web文件上传采用post的方式，与post提交表单不同的是，上传文件需要设置form的enctype属性为multipart/form-data.由于上传的文件会比较大，因此需要设置该参数指定浏览器使用二进制上传。如果不设置，enctype属性默认为application/x-www-form-urlencoded，使用浏览器将使用ascii向服务器发送数据，导致发送文件失败。
上传文件要使用文件域（<input type='file'/>，并把form的enctype设置为multipart/form-data.
客户端上传页面如图所示：
代码如下：
upload.html
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<!doctype html public "-//w3c//dtd html 4.01 transitional//en">
<html>
<head>
<title>上传文件</title>
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="this is my page">
<meta http-equiv="content-type" content="text/html; charset=utf-8">
<link rel="stylesheet" type="text/css" href="css/style.css">
</head>
<body>
<form action="servlet/uploadservlet" method="post" enctype="multipart/form-data">
<div align="center"><br/>
<fieldset style="width:90%">
<legend>上传文件</legend><br/>
<div class='line'>
<div align='left' class="leftdiv">上传文件一</div>
<div align='left' class="rightdiv">
<input type="file" name="file1" class="text">
</div>
</div>
<div class='line'>
<div align='left' class="leftdiv">上传文件二</div>
<div align='left' class="rightdiv">
<input type="file" name="file2" class="text">
</div>
</div>
<div class='line'>
<div align='left' class="leftdiv">上传文件说明一</div>
<div align='left' class="rightdiv"><input type="text" name="description1" class="text"></div>
</div>
<div class='line'>
<div align='left' class="leftdiv">上传文件说明二</div>
<div align='left' class="rightdiv"><input type="text" name="description2" class="text"></div>
</div>
<div class='line'>
<div align='left' class="leftdiv"></div>
<div align='left' class="rightdiv"><br/>
<input type="submit" value=" 上传文件 " class="button">
</div>
</div>
</fieldset>
</div>
</form>
</body>
</html>
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客户端运行的代码很简单，服务器要复杂一点。要想获取其中的内容，必须根据http协议所规定的格式来解析浏览器提交的request.
解析二进制流比较麻烦。已经有许多类库已经完成了这项工作，例如smartupload与apache commons fileupload.smartupload是一个商业类库，解析request过程中数据存放在内存里，因此速度较快，但上传较大文件时会发生内存溢出。apache commons fileupload是一个免费的开源的类库。一些框架比如struts里集成了apache common fileupload类库来实现文件上传。
如图所示：
代码如下：
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package com.helloweenvsfei.servlet;
import java.io.file;
import java.io.fileoutputstream;
import java.io.ioexception;
import java.io.inputstream;
import java.io.outputstream;
import java.io.printwriter;
import java.net.urlencoder;
import java.util.list;
import javax.servlet.servletexception;
import javax.servlet.http.httpservlet;
import javax.servlet.http.httpservletrequest;
import javax.servlet.http.httpservletresponse;
import org.apache.commons.fileupload.diskfileupload;
import org.apache.commons.fileupload.fileitem;
import org.apache.commons.fileupload.fileuploadexception;
public class uploadservlet extends httpservlet {
private static final long serialversionuid = 7523024737218332088l;
public void doget(httpservletrequest request, httpservletresponse response)
throws servletexception, ioexception {
response.setcharacterencoding("utf-8");
response.getwriter().println("请以 post 方式上传文件");
}
@suppresswarnings("unchecked")
public void dopost(httpservletrequest request, httpservletresponse response)
throws servletexception, ioexception {
file file1 = null, file2 = null;
string description1 = null, description2 = null;
response.setcharacterencoding("utf-8");
response.setcontenttype("text/html");
printwriter out = response.getwriter();
out.println("<!doctype html public \"-//w3c//dtd html 4.01 transitional//en\">");
out.println("<html>");
out.println(" <head><title>a servlet</title></head>");
out.println(" <link rel='stylesheet' type='text/css' href='../css/style.css'>");
out.println(" <body>");
out.println("<div align=center><br/>");
out.println("<fieldset style='width:90%'><legend>上传文件</legend><br/>");
out.println(" <div class='line'>");
out.println(" <div align='left' class='leftdiv'>上传日志：</div>");
out.println(" <div align='left' class='rightdiv'>");
// 使用 diskfileupload 对象解析 request
diskfileupload diskfileupload = new diskfileupload();
try {
// 将 解析的结果 放置在 list 中
list<fileitem> list = diskfileupload.parserequest(request);
out.println("遍历所有的 fileitem ... <br/>");
// 遍历 list 中所有的 fileitem
for(fileitem fileitem : list){
if(fileitem.isformfield()){
// 如果是 文本域
if("description1".equals(fileitem.getfieldname())){
// 如果该 fileitem 名称为 description1
out.println("遍历到 description1 ... <br/>");
description1 = new string(fileitem.getstring().getbytes(), "utf-8");
}
if("description2".equals(fileitem.getfieldname())){
// 如果该 fileitem 名称为 description2
out.println("遍历到 description2 ... <br/>");
description2 = new string(fileitem.getstring().getbytes(), "utf-8");
}
}
else{
// 否则，为文件域
if("file1".equals(fileitem.getfieldname())){
// 客户端文件路径构建的 file 对象
file remotefile = new file(new string(fileitem.getname().getbytes(), "utf-8"));
out.println("遍历到 file1 ... <br/>");
out.println("客户端文件位置: " + remotefile.getabsolutepath() + "<br/>");
// 服务器端文件，放在 upload 文件夹下
file1 = new file(this.getservletcontext().getrealpath("attachment"), remotefile.getname());
file1.getparentfile().mkdirs();
file1.createnewfile();
// 写文件，将 fileitem 的文件内容写到文件中
inputstream ins = fileitem.getinputstream();
outputstream ous = new fileoutputstream(file1);
try{
byte[] buffer = new byte[1024];
int len = 0;
while((len=ins.read(buffer)) > -1)
ous.write(buffer, 0, len);
out.println("已保存文件" + file1.getabsolutepath() + "<br/>");
}finally{
ous.close();
ins.close();
}
}
if("file2".equals(fileitem.getfieldname())){
// 客户端文件路径构建的 file 对象
file remotefile = new file(new string(fileitem.getname().getbytes(), "utf-8"));
out.println("遍历到 file2 ... <br/>");
out.println("客户端文件位置: " + remotefile.getabsolutepath() + "<br/>");
// 服务器端文件，放在 upload 文件夹下
file2 = new file(this.getservletcontext().getrealpath("attachment"), remotefile.getname());
file2.getparentfile().mkdirs();
file2.createnewfile();
// 写文件，将 fileitem 的文件内容写到文件中
inputstream ins = fileitem.getinputstream();
outputstream ous = new fileoutputstream(file2);
try{
byte[] buffer = new byte[1024];
int len = 0;
while((len=ins.read(buffer)) > -1)
ous.write(buffer, 0, len);
out.println("已保存文件" + file2.getabsolutepath() + "<br/>");
}finally{
ous.close();
ins.close();
}
}
}
}
out.println("request 解析完毕");
} catch (fileuploadexception e) {
// todo auto-generated catch block
e.printstacktrace();
}
out.println(" </div>");
out.println(" </div>");
if(file1 != null){
out.println(" <div class='line'>");
out.println(" <div align='left' class='leftdiv'>file1：</div>");
out.println(" <div align='left' class='rightdiv'>");
out.println(" <a href='" + request.getcontextpath() + "/attachment/" + file1.getname() + "' target=_blank>" + file1.getname() + "</a>" );
out.println(" </div>");
out.println(" </div>");
}
if(file2 != null){
out.println(" <div class='line'>");
out.println(" <div align='left' class='leftdiv'>file2：</div>");
out.println(" <div align='left' class='rightdiv'>");
out.println(" <a href='" + request.getcontextpath() + "/attachment/" + urlencoder.encode(file2.getname(), "utf-8") + "' target=_blank>" + file2.getname() + "</a>" );
out.println(" </div>");
out.println(" </div>");
}
out.println(" <div class='line'>");
out.println(" <div align='left' class='leftdiv'>description1：</div>");
out.println(" <div align='left' class='rightdiv'>");
out.println(description1);
out.println(" </div>");
out.println(" </div>");
out.println(" <div class='line'>");
out.println(" <div align='left' class='leftdiv'>description2：</div>");
out.println(" <div align='left' class='rightdiv'>");
out.println(description2);
out.println(" </div>");
out.println(" </div>");
out.println("</fieldset></div>");
out.println(" </body>");
out.println("</html>");
out.flush();
out.close();
}
}
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程序运行效果如图所示：
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持服务器之家。
原文链接：http://blog.csdn.net/wuruiaoxue/article/details/50631498