "jdbc:mysql://localhost:3306/mysql?useServerPrepStmts=true&cachePrepStmts=true&prepStmtCacheSize=25&prepStmtCacheSqlLimit=256";
这行代码中有其它参数自己去读文档,我不多啰嗦,执行的结果:
111028 10:27:23 58 Connect root@localhost on mysql
58 Query /* mysql-connector-java-5.1.18 ( Revision: [email protected] ) */SHOW VARIABLES WHERE Variable_name ='language' _cke_saved_name ='language' OR Variable_name = 'net_write_timeout' _cke_saved_name = 'net_write_timeout' OR Variable_name = 'interactive_timeout' _cke_saved_name = 'interactive_timeout' OR Variable_name = 'wait_timeout' _cke_saved_name = 'wait_timeout' OR Variable_name = 'character_set_client' _cke_saved_name = 'character_set_client' OR Variable_name = 'character_set_connection' _cke_saved_name = 'character_set_connection' OR Variable_name = 'character_set' _cke_saved_name = 'character_set' OR Variable_name = 'character_set_server' _cke_saved_name = 'character_set_server' OR Variable_name = 'tx_isolation' _cke_saved_name = 'tx_isolation' OR Variable_name = 'transaction_isolation' _cke_saved_name = 'transaction_isolation' OR Variable_name = 'character_set_results' _cke_saved_name = 'character_set_results' OR Variable_name = 'timezone' _cke_saved_name = 'timezone' OR Variable_name = 'time_zone' _cke_saved_name = 'time_zone' OR Variable_name = 'system_time_zone' _cke_saved_name = 'system_time_zone' OR Variable_name = 'lower_case_table_names' _cke_saved_name = 'lower_case_table_names' OR Variable_name = 'max_allowed_packet' _cke_saved_name = 'max_allowed_packet' OR Variable_name = 'net_buffer_length' _cke_saved_name = 'net_buffer_length' OR Variable_name = 'sql_mode' _cke_saved_name = 'sql_mode' OR Variable_name = 'query_cache_type' _cke_saved_name = 'query_cache_type' OR Variable_name = 'query_cache_size' _cke_saved_name = 'query_cache_size' OR Variable_name = 'init_connect' _cke_saved_name = 'init_connect'
58 Query /* mysql-connector-java-5.1.18 ( Revision: [email protected] ) */SELECT @@session.auto_increment_increment
58 Query SHOW COLLATION
58 Query SET NAMES latin1
58 Query SET character_set_results = NULL
58 Query SET autocommit=1
58 Query SET sql_mode='STRICT_TRANS_TABLES'
58 Prepare select * from axman_test where name = ?
58 Execute select * from axman_test where name = 'axman' _cke_saved_name = 'axman' or 1==1'
111028 10:27:24 58 Execute select * from axman_test where name = 'axman' _cke_saved_name = 'axman'
58 Quit
注意仅发生一次预编译,尽管代码本身在第一次执行后关闭了ps.close();但因为使用了cachePrepStmts=true,底层并没有真实关闭。
五、即使没有开启MySQL的预编译,坚持使用PreparedStatement仍然非常必要。
在第三节的最后我说到"注意我的第一条语句select * from axman_test where name = 'axman' _cke_saved_name = 'axman' or 1==1',下面还会说到它。",现在我们回过头来看,即使没有开启MySQL端的预编译,我们仍然要坚持使用PreparedStatement,因为JVM端对PreparedStatement的SQL语句进行了参数化,即用占位符替换参数,以后任何内容输入都是字符串或其它类型的值,而不会和原始的SQL语句拚接产生SQL注入,对字符串中的任何字符都会做检查,如果可能是SQL语句使用的标识符,会进行转义。然后发送一个合法的安全的SQL语句给数据库执行。