由於最近要用的是XML格式的字串，而不用寫到檔案中，所以對原始程式碼進行了修改如下：

要讀的xml檔案

<?xml version="1.0" encoding="GB2312"?>
<學生花名冊>
     <學生 性別 = "男">
         <姓名>李華</姓名>
         <年齡>14</年齡>
     </學生>
     <學生 性別 = "男">
         <姓名>張三</姓名>
         <年齡>16</年齡> 
     </學生>
</學生花名冊>

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.InputStream;
import java.io.OutputStreamWriter;
import java.util.Iterator;
import java.util.Vector;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Result;
import javax.xml.transform.Source;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerConfigurationException;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.w3c.dom.Text;

public class DomTest {
    Vector students_Vector;

    private Vector readXMLFile(String file) throws Exception {
        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = dbf.newDocumentBuilder();
        Document doc = builder.parse(file); // 獲取到xml檔案
        // 下面開始讀取
        Element root = doc.getDocumentElement(); // 獲取根元素
        NodeList students = root.getElementsByTagName("學生");
        students_Vector = new Vector();
        for (int i = 0; i < students.getLength(); i++) {
            // 一次取得每一個學生元素
            Element ss = (Element) students.item(i);

            // 建立一個學生的例項
            student stu = new student();
            stu.setSex(ss.getAttribute("性別"));

            NodeList names = ss.getElementsByTagName("姓名");
            Element e = (Element) names.item(0);
            Node t = e.getFirstChild();
            stu.setName(t.getNodeValue());

            NodeList ages = ss.getElementsByTagName("年齡");
            e = (Element) ages.item(0);
            t = e.getFirstChild();
            stu.setAge(Integer.parseInt(t.getNodeValue()));

            students_Vector.add(stu);
        }
        return students_Vector;
    }

    /**
     * 功能：直接提取XML格式字串中的資訊
     */
    private Vector readXMLString(String xmlStr) throws Exception {
        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = dbf.newDocumentBuilder();
        InputStream inputStream = new ByteArrayInputStream(xmlStr.getBytes());
        Document doc = builder.parse(inputStream); //
        // 下面開始讀取
        Element root = doc.getDocumentElement(); // 獲取根元素
        NodeList students = root.getElementsByTagName("學生");
        students_Vector = new Vector();
        for (int i = 0; i < students.getLength(); i++) {
            // 一次取得每一個學生元素
            Element ss = (Element) students.item(i);

            // 建立一個學生的例項
            student stu = new student();
            stu.setSex(ss.getAttribute("性別"));

            NodeList names = ss.getElementsByTagName("姓名");
            Element e = (Element) names.item(0);
            Node t = e.getFirstChild();
            stu.setName(t.getNodeValue());

            NodeList ages = ss.getElementsByTagName("年齡");
            e = (Element) ages.item(0);
            t = e.getFirstChild();
            stu.setAge(Integer.parseInt(t.getNodeValue()));

            students_Vector.add(stu);
        }
        return students_Vector;
    }

    // 將Document內容 寫入XML字串並返回
    private String callWriteXmlString(Document doc, String encoding) {

        try {
            Source source = new DOMSource(doc);
            ByteArrayOutputStream outStream = new ByteArrayOutputStream();
            OutputStreamWriter write = new OutputStreamWriter(outStream);
            Result result = new StreamResult(write);

            Transformer xformer = TransformerFactory.newInstance()
                    .newTransformer();
            xformer.setOutputProperty(OutputKeys.ENCODING, encoding);

            xformer.transform(source, result);
            return outStream.toString();

        } catch (TransformerConfigurationException e) {
            e.printStackTrace();
            return null;
        } catch (TransformerException e) {
            e.printStackTrace();
            return null;
        }

    }

    /**
     * 功能：生成XML格式的字串
     */
    public String writeXMLString() {
        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = null;
        try {
            builder = dbf.newDocumentBuilder();
        } catch (Exception e) {
        }
        Document doc = builder.newDocument();

        Element root = doc.createElement("學生花名冊");
        doc.appendChild(root); // 將根元素新增到文件上

        // 獲取學生資訊
        for (int i = 0; i < students_Vector.size(); i++) {
            student s = (student) students_Vector.get(i);
            // 建立一個學生
            Element stu = doc.createElement("學生");
            stu.setAttribute("性別", s.getSex());
            root.appendChild(stu);// 新增屬性

            // 建立文字姓名節點
            Element name = doc.createElement("姓名");
            stu.appendChild(name);
            Text tname = doc.createTextNode(s.getName());
            name.appendChild(tname);

            // 建立文字年齡節點
            Element age = doc.createElement("年齡");
            stu.appendChild(age); // 將age新增到學生節點上
            Text tage = doc.createTextNode(String.valueOf(s.getAge()));
            age.appendChild(tage); // 將文字節點放在age節點上
        }
        try {
            String result = callWriteXmlString(doc, "gb2312");
            return result;
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        }
    }

    /**
     * 主函式
     */
    public static void main(String args[]) {
        String str = "xml\\student.xml";
        DomTest t = new DomTest();
        System.out.println("解析原始XML檔案：");
        try {
            Vector v = t.readXMLFile(str);
            Iterator it = v.iterator();
            while (it.hasNext()) {
                student s = (student) it.next();
                System.out.println(s.getName() + "\t" + s.getAge() + "\t"
                        + s.getSex());
            }
        } catch (Exception e) {
            e.printStackTrace();

        }
        String xmlStr = t.writeXMLString();
        System.out.println("\n生成的XML字串：\n" + xmlStr);
        try {
            Vector v = t.readXMLString(xmlStr);
            Iterator it = v.iterator();
            System.out.println("\n解析生成的XML字串：");
            while (it.hasNext()) {
                student s = (student) it.next();
                System.out.println(s.getName() + "\t" + s.getAge() + "\t"
                        + s.getSex());
            }
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}

class student {
    private String sex;
    private String name;
    private int age;

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public void setSex(String s) {
        sex = s;
    }

    public String getSex() {
        return sex;
    }

    public void setName(String n) {
        name = n;
    }

    public String getName() {
        return name;
    }
}

輸出：

解析原始XML檔案：
李華    14    男
張三    16    男

生成的XML字串：
<?xml version="1.0" encoding="GB2312" standalone="no"?><學生花名冊><學生 性別="男"><姓名>李華</姓名><年齡>14</年齡></學生><學生 性別="男"><姓名>張三</姓名><年齡>16</年齡></學生></學生花名冊>

解析生成的XML字串：
李華    14    男
張三    16    男