在web项目中，文件上传、头像上传这样的功能经常是要用到的，下面就以在struts2中实现文件上传功能为例子，简单地理一下文件上传功能的编码思路。
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.0"
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">
<filter>
<filter-name>struts 2</filter-name>
<filter-class>org.apache.struts2.dispatcher.FilterDispatcher</filter-class>
</filter>
<filter-mapping>
<filter-name>struts 2</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
</web-app>
<span style="font-size:12px;"><?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE struts PUBLIC
"-//Apache Software Foundation//DTD Struts Configuration 2.3//EN"
"http://struts.apache.org/dtds/struts-2.3.dtd">
<struts>
<package name="default" extends="struts-default">
<action name="upload" class="com.upload.action.UploadAction" method="upload">
<result name="success">/success.jsp</result>
<result name="error">/upload.jsp</result>
</action>
</package>
</struts></span>
package com.upload.action;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.UUID;
import javax.servlet.ServletContext;
import org.apache.struts2.ServletActionContext;
import com.opensymphony.xwork2.ActionContext;
import com.opensymphony.xwork2.ActionSupport;
public class UploadAction extends ActionSupport{
private File upload; //上传文件
private String uploadFileName; //上传的文件名
public File getUpload(){
return upload;
}
public void setUpload(File upload){
this.upload = upload;
}
public String getUploadFileName(){
return uploadFileName;
}
public void setUploadFileName(String uploadFileName){
this.uploadFileName = uploadFileName;
}
public String upload() throws Exception{
//如果选择了上传功能，则执行上传操作；否则，不作任何操作
if(getUpload() != null){
//根据上传的文件得到输入流
InputStream is = new FileInputStream(getUpload());
//更改上传文件名为：随机数+上传文件名
setUploadFileName(UUID.randomUUID().toString()+ getUploadFileName());
//指定输出流地址，此处是输出到服务器项目的根目录下的images/userPhoto下
OutputStream os = new FileOutputStream(getWebRootPath() + "images\\userPhoto\\" + getUploadFileName());
byte buffer[] = new byte[1024];
int count = 0;
//把文件写到指定位置的文件中
while((count = is.read(buffer)) > 0){
os.write(buffer, 0, count);
}
//关闭输出流对象
os.close();
//关闭输入流对象
is.close();
//返回
return SUCCESS;
}
else {
return ERROR;
}
}
/**
* 获得web项目根目录
*/
public String getWebRootPath() throws Exception {
ActionContext actionContext = ActionContext.getContext();
ServletContext servletContext = (ServletContext)actionContext.get(ServletActionContext.SERVLET_CONTEXT);
String rootPath = servletContext.getRealPath("/");
return rootPath;
}
}<strong>
</strong>
<span style="font-size:12px;"><%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@ taglib uri="/struts-tags" prefix="s" %>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>文件上传</title>
</head>
<body>
<s:form action="upload.action" method="post" enctype="multipart/form-data">
<label for="photoPath">头像：</label>
<input type="text" id="photoPath" disabled="disabled"/>
<input type="button" onclick="myfile.click();" value="选择图片" id="select"/><br />
<input type="file" id="myfile" name="upload" onchange="photoPath.value=this.value" style="display:none" />
<input type="submit" value="上传" />
</s:form>
</body>
</html></span><strong style="font-size:14px;">
</strong>
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>上传成功</title>
</head>
<body>
恭喜您，文件上传成功！点<a href="upload.jsp">这里</a>回去
</body>
</html>
<constant name="struts.multipart.maxSize" value="51200"/>
原文地址：http://blog.csdn.net/wangcunhuazi/article/details/40628423
