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Asked: 2026-05-25T10:52:05+00:00

I design a DAO class this way : public void Class(Class object){ EntityManagerFactory entityManagerFactory

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I design a DAO class this way :

public void Class(Class object){

    EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory("persistUnit");
    EntityManager entityManager = entityManagerFactory.createEntityManager();

    entityManager.getTransaction().begin();
    entityManager.persist(object);
    entityManager.getTransaction().commit();

    entityManagerFactory.close();
    entityManager.close();

}

There’s my persistence.xml file:

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0" xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
    <persistence-unit name="persistUnit" transaction-type="RESOURCE_LOCAL">
        //.. classes
        <properties>
            <property name="eclipselink.jdbc.batch-writing" value="JDBC"/>
            <property name="javax.persistence.jdbc.url" value="jdbc:mysql://<hostname>:3306/<schema>"/>
            <property name="javax.persistence.jdbc.user" value="<username>"/>
            <property name="javax.persistence.jdbc.password" value="<password>"/>
            <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>
        </properties>
    </persistence-unit>
</persistence>

There’s some another way to do this kind of operation ? I mean, more sophisticated ?

I’m using Eclipse Indigo and JPA with EclipseLink 2.3.

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1 Answer

  1. Editorial Team

    Well, if the question is how to design a DAO you can find plenty of documentation in difference places like in the Java EE Pattern Catalog.

    Now, I do not think I get your code. Do you really have a method named “Class”? (I do not think that is possible given that “Class” is a reserved word, is it not?)

    Anyway, assuming the name was correct and possible, if that method is part of the public interface of your DAO then you might consider a redesign based on the following ideas:

    You do not initialize the Entity Manager Factory over and over again in method to do just a transaction. This task is quite expensive (in computational terms meaning that it consumes a lot of time and resources). Therefore, you typically initialize your factory once in the lifetime of your application, and use it to create as many entity managers as your application requires.

    An Entity Manager is handled differently depending on the type of application that you are building. For instance Java EE applications can take advantage of container-managed transactions and application context sharing. Assuming your code is that of a JSE application, you do one of two things: a) you can create a single entity manager and share it with all your DAOs, or you can create an entity manager per user-conversation (most typically by transaction) and find a way to inject into your DAOs.

    You might like to take a look at Google Juice, they have a neat way of injecting Entity Manager and transactional support to POJOs using their inversion of control framework.

    You might want to check this other answer on how JPA Entity Manager Contexts works
    Does EntityManager's find() method create new instance of JPA class?

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