我在将三重文件加载到Jena SDB模型时遇到java.lang.NullPointerException

Question

我有一个n-triple文件，我需要通过Jena SDB模型将它存储在数据库中。我写了下面的代码来做到这一点。但是我对一个java.lang.NullPointerException异常挣扎，我并不知道它是如何发生的以及如何解决它。 下面是代码：

import java.io.FileInputStream; 
import java.io.FileNotFoundException; 
import java.io.InputStream; 

import com.hp.hpl.jena.db.DBConnection; 
import com.hp.hpl.jena.ontology.OntModel; 
import com.hp.hpl.jena.ontology.ProfileRegistry; 
import com.hp.hpl.jena.rdf.model.Model; 
import com.hp.hpl.jena.rdf.model.ModelFactory; 
import com.hp.hpl.jena.rdf.model.ModelMaker; 

public class JenaRepositoryManagement { 

    private MySQLAccess mysql = null; 
    private String  dbname = null; 


    private String xmlbase = "http://www.test.org/test.owl#"; 

    private OntModel domainModel = null; 

    public JenaRepositoryManagement (String databaseName) { 

     dbname = "sdb_" + databaseName; 

     mysql = new MySQLAccess(); 

     mysql.createDatabase(dbname); 

     impotring(); 
    } 


    public void importing() { 
     // Instantiate the MySQL driver 
     try { 

      Class.forName("com.mysql.jdbc.Driver"); 


     // Create a database connection object 
     DBConnection connection = new DBConnection("jdbc:mysql://localhost/"+dbname, "root", "", "MySQL"); 

     // Get a ModelMaker for database-backed models 
     ModelMaker maker = ModelFactory.createModelRDBMaker(connection); 

     Model traceModel = maker.createModel("testModel"); 

     // Start a database transaction. Without one, each statement will be auto-committed 
     traceModel.begin();   



     InputStream in = this.getClass().getClassLoader().getResourceAsStream("data/nts/100.nt"); 

     traceModel.read(in, xmlbase, "N-TRIPLE"); 

     traceModel.write(System.out); 

     // Commit the database transaction 
     traceModel.commit(); 



    } catch (ClassNotFoundException | FileNotFoundException e) { 
     e.printStackTrace(); 
    } 


} 

}

这里是执行

CREATE DATABASE IF NOT EXISTS sdb_100_n; 
java.lang.NullPointerException 
    at java.io.Reader.<init>(Reader.java:78) 
    at java.io.InputStreamReader.<init>(InputStreamReader.java:129) 
    at com.hp.hpl.jena.util.FileUtils.asUTF8(FileUtils.java:51) 
    at com.hp.hpl.jena.rdf.model.impl.NTripleReader.read(NTripleReader.java:72) 
    at com.hp.hpl.jena.rdf.model.impl.ModelCom.read(ModelCom.java:226) 
    at soctrace.JenaRepositoryManagement.importing(JenaRepositoryManagement.java:70) 
    at soctrace.views.Main$1.run(Main.java:165) 
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251) 
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:727) 
    at java.awt.EventQueue.access$200(EventQueue.java:103) 
    at java.awt.EventQueue$3.run(EventQueue.java:688) 
    at java.awt.EventQueue$3.run(EventQueue.java:686) 
    at java.security.AccessController.doPrivileged(Native Method) 
    at java .security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76) 
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:697) 
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242) 
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161) 
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150) 
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146) 
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138) 
at java.awt.EventDispatchThread.run(EventDispatchThread.java:91) 

最后这里时的输出在n三重文件的样本

<http://www.test.org/test.owl#trace0> <http://www.test.org/test.owl#traceContainsEvent>  <http://www.test.org/test.owl#event0> . 
<http://www.test.org/test.owl#event0> <http://www.test.org/test.owl#hasTime> <http://www.test.org/test.owl#interval0> . 
<http://www.test.org/test.owl#event0> <http://www.test.org/test.owl#hasActiveTime> <http://www.test.org/test.owl#aduration0> . 
<http://www.test.org/test.owl#interval0> <http://www.test.org/test.owl#hasStartTime> <http://www.test.org/test.owl#stime0> . 
<http://www.test.org/test.owl#interval0> <http://www.test.org/test.owl#hasEndTime> <http://www.test.org/test.owl#etime0> . 
<http://www.test.org/test.owl#interval0> <http://www.test.org/test.owl#hasDuration> <http://www.test.org/test.owl#duration0> . 
<http://www.test.org/test.owl#stime0> <http://www.test.org/test.owl#hasValue> "525255"^^<http://www.w3.org/2001/XMLSchema#float> . 
<http://www.test.org/test.owl#etime0> <http://www.test.org/test.owl#hasValue> "0"^^<http://www.w3.org/2001/XMLSchema#float> . 
<http://www.test.org/test.owl#duration0> <http://www.test.org/test.owl#hasValue> "0"^^<http://www.w3.org/2001/XMLSchema#float> . 
<http://www.test.org/test.owl#aduration0> <http://www.test.org/test.owl#hasValue> "0"^^<http://www.w3.org/2001/XMLSchema#float> . 
<http://www.test.org/test.owl#event0> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.test.org/test.owl#ContextSwitch> . 
<http://www.test.org/test.owl#event0> <http://www.test.org/test.owl#switchFrom> <http://www.test.org/test.owl#mttd0> . 
<http://www.test.org/test.owl#event0> <http://www.test.org/test.owl#switchTo> <http://www.test.org/test.owl#kptrace0> . 
<http://www.test.org/test.owl#trace0> <http://www.test.org/test.owl#traceContainsEvent> <http://www.test.org/test.owl#event1> . 
<http://www.test.org/test.owl#event1> <http://www.test.org/test.owl#hasTime> <http://www.test.org/test.owl#interval1> . 
<http://www.test.org/test.owl#event1> <http://www.test.org/test.owl#hasActiveTime> <http://www.test.org/test.owl#aduration1> . 
<http://www.test.org/test.owl#interval1> <http://www.test.org/test.owl#hasStartTime> <http://www.test.org/test.owl#stime1> . 
<http://www.test.org/test.owl#interval1> <http://www.test.org/test.owl#hasEndTime> <http://www.test.org/test.owl#etime1> . 
<http://www.test.org/test.owl#interval1> <http://www.test.org/test.owl#hasDuration> <http://www.test.org/test.owl#duration1> . 
<http://www.test.org/test.owl#stime1> <http://www.test.org/test.owl#hasValue> "525292"^^<http://www.w3.org/2001/XMLSchema#float> . 
<http://www.test.org/test.owl#etime1> <http://www.test.org/test.owl#hasValue> "525306"^^<http://www.w3.org/2001/XMLSchema#float> . 
<http://www.test.org/test.owl#duration1> <http://www.test.org/test.owl#hasValue> "14"^^<http://www.w3.org/2001/XMLSchema#float> . 
<http://www.test.org/test.owl#aduration1> <http://www.test.org/test.owl#hasValue> "14"^^<http://www.w3.org/2001/XMLSchema#float> . 
<http://www.test.org/test.owl#event1> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.test.org/test.owl#TaskRunning> . 
<http://www.test.org/test.owl#event1> <http://www.test.org/test.owl#runningTask> <http://www.test.org/test.owl#kptrace0> . 

提前致谢。

Answer 1

基于此代码（我猜就行号，但我敢肯定我是对的）：

/* 69 */ InputStream in = this.getClass().getClassLoader().getResourceAsStream("data/nts/100.nt"); 
/* 70 */ traceModel.read(in, xmlbase, "N-TRIPLE"); 

和堆栈跟踪的开头：

java.lang.NullPointerException 
    at java.io.Reader.<init>(Reader.java:78) 
    at java.io.InputStreamReader.<init>(InputStreamReader.java:129) 
    at com.hp.hpl.jena.util.FileUtils.asUTF8(FileUtils.java:51) 
    at com.hp.hpl.jena.rdf.model.impl.NTripleReader.read(NTripleReader.java:72) 
    at com.hp.hpl.jena.rdf.model.impl.ModelCom.read(ModelCom.java:226) 
    … 

我猜in是null。也许这个路径名必须是"/data/nts/100.nt"（注意开头的/）。

stacktrace包含行号，我很确定他们指出你有问题的一行。这在调试器中不应该太难运行。即使你不能在调试器中运行它，如果你得到一个空指针异常，并且你有一个特定行的引用，通常是检查该行上使用哪些值并检查它们是否是一个好主意是不是null。在这种情况下，你可以这样做：

InputStream in = this.getClass().getClassLoader().getResourceAsStream("data/nts/100.nt"); 
Objects.requireNonNull(in, "InputStream for resource data/nts/100.nt should not be null."); 
traceModel.read(in, xmlbase, "N-TRIPLE");