In case JBoss AS 7 gives you  an exception like this...

Caused by: org.jboss.as.server.deployment.DeploymentUnitProcessingException: Unexpected character '=' (code 61); expected a semi-colon after the reference for entity 'characterSetResults'
 at [row,col {unknown-source}]: [9,106]
        at org.jboss.as.connector.deployers.ds.processors.DsXmlDeploymentParsingProcessor.deploy(DsXmlDeploymentParsingProcessor.java:89)
        at org.jboss.as.server.deployment.DeploymentUnitPhaseService.start(DeploymentUnitPhaseService.java:116) [jboss-as-server-7.1.2.Final.jar:7.1.2.Final]
        ... 5 more

...you forgot to escape JDBC URL in your datasource definition.

Replace & with &  (as & is a start of XML entity) and that should fix it.