java - apache tomcat 中的奇怪错误？

Question

我正在使用带有 eclipse keplee 的 apache tomcat。这是我的 jsp 文件，它运行一个使用 sparql 从 tdb 查询的 java 文件。 jsp文件:

<%@ page import="check.test4query"  %>
            <% test4query demo = new test4query();
            test4query dem = new test4query();
            String[] id =new String[20];
            String[] dat =new String[20];
            int i;
           demo.mai("SELECT ?x WHERE { ?y <TO:> 'hjcooljohny75@gmail.com' . ?y <SUB:> ?x} LIMIT 20 ");
           for(i=0;i<20;i++)
           {   id[i]=test4query.arr[i];
               id[i] = id[i].substring(0, Math.min(id[i].length(), 30));
           }
 for(i=0;i<20;i++)
            { //id[i]=test4query.arr[i];
                out.println("<tr>"+"&nbsp&nbsp&nbsp&nbsp"+id[i]+"<hr style='border-color:#E6E6E6;padding:0px;margin:0px'>"+"</tr>");
            }   
            %>

这是我的测试查询:

public static String[] arr=new String[20];
public  void  mai (String s) {
    //String s;
    //load the dataset 
    //String query1; 
    //query1="hjcooljohny75@gmail.com";
    //query1 = (String)(subjectentry.getText());
      //  s="SELECT ?x WHERE { ?y <TO:> '"+query1+"' . ?y <SUB:> ?x} LIMIT 20 ";
        System.out.println(s);
    String directory = "EMAILADDRESS" ;
    Dataset ds = TDBFactory.createDataset(directory) ;
    Model model = ds.getDefaultModel() ;
   ds.begin(ReadWrite.READ) ;
     QueryExecution qExec = QueryExecutionFactory.create(s, ds) ;
     int i=0;
     try{
     ResultSet rs = qExec.execSelect() ;
   String x=rs.toString();



    while (rs.hasNext()) {
        QuerySolution qs = rs.next();
        String rds;
        if(qs.get("x")!=null)
        rds = qs.get("x").toString();
        else rds="hi";
       // String em = (String)rs.getString();
        if(rds==null)
            break;
        //System.out.println(rds);
       arr[i] = rds;
       i++;
       //for (int i =0; i < arr.length; i++){


   }
   } finally
    {qExec.close() ;
    ds.commit();
    ds.end();
   }
    for( i=0;i<20;i++)
        System.out.println(arr[i]);
    //arr[0]="hi";


// return arr;
         //   try { 


          //      ResultSetFormatter.out(rs) ;
           // } finally { qExec.close() ; }

        // Another query - same view of the data.

}

问题是当我启动 tomcat 服务器时它运行完美显示结果但是之后如果我刷新页面它显示错误:

com.hp.hpl.jena.tdb.transaction.TDBTransactionException: Not in a transaction
    com.hp.hpl.jena.tdb.transaction.DatasetGraphTransaction.get(DatasetGraphTransaction.java:106)
    com.hp.hpl.jena.tdb.transaction.DatasetGraphTransaction.get(DatasetGraphTransaction.java:40)
    com.hp.hpl.jena.sparql.core.DatasetGraphTrackActive.getDefaultGraph(DatasetGraphTrackActive.java:91)
    com.hp.hpl.jena.sparql.core.DatasetImpl.getDefaultModel(DatasetImpl.java:103)
    check.test4query.mai(test4query.java:59)
    org.apache.jsp.grayscale.gmail_005flike_jsp._jspService(gmail_005flike_jsp.java:210)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:725)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:403)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:347)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:725)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

这一直都在发生，但是当我重新启动服务器时，它第一次显示正确的答案，然后显示错误。我不知道问题出在哪里以及如何纠正？？

Answer 1

这是错误的方式:

Model model = ds.getDefaultModel() ;
ds.begin(ReadWrite.READ) ;

改为尝试:

ds.begin(ReadWrite.READ) ;
Model model = ds.getDefaultModel() ;