java - 是否需要文件 persistence.xml？

Question

我的开发环境 (IBM RAD 8 + WAS 8) 提示我的项目没有 persistence.xml 文件。看起来我仍然可以构建和运行我的项目。该文件是必需的吗？如果添加一个这样的文件以使我的项目通过验证，该文件中应该包含什么？

该项目是一个 Web 项目，它使用来自其他项目的 session bean 和实体 bean，并且这个 persistence.xml 错误是该项目中唯一的错误，所以我很乐意摆脱它。

感谢您的帮助

更新

我在我的文件中搜索了 persistence.xml，它出现在 EJB 项目的 src/和 bin/中，而带有 servlet 和 jsp 的 web 项目没有 persistence.xml，据我的同事说 web 项目正在使用来自 EJB 项目的 persistence.xml 即:

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="1.0" 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_1_0.xsd">

    <persistence-unit name="PandoraArendeWeb" transaction-type="JTA">

        <jta-data-source>jdbc/Mainframe_TEST_ADBUTV2</jta-data-source>
        <class>se.prv.pandora.arendeprocess.entity.PRVNummer</class>
        <class>se.prv.pandora.arendeprocess.entity.Ansokan</class>
        <class>se.prv.pandora.arendeprocess.entity.NatAnsokan</class>
        <class>se.prv.pandora.arendeprocess.entity.PctAnsokan</class>
        <class>se.prv.pandora.arendeprocess.entity.ArendePerson</class>
        <class>se.prv.pandora.arendeprocess.entity.Nyregistrering</class>
        <class>se.prv.pandora.arendeprocess.entity.Anstalld</class>
        <class>se.prv.pandora.arendeprocess.entity.Handlaggare</class>
        <class>se.prv.pandora.arendeprocess.entity.OrgElement</class>
        <class>se.prv.pandora.arendeprocess.entity.FysiskHandlaggare</class>
        <class>se.prv.pandora.arendeprocess.entity.AnsvarigHandlaggare</class>
        <class>se.prv.pandora.arendeprocess.entity.AnsvarigFysiskHandlaggare</class>
        <class>se.prv.pandora.arendeprocess.entity.TeknikOmrade</class>
        <class>se.prv.pandora.arendeprocess.entity.Person</class>
        <class>se.prv.pandora.arendeprocess.entity.PRVNummerPerson</class>
        <class>se.prv.pandora.arendeprocess.entity.Notering</class>
        <class>se.prv.pandora.arendeprocess.entity.Lock</class>
        <class>se.prv.pandora.arendeprocess.entity.LandKod</class>
        <class>se.prv.pandora.arendeprocess.entity.ArbetsMomentLog</class>
        <class>se.prv.pandora.arendeprocess.entity.SystemTypDel</class>
        <class>se.prv.pandora.arendeprocess.entity.ArbetsMoment</class>
        <class>se.prv.pandora.arendeprocess.entity.UnderStatus</class>
        <class>se.prv.pandora.arendeprocess.entity.PatPers</class>
        <class>se.prv.pandora.arendeprocess.entity.PrvLandP</class>
        <class>se.prv.pandora.arendeprocess.entity.PkaPerln</class>
        <class>se.prv.pandora.arendeprocess.entity.PctnPerl</class>
        <class>se.prv.pandora.arendeprocess.entity.PersonToPatPersKoppl</class>
        <class>se.prv.pandora.arendeprocess.entity.PRVNummerPersonKoppl</class>
        <class>se.prv.pandora.arendeprocess.entity.Region</class>
        <class>se.prv.pandora.arendeprocess.entity.Historik</class>
        <class>se.prv.pandora.arendeprocess.entity.Egenskap</class>
        <exclude-unlisted-classes>true</exclude-unlisted-classes>

    </persistence-unit>

<!-- <persistence-unit name="PandoraArendeWeb_MSSQL" transaction-type="JTA">

        <jta-data-source>jdbc/MSSQL_TEST_XA</jta-data-source>
        <class>se.prv.pandora.arendeprocess.entity.PersonSearch</class>
        <exclude-unlisted-classes>true</exclude-unlisted-classes>

    </persistence-unit>
 -->    
</persistence>

Answer 1

persistence.xml 文件通常包含与您的数据库相关的详细信息，例如连接字符串及其各自的用户名和密码，包括其他 ORM 相关信息。这些详细信息可以放在其他位置，因此您无需明确拥有一个，尽管拥有这样的文件通常会使所有与持久性相关的信息在一个地方可用，从而使查找某些设置和配置更加容易。

这是一个示例 persistence.xml 文件:

<?xml version="1.0" encoding="UTF-8"?>
<persistence 
    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_1_0.xsd"
    version="1.0">
    <persistence-unit name="<PERSISTENCE UNIT NAME>">
        <properties>
            <!--
            <property name="hibernate.ejb.cfgfile" value="/hibernate.cfg.xml"/>
            <property name="hibernate.hbm2ddl.auto" value="create"/>
            -->
            <property name="hibernate.archive.autodetection" value="class, hbm"/>
            <property name="hibernate.show_sql" value="true"/>
            <property name="hibernate.connection.driver_class" value="com.mysql.jdbc.Driver"/>
            <property name="hibernate.connection.password" value="<PASSWORD>"/>
            <property name="hibernate.connection.url" value="jdbc:mysql://<HOST IP ADDRESS>/<DB NAME>"/>
            <property name="hibernate.connection.username" value="<USERNAME>"/>
            <property name="hibernate.dialect" value="org.hibernate.dialect.MySQLDialect"/>
            <property name="hibernate.c3p0.min_size" value="5"/>
            <property name="hibernate.c3p0.max_size" value="20"/>
            <property name="hibernate.c3p0.timeout" value="300"/>
            <property name="hibernate.c3p0.max_statements" value="50"/>
            <property name="hibernate.c3p0.idle_test_period" value="3000"/>
        </properties>
    </persistence-unit>
</persistence>

以上内容摘自here .