java Cron作业不能使用“For”循环？

Question

我有以下代码：

EntityManager mgr = null;
try {
    mgr = getEntityManager();
    ZooperTheme2 theme = null;
    theme = mgr.find(Theme2.class, "1");
    theme.setPopularity(7);
    mgr.persist(theme);
    for (int c = 1; c < 204; c++) {
        theme = mgr.find(Theme2.class, "" + c);
        theme.calculatePopularity();
        mgr.persist(theme);
    }
} catch (Exception e) {
} finally {
    mgr.close();
}

“For”循环之前的零件：

theme = mgr.find(Theme2.class, "1");
theme.setPopularity(7);
mgr.persist(theme);

它本身就可以正常工作。但是，当我添加“For”循环来迭代所有主题时，没有一个主题正在更新（包括使用.setPopularity（7）的主题“1”）。日志文件显示以下错误：

   Uncaught exception from servlet
javax.persistence.PersistenceException: Illegal argument
    at org.datanucleus.api.jpa.NucleusJPAHelper.getJPAExceptionForNucleusException(NucleusJPAHelper.java:298)
    at org.datanucleus.api.jpa.JPAEntityManager.close(JPAEntityManager.java:197)
    at com.companionfree.zooperthemeviewer.CronController.doGet(CronController.java:43)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
    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$CachedChain.doFilter(ServletHandler.java:1166)
    at com.google.apphosting.utils.servlet.ParseBlobUploadFilter.doFilter(ParseBlobUploadFilter.java:125)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.apphosting.runtime.jetty.SaveSessionFilter.doFilter(SaveSessionFilter.java:35)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.apphosting.utils.servlet.JdbcMySqlConnectionCleanupFilter.doFilter(JdbcMySqlConnectionCleanupFilter.java:60)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:43)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388)
    at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
    at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
    at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
    at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:418)
    at com.google.apphosting.runtime.jetty.AppVersionHandlerMap.handle(AppVersionHandlerMap.java:266)
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
    at org.mortbay.jetty.Server.handle(Server.java:326)
    at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
    at org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:923)
    at com.google.apphosting.runtime.jetty.RpcRequestParser.parseAvailable(RpcRequestParser.java:76)
    at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
    at com.google.apphosting.runtime.jetty.JettyServletEngineAdapter.serviceRequest(JettyServletEngineAdapter.java:146)
    at com.google.apphosting.runtime.JavaRuntime$RequestRunnable.run(JavaRuntime.java:446)
    at com.google.tracing.TraceContext$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 com.google.apphosting.runtime.ThreadGroupPool$PoolEntry.run(ThreadGroupPool.java:251)
    at java.lang.Thread.run(Thread.java:724)
Caused by: java.lang.IllegalArgumentException: cross-group transaction need to be explicitly specified, see TransactionOptions.Builder.withXG
    at com.google.appengine.api.datastore.DatastoreApiHelper.translateError(DatastoreApiHelper.java:39)
    at com.google.appengine.api.datastore.DatastoreApiHelper$1.convertException(DatastoreApiHelper.java:76)
    at com.google.appengine.api.utils.FutureWrapper.get(FutureWrapper.java:94)
    at com.google.appengine.api.datastore.AsyncDatastoreServiceImpl$6.getFutureWithOptionalTimeout(AsyncDatastoreServiceImpl.java:373)
    at com.google.appengine.api.datastore.AsyncDatastoreServiceImpl$6.aggregate(AsyncDatastoreServiceImpl.java:345)
    at com.google.appengine.api.datastore.AsyncDatastoreServiceImpl$6.get(AsyncDatastoreServiceImpl.java:316)
    at com.google.appengine.api.datastore.AsyncDatastoreServiceImpl$6.get(AsyncDatastoreServiceImpl.java:305)
    at com.google.appengine.api.datastore.FutureHelper$TxnAwareFuture.get(FutureHelper.java:171)
    at com.google.appengine.api.utils.FutureWrapper.get(FutureWrapper.java:86)
    at com.google.appengine.api.utils.FutureWrapper.get(FutureWrapper.java:86)
    at com.google.appengine.api.utils.FutureWrapper.get(FutureWrapper.java:86)
    at com.google.appengine.api.datastore.FutureHelper.getInternal(FutureHelper.java:71)
    at com.google.appengine.api.datastore.FutureHelper.quietGet(FutureHelper.java:58)
    at com.google.appengine.api.datastore.DatastoreServiceImpl.get(DatastoreServiceImpl.java:51)
    at com.google.appengine.datanucleus.WrappedDatastoreService.get(WrappedDatastoreService.java:70)
    at com.google.appengine.datanucleus.EntityUtils.getEntityFromDatastore(EntityUtils.java:667)
    at com.google.appengine.datanucleus.DatastorePersistenceHandler.updateObject(DatastorePersistenceHandler.java:415)
    at org.datanucleus.state.JDOStateManager.flush(JDOStateManager.java:3841)
    at org.datanucleus.ObjectManagerImpl.flushInternalWithOrdering(ObjectManagerImpl.java:3888)
    at org.datanucleus.ObjectManagerImpl.flushInternal(ObjectManagerImpl.java:3811)
    at org.datanucleus.ObjectManagerImpl.flush(ObjectManagerImpl.java:3751)
    at org.datanucleus.ObjectManagerImpl.preCommit(ObjectManagerImpl.java:4141)
    at org.datanucleus.ObjectManagerImpl.transactionPreCommit(ObjectManagerImpl.java:428)
    at org.datanucleus.TransactionImpl.internalPreCommit(TransactionImpl.java:398)
    at org.datanucleus.TransactionImpl.commit(TransactionImpl.java:287)
    at org.datanucleus.ObjectManagerImpl.close(ObjectManagerImpl.java:1090)
    at org.datanucleus.api.jpa.JPAEntityManager.close(JPAEntityManager.java:193)
    ... 35 more

CronController。java:43是一行： 经理。关闭（）

当我添加For循环时，我的代码似乎失败了，但我不知道为什么

Answer 1

根据Developer Guide

“应用程序使用factory实例为访问数据存储的每个请求创建一个EntityManager实例。”

我知道EntityManager只能调用persist一次，如果您尝试在多个对象上使用它，就会出错。我的新代码是：

EntityManager mgr=null； Theme2 theme=null

    for (int c = 1;c<204;c++) {

        try {
            mgr = getEntityManager();           
            theme = mgr.find(Theme2.class, "" + c);
            theme.calculatePopularity();

            mgr.persist(theme);


        } catch (Exception e) {

        } finally {
            mgr.close();
        }

    }

而且效果很好：）