How to use a datasource in a realm in a tomcat environment.

When coding your own realm for the tomcat webapplication-sever its sometimes very helpful to use a dataosurce. This is a very easy task to do. Just define the datasource in the serverl.xml within the GlobalNamingResource-tag like this

(example for a Oracle-DB, for more Information on configuring dataosurces refer to the tomcat manual)

<GlobalNamingResources>
...
 <Resource name="jdbc/datasource" auth="Container"
    type="javax.sql.DataSource"
    factory="org.apache.commons.dbcp.BasicDataSourceFactory"
    driverClassName="oracle.jdbc.driver.OracleDriver"
    url="jdbc:oracle:thin:@localhost:1521:xe"
    username="username" password="password" maxActive="20" maxIdle="10"
    maxWait="-1" />
...
</GlobalNamingResources>

and within your realm implemantation you make a lookup for the datasoruce like this

public class MyOwnRealm extends RealmBase
private Datasource datasoruce;
...
    public void start()  throws LifecycleException {
        super.start();
        StandardServer server = (StandardServer) ServerFactory.getServer();
        Context context = server.getGlobalNamingContext();
        try {
            dataSource = (DataSource)context.lookup("jdbc/datasource");
        } catch (NamingException e) {
           ....
        }
    }
...
    public Principal authenticate(String userId, String password) {
       // do something with the datasource
    }
}

voilà, this is as easy as been shown above.

But, in my last project i used Ibatis (very useful stuff, by the way) as persistencelayer and was unsuccessful to get access from the ibatis TransactionManager to the datasource configured in the server.xml.

Any configuration I tried was useless.

The solution at last was implementing an own com.ibatis.sqlmap.engine.datasource.DataSourceFactory and refer to it in the TransActionManager definition.

Codesnippet for JndiDataSourceFactory

public class JndiDataSourceFactory implements DataSourceFactory {
    private static DataSource dataSource;
    public void initialize(Map map) {
        StandardServer server = (StandardServer) ServerFactory.getServer();
        Context context = server.getGlobalNamingContext();
        try {
            dataSource = (DataSource)context.lookup((String)map.get("DataSource"));
        } catch (NamingException e) {
            e.printStackTrace();
        }
    }
    public DataSource getDataSource() {
        return dataSource;
    }
}

Codesnippet for TransactionManager configuration

<typeAlias alias="global" type="de.rscheuch.realm.JndiDataSourceFactory" />
<transactionManager type="JDBC" commitRequired="false">
    <dataSource type="global">
<property name="DataSource" value="jdbc/datasource"
    </dataSource>
</transactionManager>

deploy the realm, restart the server… bingo! It works!

At least it was tested on a Tomcat 5.5