Rdf addproperty和addliteral函数中出错

我正在尝试将我的电子邮件以rdf模型存储到apche tdb中。这是我的密码：

/*Program to download the mails from mail servers and then to store
  them in tdb store using rdf model*/
//import all the classes needed  




import java.io.*;
import java.util.*;
import javax.mail.*;
import javax.mail.Flags.Flag;
import javax.mail.internet.*;
import com.sun.mail.imap.IMAPFolder;
import com.sun.mail.imap.IMAPMessage;
import static com.hp.hpl.jena.query.ReadWrite.READ ;
import static com.hp.hpl.jena.query.ReadWrite.WRITE ;
import com.hp.hpl.jena.query.ReadWrite ;
import com.hp.hpl.jena.query.Dataset ;
import com.hp.hpl.jena.query.Query ;
import com.hp.hpl.jena.query.QueryExecution ;
import com.hp.hpl.jena.query.QueryExecutionFactory ;
import com.hp.hpl.jena.query.QueryFactory ;
import com.hp.hpl.jena.query.QuerySolution ;
import com.hp.hpl.jena.query.ResultSet ;
import com.hp.hpl.jena.tdb.TDBFactory ;
import email.*; // import this to add properties as entities of email
import com.hp.hpl.jena.rdf.model.Model;
import com.hp.hpl.jena.rdf.model.*;
import com.hp.hpl.jena.vocabulary.*;


public class test2 {


public static void main(String[] args) throws MessagingException, IOException {
    IMAPFolder folder = null;
    Store store = null;
    String subjec = null;
    Flag flag = null;
    //String too;
    //Directory where the tdb files will be stored
     String directory = "MYDATABASES/DATA2" ;
     //create the dataset for the tdb store
    Dataset ds = TDBFactory.createDataset(directory) ;
    //create default rdf model
    Model model = ds.getDefaultModel() ;
    //write to the tdb dataset
    ds.begin(ReadWrite.WRITE);
    try 
    { //connecting to the server to download the emails
      Properties props = System.getProperties();
      props.setProperty("mail.store.protocol", "imaps");

      Session session = Session.getDefaultInstance(props, null);

      store = session.getStore("imaps");
      store.connect("imap.gmail.com","hjcooljohny75@gmail.com", "ferry@786");

      //folder = (IMAPFolder) store.getFolder("[Gmail]/Spam"); // This doesn't work for enter code here`other email account
      //to select the paticular types of mails
      folder = (IMAPFolder) store.getFolder("inbox");// This works for both email account


      if(!folder.isOpen())
      folder.open(Folder.READ_WRITE);
      Message[] messages = folder.getMessages();
      System.out.println("No of Messages : " + folder.getMessageCount());
      System.out.println("No of Unread Messages : " + folder.getUnreadMessageCount());
      System.out.println(messages.length);
      //Displaying the info. of the messages
       for (int i=messages.length-1; i > messages.length-10;i--) 
      {

        System.out.println("*****************************************************************************");
        System.out.println("MESSAGE " + (i + 1) + ":");
        MimeMessage msg = (MimeMessage) messages[i];
        //creating rdf model of the message
        //too=toString(msg.getAllRecipients()[0]);
         Resource mail= model.createResource(msg.getMessageID())
        .addProperty(EMAILRDF.SUBJECT, msg.getSubject())  
        .addProperty(EMAILRDF.TO,msg.getAllRecipients()[0])
        .addLiteral(EMAILRDF.FROM,msg.getFrom()[0])
        .addLiteral(EMAILRDF.ENCODING,msg.getEncoding())
        .addLiteral(EMAILRDF.CONTENT,msg.getContent())
        .addLiteral(EMAILRDF.DATE,msg.getReceivedDate())
        .addLiteral(EMAILRDF.CONTENT_TYPE,msg.getContentType());

    // list the statements in the graph
    StmtIterator iter = model.listStatements();

    // print out the predicate, subject and object of each statement
    while (iter.hasNext()) {
        Statement stmt      = iter.nextStatement();         // get next statement
        Resource  subject   = stmt.getSubject();   // get the subject
        Property  predicate = stmt.getPredicate(); // get the predicate
        RDFNode   object    = stmt.getObject();    // get the object

        System.out.print(subject.toString());
        System.out.print(" "+ predicate.toString() + " ");
        if (object instanceof Resource) {
            System.out.print(object.toString());
        } else {
            // object is a literal
            System.out.print(" \"" + object.toString() + "\"");
        }
        System.out.println(" .");
    }
        //System.out.println(msg.getMessageNumber());
        //Object String;
        //System.out.println(folder.getUID(msg)

        //subject = msg.getSubject();

        //System.out.println("Subject: " + subject);
        //System.out.println("From: " + msg.getFrom()[0]);
        //System.out.println("To: "+msg.getAllRecipients()[0]);
        //System.out.println("Date: "+msg.getReceivedDate());
        //System.out.println("Size: "+msg.getSize());
        //System.out.println("Id: "+msg.getMessageID());
        //System.out.println(msg.getFlags());
        //System.out.println("Body: \n"+ msg.getContent());
        //System.out.println(msg.getContentType());

      }
    }
    finally 
    {  //closing the connection
      if (folder != null && folder.isOpen()) { folder.close(true); }
      if (store != null) { store.close(); }
    }


 //closing the dataset
ds.commit();
ds.end();
}
}

但是这会在addAlteral（）方法中产生错误。我尝试使用AddProperty（），但这也会产生错误

error: WARN [main] (LiteralLabelImpl.java:141) - inventing a datatype for class com.sun.mail.imap.protocol.IMAPAddress
Exception in thread "main" java.lang.NullPointerException
    at com.hp.hpl.jena.datatypes.TypeMapper.getTypeByValue(TypeMapper.java:156)
    at com.hp.hpl.jena.graph.impl.LiteralLabelImpl.<init>(LiteralLabelImpl.java:131)
    at com.hp.hpl.jena.graph.impl.LiteralLabelFactory.create(LiteralLabelFactory.java:77)
    at com.hp.hpl.jena.rdf.model.impl.ModelCom.createTypedLiteral(ModelCom.java:781)
    at com.hp.hpl.jena.rdf.model.impl.ResourceImpl.addLiteral(ResourceImpl.java:263)
    at test2.main(test2.java:80)

error:WARN[main]（literalabelimpl.java:141）-正在为com.sun.mail.imap.protocol.IMAPAddress类创建数据类型
线程“main”java.lang.NullPointerException中出现异常
位于com.hp.hpl.jena.datatypes.TypeMapper.getTypeByValue（TypeMapper.java:156）
位于com.hp.hpl.jena.graph.impl.LiteralLabelImpl.（LiteralLabelImpl.java:131）
在com.hp.hpl.jena.graph.impl.LiteralLabelFactory.create（LiteralLabelFactory.java:77）上
位于com.hp.hpl.jena.rdf.model.impl.ModelCom.createTypedLiteral（ModelCom.java:781）
位于com.hp.hpl.jena.rdf.model.impl.ResourceImpl.addLiteral（ResourceImpl.java:263）
位于test2.main（test2.java:80）

我认为这可能是由于我在

addproperty（）

或

addLiteral（）

函数中输入的类的数据类型造成的。

---

有什么想法吗？

JavaDoc可能充分回答了这个问题。定义许多

addLiteral

方法，每个方法都接受一个属性和第二个参数，参数类型为boolean、char、double、float、Literal、long或Object。基于警告，“WARN[main]（literalabelimpl.java:141）——为

类com.sun.mail.imap.protocol.IMAPAddress，“听起来像是在使用addLiteral（属性，对象）方法

当你这么做的时候，正如JavaDoc所说的，你在试图

将具有类型化文字值o的属性p添加到此资源，即 将（this，p，typed（o））添加到此模型中…这个 类型化文字等于使用 这个.getModel（）.createTypedLiteral（o）

---

您可以从stacktrace中看到正在调用createTypedLiteral，因此没有为com.sun.mail.imap.protocol.IMAPAddress定义数据类型也就不足为奇了。无论对addLiteral的哪个调用都有一个IMAPAddress作为第二个参数，您需要用可以转换为类型化文本的第二个参数替换为调用。最简单的方法可能是使用它的toString（）方法。

由于缺乏研究工作而投反对票；我认为这在JavaDoc中对addLiteral方法描述得非常清楚，它描述了对createTypedLiteral的后续调用，并出现在stacktrace中。