Where not to put presistance.xml

Where to put persistence.xml in web app? In all cases, persistence.xml always resides in {root-of-persistence-unit}/META-INF/ directory. For example,

foo.war: WEB-INF/classes/META-INF/persistence.xml //good WEB-INF/classes/com/foo123/jpa/Project.class WEB-INF/web.xml index.jsp You may also package entity classes and persistence.xml inside a library jar, which is packaged inside the war: WEB-INF/lib foo.war: WEB-INF/lib/my-entities.jar WEB-INF/web.xml index.jsp my-entities.jar: META-INF/persistence.xml //good com/foo123/jpa/Project.class For comparison, some invalid configurations are: foo.war: WEB-INF/persistence.xml //invalid WEB-INF/web.xml WEB-INF/classes/com/foo123/jpa/Project. index.jsp ----------------------------------------------- foo.war: META-INF/persistence.xml //invalid WEB-INF/classes/com/foo123/jpa/Project.class WEB-INF/web.xml index.jsp ----------------------------------------------- foo.war: persistence.xml //invalid WEB-INF/classes/com/foo123/jpa/Project.class WEB-INF/web.xml index.jsp ----------------------------------------------- foo.war: META-INF/persistence.xml //invalid com/foo123/jpa/Project.class WEB-INF/web.xml index.jsp

In all these invalid configurations, EntityManager lookup will fail with javax.naming.NameNotFoundException, or @PersistenceContext injection will be silently skipped and the em variable is always null, and hence NullPointerException when referenced.