如何从EntityManager的find中调试/修复永久的null返回？

Question

我正在关注此示例 。每次调用find时我都会遇到此错误： java.lang.NullPointerException at LoginAction.service(LoginAction.java:41) at Dispatcher.doWork(Dispatcher.java:82) at Dispatcher.doGet(Dispatcher.java:64) at javax.servlet.http.HttpServlet.service(HttpServlet.java:734) at javax.servlet.http.HttpServlet.service(HttpServlet.java:847) at org.apache.catalina.core.ApplicationFilterChain.servletService(ApplicationFilterChain.java:427) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:315) at org.apache.catalina.core.StandardContextValve.invokeInternal(StandardContextValve.java:287) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:218) at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:648) at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:593) at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:94) at com.sun.enterprise.web.PESessionLockingStandardPipeline.invoke(PESessionLockingStandardPipeline.java:98) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:222) at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:648) at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:593) at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:587) at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:1096) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:166) at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:648) at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:593) at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:587) at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:1096) at org.apache.coyote.tomcat5.CoyoteAdapter.service(CoyoteAdapter.java:288) at com.sun.enterprise.web.connector.grizzly.DefaultProcessorTask.invokeAdapter(DefaultProcessorTask.java:647) at com.sun.enterprise.web.connector.grizzly.DefaultProcessorTask.doProcess(DefaultProcessorTask.java:579) at com.sun.enterprise.web.connector.grizzly.DefaultProcessorTask.process(DefaultProcessorTask.java:831) at com.sun.enterprise.web.connector.grizzly.DefaultReadTask.executeProcessorTask(DefaultReadTask.java:341) at com.sun.enterprise.web.connector.grizzly.DefaultReadTask.doTask(DefaultReadTask.java:263) at com.sun.enterprise.web.connector.grizzly.DefaultReadTask.doTask(DefaultReadTask.java:214) at com.sun.enterprise.web.portunif.PortUnificationPipeline$PUTask.doTask(PortUnificationPipeline.java:380) at com.sun.enterprise.web.connector.grizzly.TaskBase.run(TaskBase.java:265) at com.sun.enterprise.web.connector.grizzly.ssl.SSLWorkerThread.run(SSLWorkerThread.java:106)

我不知道从哪里开始寻找。第41行是operator.findOperator（1），其中 @EJB private OperatorBeanService operator;

我正在尝试在Glassfish 2.1上执行此操作。这是持久性：

<persistence-unit name="persistMe" transaction-type="JTA"> <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider> <jta-data-source>jdbc/peciu</jta-data-source> <properties> <property name="eclipselink.jdbc.batch-writing" value="JDBC"/> <property name="eclipselink.target-database" value="myDB"/> <property name="eclipselink.target-server" value="host"/> <property name="eclipselink.logging.level" value="ALL"/> </properties> </persistence-unit>

我已尝试使用此持久性的单独JPA项目： <persistence-unit name="OperatorService" transaction-type="RESOURCE_LOCAL"> <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider> <class>Operator</class> <properties> <property name="eclipselink.jdbc.batch-writing" value="JDBC"/> <property name="eclipselink.jdbc.driver" value="COM.ibm.db2os390.sqlj.jdbc.DB2SQLJDriver"/> <property name="eclipselink.jdbc.url" value="jdbc:db2://host:50000/myDB"/> <property name="eclipselink.jdbc.user" value="user"/> <property name="eclipselink.jdbc.password" value="pass"/> </properties> </persistence-unit> 它运行得很好，从OPERATOR表中返回结果。 我不知道我错过了什么。感谢您的时间。尤利亚

Answer 1

您需要弄清楚为什么没有注入您的OperatorBeanService（@EJB注释）。

我有点困惑，你使用glassfish跟踪WebSphere教程/示例？也许您可以尝试使用WAS来查看它是否有效？对于非答案答案感到抱歉，但我没有太多可以解决的问题。

-Rick