ZK Developer's Reference/Integration/Persistence Layer/JDBC

ZK aims to be as thin as the presentation tier. In addition, as the code executes at the server, so connecting database is no different from any desktop applications. In other words, ZK doesn't change the way you access the database, no matter you use JDBC or other persistence framework, such as Hibernate.

Use JDBC

The simplest way to use JDBC, like any JDBC tutorial might suggest, is to use java.sql.DriverManager. Here is an example to store the name and email into a MySQL database.

<window title="JDBC demo" border="normal" apply="org.zkoss.reference.developer.integration.JdbcComposer">
     <vbox>
         <hbox>Name : <textbox id="name"/></hbox>
         <hbox>Email: <textbox id="email"/></hbox>
         <button label="submit"/>
     </vbox>
 </window>

 
public class JdbcComposer extends SelectorComposer<Window> {

	private static Logger log = Logger.getLogger(JdbcComposer.class.getName());
	@Wire
	private Textbox name;
	@Wire
	private Textbox email;

	@Listen("onClick = button")
	public void submit() {
		PreparedStatement stmt = null;
		Connection conn = null;
		try {
			//load driver and get a database connection
			Class.forName("com.mysql.jdbc.Driver");
			conn = DriverManager.getConnection(
					"jdbc:mysql://localhost/test?user=root&password=R3f@ct0r");
			stmt = conn.prepareStatement("INSERT INTO user values(?, ?)");

			//insert what end user entered into database table
			stmt.setString(1, name.getValue());
			stmt.setString(2, email.getValue());

			//execute the statement
			stmt.executeUpdate();
		} catch(Exception e){
			log.severe(e.toString());
		}finally { //cleanup
			if (stmt != null) {
				try {
					stmt.close();
				} catch (SQLException ex) {
					log.severe(ex.toString()); //log and ignore
				}
			}
			if (conn != null) {
				try {
					conn.close();
				} catch (SQLException ex) {
					log.severe(ex.toString()); //log and ignore
				}
			}
		}
	}	
}

Though simple, it is not recommended. After all, ZK applications are web-based applications, where loading is unpredictable and treasurable resources such as database connections have to be managed more effectively.

Luckily, all J2EE frameworks and Web servers support a utility called connection pooling. It is straightforward to use, while managing the database connections well. We will discuss more in the next section.

---

Tip: Unlike other Web applications, it is possible to use DriverManager with ZK, though not recommended.

First, you could cache the connection in the desktop, reuse it for each event, and close it when the desktop becomes invalid. It works just like traditional Client/Server applications. Like Client/Server applications, it works efficiently only if there are at most tens concurrent users.

To know when a desktop becomes invalid, you have to implement a listener by use of DesktopCleanup.

Use a Connection Pool

Connection pool is a mechanism for creating and managing a pool of connections that are ready to use by a thread that needs them. Instead of closing a connection immediately, it keeps them in a pool such that the next connection request could reuse them. Connection pool, in addition, has a lot of benefits, such as control resource usage.

It's recommended to use connection pool if you want to operate Java Connection directly when developing web-based applications, including ZK applications.

The usage of connection pool is simple: configure, connect and close. The way to connect and close a connection is very similar to the ad-hoc approach, while the configuration depends on what web server and database server are in use.

Connect and Close a Connection

After configuring the connection pool (which will be discussed in the following section), you could use JNDI to retrieve an connection as follows.

 <window title="JDBC demo" border="normal">
	<zscript><![CDATA[
		import java.sql.*;
		import javax.sql.*;
		import javax.naming.InitialContext;
		void submit() {
			DataSource ds = (DataSource) new InitialContext()
					.lookup("java:comp/env/jdbc/MyDB");
	
			Connection conn = null;
			PreparedStatement stmt = null;
			try {
				conn = ds.getConnection();
				//remember that we specify autocommit as false in the context.xml 
				conn.setAutoCommit(true);
				stmt = conn.prepareStatement("INSERT INTO user values(?, ?)");
				stmt.setString(1, name.value);
				stmt.setString(2, email.value);
				stmt.executeUpdate();
	
				stmt.close();
				stmt = null;
			} catch (SQLException e) {
				conn.rollback();
				//(optional log and) ignore
			} 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
					}
				}
			}
		}
	]]>
     </zscript>
	<vbox>
		<hbox>Name :<textbox id="name" />
		</hbox>
		<hbox>Email:<textbox id="email" />
		</hbox>
		<button label="submit" onClick="submit()" />
	</vbox>
</window>

Notes:

• It is important to close the statement and connection after use.
• You could access multiple databases at the same time by the use of multiple connections. Depending on the configuration and J2EE/Web servers, these connections could even form a distributed transaction.

Configure Connection Pool

The configuration of connection pool varies from one J2EE/Web/Database server to another. Here we illustrate some of them. You have to consult the document of the server you are using.

Tomcat 5.5 (and above) + MySQL

To configure connection pool for Tomcat 5.5, you have to edit $TOMCAT_DIR/conf/context.xml, and add the following content under the <Context> element. The information that depends on your installation and usually need to be changed is marked in the blue color.

 <!-- 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" />

Then, in web.xml, you have to add the following content under the <web-app> element as follows.

 <resource-ref>
   <res-ref-name>jdbc/MyDB</res-ref-name>
   <res-type>javax.sql.DataSource</res-type>
   <res-auth>Container</res-auth>
 </resource-ref>

Notes

JBoss + MySQL

The following instructions is based on section 23.3.4.3 of the reference manual of MySQL 5.0.

To configure connection pool for JBoss, you have to add a new file to the directory called deploy ($JBOSS_DIR/server/default/deploy). The file name must end with "*-ds.xml" (* means the database, please refer to $JBOSS_DIR/docs/examples/jca/), which tells JBoss to deploy this file as JDBC Datasource. The file must have the following contents. The information that depends on your installation and usually need to be changed is marked in the blue color.

mysql-ds.xml:

 <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>someuser</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>

To specify the JNDI name at which the datasource is available , you have to add a jboss-web.xml file under the WEB-INF folder.

jboss-web.xml

<jboss-web>
<resource-ref> 
    <res-ref-name>jdbc/MyDB</res-ref-name> 
    <jndi-name> java:/MyDB </jndi-name> 
</resource-ref>
</jboss-web>

In web.xml, you have to add the following content under the <web-app> element as follows.

 <resource-ref>
   <res-ref-name>jdbc/MyDB</res-ref-name>
   <res-type>javax.sql.DataSource</res-type>
   <res-auth>Container</res-auth>
 </resource-ref>

JBoss + PostgreSQL

 <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>

download

• Please download the source(Tomcat 5.5 (and above) + MySQL)
• Please download the source(JBoss + MySQL)

Version History

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