java - Jena Fuseki 客户端

Question

我正在尝试用 Java 编写一个简单的 Jena Fuseki 客户端来发送 SELECT SPARQL 查询并获取结果。

我发现下面的代码是别人写的。它在运行时不断崩溃。

我正在使用jena-arq-3.1.0.jar

javac -cp .;jena-arq-3.1.0.jar Main.java 打印无错误

java -cp .;jena-arq-3.1.0.jar Main 崩溃!

错误日志

Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/jena/atlas/io/Printable
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClass(Unknown Source)
        at java.security.SecureClassLoader.defineClass(Unknown Source)
        at java.net.URLClassLoader.defineClass(Unknown Source)
        at java.net.URLClassLoader.access$100(Unknown Source)
        at java.net.URLClassLoader$1.run(Unknown Source)
        at java.net.URLClassLoader$1.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at org.apache.jena.query.QueryFactory.create(QueryFactory.java:78)
        at org.apache.jena.query.QueryFactory.create(QueryFactory.java:52)
        at org.apache.jena.query.QueryFactory.create(QueryFactory.java:40)
        at Main.main(Main.java:24)
Caused by: java.lang.ClassNotFoundException: org.apache.jena.atlas.io.Printable
        at java.net.URLClassLoader.findClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        ... 16 more

Main.java

import java.net.URL;
import java.util.List; 

import org.apache.jena.query.Query; 
import org.apache.jena.query.QueryExecution; 
import org.apache.jena.query.QueryExecutionFactory; 
import org.apache.jena.query.QueryFactory; 
import org.apache.jena.query.QuerySolution; 
import org.apache.jena.query.ResultSet; 

class Main { 

    public static void main(final String[] args) throws Exception { 
        String queryString=
        "prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#>"+
        "prefix owl: <http://www.w3.org/2002/07/owl#>"+

        "SELECT ?subject ?predicate ?object"+
        "WHERE {"+
        " ?subject ?predicate ?object"+
        " } LIMIT 25";

        // now creating query object
        Query query = QueryFactory.create(queryString);
        // initializing queryExecution factory with remote service.
        // **this actually was the main problem I couldn't figure out.**
        QueryExecution qexec = QueryExecutionFactory.sparqlService("http://localhost:3030/FirstEndpoint/sparql", query);

        //after it goes standard query execution and result processing which can
        // be found in almost any Jena/SPARQL tutorial.
        try {
            ResultSet results = qexec.execSelect();
            for (; results.hasNext();) {

            // Result processing is done here.
            }
        }
        finally {
           qexec.close();
        }
    } 

}

Answer 1

您需要类路径中的所有必需库，而不仅仅是 jena-arq。

javac 之所以有效，是因为您仅使用 jena-arq JAR 中的类。java 不起作用，因为在运行时 ARQ 的类引用其他类，例如包含在 jena-core、jena-iri 等中

最简单的方法是添加 Jena 发行版中的所有库。将 lib 文件夹本身添加到类路径中。