best practise of creating entitymanager

I am using resource local entitymanager with JPA 1 . What is the best practice for creating EntityManager that is

1. Create do job close entitymanager everytime.(Entitymanager开发者_运维问答 not heavy weight but still boring )

2. Create a entitymanager for every thread and store it as ThreadLocal variable and use it (a-where should i close entitymanager b-Any entitystored in a session scoped bean will be a detached entity because entitymanager which entity in its persistense context closed or belong another thread now.)

3. Store entitymanager in a session bean and use same entitymanager during session(Sessions unawere of each others )

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You should be injecting the EntityManager using the @PersistenceContext annotation. Don't worry about where it comes from — that's dependency injection at work.

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I create EntityManagers per request and close them in a ServletRequestListener.