jpa和struts项目中持久性提供程序的问题

Question

我正在开发一个java ee应用程序，使用jpa来控制mysql db和Struts。不幸的是，当我在tomcat服务器上运行该项目时，我得到了这个错误。

javax.persistence.PersistenceException: No Persistence provider for EntityManager named prova
    javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:56)
    javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:34)
    test.testing.initEntityManager(testing.java:37)
    test.testing.add(testing.java:16)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    java.lang.reflect.Method.invoke(Unknown Source)
    com.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:440)
    com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:279)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:242)
    com.googlecode.s2hibernate.struts2.plugin.s2hibernatevalidator.interceptor.HibernateValidatorInterceptor.intercept(HibernateValidatorInterceptor.java:38)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:163)
    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:122)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:195)
    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:148)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    org.apache.struts2.interceptor.CheckboxInterceptor.intercept(CheckboxInterceptor.java:93)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    org.apache.struts2.interceptor.FileUploadInterceptor.intercept(FileUploadInterceptor.java:235)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor.intercept(ModelDrivenInterceptor.java:89)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept(ScopedModelDrivenInterceptor.java:128)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    org.apache.struts2.interceptor.ProfilingActivationInterceptor.intercept(ProfilingActivationInterceptor.java:104)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    org.apache.struts2.interceptor.debugging.DebuggingInterceptor.intercept(DebuggingInterceptor.java:267)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.interceptor.ChainingInterceptor.intercept(ChainingInterceptor.java:126)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept(I18nInterceptor.java:148)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept(PrepareInterceptor.java:138)
    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    org.apache.struts2.interceptor.ServletConfigInterceptor.intercept(ServletConfigInterceptor.java:164)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept(AliasInterceptor.java:128)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:176)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:52)
    org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:468)
    org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:77)
    org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:76)

我已经在网上搜索了一个解决方案，但没有解决我的问题。以下是文件：

src/test/libro.java

src/meta-inf/persistence.xml

src/struts.xml

webContent/web-inf/web.xml

感谢您的帮助：）

Answer 1

从屏幕截图Lib我们可以看到，您有一个非常“混合”的库组合。问题就在这里！您不能混合JPA的不同API级别。您将非常旧/早期版本的1.x版本与JPA2.2的最新变体混合使用。

您将persistence-api-1.0.2.jar和javax.persistence-api-2.2.jar放入项目的web-inf中的lib目录中。这会在运行时引起冲突。

因此：

• 从文件夹中删除过时的persistence-api-1.0.2.jar并检查这是否解决了观察到的异常。如果出现其他异常，则在运行时与您的安装程序有更多的不一致。

您错误地使用了createPlaces()方法中的testing类中的事务处理概念。您的代码是：

em.persist();
em.getTransaction().begin();
em.getTransaction().commit();

这会将persist()调用放在该行之后打开的受控事务之外。您应该更好地将这些行重新表述为下面，而不是像上面那样坚持。代码段在事务边界内移动persist操作：

EntityTransaction tx = null;
try {
    tx = em.getTransaction();
    tx.begin();
    // Only within a tx to prevent inconsistent states in the DB if sth fails here!
    em.persist(); 
    tx.commit();
} catch(RuntimeException) {
    if(if(tx != null && tx.isActive()) {
        tx.rollback();
    }   
}

要了解更多细节，请查看我曾经写过的关于事务处理的另一个答案。它参考了JPA2.2，并进一步深入讨论了这个主题。

希望有帮助。