我正在为教育目的构建一个简单的Spring Web应用程序，并且我在持久性级别上遇到一些问题 - 当我尝试从数据库中获取某些内容时，会抛出java.lang.IllegalStateException: EntityManager is closed。对象是持久化的，但是当我尝试进行查询时抛出异常。所以我使用Hibernate和HSQL inmemory db，这是我的persistence.xml：
<?xml version="1.0" encoding="UTF-8"?>
<persistence 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"
version="2.0">
<persistence-unit name="pp_persistence_unit" transaction-type="RESOURCE_LOCAL">
<provider>org.hibernate.ejb.HibernatePersistence</provider>
<properties>
<property name="javax.persistence.jdbc.driver" value="org.hsqldb.jdbcDriver"/>
<property name="javax.persistence.jdbc.url" value="jdbc:hsqldb:mem:testDB"/>
<property name="sqltool.charset" value="UTF-8" />
<property name="hibernate.dialect" value="org.hibernate.dialect.HSQLDialect"/>
<property name="show_sql" value="true"/>
<property name="hibernate.hbm2ddl.auto" value="create"/>
<property name="current_session_context_class" value="thread"/>
<property name="hibernate.show_sql" value="true" />
</properties>
</persistence-unit>
错误的堆栈跟踪如下：
SEVERE: Servlet.service() for servlet [dispatcher] in context with path [/web-app] threw exception [Request processing failed; nested exception is
java.lang.IllegalStateException: EntityManager is closed] with root cause
java.lang.IllegalStateException: EntityManager is closed
at org.hibernate.jpa.internal.EntityManagerImpl.checkOpen(EntityManagerImpl.java:105)
at org.hibernate.jpa.internal.QueryImpl.getSingleResult(QueryImpl.java:491)
at web.task.dao.ConnectionDao.getConnectionsCount(ConnectionDao.java:67)
at web.task.transformation.ConnectionTransformator.getPagesCount(ConnectionTransformator.java:48)
at web.task.business.ConnectionService.getPagesCount(ConnectionService.java:45)
at web.task.controllers.ConnectionController.getAllConnections(ConnectionController.java:71)
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.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:176)
at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:440)
at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:428)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:925)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:856)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:953)
at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:844)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:620)
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:829)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:501)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1040)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:607)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:315)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:744)
这里是getConnectionsCount（）方法
public int getConnectionsCount() {
Query query = entityManager.createQuery("select count(c.id) from Connection c");
return (Integer)query.getSingleResult();
}
我真的不知道是什么问题。我假设它可能来自数据库的编码，但我试图将其设置为UTF-8，但错误仍然是相同的。
很抱歉忘了，这是我的application-context.xml：
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:tx="http://www.springframework.org/schema/tx"
xmlns:mvc="http://www.springframework.org/schema/mvc"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.2.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.2.xsd
http://www.springframework.org/schema/tx
http://www.springframework.org/schema/tx/spring-tx-3.2.xsd ">
<context:component-scan base-package="web.task.business">
<context:include-filter type="annotation" expression="org.springframework.stereotype.Service" />
</context:component-scan>
<context:component-scan base-package="web.task.dao">
<context:include-filter type="annotation" expression="org.springframework.stereotype.Repository" />
</context:component-scan>
<context:component-scan base-package="web.task.transformation">
<context:include-filter type="annotation" expression="web.task.annotations.Transformation" />
</context:component-scan>
<bean id="ppEntityManagerFactory" class="org.springframework.orm.jpa.LocalEntityManagerFactoryBean">
<property name="persistenceUnitName" value="pp_persistence_unit" />
</bean>
<bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager">
<property name="entityManagerFactory" ref="ppEntityManagerFactory" />
</bean>
<tx:annotation-driven transaction-manager="transactionManager"/>
<bean class="org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessor" />