连接池是一种创建和管理多个(a pool of )连接的技术，这些连接是为任何需要它们的线程准备的。连接池不会马上关闭连接，而是将连接保存在一个pool中，这样可以很高效地服务下一个连接。除此之外，连接池还有很多好处，例如，控制资源的使用。
当开发基于Web的应用程序时，没有理由不使用连接池，包括ZK应用程序。
连接池的概念很简单：配置，连接及关闭。打开和关闭一个连接与点对点(ad-hoc )方法很相似，而配置依赖于使用的Web服务器和数据库。
配置好连接池(将会在下面的章节讨论)之后，你可以使用JNDI 获取一个连接，如下。
import java.sql.Connection;
import java.sql.SQLException;
import java.sql.Statement;
import javax.naming.InitialContext;
import javax.sql.DataSource;
import org.zkoss.zul.Window;
public class MyWindows extends Window {
private Textbox name, email;
public void onCreate() {
//initial name and email
name = getFellow("name");
email = getFellow("email");
}
public void onOK() throws Exception {
DataSource ds = (DataSource)new InitialContext()
.lookup("java:comp/env/jdbc/MyDB");
//Assumes your database is configured and
//named as "java:comp/env/jdbc/MyDB"
Connection conn = null;
Statement stmt = null;
try {
conn = ds.getConnection();
stmt = conn.prepareStatement("INSERT INTO user values(?, ?)");
//insert what end user entered into database table
stmt.set(1, name.value);
stmt.set(2, email.value);
//execute the statement
stmt.executeUpdate();
stmt.close(); stmt = null;
//optional because the finally clause will close it
//However, it is a good habit to close it as soon as done, especially
//you might have to create a lot of statement to complete a job
} finally { //cleanup
if (stmt != null) {
try {
stmt.close();
} catch (SQLException ex) {
//(optional log and) ignore
}
}
if (conn != null) {
try {
conn.close();
} catch (SQLException ex) {
//(optional log and) ignore
}
}
}
}
}
[注]:
使用之后关闭语句和连接是很重要的。
使用多个连接，你可以同时访问多个数据库。依赖于配置和J2EE/Web服务器，这些连接甚至可以形成一个分布式事务处理(distributed transaction)。
连接池的配置随J2EE/Web/数据库服务器的不同而不同。这里我们说明其中一些的配置。你需要参考(consult)你使用的服务器的文档。
为配置Tomcat 5.5配置连接池，你必须编辑$TOMCAT_DIR/conf/context.xml
[66],，在<Context>元素的下添加下面的内容。标记为蓝色的的信息依赖于你的安装，且通常需要修改。
<!-- The name you used above, must match _exactly_ here! The connection pool will be bound into JNDI with the name "java:/comp/env/jdbc/MyDB" --> <Resource name="jdbc/MyDB" username="someuser" password="somepass" url="jdbc:mysql://localhost:3306/test" auth="Container" defaultAutoCommit="false" driverClassName="com.mysql.jdbc.Driver" maxActive="20" timeBetweenEvictionRunsMillis="60000" type="javax.sql.DataSource" /> </ResourceParams>
然后在web.xml内，你需要在<web-app>元素下添加下面的内容。
<resource-ref> <res-ref-name>jdbc/MyDB</res-ref-name> <res-type>javax.sql.DataSource</res-type> <res-auth>Container</res-auth> </resource-ref>
下列的指令基于MySQL 5.0 参考手册的23.3.4.3 章节(section 23.3.4.3 of the reference manual of MySQL 5.0)。
为JBoss配置连接池，你必须在deploy ($JBOSS_DIR/server/default/deploy)目录下添加一个新文件。文件名要以"-ds.xml"结尾，即告诉JBoss将此文件部署为JDBC数据源。文件必须包含下列内容。标记为蓝色的的信息依赖于你的安装，且通常需要修改。
<datasources>
<local-tx-datasource>
<!-- This connection pool will be bound into JNDI with the name
"java:/MyDB" -->
<jndi-name>MyDB</jndi-name>
<connection-url>jdbc:mysql://localhost:3306/test</connection-url>
<driver-class>com.mysql.jdbc.Driver</driver-class>
<user-name>someser</user-name>
<password>somepass</password>
<min-pool-size>5</min-pool-size>
<!-- Don't set this any higher than max_connections on your
MySQL server, usually this should be a 10 or a few 10's
of connections, not hundreds or thousands -->
<max-pool-size>20</max-pool-size>
<!-- Don't allow connections to hang out idle too long,
never longer than what wait_timeout is set to on the
server...A few minutes is usually okay here,
it depends on your application
and how much spikey load it will see -->
<idle-timeout-minutes>5</idle-timeout-minutes>
<!-- If you're using Connector/J 3.1.8 or newer, you can use
our implementation of these to increase the robustness
of the connection pool. -->
<exception-sorter-class-name>com.mysql.jdbc.integration.jboss.ExtendedMysqlExceptionSorter</exception-sorter-class-name>
<valid-connection-checker-class-name>com.mysql.jdbc.integration.jboss.MysqlValidConnectionChecker</valid-connection-checker-class-name>
</local-tx-datasource>
</datasources>
<datasources>
<local-tx-datasource>
<!-- This connection pool will be bound into JNDI with the name
"java:/MyDB" -->
<jndi-name>MyDB</jndi-name>
<!-- jdbc:postgresql://[servername]:[port]/[database name] -->
<connection-url>jdbc:postgresql://localhost/test</connection-url>
<driver-class>org.postgresql.Driver</driver-class>
<user-name>someuser</user-name>
<password>somepass</password>
<min-pool-size>5</min-pool-size>
<max-pool-size>20</max-pool-size>
<track-statements>false</track-statements>
</local-tx-datasource>
</datasources>