sesame芝麻开门operrdf研究2

再来看个完整的读写例子:

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;

import org.openrdf.model.Model;
import org.openrdf.model.URI;
import org.openrdf.model.util.ModelUtil;
import org.openrdf.model.vocabulary.RDFS;
import org.openrdf.rio.RDFFormat;
import org.openrdf.rio.RDFHandlerException;
import org.openrdf.rio.RDFParser;
import org.openrdf.rio.RDFWriter;
import org.openrdf.rio.Rio;
import org.openrdf.rio.UnsupportedRDFormatException;
import org.openrdf.rio.helpers.StatementCollector;
import org.openrdf.sail.memory.model.MemValueFactory;

public class Test {
	static String NS = "http://www.steeven.org/rdf#";

	public static void main(String[] args) throws Exception {
		for (RDFFormat format : RDFFormat.values()) {
			String file = "test." + format.getDefaultFileExtension();
			testWrite(format, file);
			testRead(format, file);
		}
	}

	private static void testRead(RDFFormat format, String file)
			throws Exception {
		RDFParser parser = Rio.createParser(format, MemValueFactory
				.getInstance());
		StatementCollector sc = new StatementCollector();
		parser.setRDFHandler(sc);
		parser.parse(new FileInputStream(file), NS);
		Model model = sc.getModel();
		System.out.println(model.contains(createNS("steeven"), RDFS.LABEL, null));
		System.out.println(model.filter(null, RDFS.LABEL, null));
		System.out.println(model.filter(null, createNS("desc"), null));
		System.out.println(model.filter(null, null, MemValueFactory
				.getInstance().createLiteral("steeven li")));
		System.out.println(ModelUtil.getUniqueObjectLiteral(model,
				createNS("steeven"), RDFS.LABEL));
		System.out.println(model.filter(createNS("steeven"), null, null).size());
	}

	private static URI createNS(String name) {
		return MemValueFactory.getInstance().createURI(NS, name);
	}

	private static void testWrite(RDFFormat format, String file)
			throws RDFHandlerException, UnsupportedRDFormatException,
			FileNotFoundException {
		// System.out.println("=======format: " + format + "========");
		RDFWriter w = Rio.createWriter(format,
				new FileOutputStream(file, false));
		w.setBaseURI(NS);
		w.handleNamespace("myns", NS);
		w.handleNamespace("w3", RDFS.NAMESPACE);
		w.startRDF();
		w.handleComment("my first rdf file");

		URI res = createNS("steeven");
		w.handleStatement(MemValueFactory.getInstance().createStatement(res,
				RDFS.LABEL,
				MemValueFactory.getInstance().createLiteral("steeven li")));
		w.handleStatement(MemValueFactory.getInstance().createStatement(res,
				createNS("desc"),
				MemValueFactory.getInstance().createLiteral("good blogger")));
		w.endRDF();
		System.out.println("\n");
	}
}

输出如下:

true
[(http://www.steeven.org/rdf#steeven, http://www.w3.org/2000/01/rdf-schema#label, "steeven li")]
[(http://www.steeven.org/rdf#steeven, http://www.steeven.org/rdf#desc, "good blogger")]
[(http://www.steeven.org/rdf#steeven, http://www.w3.org/2000/01/rdf-schema#label, "steeven li")]
"steeven li"
2

RDFParser/RdfWriter主要针对流来操作. 而后面要介绍的sail则基于库的概念,可以查询.类似数据库的概念.
数据库的概念过于平面化.RDf的结构复杂些,能根据主谓宾中的任意元素组合查询/遍历. 其内置的索引机制负责加速查询. 开发过程中可以省去复杂的数据建模.