File Upload (Java web)

File Upload:

Requirements for the form:

* method= "POST"
* enctype= "Multipart/form-data"
* You need to add a file form item to the form: <input type= "file" name= "xxx"/>

Requirements for Servlets:

* Request.getparametere ("xxx"); This method always returns NULL when the form is Enctype= "Multipart/form-data".
* ServletInputStream Request.getinputstream (); the body containing the entire request!

steps for uploading files (First you need to guide the package--Commons-fileupload.jar and Commons-io.jar):

1. Create factory: Diskfileitemfactory factory = new Diskfileitemfactory ();

2. Create parser: Servletfileupload SFU = new Servletfileupload (factory);

3. Use parser to parse request, get Fileitem set:list<fileitem> fileitemlist = sfu.parserequest (request);

Related Methods of Fileitem:

* Boolean Isformfield (): Whether it is a normal form item! Returns true for normal form items if False is the file form item!
* String getfieldname (): Returns the name of the current form item;
* String getString (String charset): Returns the value of the table item;
* String getName (): Returns the uploaded file name
* Long GetSize (): Returns the number of bytes uploaded to the file
* InputStream getInputStream (): Returns the input stream corresponding to the uploaded file
* Void Write (file destfile): Saves the contents of uploaded files to the specified file.

Code implementation in the servlet in the upload file (V1.0):

1Request.setcharacterencoding ("Utf-8");2Response.setcontenttype ("Text/html;charset=utf-8");3         4         /**5 * File upload 3 steps away6 * 1. Create a factory7 * 2. Create a parser8 * 3. Use parser to parse request, get Fileitem collection9          */Ten          One         //Create a factory ADiskfileitemfactory factory =Newdiskfileitemfactory (); -         //Creating a parser -Servletfileupload SFU =Newservletfileupload (factory); the          -         //Get Fileitem Collection -         Try { -list<fileitem> list =sfu.parserequest (request); +              -Fileitem fi1 = list.get (0); +Fileitem Fi2 = list.get (1); AString FileName =fi2.getname (); atSystem.out.println ("Name:" +fi2.getname ()); -System.out.println ("Size:" +fi2.getsize ()); -              -File DestFile =NewFile ("D://demo", fileName);//Set Storage location -             Try { - Fi2.write (destfile); in}Catch(Exception e) { -                 //TODO auto-generated Catch block to e.printstacktrace (); +             } -}Catch(fileuploadexception e) { the e.printstacktrace (); *}

Issues to note in file uploads:

1. The file must be saved to Web-inf!
* Purpose is to not allow the browser to directly access the

2. File name Related issues
* Some browsers upload filenames that are absolute paths, which require cutting! C:\files\xxx.jpg
String filename = fi2.getname ();
int index = filename.lastindexof ("\ \");  //test whether you need to cut
if (index! =-1) { 
filename = filename.substring (index+1);
}
* File name garbled or normal table item garbled: request.setcharacterencoding ("Utf-8"), because FileUpload inside will call Request.getcharacterencoding ();
> Request.setcharacterencoding ("Utf-8");//Priority Low
> Servletfileupload.setheaderencoding ("Utf-8");// High priority
* file with the same name, we need to add a prefix to each file, which is guaranteed to not be duplicated. UUID

3. Directory break down
* Multiple files cannot be stored in one directory.
> First character break: Use the first letter of the file as the directory name, for example: Abc.txt, then we save the file to a directory. If the A directory does not exist at this time, then create it.
> Time Break: Use the current date as a table of contents.
> Hash Break:
* Get int value by file name, call Hashcode ()
* It int value to 16 binary 0~9, a~f
* Get 16 binary top two to generate directory, directory two layer! For example: 1b2c3d4e5f,/1/b/Save the file.

4. Size limit for uploaded files
* Single File size limit
> Sfu.setfilesizemax (100*1024): Limit single file size to 100KB
> The above method call must be called before parsing begins!
> If the uploaded file exceeds the limit, an exception will be thrown when the Parserequest () method executes! Fileuploadbase.filesizelimitexceededexception
* Entire request all data size limit
> Sfu.setsizemax (1024 * 1024);//Limit the entire form size to 1M
> This method must also be called before the Parserequest () method
> If the uploaded file exceeds the limit, an exception will be thrown when the Parserequest () method executes! Fileuploadbase.sizelimitexceededexception

5. Cache size and Temp directory
* Cache Size: How big it is before you save it to your hard drive! Default is 10KB
* Temp directory: What directory is saved to the hard disk
Set cache size with temp directory: New Diskfileitemfactory (20*1024, New File ("F:/temp"))//cache is 20KB, temporary directory is f:/temp

File Upload (Java web)