sax 动态切换 抓取感兴趣的内容（把element当做documnet 处理）

由switch 类触发事件

import org.xml.sax.Attributes;

import org.xml.sax.SAXException;

import org.xml.sax.helpers.DefaultHandler;

abstract class DelegateHandler extends DefaultHandler{

    public abstract void startDocument(String uri, String localName, String qName, Attributes attributes) throws SAXException;

    public abstract void endDocument(String uri, String localName, String qName) throws SAXException;

}

由api 触发事件

import java.util.ArrayList;

import java.util.List;

import java.util.Map;

import org.xml.sax.Attributes;

import org.xml.sax.SAXException;

import org.xml.sax.helpers.DefaultHandler;

class SwitchHandler extends DefaultHandler {

    private final Map<String, DelegateHandler> handlerMap;

    private List<String> path = new ArrayList<String>();

    private String currentHandlerPath = null;

    public SwitchHandler(Map<String, DelegateHandler> handlerMap) {

        this.handlerMap = handlerMap;

    }

    @Override

    public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {

        // update path (increase)

        setPath(qName, true);

        String path = getPath();

        // startDocument

        if (handlerMap.containsKey(path)) {

            handlerMap.get(path).startDocument(uri, localName, qName, attributes);

            currentHandlerPath = path;

        }

        // startElement

        else if (currentHandlerPath != null && path.startsWith(currentHandlerPath)) {

            handlerMap.get(currentHandlerPath).startElement(uri, localName, qName, attributes);

        }

    }

    @Override

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

        if (currentHandlerPath != null) {

            handlerMap.get(currentHandlerPath).characters(ch, start, length);

        }

    }

    @Override

    public void endElement(String uri, String localName, String qName) throws SAXException {

        String path = getPath();

        // endDocument

        if (handlerMap.containsKey(path)) {

            handlerMap.get(path).endDocument(uri, localName, qName);

            currentHandlerPath = null;

        }

        // endElement

        else if (currentHandlerPath != null && path.startsWith(currentHandlerPath)) {

            handlerMap.get(currentHandlerPath).endElement(uri, localName, qName);

        }

        // update path (reduce)

        setPath(qName, false);

    }

    public String getPath() {

        StringBuilder sb = new StringBuilder();

        for (String str : this.path) {

            sb.append("/");

            sb.append(str);

        }

        return sb.toString();

    }

    public void setPath(String qName, boolean add) {

        if (add) {

            this.path.add(qName);

        } else {

            this.path.remove(path.size() - 1);

        }

    }

}

具体的实现

import java.io.InputStream;

import java.io.InputStreamReader;

import java.io.Reader;

import java.io.StringWriter;

import java.util.ArrayList;

import java.util.HashMap;

import java.util.List;

import java.util.Map;

import javax.xml.parsers.SAXParser;

import javax.xml.parsers.SAXParserFactory;

import org.xml.sax.Attributes;

import org.xml.sax.InputSource;

import org.xml.sax.SAXException;

import org.xml.sax.XMLReader;

public class SaxTest {

    public static void main(String[] args) throws Exception {

        SaxTest saxTest = new SaxTest();

        InputStream in = SaxTest.class.getResourceAsStream("test.xml");

        InputStreamReader inr = new InputStreamReader(in);

        System.out.println(saxTest.exchange(inr));

    }

    public String exchange(Reader reader) throws Exception {

        // xpath

        Map<String, DelegateHandler> handlerMap = new HashMap<String, DelegateHandler>();

        TeacherHandler teacherHandler = new TeacherHandler();

        StudentHandler studentHandler = new StudentHandler();

        handlerMap.put("/class/teacher", teacherHandler);

        handlerMap.put("/class/student", studentHandler);

        SwitchHandler switchHandler = new SwitchHandler(handlerMap);

        // sax

        SAXParserFactory factory = SAXParserFactory.newInstance();

        SAXParser parser = factory.newSAXParser();

        XMLReader xmlReader = parser.getXMLReader();

        xmlReader.setContentHandler(switchHandler);

        xmlReader.parse(new InputSource(reader));

        // data

        StringWriter writer = new StringWriter();

        for (String teacher : teacherHandler.teacherList) {

            writer.write("teacher:" + teacher + "\n");

        }

        for (String student : studentHandler.studentList) {

            writer.write("student:" + student + "\n");

        }

        return writer.toString();

    }

    private class TeacherHandler extends DelegateHandler {

        List<String> teacherList = new ArrayList<String>();

        StringBuilder characters = new StringBuilder();

        String id = null;

        String name = null;

        @Override

        public void startDocument(String uri, String localName, String qName, Attributes attributes)

                throws SAXException {

        }

        @Override

        public void startElement(String uri, String localName, String qName, Attributes attributes)

                throws SAXException {

        }

        @Override

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

            characters.append(ch, start, length);

        }

        @Override

        public void endElement(String uri, String localName, String qName) throws SAXException {

            if (qName.equals("id")) {

                id = characters.toString().trim();

            } else if (qName.equals("name")) {

                name = characters.toString().trim();

                teacherList.add(id + " = " + name);

            }

            characters.setLength(0);

        }

        @Override

        public void endDocument(String uri, String localName, String qName) throws SAXException {

        }

    }

    private class StudentHandler extends DelegateHandler {

        List<String> studentList = new ArrayList<String>();

        StringBuilder characters = new StringBuilder();

        String id = null;

        String name = null;

        @Override

        public void startDocument(String uri, String localName, String qName, Attributes attributes)

                throws SAXException {

        }

        @Override

        public void startElement(String uri, String localName, String qName, Attributes attributes)

                throws SAXException {

        }

        @Override

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

            characters.append(ch, start, length);

        }

        @Override

        public void endElement(String uri, String localName, String qName) throws SAXException {

            if (qName.equals("id")) {

                id = characters.toString().trim();

            } else if (qName.equals("name")) {

                name = characters.toString().trim();

                studentList.add(id + " = " + name);

            }

            characters.setLength(0);

        }

        @Override

        public void endDocument(String uri, String localName, String qName) throws SAXException {

        }

    }

}

测试文件：

<class>

    <teacher>

        <id>t01</id>

        <name>SUN</name>

    </teacher>

    <teacher>

        <id>t02</id>

        <name>ZHANG</name>

    </teacher>

    <student>

        <id>s01</id>

        <name>Lucy</name>

    </student>

    <student>

        <id>s02</id>

        <name>Lili</name>

    </student>

</class>

结果：

teacher:t01 = SUN

teacher:t02 = ZHANG

student:s01 = Lucy

student:s02 = Lili

补充：

可通过构造函数传入感兴趣的字段，“a,b,c,d”

补充（如果控制顺序）：

import java.util.LinkedHashMap;

import java.util.Map;

public class Main {

    public static void main(String[] args) {

        Map<String, String> linkedHashMap = new LinkedHashMap<String, String>();

        linkedHashMap.put("a", "1");

        linkedHashMap.put("b", "2");

        // 这里不改变原有顺序

        linkedHashMap.put("a", "3");

        System.out.println(linkedHashMap);

    }

}

{a=3, b=2}