java.lang.ClassNotFoundException：JPA找不到javax.persistence.Persistence [英] java.lang.ClassNotFoundException: javax.persistence.Persistence cannot be found with JPA

问题描述

我正在使用JPA API。我收到错误

I'm praticing with JPA API. I got an error

java.lang.ClassNotFoundException: javax.persistence.Persistence cannot be found

我的代码如下：

EntityManagerFactory emf;
emf = Persistence.createEntityManagerFactory("mail");
EntityManager em = emf.createEntityManager();
Query query = em.createQuery("SELECT v FROM Version v");
List<Version> versions = query.getResultList();

行 emf = Persistence.createEntityManagerFactory（mail）的错误;

任何解决方案？

推荐答案

您正在尝试设置一个独立的JPA项目。为此，您需要一个JPA提供者jar。两个更受欢迎的提供商是Eclipselink和Hibernate。如果您正在使用maven，则可以向其实现添加依赖项。

You are trying to set up a standalone JPA project. In order to do so you need a JPA provider jars. The two more popular providers are Eclipselink and Hibernate. If you are using maven you can add dependencies to their implementations.

• 对于Eclipselink

• For Eclipselink

<dependency>
    <groupId>org.eclipse.persistence</groupId>
    <artifactId>eclipselink</artifactId>
    <version>2.5.1</version>
</dependency>

对于Hibernate

For Hibernate

<dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-core</artifactId>
    <version>4.3.6.Final</version>
</dependency>
<dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-entitymanager</artifactId>
    <version>4.3.6.Final</version>
</dependency>

如果您不使用maven，可以下载他们从他们的网站实现并将它放在你的类路径中。

If you are not using maven you can download their implementations from their sites and put it in your classpath.

• 对于Eclipselink： http://www.eclipse.org/eclipselink/downloads/


• 对于Hibernate： http://hibernate.org/orm/

• For Eclipselink: http://www.eclipse.org/eclipselink/downloads/
• For Hibernate: http://hibernate.org/orm/

有些JPA快速入门推荐给仅添加JPA API（仅限接口声明）依赖项与maven。

Some JPA quickstarts are recommending to add only the JPA API (interface declarations only) dependencies with maven.

    <dependency>
        <groupId>org.eclipse.persistence</groupId>
        <artifactId>javax.persistence</artifactId>
        <version>2.1.0</version>
    </dependency>

或

    <dependency>
        <groupId>org.hibernate.javax.persistence</groupId>
        <artifactId>hibernate-jpa-2.1-api</artifactId>
        <version>1.0.0.Final</version>
    </dependency>

这种方法仅在服务器环境中成功，因为服务器将在运行时提供适当的实现。

This approach will be successful only in server environment as the server will provide appropriate implementation at runtime.

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