This howto is intended to Servlet/JSP developpers using Tomcat who want to take advantage of distributed transactions when using JDBC code in their servlets
This howto was written based on the JNDI Datasource HOW-TO provided by Tomcat.
It has been written for:
It has been successfully reported to work on
JOTM (Java Open Transaction Manager) is a transaction manager written in Java and implementating JTA (Java Transaction API). It is an Open Source project released under LGPL.
Tomcat is the servlet container that is used in the official Reference Implementation for the Java Servlet and JavaServer Pages (JSP) technologies. Tomcat is released under the Apache Software License
Ensure that you follow these instructions as variations can cause problems.
Create a new test user, a new database and a single test table. Your MySQL user must have a password assigned. The driver will fail if you try to connect with an empty password.
mysql> GRANT ALL PRIVILEGES ON *.* TO mojo@localhost -> IDENTIFIED BY 'jojo' WITH GRANT OPTION; mysql> create database javatest; mysql> use javatest; mysql> create table testdata ( -> id int not null auto_increment primary key, -> foo int)type=InnoDB; mysql>
Note: the above user should be removed once testing is complete!
Next insert some test data into the testdata table.
mysql> insert into testdata values(null, 1); Query OK, 1 row affected (0.00 sec) mysql> select * from testdata; +----+-----+ | ID | FOO | +----+-----+ | 1 | 1 | +----+-----+ 1 row in set (0.00 sec) mysql>
PostgreSQL configuration is similar.
In order for a web application to use JOTM, the webapp and Tomcat need to have access to the JOTM jars, as well as the jars it requires
Here is a list of the required jars. They are all included with JOTM 1.4 binary distribution, available at http://www.objectweb.org/jotm
lib/
directory
jotm.jar
jotm_jrmp_stubs.jar
jonas_timer.jar
carol.jar
jta-spec1_0_1.jar
jts1_0.jar
objectweb-datasource.jar
xapool.jar
All these jar files need to be placed on
$TOMCAT_HOME/common/lib/
so that both Tomcat and
your web application will see them.
You also need to copy the jar of your JDBC driver to
$TOMCAT_HOME/common/lib/
.
You'll need to create a file named
carol.properties
with the following properties:
# lmi stands for Local Method Invocation (it's a "fake" RMI) carol.protocols=lmi # do not use CAROL JNDI wrapper carol.start.jndi=false # do not start a name server carol.start.ns=false
this file needs to be placed on
$TOMCAT_HOME/common/classes/
so that Tomcat and
JOTM will see it.
Now that you've installed JOTM in Tomcat, you need to configure
Tomcat so that it can access JDBC and transaction resources.
This is done in the dbtest.xml
file which will be
used by Tomcat to initialize the resources used by your web application.
<Context path="/dbtest" docBase="dbtest.war" debug="0" reloadable="true" crossContext="true"> <!-- Resource configuration for JDBC datasource use XAPool --> <Resource name="jdbc/myDB" auth="Container" type="javax.sql.DataSource"/> <ResourceParams name="jdbc/myDB"> <parameter> <name>factory</name> <value>org.objectweb.jndi.DataSourceFactory</value> </parameter> <!-- configured by default for PostgreSQL, just change the values to set it for your database --> <parameter><name>username</name><value>mojo</value></parameter> <parameter><name>password</name><value>jojo</value></parameter> <parameter><name>driverClassName</name> <value>org.postgresql.Driver</value></parameter> <parameter><name>url</name> <value>jdbc:postgresql://localhost/javatest</value></parameter> <!-- <parameter><name>driverClassName</name> <value>org.gjt.mm.mysql.Driver</value></parameter> <parameter><name>url</name> <value>jdbc:mysql://localhost/javatest</value></parameter> --> </ResourceParams> <!-- Resource configuration for UserTransaction use JOTM --> <Resource name="UserTransaction" auth="Container" type="javax.transaction.UserTransaction"/> <ResourceParams name="UserTransaction"> <parameter> <name>factory</name> <value>org.objectweb.jotm.UserTransactionFactory</value> </parameter> <parameter> <name>jotm.timeout</name> <value>60</value> </parameter> </ResourceParams> </Context>
web.xml
configurationNow you have to configure the web.xml
file of your
web application
<?xml version="1.0" encoding="ISO-8859-1"?> <!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN" "http://java.sun.com/dtd/web-app_2_3.dtd"> <web-app> <resource-env-ref> <description> DB Connection </description> <resource-env-ref-name> jdbc/myDB </resource-env-ref-name> <resource-env-ref-type> javax.sql.DataSource </resource-env-ref-type> </resource-env-ref> </web-app>
Now create a simple test.jsp
for use later.
<html> <head> <title>DB Test</title> </head> <body> <% String completion = request.getParameter("completion"); foo.DBTest test = new foo.DBTest(); test.init(completion); %> <h2>Transaction completion</h2> Transaction completion is :<strong><%= completion %></strong> <h2>Results</h2> Int stored in JDBC : <strong><%= test.getFoo() %></strong><br /> <hr /> <form action="test.jsp" method="get"> <input type="radio" name="completion" value="commit" checked="true"> Commit<BR> <input type="radio" name="completion" value="rollback">Rollback<BR> <button type="submit">Completion</button> </form> </body> </html>
And create a Java class to actually use your new Datasource and transactions. Note: this code isn't anywhere near production ready - it's only supposed to be used as a simple test :-)
package foo; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.Statement; import javax.naming.Context; import javax.naming.InitialContext; import javax.sql.DataSource; import javax.transaction.UserTransaction; public class DBTest{ int foo = -1; // value stored in DB public void init(String completion) { try{ Context ctx = new InitialContext(); // JDBC stuff DataSource ds = (DataSource)ctx.lookup("java:comp/env/jdbc/myDB"); UserTransaction ut = (UserTransaction)ctx.lookup("java:comp/UserTransaction"); java.sql.Connection conn = ds.getConnection(); System.out.println("<<< beginning the transaction >>>"); ut.begin(); // JDBC statements Statement stmt = conn.createStatement(); ResultSet rst = stmt.executeQuery("select id, foo from testdata"); if(rst.next()) { foo=rst.getInt(2); } System.out.println("foo = "+ foo +" (before completion)"); PreparedStatement pstmt = conn.prepareStatement("update testdata set foo=? where id=1"); pstmt.setInt(1,++foo); pstmt.executeUpdate(); if (completion != null && completion.equals("commit")) { System.out.println("<<< committing the transaction >>>"); ut.commit(); } else { System.out.println("<<< rolling back the transaction >>>"); ut.rollback(); } // we set foo to the value stored in the DB rst = stmt.executeQuery("select id, foo from testdata"); if(rst.next()) { foo=rst.getInt(2); } System.out.println("foo = "+ foo +" (after completion)"); conn.close(); System.out.println("<<< done >>>"); }catch(Exception e) { System.out.print("DBTest >> "); e.printStackTrace(); } } public String getFoo() { return ""+foo; } }
Finally deploy your web app into
$CATALINA_HOME/webapps
as a warfile called
dbtest.war
.
Once deployed, point a browser at
http://localhost:8080/dbtest/test.jsp
to view the
fruits of your hard work.