JPA中手动将EntityManager和线程绑定

package com.dimples.service;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;

public class MyJPAUtils {
	private static EntityManagerFactory factory;
	private static ThreadLocal<EntityManager> tl;
	static {
		factory = Persistence.createEntityManagerFactory("jpaUnit");
		tl = new ThreadLocal<EntityManager>();
	}
	
	public static EntityManager getEntityManager() {
		EntityManager em = tl.get();
		if(em == null) {
			em = factory.createEntityManager();
			tl.set(em);
		}
		return em;
	 	
	}
}