基于Java文件输入输出流实现文件上传下载功能

基于Java文件输入输出流实现文件上传下载功能

本文为大家分享了java实现文件上传下载功能的具体代码，供大家参考，具体内容如下

前端通过form表单的enctype属性，将数据传递方式修改为二进制”流“的形式，服务端（servlet）通过  getInputStream() 获取流信息， 运用java I/O 流的基础操作将流写入到一个服务端临时创建的文件temp中，然后再次利用文件基本操作，读取并截取临时文件内容，根据其中信息创建相应的文件，将读取出来的具体信息写入，下载时，根据提交的文件名称，找到服务器端相应的文件，然后根据输出流outStream输出到页面，同时将servlet的响应类型和响应头进行设置。

具体传输流程如下图：

流信息的部分为：

具体代码如下：

前端代码：

文件下载：${filename}

上传servlet部分（核心）

@WebServlet("/FileUpServlet")

public class FileUpServlet extends HttpServlet {

private static final long serialVersionUID = 1L;

/**

* @see HttpServlet#HttpServlet()

*/

public FileUpServlet() {

super();

// TODO Auto-generated constructor stub

}

/**

* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)

*/

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

// TODO Auto-generated method stub

doPost(request, response);

}

/**

* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)

*/

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

// TODO Auto-generated method stub

request.setCharacterEncoding("utf-8");

InputStream filesource = request.getInputStream();//request获取流信息

String tempname = "D:/temp";//tempfile代表临时存放文件

File tempfile = new File(tempname);//创建临时文件

FileOutputStream outputStream = new FileOutputStream(tempfile);//输出流对象，指定输出指tempfile目录下

byte b[] = new byte[1024];

int n;

while((n = filesource.read(b))!= -1)//从输出流中每次读取1024字节,直至读完

{

outputStream.write(b,0,n);

}

outputStream.close();

filesource.close();//关闭输入输出流

/*以下为具体的文件操作，主要为解析临时产生的 temp文件 ，知识多为java输入输出流的内容！*/

RandomAccessFile randomfile = new RandomAccessFile(tempfile, "r");//随机流，指定要读临时文件，只读

randomfile.readLine();//读取第一行,无效数据，不需要

String str = randomfile.readLine();//读取第二行

int beginIndex = str.lastIndexOf("=")+2;//指定所需数据的开始位置

int endIndex = str.lastIndexOf(vcXtKZ"\"");//指定所需数据截至位置

String filename = str.substring(beginIndex,endIndex);//截取文件名

//重新定位文件指针，获取文件内容

randomfile.seek(0);//文件指针从头开始

long startext = 0;

int i = 1;

//文件内容开始位置

while((n=randomfile.readByte()) != -1&&i <= 4)

{

if(n=='\n')

{

startext = randomfile.getFilePointer();

i++;

}

}

startext = randomfile.getFilePointer() - 1;

//获取文件内容 结束位置

randomfile.seek(randomfile.length());

long endtext = randomfile.getFilePointer();

int j = 1;

while(endtext >= 0 && j <= 2)

{

endtext--;

randomfile.seek(endtext);

if(randomfile.readByte()=='\n')

{

j++;

}

}

endtext = endtext-1;

//将临时文件保存至指定目录中

String realpath = getServletContext().getRealPath("/")+"images";//设置文件保存目录

System.out.println(realpath);

File fileupload = new File(realpath);

if(!fileupload.exists())

{

fileupload.mkdir();//目录不存在则创建

}

File savefile = new File(realpath,filename);

RandomAccessFile randomAccessFile = new RandomAccessFile(savefile, "rw");

randomfile.seek(startext);

while(startext

randomAccessFile.write(randomfile.readByte());//文件写入

startext = randomfile.getFilePointer();

}

//关闭各种输入输出流

randomAccessFile.close();

randomfile.close();

tempfile.delete();//删除临时文件

SimpleDateFormat timed = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

Date nowdate = new Date();

String time = timed.format(nowdate.getTime());

request.setAttribute("info", time+" "+filename+"上传成功！");

request.setAttribute("filename", filename);

request.getRequestDispatcher("/fildeOp.jsp").forward(request, response);

}

}

下载部分

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

// TODO Auto-generated method stub

String filename = request.getParameter("filename");

String path =http:// getServletContext().getRealPath("/")+"images/";

File file = new File(path+filename);//找到文件

if(file.exists())

{

response.setContentType("application/x-msdownload"); //设置响应类型,此处为下载类型

response.setHeader("Content-Disposition", "attachment;filename=\""+filename+"\"");//以附件的形式http://打开

InputStream inputStream = new FileInputStream(file);

ServletOutputStream outputStream = response.getOutputStream();

byte b[] = new byte[1024];

int n;

while((n = inputStream.read(b)) != -1)

{

outputStream.write(b,0,n);

}

outputStream.close();

inputStream.close();

}else{

request.setAttribute("result", "文件不存在！下载失败！");

request.getRequestDispatcher("/fildeOp.jsp").forward(request, response);

}

}

randomAccessFile.write(randomfile.readByte());//文件写入

startext = randomfile.getFilePointer();

}

//关闭各种输入输出流

randomAccessFile.close();

randomfile.close();

tempfile.delete();//删除临时文件

SimpleDateFormat timed = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

Date nowdate = new Date();

String time = timed.format(nowdate.getTime());

request.setAttribute("info", time+" "+filename+"上传成功！");

request.setAttribute("filename", filename);

request.getRequestDispatcher("/fildeOp.jsp").forward(request, response);

}

}

下载部分

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

// TODO Auto-generated method stub

String filename = request.getParameter("filename");

String path =http:// getServletContext().getRealPath("/")+"images/";

File file = new File(path+filename);//找到文件

if(file.exists())

{

response.setContentType("application/x-msdownload"); //设置响应类型,此处为下载类型

response.setHeader("Content-Disposition", "attachment;filename=\""+filename+"\"");//以附件的形式http://打开

InputStream inputStream = new FileInputStream(file);

ServletOutputStream outputStream = response.getOutputStream();

byte b[] = new byte[1024];

int n;

while((n = inputStream.read(b)) != -1)

{

outputStream.write(b,0,n);

}

outputStream.close();

inputStream.close();

}else{

request.setAttribute("result", "文件不存在！下载失败！");

request.getRequestDispatcher("/fildeOp.jsp").forward(request, response);

}

}

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