在Google App引擎中更新实体时出错 - com.google.api.server.spi.SystemService invokeServiceMethod：null java.lang.NullPointerException

Question

我在我的app引擎应用程序中实现了One-To-Many关系。

实体如下：

User.java

    @Entity
    public class UserMaster {
      @Id
      @GeneratedValue(strategy = GenerationType.IDENTITY)
      private Key key;
      private String userName;

      @OneToMany(mappedBy = "user")
      List<FeedMaster> feeds;
    }

Feed.java

@Entity
public class FeedMaster {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Key feedId;
    @ManyToOne(fetch = FetchType.LAZY)
    UserMaster user;
}

当我尝试更新FeedMaster实体时。 它抛出

    com.google.api.server.spi.SystemService invokeServiceMethod: null
java.lang.NullPointerException
    at com.google.appengine.api.datastore.KeyTranslator.convertToPb(KeyTranslator.java:49)
    at com.google.appengine.api.datastore.AsyncDatastoreServiceImpl$V3KeyBatcher.toPb(AsyncDatastoreServiceImpl.java:111)
    at com.google.appengine.api.datastore.AsyncDatastoreServiceImpl$V3KeyBatcher.toPb(AsyncDatastoreServiceImpl.java:102)
    at com.google.appengine.api.datastore.Batcher$BatchIterator.<init>(Batcher.java:176)
    at com.google.appengine.api.datastore.Batcher$1.<init>(Batcher.java:270)
    at com.google.appengine.api.datastore.Batcher.getBatches(Batcher.java:270)
    at com.google.appengine.api.datastore.AsyncDatastoreServiceImpl.doBatchGet(AsyncDatastoreServiceImpl.java:301)
    at com.google.appengine.api.datastore.AsyncDatastoreServiceImpl.get(AsyncDatastoreServiceImpl.java:280)
    at com.google.appengine.api.datastore.DatastoreServiceImpl$1.runInternal(DatastoreServiceImpl.java:69)
    at com.google.appengine.api.datastore.DatastoreServiceImpl$1.runInternal(DatastoreServiceImpl.java:66)
    at com.google.appengine.api.datastore.TransactionRunner.runInTransaction(TransactionRunner.java:29)
    at com.google.appengine.api.datastore.DatastoreServiceImpl.get(DatastoreServiceImpl.java:66)
    at com.google.appengine.api.datastore.DatastoreServiceImpl.get(DatastoreServiceImpl.java:56)
    at com.google.appengine.datanucleus.WrappedDatastoreService.get(WrappedDatastoreService.java:60)
    at com.google.appengine.datanucleus.EntityUtils.getEntityFromDatastore(EntityUtils.java:665)
    at com.google.appengine.datanucleus.DatastorePersistenceHandler.fetchObject(DatastorePersistenceHandler.java:543)
    at org.datanucleus.state.JDOStateManager.loadFieldsFromDatastore(JDOStateManager.java:1638)
    at org.datanucleus.state.JDOStateManager.loadUnloadedFieldsInFetchPlan(JDOStateManager.java:1363)
    at org.datanucleus.state.JDOStateManager.detach(JDOStateManager.java:2718)
    at org.datanucleus.ObjectManagerImpl.performDetachOnCloseWork(ObjectManagerImpl.java:4571)
    at org.datanucleus.ObjectManagerImpl.performDetachOnClose(ObjectManagerImpl.java:4534)
    at org.datanucleus.ObjectManagerImpl.close(ObjectManagerImpl.java:1105)
    at org.datanucleus.api.jpa.JPAEntityManager.close(JPAEntityManager.java:193)
    at com.sampleregistrationapp.FeedMasterEndpoint.containsFeedMaster(FeedMasterEndpoint.java:171)
    at com.sampleregistrationapp.FeedMasterEndpoint.updateFeedMaster(FeedMasterEndpoint.java:133)
    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:45)
    at com.google.api.server.spi.SystemService.invokeServiceMethod(SystemService.java:359)
    at com.google.api.server.spi.SystemServiceServlet.execute(SystemServiceServlet.java:124)
    at com.google.api.server.spi.SystemServiceServlet.doPost(SystemServiceServlet.java:82)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1166)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388)
    at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
    at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
    at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
    at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:418)
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
    at org.mortbay.jetty.Server.handle(Server.java:326)
    at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
    at org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:923)
    at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
    at com.google.tracing.TraceContext$TraceContextRunnable.runInContext(TraceContext.java:437)
    at com.google.tracing.TraceContext$TraceContextRunnable$1.run(TraceContext.java:444)
    at com.google.tracing.CurrentContext.runInContext(CurrentContext.java:188)
    at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContextNoUnref(TraceContext.java:308)
    at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContext(TraceContext.java:300)
    at com.google.tracing.TraceContext$TraceContextRunnable.run(TraceContext.java:441)
    at java.lang.Thread.run(Thread.java:724)

我哪里错了？ 请帮我解决这个问题。 谢谢。

Answer 1

您可以将用户主键从“Key”更改为“Long”并再次测试。

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long key;

并保持Feed的主键不变。