java JPA - createEntityManagerFactory 返回 Null
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JPA - createEntityManagerFactory returns Null
提问by Gaston
Noob question here. I'm following this example/tutorialto try and isolate a problem I keep getting on my main project. Problem is, the entityManagerFactory keeps returning null (thus, I get a NullPointerExcept when trying to run the first JUnit test.)
菜鸟问题在这里。我正在按照此示例/教程尝试隔离我在主要项目中不断遇到的问题。问题是，entityManagerFactory 不断返回 null（因此，我在尝试运行第一个 JUnit 测试时得到 NullPointerExcept。）
I'm currently on Eclipse Indigo (JavaEE) - JRE7 - Hibernate 3.6.7 and JBoss 7
我目前使用 Eclipse Indigo (JavaEE) - JRE7 - Hibernate 3.6.7 和 JBoss 7
And here's my persistence.xml (again, a copipasta taken right from the tutorial)
这是我的persistence.xml（同样，从教程中获取的copipasta）
<persistence>
<persistence-unit name="examplePersistenceUnit"
transaction-type="RESOURCE_LOCAL">
<properties>
<property name="hibernate.show_sql" value="false" />
<property name="hibernate.format_sql" value="false" />
<property name="hibernate.connection.driver_class"
value="org.hsqldb.jdbcDriver" />
<property name="hibernate.connection.url"
value="jdbc:hsqldb:mem:mem:aname" />
<property name="hibernate.connection.username" value="sa" />
<property name="hibernate.dialect"
value="org.hibernate.dialect.HSQLDialect" />
<property name="hibernate.hbm2ddl.auto" value="create" />
</properties>
</persistence-unit>
</persistence>
Things I've already tried/found out so far:
到目前为止我已经尝试/发现的事情：
Seems this problem tends to occurif you try to create a factory with a persistence unit that is not listed in the persistence.xml
Double-checked that the necessary JARs are included in Eclipse's Build Path Libraries, which Google suggested may be a possible cause for a createEntityManagerFactory() call to short-circuit and return null (instead of just throwing an exception or logging a message)
Might be due to a possible error whilst configuringHibernate connection?
如果您尝试使用未在persistence.xml 中列出的持久性单元创建工厂，似乎会出现此问题
仔细检查必要的 JAR 是否包含在 Eclipse 的构建路径库中，谷歌建议这可能是 createEntityManagerFactory() 调用短路并返回 null（而不是仅仅抛出异常或记录消息）的可能原因
可能是由于配置Hibernate 连接时可能出现的错误？
I've been hitting this wall for the past couple of weeks, so it goes without saying that any help/general direction tips are MUCH appreciated :D
过去几周我一直在碰壁，所以不用说，非常感谢任何帮助/一般方向提示：D
采纳答案by André
Gaston, I have some suggestions/questions for you:
加斯顿，我有一些建议/问题要问你：
1 - Is this the code you're trying to execute?
1 - 这是您要执行的代码吗？
package entity;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import org.apache.log4j.BasicConfigurator;
import org.apache.log4j.Level;
import org.apache.log4j.Logger;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
public class PersonTest {
private EntityManagerFactory emf;
private EntityManager em;
@Before
public void initEmfAndEm() {
BasicConfigurator.configure();
Logger.getLogger("org").setLevel(Level.ERROR);
emf = Persistence.createEntityManagerFactory("examplePersistenceUnit");
em = emf.createEntityManager();
}
@After
public void cleanup() {
em.close();
}
@Test
public void emptyTest() {
}
}
If it is, try to comment this line: "Logger.getLogger("org").setLevel(Level.ERROR);". Or change it to "Logger.getLogger("org").setLevel(Level.ALL);". Then you should see the errors on the output console.
如果是，请尝试注释此行：“Logger.getLogger("org").setLevel(Level.ERROR);”。或者将其更改为“Logger.getLogger("org").setLevel(Level.ALL);”。然后您应该会在输出控制台上看到错误。
2 - In your persistence.xml I see you're using hsqldb database. Did you installed/configured it properly?
2 - 在您的 persistence.xml 中，我看到您正在使用 hsqldb 数据库。您是否正确安装/配置了它？
If you dont't know this database, I suggest you use MySQL, PostgreSQL, or some database you are familiar with.
如果你不了解这个数据库，我建议你使用 MySQL、PostgreSQL 或一些你熟悉的数据库。
3 - Check you persistence.xml. Mine is a little bite different:
3 - 检查你的persistence.xml。我的有点不同：
<?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="App1PU" transaction-type="RESOURCE_LOCAL">
<provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
<class>com.entities.User</class>
<class>com.entities.Group</class>
<properties>
<property name="javax.persistence.jdbc.url" value="jdbc:mysql://myIP:3306/mydatabase"/>
<property name="javax.persistence.jdbc.password" value="secret"/>
<property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>
<property name="javax.persistence.jdbc.user" value="myUser"/>
</properties>
</persistence-unit>
</persistence>
Notice the header has some XML declarations that might be important, since Hibernate is telling you that your file is incorrect.
请注意，标题有一些可能很重要的 XML 声明，因为 Hibernate 告诉您您的文件不正确。
