文件上传和下载
文件上传
要实现Web开发的上传功能,通常需要完成两步操作:一是在Web页面中添加上传输入项;二是在Servlet中读取上传文件的数据,并保存到本地硬盘中。
上传大多数情况是通过表单的形式提交给服务器,使用标签。
使用标签需要注意以下两点:
1.必须设置name属性,不然浏览器不会发送上传文件的数据。
2.必须将method属性设置为post,ectype属性设置为“multipart/form-data”类型。
由于在Servlet直接读取上传数据,并且解析出相应文件数据是一项非常麻烦的工作。为了方便处理上传数据,Apache组织提供了一个开源组件Commons-FileUpload。该组件可以将“multipart/form-data”类型请求的各种表单域解析出来,并实现一个或多个文件上传,同时也可以限制上传文件的大小等内容。其性能十分优异,使用极其简单。
对于文件上传,浏览器在上传的过程中是将文件以流的形式提交到服务器端的,如果直接使用Servlet获取上传文件的输入流然后再解析里面的请求参数是比较麻烦,所以一般选择采用apache的开源工具common-fileupload这个文件上传组件。这个common-fileupload上传组件的jar包可以去apache官网上面下载,也可以在struts的lib文件夹下面找到,struts上传的功能就是基于这个实现的。common-fileupload是依赖于common-io这个包的,所以还需要下载这个包。
开发环境搭建
创建一个chapter12项目,加入Apache的commons-fileupload文件上传组件的相关Jar包
实现文件上传
创建上传页面
创建一个form.jsp的j页面,该页面用于提供文件上传的form表单
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>文件上传</title>
</head>
<body>
<form action="UploadServlet" method="post" enctype="multipart/form-data">
<table width="600px">
<tr>
<td>上传者</td>
<td><input type="text" name="username" /></td>
</tr>
<tr>
<td>上传文件</td>
<td><input type="file" name="myfile" /></td>
</tr>
<tr>
<td colspan="2"><input type="submit" value="上传" /></td>
</tr>
</table>
</form>
</body>
</html>
创建Servlet
编写一个UploadServlet的类,该类主要用于获取表单及其上传文件的信息
package cn.itcast.fileupload;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
import java.util.UUID;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
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;
/**
* Servlet implementation class UploadServlet
*/
@WebServlet("/UploadServlet")
public class UploadServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
try {
response.setContentType("text/html;charset=utf-8");
DiskFileItemFactory factory=new DiskFileItemFactory();
File f=new File("d:\\Temp");
if(!f.exists()) {
f.mkdirs();
}
factory.setRepository(f);
factory.setSizeThreshold(1024*1024);
ServletFileUpload fileupload=new ServletFileUpload(factory);
fileupload.setHeaderEncoding("utf-8");
List<FileItem> fileitems=fileupload.parseRequest(request);
for(FileItem fileitem:fileitems) {
boolean flag=fileitem.isFormField();
if(flag) {
String name=fileitem.getFieldName();
if(name.equals("username")) {
if(!fileitem.getString().equals("")) {
String value=fileitem.getString("utf-8");
response.getWriter().print("上传者:"+value+"<br/>");
}
}
}else {
String filename=fileitem.getName();
if(filename!=null&& !filename.equals("")) {
response.getWriter().print("上传的文件名称:"+filename+"<br/>");
filename=filename.substring(filename.lastIndexOf("\\")+1);
filename=UUID.randomUUID().toString()+"_"+filename;
String webPath="/upload2005/";
String filepath=getServletContext().getRealPath(webPath+filename);
File file=new File(filepath);
file.getParentFile().mkdirs();
file.createNewFile();
InputStream in=fileitem.getInputStream();
FileOutputStream out=new FileOutputStream(file);
byte[] buffer=new byte[1024];
int len=0;
while((len=in.read(buffer))>0) {
out.write(buffer,0,len);
}
in.close();
out.close();
fileitem.delete();
response.getWriter().print("文件上传成功"+"<br/>");
}
}
}
} catch (FileUploadException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}
}
启动项目,查看运行结果
文件下载
创建下载页面download.jsp该页面中编写了一个用于下载的链接
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%@page import="java.net.URLEncoder"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>文件下载</title>
</head>
<body>
<a href="/chapter12/DownloadServlet?filename=重庆.jpg">文件下载</a>
</body>
</html>
创建Servlet
创建DownloadServlet类,该类主要用于设置所要下载的下载以及文件在浏览器中的打开方式
package cn.itcast.fileupload;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Servlet implementation class DownloadServlet
*/
@WebServlet("/DownloadServlet")
public class DownloadServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType("text/html;charset=utf-8");
String filename=request.getParameter("filename");
filename=new String (filename.getBytes("iso-8859-1"),"utf-8");
String fileType=getServletContext().getMimeType(filename);
response.addHeader("Content-Type", fileType);
response.addHeader("Content-Disposition", "attachment;filename");
String folder="/download/";
InputStream in=getServletContext().getResourceAsStream(folder+filename);
OutputStream out=response.getOutputStream();
byte[] buffer=new byte[1024];
int len=0;
while((len=in.read(buffer))>0) {
out.write(buffer,0,len);
}
in.close();
out.close();
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}
}
创建下载目录及文件
在项目的WebContent目录下创建一个名称为download的文件夹,在该文件中放置一个重庆.jpg文件。
启动项目,查看结果