Question

我是GAE开发的新手。对我来说，使用jpa插入数据存储区工作正常，但检索没有发生。

以下是一种在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;
}

但是在尝试通过传递具有有效用户名和密码的用户对象来执行该方法时，我收到以下错误。

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日下午3:25:02 com.google.appengine.tools.development.LocalResourceFileServlet doGet

第63行 [at com.soa.managers.UserManager.loginUser（UserManager.java:63）] 是“user =（User）query.getSingleResult（）;”

请帮帮我

Answer 1

仍在搜索？

我遇到了同样的问题，我的实体User有一个名为userId的primaryKey，类型为'int'。现在我将它改为'Long'，我所有的问题和警告都消失了！也许这会帮助你！

我期待着你的回音！

此致斯蒂芬

Answer 2

你得到nullpointerexception的原因是getSingleResult方法返回null。因为你使用了（User）query.getSingleResult（），所以null值的类型转换会抛出异常。

我认为数据存储区中没有相关用户，因此您将获得异常。

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。写下您的表名而不是HABERLER。然后在WEB-INF目录中创建一个datastore-indexes.xml文件。然后将上面的代码复制到此文件中。

Answer 4

确保您实体的密钥的有效类型如下所示： https://developers.google.com/appengine/docs/java/datastore/jdo/creatinggettinganddeletingdata#Keys

您获得的例外情况很可能与关键问题有关。

尝试检索对象时GAE Java- Null指针异常

4 个答案: