试图检索对象时，Gae Java-null指针异常

Question

我是GAE开发的新手。对我而言，使用JPA插入数据存储的工作正常，但是检索没有发生。

以下是用户尝试登录时对用户进行身份验证的方法。

public boolean loginUser(User user) {
    EntityManagerFactory emf = Persistence
            .createEntityManagerFactory("SOAApp");
    EntityManager mgr = emf.createEntityManager();
    boolean login=false;
    Query query=mgr.createQuery("select u from User u where u.userName=:uid and u.password=:pwd");
    query.setParameter("uid", user.getUserName());
    query.setParameter("pwd",user.getPassword());
    query.setMaxResults(1);
    try {
        user=(User) query.getSingleResult();
        System.out.println("user : "+user.getName());
        if(user!=null)  {
            System.out.println("logged in...");
            login=true;
        }
    }
    catch(Exception e) {
        e.printStackTrace();
    }
    finally {
        mgr.close();
    }
    return login;
}

但是，通过使用有效的用户名和密码传递用户对象执行该方法时，我会遇到以下错误。

java.lang.NullPointerException
at com.google.appengine.datanucleus.query.QueryEntityPKFetchFieldManager.fetchIntField(QueryEntityPKFetchFieldManager.java:70)
at org.datanucleus.identity.IdentityUtils.getApplicationIdentityForResultSetRow(IdentityUtils.java:93)
at com.google.appengine.datanucleus.EntityUtils.entityToPojo(EntityUtils.java:1009)
at com.google.appengine.datanucleus.query.DatastoreQuery$2.apply(DatastoreQuery.java:228)
at com.google.appengine.datanucleus.query.DatastoreQuery$2.apply(DatastoreQuery.java:225)
at com.google.appengine.datanucleus.query.LazyResult.resolveNext(LazyResult.java:96)
at com.google.appengine.datanucleus.query.LazyResult.resolveAll(LazyResult.java:121)
at com.google.appengine.datanucleus.query.LazyResult.size(LazyResult.java:115)
at com.google.appengine.datanucleus.query.StreamingQueryResult.size(StreamingQueryResult.java:151)
at org.datanucleus.store.query.Query.executeQuery(Query.java:1808)
at org.datanucleus.store.query.Query.executeWithMap(Query.java:1693)
at org.datanucleus.api.jpa.JPAQuery.getSingleResult(JPAQuery.java:231)
at com.soa.managers.UserManager.loginUser(UserManager.java:63)
at com.soa.servlets.LoginServlet.doPost(LoginServlet.java:48)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1166)
at com.google.appengine.api.socket.dev.DevSocketFilter.doFilter(DevSocketFilter.java:74)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.tools.development.ResponseRewriterFilter.doFilter(ResponseRewriterFilter.java:123)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.tools.development.HeaderVerificationFilter.doFilter(HeaderVerificationFilter.java:34)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.api.blobstore.dev.ServeBlobFilter.doFilter(ServeBlobFilter.java:61)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:43)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.tools.development.StaticFileFilter.doFilter(StaticFileFilter.java:125)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.tools.development.BackendServersFilter.doFilter(BackendServersFilter.java:97)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388)
at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:418)
at com.google.appengine.tools.development.DevAppEngineWebAppContext.handle(DevAppEngineWebAppContext.java:94)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at com.google.appengine.tools.development.JettyContainerService$ApiProxyHandler.handle(JettyContainerService.java:383)
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$RequestHandler.content(HttpConnection.java:938)
at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:755)
at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:218)
at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:409)
at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:582)

2012年11月3日3:25:02 pm com.google.appengine.tools.development.localresourcefileservlet doget

行号-63 [在com.soa.managers.usermanager.loginuser（usermanager.java:63）]] 是" user =（用户）Query.getSingleresult（）;"

请帮助我

Answer 1

仍在搜索？

我遇到了相同的问题，我的实体用户有一个名为" int"类型的primarykey用户。现在，我将其更改为" Long"，我所有的问题和警告都消失了！也许这对您有帮助！

我期待您的回音！

问候，斯蒂芬

Answer 2

您获得nullpoInterException的原因是getingleresult方法返回null。因为u用过（用户）QUERY.GETSINGELESULT（），因此null值的打字引发异常。

我认为数据存储中没有相关用户，因此您会得到例外。

Answer 3

<?xml version="1.0" encoding="UTF-8"?>
<datastore-indexes  autoGenerate="true">
    <datastore-index kind="HABERLER" ancestor="false" source="manual">
        <property name="__key__" direction="desc"/>
    </datastore-index>

Haberler是表名。写下您的桌子名称而不是哈伯勒。然后在Web-Inf Directory中创建一个DataStore-indexes.xml文件。然后将上述代码复制到此文件中。

Answer 4

确保您的实体的密钥是有效类型的，如下所示：https://developers.google.com/appengine/docs/java/datastore/jdo/creatinggettingtinganddeletdeletdata#keys

您获得的例外很可能与关键问题有关。