Servlets GAE+;JPA:java.lang.NoClassDefFoundError:无法初始化类EMF
当我尝试通过JPA连接我的云SQL时,生成了以下错误:Servlets GAE+;JPA:java.lang.NoClassDefFoundError:无法初始化类EMF,servlets,jpa,eclipselink,google-cloud-sql,Servlets,Jpa,Eclipselink,Google Cloud Sql,当我尝试通过JPA连接我的云SQL时,生成了以下错误: 2012-10-25 10:07:38.439 Error for /jpatest java.lang.NoClassDefFoundError: Could not initialize class com.my.jpa.EMF at com.my.jpa.ContactService.createContact(ContactService.java:20) at com.my.jpa.JPATestServlet.d
2012-10-25 10:07:38.439
Error for /jpatest
java.lang.NoClassDefFoundError: Could not initialize class com.my.jpa.EMF
at com.my.jpa.ContactService.createContact(ContactService.java:20)
at com.my.jpa.JPATestServlet.doGet(JPATestServlet.java:14)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
2012-10-25 10:07:38.440
Uncaught exception from servlet
java.lang.NoClassDefFoundError: Could not initialize class com.my.jpa.EMF
at com.my.jpa.ContactService.createContact(ContactService.java:20)
at com.my.jpa.JPATestServlet.doGet(JPATestServlet.java:14)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
我的EMF课是
public final class EMF {
private static final EntityManagerFactory emfInstance = Persistence
.createEntityManagerFactory("JPATest");
private EMF() {
}
public static EntityManagerFactory get() {
return emfInstance;
}
}
EMF初始化部分为
public class ContactService {
private static Logger logger = Logger.getLogger(ContactService.class
.getName());
public void createContact(Contact c) {
logger.info("Entering createContact: [" + c.getFirstName() + ","
+ c.getLastName() + "]");
EntityManager mgr = EMF.get().createEntityManager();
try {
mgr.getTransaction().begin();
mgr.persist(c);
mgr.getTransaction().commit();
} finally {
mgr.close();
}
logger.info("Exiting createContact");
}
}
我的Servlet是:
public class JPATestServlet extends HttpServlet {
public void doGet(HttpServletRequest req, HttpServletResponse resp)
throws IOException {
ContactService service = new ContactService();
service.createContact(new Contact("Manu", "Mohan", "686019", "TVM"));
resp.setContentType("text/plain");
resp.getWriter().println("Hello, world");
}
}
xml是
<?xml version="1.0" encoding="utf-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" version="2.5">
<servlet>
<servlet-name>JPATest</servlet-name>
<servlet-class>com.my.jpa.JPATestServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>JPATest</servlet-name>
<url-pattern>/jpatest</url-pattern>
</servlet-mapping>
<welcome-file-list>
<welcome-file>index.html</welcome-file>
</welcome-file-list>
</web-app>
JPATest
com.my.jpa.JPATestServlet
JPATest
/jpatest
index.html
persistence.xml
<?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="JPATest">
<provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
<class>com.my.jpa.Contact</class>
<properties>
<property name="javax.persistence.jdbc.driver" value="com.google.cloud.sql.Driver" />
<property name="javax.persistence.jdbc.url" value="jdbc:google:rdbms://instance-name/stock" />
<property name="javax.persistence.jdbc.user" value="" />
<property name="javax.persistence.jdbc.password" value="" />
<!-- EclipseLink should create the database schema automatically -->
<property name="eclipselink.ddl-generation" value="create-tables" />
<property name="eclipselink.ddl-generation.output-mode"
value="database" />
</properties>
</persistence-unit>
</persistence
org.eclipse.persistence.jpa.PersistenceProvider
com.my.jpa.Contact
您是否需要在EMF
中为EntityManagerFactory
使用final
。尝试对EMF
使用Singleton设计模式EntityManagerFactory
类是线程安全的
EMF.java
public final class EMF {
private EntityManagerFactory emfInstance;
private static EMF emf;
private EMF() {
}
public EntityManagerFactory get() {
if(emfInstance == null) {
emfInstance = Persistence.createEntityManagerFactory("JPATest");
}
return emfInstance;
}
public static EMF getInstance() {
if(emf == null) {
emf = new EMF();
}
return emf;
}
}
// usages
EntityManagerFactory emf = Emf.getInstance().get();
在web应用程序中使用EntityManagerFactory
的更好方法。您是否在web.xml中配置了EMF
?您可以发布web.xml
configuration吗?@CycDemo查看修改后的qn.。根据您昨天的问题,您还没有引用persistence.xml,而类似“找不到数据存储URL键“jdbc”的可用StoreManager”的消息意味着您还没有在persistence.xml中设置持久性“提供者”。@DataNucleus我给出了它,请看我在上面的问题中添加的内容,您的问题中仍然没有引用它。如果类路径中有多个JPA实现,那么您必须指定它,并且它将只找到合适的一个。正如我昨天所说的,您可以从类路径中删除除所需之外的所有内容,或者执行此操作。此错误已解决,然后出现另一个错误..jpatest javax.jdo.JDOFatalUserException:找不到数据存储URL键“jdbc”可用的StoreManager。请确保您在类路径中拥有所有相关的插件(例如,DATANNROCUS RDBMS,DATANNURBUS DB4O),并考虑将持久性属性“DATANONUC.StuteMaGeReType”设置为使用RDBMS、DB4O的存储类型。