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.

Tags: jpa, persistence.xml, webapp, PersistenceContext