文件上传专栏

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1．客户端上传文件

客户端通过一个Jsp页面，上传文件到服务器，该Jsp页面必须含有File类表单，并且表单必须设置enctype="multipart/form-data"。提交表单时通过内置对象request，request.getInputStream();方法获得一个输入流。

在上传文件时，会有附加信息，如下所示：

-----------------------------7d71042a40328

Content-Disposition: form-data; name="fileforload"; filename="C:/Documents and Settings/ZJ/桌面/book.txt"

Content-Type: text/plain

//此处为文件内容

-----------------------------7d71042a40328

Content-Disposition: form-data; name="submit"

commit

-----------------------------7d71042a40328--

附加信息大小为297字节（不确定这个值，测试得到），可通过request.getContentLength()>297来判断是否上传了文件还是提交空字符串。

2．测试

fileupload.jsp负责提交文件，accept.jsp负责实现上传功能。

fileupload.jsp

<html>

<head>

<title>This page for FileUpload</title>

</head>

<body>

<p>Choose the file for uploading:

<br>

</form>

</body>

</html>

accept.jsp

<html>

<head>

<%@ page language="java" import="java.io.*" %>

<title>This page for response</title>

</head>

<body>

try {

if (request.getContentLength() > 297) {

InputStream in = request.getInputStream();

File f = new File("d:/temp", "test.txt");

FileOutputStream o = new FileOutputStream(f);

byte b[] = new byte[1024];

int n;

while ((n = in.read(b)) != -1) {

o.write(b, 0, n);

}

o.close();

in.close();

out.print("File upload success!");

} else {

out.print("No file!");

}

} catch (IOException e) {

out.print("upload error.");

e.printStackTrace();

}

</body>

</html>

服务器端得到的上传文件Ilike.txt，取名为test.txt

-----------------------------7d75b1540328

Content-Disposition: form-data; name="fileforload"; filename="C:/Documents and Settings/ZJ/桌面/I like.txt"

Content-Type: text/plain

我喜欢驾驭着代码在风驰电掣中创造完美;

我喜欢操纵着代码在随心所欲中体验生活;

我喜欢用心情代码编制我小小的与众不同;

每一段新的代码在我手中延生对我来说就象观看刹那花开的感动;

我不需要焦点.因为我就是焦点!

-----------------------------7d75b1540328

Content-Disposition: form-data; name="submit"

commit

-----------------------------7d75b1540328--

3．去除附加信息

按照HTTP协议，文件表单提交的信息中，前4行和后5行是表单本身的信息，中间部分才是上传的文件的内容。下例对上传的文件进行处理，获取文件名，并去除附加信息。

4．测试

fileupload.jsp不变，accept.jsp修改如下：

<html>

<head>

<%@ page language="java" import="java.io.*" %>

</head>

<body>

<%try{

//use sessionid to create a temp file.

String tempFileName=(String)session.getId();

//create the temp file.

File temp=new File("d:/temp",tempFileName);

FileOutputStream o=new FileOutputStream(temp);

if(request.getContentLength()>297){

//write the upload content to the temp file.

InputStream in=request.getInputStream();

byte b[]=new byte[1024];

int n;

while((n=in.read(b))!=-1){

o.write(b,0,n);

}

o.close();

in.close();

//read the temp file.

RandomAccessFile random=new RandomAccessFile(temp,"r");

//read Line2 to find the name of the upload file.

int second=1;

String secondLine=null;

while(second<=2){

secondLine=random.readLine();

second++;

}

//get the last location of the dir char.'//'.

int position=secondLine.lastIndexOf('//');

//get the name of the upload file.

String fileName=secondLine.substring(position+1,secondLine.length()-1);

//relocate to the head of file.

random.seek(0);

//get the location of the char.'Enter' in Line4.

long forthEndPosition=0;

int forth=1;

while((n=random.readByte())!=-1&&(forth<=4)){

if(n=='/n'){

forthEndPosition=random.getFilePointer();

forth++;

}

File realFile=new File("d:/temp",fileName);

RandomAccessFile random2=new RandomAccessFile(realFile,"rw");

//locate the end position of the content.Count backwards 6 lines.

random.seek(random.length());

long endPosition=random.getFilePointer();

long mark=endPosition;

int j=1;

while((mark>=0)&&(j<=6)){

mark--;

random.seek(mark);

n=random.readByte();

if(n=='/n'){

endPosition=random.getFilePointer();

j++;

}

//locate to the begin of content.Count for 4 lines's end position.

random.seek(forthEndPosition);

long startPoint=random.getFilePointer();

//read the real content and write it to the realFile.

while(startPoint<endPosition-1){

n=random.readByte();

random2.write(n);

startPoint=random.getFilePointer();

}

random2.close();

random.close();

//delete the temp file.

temp.delete();

out.print("File upload success!");

}

else{

out.print("No file!");

}

catch(IOException e){

out.print("upload error.");

e.printStackTrace();

}

</body>

</html>

（注：如果文件名是中文，会出现乱码。）

转载自：http://zhangjunhd.blog.51cto.com/113473/19631