Detailed explanation of java_file upload example

Today’s content:

File upload------commons-fileupload

The essence of file upload and download: copy of file

File upload: copy from local to server disk The client needs to write a file upload form---- >The server needs to write code to accept uploaded files

File download: copy from the server disk to the local disk You need to write server-side code, and the client's download work is solved by the browser kernel

##1. File upload

1 , File upload steps:

(1) Need to write a file upload form

(2) Write server-side code with For receiving uploaded files

2, client encoding

Notes:

3, the server accepts the form for file upload Data

Principle of file upload and reception

Easy and quick to use File upload tool---Apache Commons-fileupload.jar

Usage steps:

(1) Download the jar package for file upload fileuplaod with the help of commons-io.jar

(2) Use the API in the fileupload tool Encoding

4, the three core objects in the FileUpload tool

DiskFileItemFactory: Disk file item factory--some related configuration settings The size of the cache and the location of the temporary directory

ServletFileUplaod: A core class for file upload

FileItem: Represents each form item

5. Quick Start

6, Detailed explanation of file upload API

(1) DiskFileItemFactory

Set the cache size: factory.setSizeThreshold() in bytes

Set the directory of temporary files: factory.setRepository(File)

(2) ServletFileUpload

Determine whether it is a file upload form: ServletFileUpload.isMultipartContent(request);

Parse request to obtain a collection of form items: upload.parseRequest(request);

Set the encoding method of the uploaded file name: upload.setHeaderEncoding("UTF- 8");

(3) FileItem

Determine whether it is a normal form item ：item.isFormField();

Get the name attribute value of the form: item.getFieldName();

Get the value value of the form: item.getString("UTF-8") --- UTF-8 represents the encoding when obtaining Chinese

Get the name of the uploaded file: item.getName()

Get uploaded files: item.getInputStream();

Delete temporary files: item.delete();

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