HTTP 状态 500 - Servlet 执行引发异常

我在 servlet 中调用 java 类时收到此错误。

这是错误。

type Exception report

message Servlet execution threw an exception

description The server encountered an internal error that prevented it from fulfilling this request.

exception

javax.servlet.ServletException: Servlet execution threw an exception
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

root cause

java.lang.NoClassDefFoundError: com/hp/hpl/jena/query/QueryFactory
    com.complexible.common.csv.MuseumData.gts(MuseumData.java:109)
    com.complexible.common.csv.MuseumData.ass(MuseumData.java:89)
    com.complexible.common.csv.MuseumRDF.doGet(MuseumRDF.java:48)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:620)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

root cause

java.lang.ClassNotFoundException: com.hp.hpl.jena.query.QueryFactory
    org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1720)
    org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1571)
    com.complexible.common.csv.MuseumData.gts(MuseumData.java:109)
    com.complexible.common.csv.MuseumData.ass(MuseumData.java:89)
    com.complexible.common.csv.MuseumRDF.doGet(MuseumRDF.java:48)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:620)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

note The full stack trace of the root cause is available in the Apache Tomcat/7.0.55 logs.

这是我的java类的代码，它将使用SPARQL从RDF文件中获取记录，并在控制台中以JSON格式返回输出，然后在我捕获输出并将其转换为字符串之后，我可以使用该字符串到 servlet 中。

package com.complexible.common.csv;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.PrintStream;
import java.lang.NoClassDefFoundError;
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.ResultSet;
import com.hp.hpl.jena.query.ResultSetFormatter;
import com.hp.hpl.jena.rdf.model.Model;
import com.hp.hpl.jena.rdf.model.ModelFactory;

public class MuseumData {
     public static void main( String[] args ) throws IOException {


         String output=getrec();
         System.out.println(output);
         }


     public static String getrec() throws IOException 
        {
         String spr="prefix rdf:  <http://www.w3.org/1999/02/22-rdf-syntax-ns#>\n"+ 
                 "prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#>\n"+
                    "prefix crm:  <http://www.cidoc-crm.org/cidoc-crm/>\n"+        
                    "prefix owl: <http://www.w3.org/2002/07/owl#>\n"+
                     "prefix xsd: <http://www.w3.org/2001/XMLSchema#>\n"+
                     "prefix crm: <http://www.cidoc-crm.org/rdfs/cidoc_crm_v5.0.4_official_release.rdfs#>\n"+       
                 "\n"+
                     //?title ?person ?type instead of *
                 "SELECT  * WHERE   { <http://phdprototype.tk/collectionimage/4D0BFF17-5810-4644-A550-D35EE090D4A8.png>"+
                     "crm:P3_has_note ?title ; "+
                 "crm:E21_Person ?person ;"+
                     "crm:E62_String ?type ;"+
                 "crm:P82_at_some_time_within ?year;"+
                     "crm:P33_used_specific_technique ?material;}";

          Query query = QueryFactory.create(spr);

         Model model = ModelFactory.createDefaultModel();

         File f = new File("J:/Museum/data.rdf");
         model.read(new FileInputStream(f), "RDF/XML");

         //model.write(System.out, "TTL");

         final QueryExecution exec = QueryExecutionFactory.create(query, model);
         //ResultSetFormatter.out(System.out, exec.execSelect(), query);


         ByteArrayOutputStream baos = new ByteArrayOutputStream();
            PrintStream ps = new PrintStream(baos);
            // IMPORTANT: Save the old System.out!
            PrintStream old = System.out;
            // Tell Java to use your special stream
            System.setOut(ps);
            // Print some output: goes to your special stream
            ResultSetFormatter.outputAsJSON(System.out, exec.execSelect());
            // Put things back
            System.out.flush();
            System.setOut(old);
            // Show what happened

           // return baos.toString();

            String gcr=baos.toString();
               return gcr;

        }

}

下面是一个 servlet 代码，它将在浏览器中显示输出。

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // TODO Auto-generated method stub

    PrintWriter out= response.getWriter();
    String rec=MuseumData.getrec();
    out.print(rec);


}

找到 com/hp/hpl/jena/query/QueryFactory 的 .jar 并将其放入 .war 文件的 WEB-INF lib 中。

如果您碰巧在 Eclipse IDE 中开发 servlet，则可以执行以下操作：

• 使用 Eclipse/Tomcat 自动将第 3 方 jar 添加到 WEB-INF/lib