1.读取XML文件,获得document对象.
            SAXReader reader = new SAXReader();
            Document  document = reader.read(new File("input.xml"));

2.解析XML格式的字符串,获得document对象.
            String text = "<members></members>";
            Document document = DocumentHelper.parseText(text);
3.创建document空对象.
            Document document = DocumentHelper.createDocument();
            Element  root = document.addElement("members");// 创建根节点,只有空DOCUMENT对象才能创建ROOT结点

1.获取文档的根节点.
           Element   root = document.getRootElement();
2.取得节点的文本
           String text=memberElm.getText();
也可以用：
           String text=root.elementText("name");   //这个是取得根节点下的name字节点的文字;可以类推任何节点下的文本
3.设置节点文字.
           ageElm.setText("29");
4.父节点下获得单个子节点对象.
           Element memberElm=root.element("member");  // "member"是节点名

5.取得父节点下遍历名为"member"的所有子节点.
           List nodes = rootElm.elements("member");
           for (Iterator it = nodes.iterator(); it.hasNext();) {
                 Element elm = (Element) it.next();
                 // do something
            }
6.父节点下的遍历所有子节点进行.
            for(Iterator it=root.elementIterator();it.hasNext();){
                Element element = (Element) it.next();
                // do something
            }
7.父节点下添加子节点.
           Element ageElm = newMemberElm.addElement("age");

8.父节点下删除子节点.
           parentElm.remove(childElm);// childElm是待删除的节点,parentElm是其父节点

三.属性相关.
1.取得某节点下的某属性
            Element root=document.getRootElement();   
            Attribute attribute=root.attribute("size");// 属性名name
2.取得属性的文字
            String text=attribute.getText();
也可以用:
String text2=root.element("name").attributeValue("firstname");这个是取得根节点下name字节点的属性firstname的值.

3.遍历某节点的所有属性
            Element root=document.getRootElement();   
            for(Iterator it=root.attributeIterator();it.hasNext();){
                Attribute attribute = (Attribute) it.next();
                String text=attribute.getText();
                System.out.println(text);
            }
4.设置某节点的属性和文字.
newMemberElm.addAttribute("name", "sitinspring");
5.设置属性的文字
            Attribute attribute=root.attribute("name");
            attribute.setText("sitinspring");
6.删除某属性
            Attribute attribute=root.attribute("size");// 属性名name
            root.remove(attribute);
四.将文档写入XML文件.
1.文档中全为英文,不设置编码,直接写入的形式.
XMLWriter writer = new XMLWriter(new FileWriter("output.xml"));
writer.write(document);
writer.close();
2.文档中含有中文,设置编码格式写入的形式.
            OutputFormat format = OutputFormat.createPrettyPrint();
            format.setEncoding("GBK");    // 指定XML编码       
            XMLWriter writer = new XMLWriter(new FileWriter("output.xml"),format);
           
            writer.write(document);
            writer.close();
五.字符串与XML的转换
1.将字符串转化为XML
String text = "<members> <member>sitinspring</member> </members>";
Document document = DocumentHelper.parseText(text);
2.将文档或节点的XML转化为字符串.
            SAXReader reader = new SAXReader();
            Document  document = reader.read(new File("input.xml"));           
            Element root=document.getRootElement();               
            String docXmlText=document.asXML();
            String rootXmlText=root.asXML();
            Element memberElm=root.element("member");
            String memberXmlText=memberElm.asXML();
六.使用XPath快速找到节点.
读取的XML文档示例
<?xml version="1.0" encoding="UTF-8"?>
<projectDescription>
  <name>MemberManagement</name>
  <comment></comment>
  <projects>
    <project>PRJ1</project>
    <project>PRJ2</project>
    <project>PRJ3</project>
    <project>PRJ4</project>
  </projects>
  <buildSpec>
    <buildCommand>
      <name>org.eclipse.jdt.core.javabuilder</name>
      <arguments>
      </arguments>
    </buildCommand>
  </buildSpec>
  <natures>
    <nature>org.eclipse.jdt.core.javanature</nature>
  </natures>
</projectDescription>

使用XPath快速找到节点project.
 public static void main(String[] args){
    SAXReader reader = new SAXReader();
   
    try{
      Document  doc = reader.read(new File("sample.xml"));
     
      List projects=doc.selectNodes("/projectDescription/projects/project");
     //Element nodes0=xmlDoc.selectSingleNode("/bookstore"); //采用相对路径,即当前结点(包括当前结点)开始查找,与下列结果相同.
     //Element nodes=nodes0.selectNodes("book");      ////采用绝对路径,即当前结点(包括当前结点)开始查找,
     //XPATH语法详见: http://www.w3school.com.cn/xpath/xpath_syntax.asp

      Iterator it=projects.iterator();
     
      while(it.hasNext()){
        Element elm=(Element)it.next();      
        System.out.println(elm.getText());
      }
     
    }
    catch(Exception ex){
       ex.printStackTrace();
    }
  }

 
</script>

属性来指定。
<%=  ((DataObject)pageContext.getAttribute("id1")).getString("paramDictname") %>

Jsp中实现文件上传与下载  

1．客户端上传文件
    客户端通过一个Jsp页面，上传文件到服务器，该Jsp页面必须含有File类表单，并且表单必须设置enctype="multipart/form- data"。提交表单时通过内置对象request，request.getInputStream();方法获得一个输入流。
    在上传文件时，会有附加信息，如下所示：

-----------------------------7d71042a40328
Content-Disposition: form-data; name="fileforload"; filename="C:"Documents and Settings"ZJ"桌面"book.txt"
Content-Type: text/plain
//此处为文件内容
-----------------------------7d71042a40328
Content-Disposition: form-data; name="submit"

commit
-----------------------------7d71042a40328--

    附加信息大小为297字节（不确定这个值，测试得到），可通过request.getContentLength()>297来判断是否上传了文件还是提交空字符串。

2．测试
    fileupload.jsp负责提交文件，accept.jsp负责实现上传功能。
fileupload.jsp

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=GB18030">
<title>This page for FileUpload</title>
</head>
<body>
<p>Choose the file for uploading:
<form action="accept.jsp" method=post enctype="multipart/form-data">
  <input type=file name=fileforload size=30>
  <br>
  <input type=submit value=commit name=submit>
</form>
</body>
</html>

accept.jsp

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=GB18030">
<title>This page for response</title>
</head>
<body>
<%try{
 if(request.getContentLength()>297){
   InputStream in=request.getInputStream();
   File f=new File("d:/temp","test.txt");
   FileOutputStream o=new FileOutputStream(f);
   byte b[]=new byte[1024];
   int n;
   while((n=in.read(b))!=-1){
  o.write(b,0,n);
   }
   o.close();
   in.close();
   out.print("File upload success!");
 }
 else{
  out.print("No file!");
 }
}
catch(IOException e){
 out.print("upload error.");
 e.printStackTrace();
}
%>
</body>
</html>

    服务器端得到的上传文件I like.txt，取名为test.txt

-----------------------------7d75b1540328
Content-Disposition: form-data; name="fileforload"; filename="C:"Documents and Settings"ZJ"桌面"I like.txt"
Content-Type: text/plain

我喜欢驾驭着代码在风驰电掣中创造完美;
我喜欢操纵着代码在随心所欲中体验生活;
我喜欢用心情代码编制我小小的与众不同;
每一段新的代码在我手中延生对我来说就象观看刹那花开的感动;
我不需要焦点.因为我就是焦点!

-----------------------------7d75b1540328
Content-Disposition: form-data; name="submit"

commit
-----------------------------7d75b1540328--

3．去除附加信息
    按照HTTP协议，文件表单提交的信息中，前4行(不足的自动空行)和后5行是表单本身的信息，中间部分才是上传的文件的内容。下例对上传的文件进行处理，获取文件名，并去除附加信息。

4．测试
    fileupload.jsp不变，accept.jsp修改如下：

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=GB18030">
<title>The real file</title>
</head>
<body>
<%try{
 //use sessionid to create a temp file.
 String tempFileName=(String)session.getId();
 //create the temp file.
 File temp=new File("d:/temp",tempFileName);
 FileOutputStream o=new FileOutputStream(temp);
 if(request.getContentLength()>297){
   //write the upload content to the temp file.
   InputStream in=request.getInputStream();
   byte b[]=new byte[1024];
   int n;
   while((n=in.read(b))!=-1){
    o.write(b,0,n);
   }
   o.close();
   in.close();
   //read the temp file.
   RandomAccessFile random=new RandomAccessFile(temp,"r");
   //read Line2 to find the name of the upload file.
   int second=1;
   String secondLine=null;
   while(second<=2){
    secondLine=random.readLine();
    second++;
   }
   //get the last location of the dir char.'""'.
   int position=secondLine.lastIndexOf('""');
   //get the name of the upload file.
   String fileName=secondLine.substring(position+1,secondLine.length()-1);
   //relocate to the head of file.
   random.seek(0);
   //get the location of the char.'Enter' in Line4.
   long forthEndPosition=0;
   int forth=1;
   while((n=random.readByte())!=-1&&(forth<=4)){
    if(n=='"n'){
     forthEndPosition=random.getFilePointer();
     forth++;
    }
   }
   File realFile=new File("d:/temp",fileName);
   RandomAccessFile random2=new RandomAccessFile(realFile,"rw");
   //locate the end position of the content.Count backwards 6 lines.
   random.seek(random.length());
   long endPosition=random.getFilePointer();
   long mark=endPosition;
   int j=1;
   while((mark>=0)&&(j<=6)){
    mark--;
    random.seek(mark);
    n=random.readByte();
    if(n=='"n'){
     endPosition=random.getFilePointer();
     j++;
    }
   }
   //locate to the begin of content.Count for 4 lines's end position.
   random.seek(forthEndPosition);
   long startPoint=random.getFilePointer();
   //read the real content and write it to the realFile.
   while(startPoint<endPosition-1){
    n=random.readByte();
    random2.write(n);
    startPoint=random.getFilePointer();
   }
   random2.close();
   random.close();
   //delete the temp file.
   temp.delete();
   out.print("File upload success!");
 }
 else{
  out.print("No file!");
 }
}
catch(IOException e){
 out.print("upload error.");
 e.printStackTrace();
}
%>
</body>
</html>

    （注：如果文件名是中文，会出现乱码。）

5．文件下载
    Jsp内置对象response调用方法getOutputStream（）可以获取一个指向客户的输出流，服务器将文件写入这个流，然后可下载此文件。

6．测试
    download.jsp显示下载选项，LoadFile.java（Servlet）负责下载文件。
download.jsp

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=GB18030">
<title>download page</title>
</head>
<body>
<a href=loadFile>Download:test.zip</a>
</body>
</html>

LoadFile.java

package com.zj.sample;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.OutputStream;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@SuppressWarnings("serial")
public class LoadFile extends HttpServlet{
 public void doGet(HttpServletRequest request,HttpServletResponse response)
   throws IOException,ServletException{
    OutputStream o=response.getOutputStream();
    byte b[]=new byte[1024];
    //the file to download.
    File fileLoad=new File("d:/temp","test.rar");
    //the dialogbox of download file.
    response.setHeader("Content-disposition",
      "attachment;filename="+"test.rar");
    //set the MIME type.
    response.setContentType("application/x-tar");
    //get the file length.
    long fileLength=fileLoad.length();
    String length=String.valueOf(fileLength);
    response.setHeader("Content_Length",length);
    //download the file.
    FileInputStream in=new FileInputStream(fileLoad);
    int n=0;
    while((n=in.read(b))!=-1){
     o.write(b,0,n);
    }
 }
 public void doPost(HttpServletRequest request,HttpServletResponse response)
 throws IOException,ServletException{
  doGet(request,response);
 }

}

web.xml（注册servlet）

<servlet>
  <servlet-name>LoadFileServlet</servlet-name>
  <servlet-class>com.zj.sample.LoadFile</servlet-class>
</servlet>
<servlet-mapping>
  <servlet-name>LoadFileServlet</servlet-name>
  <url-pattern>/loadFile</url-pattern>
</servlet-mapping>