JavaEE实现前后台交互的文件上传与下载

<span style="font-size:14px;"><a href="img">查找文件夹下面的所有图片</a><br/></span> 

<span style="font-size:14px;">public class ShowImg extends HttpServlet { 
 public void doGet(HttpServletRequest request, HttpServletResponse response) 
   throws ServletException, IOException { 
<span style="white-space:pre"> </span>doPost(request, response);//为了防止异常，将doGet和doPost连接在一起 
 }</span> 
 
<span style="font-size:14px;">public void doPost(HttpServletRequest request, HttpServletResponse response) 
   throws ServletException, IOException { 
 
  request.setCharacterEncoding("utf-8"); 
  response.setContentType("text/html;charset=utf-8"); 
  PrintWriter out = response.getWriter();</span> 
 
<pre name="code" class="html"><span style="font-size:14px;">//<span style="white-space:pre">  </span>调出Servletcontext，当然也可以直接调用---当一一列出图片的时候需要文件的绝对路径</span> 

ServletContext context =getServletContext();String path=context.getRealPath("/imgs");//找到该文件夹的绝对路径File file =new File(path);
 
<span style="font-size:14px;">//<span style="white-space:pre">  </span>找到文件夹之后，列出所有图片供用户浏览 
  String files[] =file.list(); 
  for(String fn:files){</span> 
 
<pre name="code" class="html"><span style="font-size:14px;">//一个个的全部显示出来</span> 

<span style="white-space:pre"> </span><span style="font-size:18px;"><strong>response.setContentType("application/force-download"</strong>);//设置相应头</span> 

<span style="font-size:18px;"> <span style="white-space:pre"> </span>OutputStream out=response.getOutputStream();//获得输出流 
 String name=request.getParameter("name");//从客服端传过来的参数名 
 int num=name.lastIndexOf("/"); 
 String aa=name.substring(num+1); 
 aa=URLEncoder.encode(aa, "UTF-8");//若是中文需要重新编码 
 //System.out.println(aa); 
 response.setHeader("Content-Disposition",<span style="color:#ff0000;">"<strong>attachment;filename</strong></span>='"+aa+"'");//获取从那边传过来的文件名,以便于存储的时候为下载用户名</span> 

<span style="font-size:18px;"> String filename=this.getServletContext().getRealPath(name);//获得绝对路径，传文件名过来，同时传了可以获得的绝对路径就可以进行读可写了 
 InputStream in=new FileInputStream(filename); 
 byte[] b=new byte[1024]; 
 int len=0; 
 while((len=in.read(b))!=-1){ 
 out.write(b, 0, len); 
 }</span> 

<span style="font-size:18px;"><h2>上传文件</h2> 
 <form action="UpFile" method="post" <span style="color:#ff0000;">enctype="multipart/form-data"</span> >//必须要写，不然后台没办法去接收数据 
 <!-- 必须添加这个enctype="multipart/form-data"--> 
 File1<input type="file"<span style="color:#ff6666;"> name</span>="file"/><br/> 
 请输入名称：<input type="text" <span style="color:#ff6666;">name</span>="desc"/><br/> 
 File2<input type="file"<span style="color:#ff6666;"> name</span>="file"/><br/> 
 请输入名称：<input type="text"<span style="color:#ff0000;"> name</span>="desc"/><br/> 
 <input type="submit" value="提交"/> 
 </form></span> 

//指定临时存放位置 
File f = new File("F:/ex/temp");//指定临时文件存放位置 
DiskFileItemFactory ff =new DiskFileItemFactory(1024*1024*5, f);//临时文件的大小和存放位置 

//创建用于解析的对象 
 ServletFileUpload sf =new ServletFileUpload(ff); 
 sf.setFileSizeMax(1024*1024*10);//仅仅允许单个存放位置最大值是 10M 
 sf.setSizeMax(1024*1024*20);//所有文件的最大值是20M 
 String path =this.getServletContext().getRealPath("/imgs"); 
 System.out.println("存储路径："+path); 

<span style="white-space:pre"> </span>List<FileItem> list=sf.parseRequest(request);//获得从前台传过来的所有信息,前台必须填写enctype="multipart/form-data" 
  for(FileItem it:list){ 
  it0=it; 
//<span style="white-space:pre">  </span>若是普通表单对象--可以直接判断出 
  if(it.isFormField()){//是普通表单项，如 type=text里面name的值 
   String name=it.getString("utf-8"); 
   System.out.println("基本表单项 name:"+name);//下面写的解释的名字 
  }else{ 
<span style="white-space:pre">  </span>// 这就是前台选择的文件名 
   String name=it.getName();//具体的文件路径---绝对路径 
//   String str=it.getString();//文件里面的内容 
//   System.out.println("str"+str); 
   String contenttype=it.getContentType(); 
   Long size=it.getSize(); 
 <span style="white-space:pre">  </span>System.out.println(name+","+contenttype+","+size); 
<pre name="code" class="html" style="font-size: 18px;">//<span style="white-space:pre">   </span>在服务器端的资源文件名不能用中文，浏览器会自动编码-------必须要把用户上传的文件名转成没有中文的名字存储， 
   //为了让用户在下载时能还原出原来的名字，就要把原文件名和映射名的对应关系存储起来，在用户下载时再转换回来 

<span style="font-size:14px;">package cn.hncu.UPfile;import java.io.File; 
import java.io.IOException; 
import java.io.PrintWriter; 
import java.io.Writer; 
import java.util.List; 
import java.util.UUID; 
import javax.servlet.ServletException; 
import javax.servlet.http.HttpServlet; 
import javax.servlet.http.HttpServletRequest; 
import javax.servlet.http.HttpServletResponse;import org.apache.commons.fileupload.FileItem; 
import org.apache.commons.fileupload.FileUploadException; 
import org.apache.commons.fileupload.disk.DiskFileItemFactory; 
import org.apache.commons.fileupload.servlet.ServletFileUpload; 
import org.apache.commons.io.FileUtils; 
public class MyupFile extends HttpServlet { 
<span style="white-space: pre;"> </span>//doGET防止有人在用户栏输入地址。没有响应 
<span style="white-space: pre;"> </span>@Override 
<span style="white-space: pre;"> </span>protected void doGet(HttpServletRequest req, HttpServletResponse resp) 
<span style="white-space: pre;"> </span>throws ServletException, IOException { 
<span style="white-space: pre;"> </span>resp.setContentType("utf-8"); 
<span style="white-space: pre;"> </span>Writer wr=resp.getWriter(); 
<span style="white-space: pre;"> </span>wr.write("暂不支持该上传方式"); 
<span style="white-space: pre;"> </span>} 
<span style="white-space: pre;"> </span> 
<span style="white-space: pre;"> </span>public void doPost(HttpServletRequest request, HttpServletResponse response) 
<span style="white-space: pre;"> </span>throws ServletException, IOException { 
<span style="white-space: pre;"> </span>request.setCharacterEncoding("utf-8"); 
<span style="white-space: pre;"> </span>response.setContentType("text/html;charset=utf-8"); 
<span style="white-space: pre;"> </span>PrintWriter out=response.getWriter(); 
<span style="white-space: pre;"> </span>//防护 以普通表单上传 法一： 
<span style="white-space: pre;"> </span>//返回值 GET （null） POST1(apllication/x-form-urlencoded,普通表单) POST2(file:multipart/form-data,文件上传表单) 
//<span style="white-space: pre;"> </span>String type =request.getContentType(); 
//<span style="white-space: pre;"> </span>if(!type.contains("mulitpart/form-data")){ 
//<span style="white-space: pre;"> </span>out.write("不支持普通表单的上传2"); 
//<span style="white-space: pre;"> </span>return ; 
//<span style="white-space: pre;"> </span>} 
<span style="white-space: pre;"> </span>// 法二 
<span style="white-space: pre;"> </span>boolean boo=ServletFileUpload.isMultipartContent(request); 
<span style="white-space: pre;"> </span>if(boo==false){ 
<span style="white-space: pre;"> </span>out.print("不支持普通表单的上传1"); 
<span style="white-space: pre;"> </span> 
<span style="white-space: pre;"> </span>} 
<span style="white-space: pre;"> </span> 
<span style="white-space: pre;"> </span>//指定临时存放位置 
<span style="white-space: pre;"> </span>File f = new File("F:/ex/temp");//指定临时文件存放位置 
<span style="white-space: pre;"> </span>DiskFileItemFactory ff =new DiskFileItemFactory(1024*1024*5, f);//临时文件的大小和存放位置 
<span style="white-space: pre;"> </span> 
<span style="white-space: pre;"> </span>//创建用于解析的对象 
<span style="white-space: pre;"> </span>ServletFileUpload sf =new ServletFileUpload(ff); 
<span style="white-space: pre;"> </span>sf.setFileSizeMax(1024*1024*10);//仅仅允许单个存放位置最大值是 10M 
<span style="white-space: pre;"> </span>sf.setSizeMax(1024*1024*20);//所有文件的最大值是20M 
<span style="white-space: pre;"> </span>String path =this.getServletContext().getRealPath("/imgs"); 
<span style="white-space: pre;"> </span>System.out.println("存储路径："+path); 
<span style="white-space: pre;"> </span>//开始进行解析 
<span style="white-space: pre;"> </span>FileItem it0=null;//用于在finally中进行删除临时文件 
<span style="white-space: pre;"> </span>try { 
<span style="white-space: pre;"> </span>List<FileItem> list=sf.parseRequest(request);//获得从前台传过来的所有信息,前台必须填写enctype="multipart/form-data" 
<span style="white-space: pre;"> </span>for(FileItem it:list){ 
<span style="white-space: pre;"> </span>it0=it; 
<span style="white-space: pre;"> </span>if(it.isFormField()){//是普通表单项，如 type=text里面name的值 
<span style="white-space: pre;">  </span>String name=it.getString("utf-8"); 
<span style="white-space: pre;">  </span>System.out.println("基本表单项 name:"+name);//下面写的解释的名字 
<span style="white-space: pre;"> </span>}else{ 
<span style="white-space: pre;">  </span>String name=it.getName();//具体的文件路径 
//<span style="white-space: pre;">  </span>String n1=it.getFieldName(); 
//<span style="white-space: pre;">  </span>String str=it.getString();//文件里面的内容 
//<span style="white-space: pre;">  </span>System.out.println("str"+str); 
//<span style="white-space: pre;">  </span>System.out.println("n1:"+n1); 
<span style="white-space: pre;">  </span>String contenttype=it.getContentType(); 
<span style="white-space: pre;">  </span>Long size=it.getSize(); 
<span style="white-space: pre;">  </span>//防止文件为空 
<span style="white-space: pre;">  </span>if(size==0){ 
<span style="white-space: pre;">  </span>continue;//文件为空，直接返回； 
<span style="white-space: pre;">  </span>} 
<span style="white-space: pre;">  </span>//用户名。必须要填写 
<span style="white-space: pre;">  </span>if(name==null||name.trim()==""){ 
<span style="white-space: pre;">  </span>continue; 
<span style="white-space: pre;">  </span>} 
<span style="white-space: pre;"> </span>//<span style="white-space: pre;"> </span>System.out.println(name+","+contenttype+","+size); 
<span style="white-space: pre;">  </span>//在服务器端的资源文件名不能用中文，浏览器会自动编码-------必须要把用户上传的文件名转成没有中文的名字存储， 
<span style="white-space: pre;">  </span>//为了让用户在下载时能还原出原来的名字，就要把原文件名和映射名的对应关系存储起来，在用户下载时再转换回来 
<span style="white-space: pre;">  </span>//映射名 
<span style="white-space: pre;">  </span>String id=UUID.randomUUID().toString().replace("-", ""); 
<span style="white-space: pre;">  </span>//文件名 
<span style="white-space: pre;">  </span>String lastname=name.substring(name.lastIndexOf(".")); 
<span style="white-space: pre;">  </span>//名字文件格式都找到了---组合 
<span style="white-space: pre;">  </span>String filename =id+lastname; 
<span style="white-space: pre;">  </span>//拷贝流。让它写到相应位置 
<span style="white-space: pre;">  </span>FileUtils.copyInputStreamToFile(it.getInputStream(), new File(path+"/"+filename));}<span style="white-space: pre;"> </span>}} catch (FileUploadException e) { 
<span style="white-space: pre;"> </span>throw new RuntimeException("文件上传解析错误。"+e); 
<span style="white-space: pre;"> </span>}finally{ 
<span style="white-space: pre;"> </span>if(it0==null){ 
<span style="white-space: pre;"> </span>it0.delete();//删除临时文件 
<span style="white-space: pre;"> </span>}}out.close();}}</span><span style="font-size: 18px;"> 
</span> 
文件下载源代码：
[html] view plaincopyprint?
<span style="font-size:14px;">package cn.hncu.downImg; 
 
import java.io.FileInputStream; 
import java.io.IOException; 
import java.io.InputStream; 
import java.io.OutputStream; 
import java.io.PrintWriter; 
import java.net.URLEncoder; 
 
import javax.servlet.ServletException; 
import javax.servlet.http.HttpServlet; 
import javax.servlet.http.HttpServletRequest; 
import javax.servlet.http.HttpServletResponse; 
 
public class DownImgDemo extends HttpServlet { 
 
 
 public void doGet(HttpServletRequest request, HttpServletResponse response) 
 throws ServletException, IOException { 
 doPost(request, response); 
 } 
 
 
 public void doPost(HttpServletRequest request, HttpServletResponse response) 
 throws ServletException, IOException { 
 //设置相应头 
 response.setContentType("application/force-download"); 
 //给前台传用户名 
 /*传固定的用户名 
 String aa="1.jpg";//若是中文，需要编码 
 aa=URLEncoder.encode(aa, "UTF-8"); 
 response.setHeader("Content-Disposition", "attachment;filename='"+aa+"'");////必须要加“attachment;”，否则会变成浏览 
 */ 
 
 OutputStream out=response.getOutputStream();//获得输出流 
 String name=request.getParameter("name");//从客服端传过来的参数名 
 int num=name.lastIndexOf("/"); 
 String aa=name.substring(num+1); 
 aa=URLEncoder.encode(aa, "UTF-8");//若是中文需要重新编码 
 //System.out.println(aa); 
 response.setHeader("Content-Disposition","attachment;filename='"+aa+"'");//获取从那边传过来的文件名,以便于存储的时候为下载用户名 
 
 String filename=this.getServletContext().getRealPath(name);//获得绝对路径 
 InputStream in=new FileInputStream(filename); 
 byte[] b=new byte[1024]; 
 int len=0; 
 while((len=in.read(b))!=-1){ 
 out.write(b, 0, len);}}}</span><span style="font-size: 18px;"> 
</span>