java实现文件上传下载的三种方法
JSP+Servlet
一、文件上传下载原理
在TCP/IP中，最早出现的文件上传机制是FTP。它是将文件由客户端发送到服务器的标准机制。但是在jsp编程中不能使用FTP方法来上传文件，这是由jsp的运行机制所决定的。
通过为表单元素设置Method=“post” enctype="multipart/form-data"属性，让表单提交的数据以二进制编码的方式提交，在接收此请求的Servlet中用二进制流来获取内容，就可以取得上传文件的内容，从而实现文件的上传。
二、enctype属性的选择值范围
1、application/x-www-form-urlencoded:这是默认编码方式，它只处理表单域里的value属性值，采用这种编码方式的表单会将表单域的值处理成url编码方式。
2、multipart/form-data:这种编码方式的表单会以二进制流的方式来处理表单数据，这种编码方式会把文件域指定的文件内容也封装到请求参数里。
3、text/plain:这种方式主要适用于直接通过表单发送邮件的方式。
代码内容
1.将文件读取到服务器指定目录下
2.获取文件内容的起止位置，和文件名称
3.将文件保存到项目的指定目录下
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//从request中获取输入流信息
InputStream fileSource = request.getInputStream();
//创建存储在服务器的路径信息
String tempFileName = "H:/tempFile";
//指向临时文件
File tempFile = new File(tempFileName);
//outPutStream输出流指向临时文件
FileOutputStream outputStream = new FileOutputStream(tempFile);
//每次读取文件字节
byte b[] = new byte[1024];
int n;
while((n=fileSource.read(b))!=-1){
outputStream.write(b,0,n);
}
//关闭输出输入流
fileSource.close();
outputStream.close();
//获取上传文件的名称
RandomAccessFile randomFile = new RandomAccessFile(tempFile, "r");
randomFile.readLine(); //获取第一行数据（对我们来说没有意义）
String str = randomFile.readLine(); //获取第二行数据，内容为：Content-Disposition: form-data; name="myfile"; filename="C:\Users\lihf\Desktop\hello.txt"
int beginIndex = str.lastIndexOf("\\")+1;
int endIndex = str.lastIndexOf("\"");
String fileName = str.substring(beginIndex, endIndex);
//重新定位文件指针到头文件
randomFile.seek(0);
long startPosition=0;
int i=1;
//获取文件内容开始位置
while((n=randomFile.readByte())!=-1&&i<=4){
if(n=='\n'){
startPosition = randomFile.getFilePointer();
i++;
}
}
startPosition = randomFile.getFilePointer() -1;
//获取文件结束位置
randomFile.seek(randomFile.length()); //文件指针定位到文件末尾
long endPosition = randomFile.getFilePointer();
int j=1;
while(endPosition>=0&&j<=2){
endPosition--;
randomFile.seek(endPosition);
if(randomFile.readByte()=='\n'){
j++;
}
}
endPosition = endPosition -1;
//设置保存文件上传的路径
String realPath = getServletContext().getRealPath("/")+"images";
System.out.println("保存文件上传的路径："+realPath);
File fileupload = new File(realPath);
if(!fileupload.exists()){
fileupload.mkdir(); //创建此抽象路径名指定的目录。
}
File saveFile = new File(realPath, fileName);
RandomAccessFile randomAccessFile = new RandomAccessFile(saveFile,"rw");
//从临时文件中读取文件内容（根据文件起止位置获取）
randomFile.seek(startPosition);
while(startPosition三、文件下载原理
1、step1:需要通过HttpServletResponse.setContentType方法设置Content-type头字段的值，为浏览器无法使用某种方式或激活某个程序来处理的MIME类型，例如，“application/octet-stream”或“application/x-msdownload”等。
2、step2:需要通过HttpServletResponse.setHeader方法设置Content-Disposition头的值为“attachment；filename=文件名”。
3、step3:读取下载文件，调用HttpServletResponse.getOutputStream方法返回的OutputStream对象来向客户端写入附件文件内容。
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//获取文件下载路径
String path = getServletContext().getRealPath("/") + "images/";
String filename = request.getParameter("filename");
File file = new File(path + filename);
if(file.exists()){
//设置相应类型application/octet-stream
response.setContentType("application/x-msdownload");
//设置头信息
response.setHeader("Content-Disposition", "attachment;filename=\"" + filename + "\"");
InputStream inputStream = new FileInputStream(file);
ServletOutputStream ouputStream = response.getOutputStream();
byte b[] = new byte[1024];
int n ;
while((n = inputStream.read(b)) != -1){
ouputStream.write(b,0,n);
}
//关闭流、释放资源
ouputStream.close();
inputStream.close();
}else{
request.setAttribute("errorResult", "文件不存在下载失败！");
RequestDispatcher dispatcher = request.getRequestDispatcher("jsp/01.jsp");
dispatcher.forward(request, response);
}
}<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
My JSP '01.jsp' starting page
下载hello.txt ${errorResult}
图片预览
使用非常简单，直接引入SmartUpload的jar文件就可以啦
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//设置上传文件保存路径
String filePath = getServletContext().getRealPath("/")+"images";
File file = new File(filePath);
if(!file.exists()){
file.mkdir();
}
SmartUpload su = new SmartUpload();
//初始化smartUpload
su.initialize(getServletConfig(), request, response);
//设置上传文件大小
su.setMaxFileSize(1024*1024*10);
//设置所有文件的大小
su.setTotalMaxFileSize(102481024*100);
//设置允许上传文件的类型
su.setAllowedFilesList("txt,jpg,gif");
String result = "上传能成功";
try {
//设置禁止上传文件类型
su.setDeniedFilesList("jsp,rar");
su.upload();
int count = su.save(filePath);
System.out.println("上传成功"+count+"文件！");
} catch (Exception e) {
result="上传文件失败！";
if(e.getMessage().indexOf("1015")!=-1){
result = "上传文件失败:上传文件类型不正确！";
}else if(e.getMessage().indexOf("1010")!=-1){
result = "上传文件失败:上传文件类型不正确！";
}else if(e.getMessage().indexOf("1105")!=-1){
result = "上传文件失败:上传文件大小大于允许上传的最大值！";
}else if(e.getMessage().indexOf("1110")!=-1){
result = "上传文件失败:上传文件的总大小大于我们允许上传总大小的最大值！";
}
e.printStackTrace();
}
for(int i=0;i com.jspsmart.upload.File tempFile = su.getFiles().getFile(i);
System.out.println("表单当中name属性值："+tempFile.getFieldName());
System.out.println("上传文件名："+tempFile.getFileName());
System.out.println("上传文件的大小："+tempFile.getSize());
System.out.println("上传文件名拓展名："+tempFile.getFileExt());
System.out.println("上传文件的全名："+tempFile.getFilePathName());
}
request.setAttribute("result",result);
request.getRequestDispatcher("jsp/02.jsp").forward(request, response);
}<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
My JSP '02.jsp' starting page
下载：img5-lg.jpg
图片预览
下载部分的代码public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String filename = request.getParameter("filename");
SmartUpload su = new SmartUpload();
su.initialize(getServletConfig(), request, response);
su.setContentDisposition(null);
try {
su.downloadFile("/images/"+filename);
} catch (SmartUploadException e) {
e.printStackTrace();
}
}Struts2实现上传下载：
上传jsp页面代码：
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
My JSP '03.jsp' starting page
文件上传
图片预览
/jsp/03.jsp
/jsp/error.jsp
image/bmp,image/x-png,image/gif,image/pjpeg
2M
/images/img2-lg.jpg
application/octet-stream
inputStream
attachment;filename="${downloadFileName}"
8192
scxz
UploadServlet
com.lihf.servlet.UploadServlet
DownloadServlet
com.lihf.servlet.DownloadServlet
SmartUploadServlet
com.lihf.servlet.SmartUploadServlet
SmartDownloadServlet
com.lihf.servlet.SmartDownloadServlet
UploadServlet
/uploadServlet.do
DownloadServlet
/downloadServlet.do
SmartUploadServlet
/smartUploadServlet.do
SmartDownloadServlet
/smartDownloadServlet.do
struts2
org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter
struts2
/*
index.jsp
package com.lihf.action;
import java.io.File;
import java.util.List;
import org.apache.commons.io.FileUtils;
import org.apache.struts2.ServletActionContext;
import com.opensymphony.xwork2.ActionSupport;
public class FileUploadAction extends ActionSupport {
private List upload;
private List uploadContentType;
private List uploadFileName;
private String result;
public List getUpload() {
return upload;
}
public void setUpload(List upload) {
this.upload = upload;
}
public List getUploadContentType() {
return uploadContentType;
}
public void setUploadContentType(List uploadContentType) {
this.uploadContentType = uploadContentType;
}
public List getUploadFileName() {
return uploadFileName;
}
public void setUploadFileName(List uploadFileName) {
this.uploadFileName = uploadFileName;
}
public String getResult() {
return result;
}
public void setResult(String result) {
this.result = result;
}
@Override
public String execute() throws Exception {
String path = ServletActionContext.getServletContext().getRealPath("/images");
File file = new File(path);
if(!file.exists()){
file.mkdir();
}
for(int i=0;i action方法：
package com.lihf.action;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;
import java.net.URLEncoder;
import org.apache.commons.io.FileUtils;
import org.apache.struts2.ServletActionContext;
import com.opensymphony.xwork2.ActionSupport;
public class DownLoadAction extends ActionSupport {
public String inputPath;
public String fileName;
public String getFileName() {
return fileName;
}
public void setFileName(String fileName) {
this.fileName = fileName;
}
public String getInputPath() {
return inputPath;
}
public void setInputPath(String inputPath) {
this.inputPath = inputPath;
}
@Override
public String execute() throws Exception {
return SUCCESS;
}
public InputStream getInputStream() throws IOException{
String path = ServletActionContext.getServletContext().getRealPath("/images");
String filePath = path+"\\"+fileName;
File file = new File(filePath);
return FileUtils.openInputStream(file);
//根据文件路径获取流信息固定下载文件使用方法
//return ServletActionContext.getServletContext().getResourceAsStream(inputPath);
}
public String getDownloadFileName(){
//如果是中文的文件名称需要转码
String downloadFileName = "";
try {
downloadFileName = URLEncoder.encode("文件下载.jpg","UTF-8");
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
return downloadFileName;
}
}
