我正在修改Jersey Webservice，它访问集成到Glassfish4 Application Server中的默认JavaDB。我们的想法是在服务器上的应用程序运行时创建新对象，并使用Java Persistence API（JPA）访问它们，即使服务器已关闭或应用程序正从服务器中删除。
第一个问题是，如果这是一个可行的选择吗？
第二个问题是关于注入EntityManagerFactory时遇到的一些问题，所以我可以在处理HTTP请求时访问它。
我的简单测试用例如下：
@Path("jpaResource/")
public class JpaResource {
@PersistenceUnit
private EntityManagerFactory emf;
@GET
@Path("html")
@Produces(MediaType.TEXT_HTML)
public String getHtml() {
EntityManagerFactory factory = Persistence.createEntityManagerFactory("WebApp"); System.out.println(aThing); }
Thing thing = (Thing) factory.createEntityManager().createQuery("select u from Thing u").getResultList().get(1);
return "<h1>Hey HTML! I'm: " + thing.getDescription() + "</h1>";
}
@GET
@Path("text")
@Produces(MediaType.TEXT_PLAIN)
public String getText() {
Thing thing = (Thing) emf.createEntityManager().createQuery("select u from Thing u").getResultList().get(0);
return "Hey text! I'm: " + thing.getDescription();
}
}
第一个GET方法运行正常。但是第二个不是因为EntityManagerFactory emf是NULL。
Thing对象是一个简单的POJO，看起来像：
@Entity
@NamedQuery(name="Thing.findAll", query="SELECT t FROM Thing t")
public class Thing {
@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private long id;
private String description;
private String summary;
public Thing() {
}
public long getId() {
return this.id;
}
public void setId(long id) {
this.id = id;
}
public String getDescription() {
return this.description;
}
public void setDescription(String description) {
this.description = description;
}
public String getSummary() {
return this.summary;
}
public void setSummary(String summary) {
this.summary = summary;
}
}
persistence.xml文件存储在我的eclipse项目的... / src / main / resources / META-INF文件夹中，如下所示：
<?xml version="1.0" encoding="UTF-8" ?>
<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"
version="2.0" xmlns="http://java.sun.com/xml/ns/persistence">
<persistence-unit name="WebApp" transaction-type="RESOURCE_LOCAL">
<!--provider>org.eclipse.persistence.jpa.PersistenceProvider</provider-->
<!--provider>org.hibernate.ejb.HibernatePersistence</provider-->
<jta-data-source>jdbc/__default</jta-data-source>
<class>com.test.webapp.objects.Thing</class>
<properties>
<property name="eclipselink.ddl-generation" value="create-tables"/>
<property name="eclipselink.ddl-generation.output-mode" value="database"/>
</properties>
</persistence-unit>
</persistence>
stacktrace看起来像这样：
StandardWrapperValve[Jersey Web Application]: Servlet.service() for servlet Jersey Web Application threw exception
java.lang.NullPointerException
at com.test.webapp.resources.JpaResource.getText(JpaResource.java:66)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.glassfish.jersey.server.model.internal.ResourceMethodInvocationHandlerFactory$1.invoke(ResourceMethodInvocationHandlerFactory.java:81)
at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.invoke(AbstractJavaResourceMethodDispatcher.java:125)
at org.glassfish.jersey.server.model.internal.JavaResourceMethodDispatcherProvider$TypeOutInvoker.doDispatch(JavaResourceMethodDispatcherProvider.java:195)
at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.dispatch(AbstractJavaResourceMethodDispatcher.java:91)
at org.glassfish.jersey.server.model.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:346)
at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:341)
at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:101)
at org.glassfish.jersey.server.ServerRuntime$1.run(ServerRuntime.java:224)
at org.glassfish.jersey.internal.Errors$1.call(Errors.java:271)
at org.glassfish.jersey.internal.Errors$1.call(Errors.java:267)
at org.glassfish.jersey.internal.Errors.process(Errors.java:315)
at org.glassfish.jersey.internal.Errors.process(Errors.java:297)
at org.glassfish.jersey.internal.Errors.process(Errors.java:267)
at org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:317)
at org.glassfish.jersey.server.ServerRuntime.process(ServerRuntime.java:198)
at org.glassfish.jersey.server.ApplicationHandler.handle(ApplicationHandler.java:946)
at org.glassfish.jersey.servlet.WebComponent.service(WebComponent.java:323)
at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:372)
at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:335)
at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:218)
at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1682)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:318)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:160)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:734)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:673)
at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:99)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:174)
at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:357)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:260)
at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:188)
at org.glassfish.grizzly.http.server.HttpHandler.runService(HttpHandler.java:191)
at org.glassfish.grizzly.http.server.HttpHandler.doHandle(HttpHandler.java:168)
at org.glassfish.grizzly.http.server.HttpServerFilter.handleRead(HttpServerFilter.java:189)
at org.glassfish.grizzly.filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:119)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:288)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:206)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:136)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:114)
at org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:77)
at org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:838)
at org.glassfish.grizzly.strategies.AbstractIOStrategy.fireIOEvent(AbstractIOStrategy.java:113)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:115)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:55)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:135)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:564)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:544)
at java.lang.Thread.run(Thread.java:744)
如果有人知道我做错了什么，请告诉我。
问候
[edit：]好的我做了一些测试，我在项目中有一个ServletContextListener接口的实现，它在第一次启动应用程序时处理初始化。
public class ServletContextClass implements ServletContextListener {
@PersistenceUnit(unitName="WebApp")
private EntityManagerFactory emf;
@Override
public void contextInitialized(ServletContextEvent servletContextEvent) {
System.out.println("##############################");
System.out.println("ServletContextListener started");
System.out.println("##############################");
}
@Override
public void contextDestroyed(ServletContextEvent servletContextEvent) {
System.out.println("###############################");
System.out.println("SevletContextListener destroyed");
System.out.println("###############################");
}
}
在这个类中，注入工作没有任何问题，我可以访问JavaDB来检索对象。
我看过的教程使用的是Glassfish3服务器。是否有可能从Java EE7中删除此功能，因此无法在Glassfish4服务器上运行？我发现了一个类似的问题，表明我的方法应该适用于Java EE 6（PersistenceContext EntityManager injection NullPointerException）。现在我真的很困惑。
我将添加我的web.xml，以便有人有兴趣回答我的问题并需要部署描述符。
<?xml version="1.0" encoding="UTF-8"?>
<!-- This web.xml file is not required when using Servlet 3.0 container,
see implementation details http://jersey.java.net/nonav/documentation/latest/jax-rs.html -->
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
<listener>
<listener-class>com.test.webapp.startup.ServletContextClass</listener-class>
</listener>
<servlet>
<servlet-name>Jersey Web Application</servlet-name>
<servlet-class>org.glassfish.jersey.servlet.ServletContainer</servlet-class>
<init-param>
<param-name>jersey.config.server.provider.packages</param-name>
<param-value>com.test.webapp.resources</param-value>
</init-param>
<init-param>
<param-name>com.sun.jersey.api.json.POJOMappingFeature</param-name>
<param-value>true</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>Jersey Web Application</servlet-name>
<url-pattern>/*</url-pattern>
</servlet-mapping>
</web-app>