在文章 SPARQL入门(一)SPARQL简介与简单使用 中,我们了解了RDF、SPARQL以及基于Java编写的SPARQL处理器ARQ。在本文中,笔者将会如何使用Java来操作ARQ。
注意到在Jena的官网 http://jena.apache.org/download/index.cgi 说明中,有关于Maven的使用方法介绍:
因此可以使用Maven,然后再用Java来操作ARQ,Javadoc的网址为: http://jena.apache.org/documentation/javadoc/arq/ 。
在本文中我们使用另一种项目构建工具——Gradle,项目工程截图如下:
我们需要修改的文件为build.gradle, ex002.ttl以及ARQ_TEST.java。其中build.gradle可以加载jena的jar,具体内容如下:
plugins { id 'java' } group 'com.kg.learn' version '1.0-SNAPSHOT' sourceCompatibility = 1.8 repositories { mavenCentral() } dependencies { testCompile group: 'junit', name: 'junit', version: '4.12' // https://mvnrepository.com/artifact/org.apache.jena/jena-arq compile group: 'org.apache.jena', name: 'jena-arq', version: '3.11.0' // https://mvnrepository.com/artifact/org.slf4j/slf4j-api compile group: 'org.slf4j', name: 'slf4j-api', version: '1.7.26' // https://mvnrepository.com/artifact/org.slf4j/slf4j-simple compile group: 'org.slf4j', name: 'slf4j-simple', version: '1.7.26' }
ex002.ttl为RDF文档,储存了我们的示例三元组,内容如下:
# filename: ex002.ttl @prefix ab: <http://learningsparql.com/ns/addressbook#> . ab:richard ab:homeTel "(229) 276-5135" . ab:richard ab:email "richard49@hotmail.com" . ab:cindy ab:homeTel "(245) 646-5488" . ab:cindy ab:email "cindym@gmail.com" . ab:craig ab:homeTel "(194) 966-1505" . ab:craig ab:email "craigellis@yahoo.com" . ab:craig ab:email "c.ellis@usairwaysgroup.com" .
接着就是我们的项目主角ARQ_TETS.java,代码如下:
import org.apache.jena.query.*; import org.apache.jena.rdf.model.Model; import org.apache.jena.rdf.model.ModelFactory; public class ARQ_TEST { public static void main(String[] args) { Model model = ModelFactory.createDefaultModel(); //ttl文件路径 model.read("/Users/kg/IdeaProjects/arq_test/src/main/java/ex002.ttl"); //查询语句, 查询craig的电子邮件地址 String queryString = "PREFIX ab: <http://learningsparql.com/ns/addressbook#> /n" + "/n" + "SELECT ?craig_email/n" + "WHERE/n" + "{ ab:craig ab:email ?craig_email . }"; Query query = QueryFactory.create(queryString); QueryExecution qe = QueryExecutionFactory.create(query, model); ResultSet results = qe.execSelect(); // 输出结果 ResultSetFormatter.out(System.out, results, query); } }
输出结果如下:
-------------------------------- | craig_email | ================================ | "c.ellis@usairwaysgroup.com" | | "craigellis@yahoo.com" | --------------------------------
以上是查询“craig的电子邮件地址” 的代码。如果我们想要知道cindy的全部属性及属性值,可以使用以下Java代码:
import org.apache.jena.query.*; import org.apache.jena.rdf.model.Model; import org.apache.jena.rdf.model.ModelFactory; public class ARQ_TEST { public static void main(String[] args) { Model model = ModelFactory.createDefaultModel(); //ttl文件路径 model.read("/Users/kg/IdeaProjects/arq_test/src/main/java/ex002.ttl"); //查询语句, 查询cindy的全部属性及属性值 String queryString = "PREFIX ab: <http://learningsparql.com/ns/addressbook#> /n" + "/n" + "SELECT ?propertyName ?propertyValue/n" + "WHERE/n" + "{ ab:cindy ?propertyName ?propertyValue . }"; Query query = QueryFactory.create(queryString); QueryExecution qe = QueryExecutionFactory.create(query, model); ResultSet results = qe.execSelect(); // 输出结果 ResultSetFormatter.out(System.out, results, query); } }
输出结果如下:
------------------------------------- | propertyName | propertyValue | ===================================== | ab:email | "cindym@gmail.com" | | ab:homeTel | "(245) 646-5488" | -------------------------------------
本次分享到此结束,有机会我们再来深入地学习ARQ的Javadoc 。
注意:不妨了解下笔者的微信公众号: Python爬虫与算法(微信号为:easy_web_scrape), 欢迎大家关注~