public Guest getGuestByEmailAddress(String emailAddress) {
try {
String query
= "FROM Guest WHERE Guest.emailAddress = :emailAddress";
if(entityManager == null) {
System.out.println("null entityManager");
} else {
System.out.println("entity manager not null");
System.out.println(query);
}
Query q = entityManager.createQuery(query);
q.setParameter("emailAddress", emailAddress);
return (Guest) q.getSingleResult();
} catch (EntityNotFoundException e) {
return null;
}
}
运行时，会打印entity manager not null。使用相同的实体管理器在同一个类中的早期调用也是成功的。
我有堆栈跟踪：
Nov 04, 2017 3:50:44 PM org.hibernate.hql.internal.QueryTranslatorFactoryInitiator initiateService
INFO: HHH000397: Using ASTQueryTranslatorFactory
Exception in Application start method
java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:389)
at com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:328)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:767)
Caused by: java.lang.RuntimeException: Exception in Application start method
at com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:917)
at com.sun.javafx.application.LauncherImpl.lambda$launchApplication$155(LauncherImpl.java:182)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.NullPointerException
at java.lang.String$CaseInsensitiveComparator.compare(String.java:1192)
at java.lang.String$CaseInsensitiveComparator.compare(String.java:1186)
at java.util.TreeMap.getEntryUsingComparator(TreeMap.java:376)
at java.util.TreeMap.getEntry(TreeMap.java:345)
at java.util.TreeMap.get(TreeMap.java:278)
at org.hibernate.dialect.function.SQLFunctionRegistry.findSQLFunction(SQLFunctionRegistry.java:45)
at org.hibernate.hql.internal.ast.util.SessionFactoryHelper.findSQLFunction(SessionFactoryHelper.java:369)
at org.hibernate.hql.internal.ast.tree.IdentNode.getDataType(IdentNode.java:374)
at org.hibernate.hql.internal.ast.HqlSqlWalker.lookupProperty(HqlSqlWalker.java:654)
at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.addrExpr(HqlSqlBaseWalker.java:5003)
at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.expr(HqlSqlBaseWalker.java:1286)
at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.exprOrSubquery(HqlSqlBaseWalker.java:4707)
at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.comparisonExpr(HqlSqlBaseWalker.java:4175)
at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.logicalExpr(HqlSqlBaseWalker.java:2138)
at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.whereClause(HqlSqlBaseWalker.java:815)
at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.query(HqlSqlBaseWalker.java:609)
at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.selectStatement(HqlSqlBaseWalker.java:313)
at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.statement(HqlSqlBaseWalker.java:261)
at org.hibernate.hql.internal.ast.QueryTranslatorImpl.analyze(QueryTranslatorImpl.java:266)
at org.hibernate.hql.internal.ast.QueryTranslatorImpl.doCompile(QueryTranslatorImpl.java:189)
at org.hibernate.hql.internal.ast.QueryTranslatorImpl.compile(QueryTranslatorImpl.java:141)
at org.hibernate.engine.query.spi.HQLQueryPlan.<init>(HQLQueryPlan.java:115)
at org.hibernate.engine.query.spi.HQLQueryPlan.<init>(HQLQueryPlan.java:77)
at org.hibernate.engine.query.spi.QueryPlanCache.getHQLQueryPlan(QueryPlanCache.java:153)
at org.hibernate.internal.AbstractSharedSessionContract.getQueryPlan(AbstractSharedSessionContract.java:553)
at org.hibernate.internal.AbstractSharedSessionContract.createQuery(AbstractSharedSessionContract.java:662)
at org.hibernate.internal.AbstractSessionImpl.createQuery(AbstractSessionImpl.java:23)
at com.gitrekt.resort.model.services.GuestService.getGuestByEmailAddress(GuestService.java:49)
at com.gitrekt.resort.GitRekt.testHibernate(GitRekt.java:95)
at com.gitrekt.resort.GitRekt.start(GitRekt.java:46)
at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$162(LauncherImpl.java:863)
at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$175(PlatformImpl.java:326)
at com.sun.javafx.application.PlatformImpl.lambda$null$173(PlatformImpl.java:295)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.application.PlatformImpl.lambda$runLater$174(PlatformImpl.java:294)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$148(WinApplication.java:191)
... 1 more
Exception running application com.gitrekt.resort.GitRekt
我应该注意这是一个Java SE环境。没有依赖注入，EJB，Spring或任何那种幻想。为什么在实体管理器不为空时我得到空指针异常？
这就是我在调用相关方法的类中管理entityManager的方法：
private final EntityManager entityManager;
public GuestService() {
this.entityManager = HibernateUtil.getEntityManager();
}
@Override
public void finalize() throws Throwable {
super.finalize();
this.entityManager.close();
}
我在调用抛出异常的方法之前立即调用了这个方法，并且它正常运行：
public Guest getGuestById(Long id) {
try {
Guest guest = entityManager.getReference(Guest.class,id);
return guest;
} catch (EntityNotFoundException e) {
System.out.println("entity not found");
return null;
}
}
是什么给出了？
答案 0 :(得分：2)
空指针异常源自框架代码，而不是代码。
您的特定查询似乎会导致问题。尝试按如下方式更改它：
SELECT g FROM Guest g WHERE g.emailAddress = :emailAddress