Java如何使用SAX从XML文件构建对象？

本示例将向您展示如何使用SAX解析器解析XML文件并从解析的XML构建对象图。我们将读取records.xml包含一些记录信息的文件，并Record从中创建对象。

将DefaultHandler在本例中为匿名类创建。我们覆盖相关的一些方法ContentHandler接口，比如startElement，endElement和characters方法。

package org.nhooo.example.xml;

import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;

import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;
import java.util.Stack;

public class SAXDataDemo {
    // 我们的记录数据列表。
    private List<Record> records = new ArrayList<Record>();

    // 用于存储元素和对象的堆栈。
    private Stack<String> elements = new Stack<String>();
    private Stack<Record> objects = new Stack<Record>();


    public static void main(String[] args) {
        SAXDataDemo demo = new SAXDataDemo();
        demo.run();
    }

    private void run() {
        try {
            SAXParserFactory factory = SAXParserFactory.newInstance();
            SAXParser parser = factory.newSAXParser();

            String filename = "/records.xml";
            InputStream is = getClass().getResourceAsStream(filename);

            parser.parse(is, new DefaultHandler() {
                @Override
                public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {
                    elements.push(qName);
                    if ("record".equals(qName)) {
                        Record record = new Record();
                        objects.push(record);
                        records.add(record);
                    }
                }

                @Override
                public void endElement(String uri, String localName, String qName) throws SAXException {
                    elements.pop();
                }

                @Override
                public void characters(char[] ch, int start, int length) throws SAXException {

                    String value = new String(ch, start, length);
                    if (value.length() == 0) {
                        return;
                    }

                    if ("title".equals(currentElement())) {
                        Record record = objects.peek();
                        record.setTitle(value);
                    } else if ("artist".equals(currentElement())) {
                        Record record = objects.peek();
                        record.setArtist(value);
                    } else if ("genre".equals(currentElement())) {
                        Record record = objects.peek();
                        record.setGenre(value);
                    } else if ("year".equals(currentElement())) {
                        Record record = objects.peek();
                        record.setYear(Integer.valueOf(value));
                    }
                }
            });
        } catch (Exception e) {
            e.printStackTrace();
        }

        for (Record record : records) {
            System.out.println("record = " + record);
        }
    }

    private String currentElement() {
        return elements.peek();
    }
}

记录类。

package org.nhooo.example.xml;

public class Record {
    private String title;
    private String artist;
    private String genre;
    private int year;

    public Record() {
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public void setArtist(String artist) {
        this.artist = artist;
    }

    public void setGenre(String genre) {
        this.genre = genre;
    }

    public void setYear(int year) {
        this.year = year;
    }

    @Override
    public String toString() {
        return "Record{" +
                "title='" + title + "'n" +
                ", artist='" + artist + "'n" +
                ", genre='" + genre + "'n" +
                ", year=" + year +
                '}';
    }
}

以下XML是我们records.xml文件的内容。

<?xml version="1.0"?>
<root>
    <records>
        <record>
            <title>Brand New Eyes</title>
            <artist>Paramore</artist>
            <genre>Punk Rock</genre>
            <year>2011</year>
        </record>
        <record>
            <title>Rock Beatles</title>
            <artist>Various Artist</artist>
            <genre>Rock</genre>
            <year>2010</year>
        </record>
    </records>
</root>

当我们运行此示例时，将获得以下输出：

record = Record{title='Brand New Eyes'
, artist='Paramore'
, genre='Punk Rock'
, year=2011}
record = Record{title='Rock Beatles'
, artist='Various Artist'
, genre='Rock'
, year=2010}