1. Introduce EncType
The encType attribute specifies how form data should be encoded before being sent to the server.
Enctype tells the server the MIME type of the request body (the request header content-type does the same thing).
1, 1 There are three values of encType
value
describe
application/x-www-form-urlencoded
Encodes all characters before sending (default)
multipart/form-data
No character encoding. Each form item is split into a part
text/plain
Spaces are converted to “+” plus signs, but no special character encoding.
1. When the enctype = “application/x – WWW – form – urlencoded ‘
2. When the enctype = “multipart/form – data ‘
Just by looking at this, the body of the request has changed. This request body is called the multi-part request body.
What is a multi-part request body? It splits each form item into a part.
A random string following the content-type boundary of the request header is used as the partition identifier
Common form items:
// Name means the name attribute value in the text box, and admin is the text value we entered
Content-Disposition: form-data; name=”username”
admin
File form item
//filename means the name of the file we uploaded, content-type means the MIME Type, and asdasdas means the content of the file
Content-Disposition: form-data; name=”upload”; filename=”a.txt”
Content-Type: text/plain
asdasdas
3. When the enctype = “text/plain”
The W3C says that Spaces will become “+” + signs, but I don’t see that here, only Spaces will become “+” signs for GET requests
Get into the business
Three conditions must be met to complete the upload
Provide a form. Method must be POST because the transfer data for GET requests is typically 2KB, depending on the browser.
The encType attribute of the form must be multipart/form-data
Provide an upload input field for the input type= “file” class
General implementation principle: When the value of encType is multipart/form-data, the browser will divide each form entry into different parts and use the value of boundary as the segmentation identifier. The character string of this identifier is randomly generated. There will be two more “-” at the end of the segmentation identifier string of the last form entry, representing the end. The server gets the split string with Request. getHeader(” content-type “) and parses it.
Code implementation
I. Construction of development environment
Prepare two third-party JAR packages
Commons – IO package
Commons – upload package
All dependency packages
Code implementation
Prerequisites for downloading
Two heads and one stream
content-type
The content-type is the very important Content in the return message, indicating what MIME Type the document Content belongs to.
The browser determines how to display the returned message body Content based on the Content-Type.
The default value is text/ HTML
You can use the request. GetServletContext (.) getMimeType (” name “) for the MIME type.
Content-Disposition
Content-disposition is an extension of the MIME protocol that instructs the MIME user agent how to display attached files.
The default is inline, which opens in a browser window.
When the server sends a file to the client browser, if the file type supported by the browser is generally opened by the browser by default, such as TXT and JPG, which will be directly displayed in the browser.
If you need to prompt the user to save, do something with Content-Disposition, and the key is to always include an attachment.
For example: the Content – Disposition: attachment; Filename = XXX, the browser will activate the download dialog box, attachment represents the attachment, filname is followed by the filename displayed in the download box.
flow
Downloading is responding bytes of data to the client! To turn a file into a byte array, use Response.getOutputStream ()
To respond to the browser.
The code is as follows, this code has realized the breakpoint continuation function, the user can pause in the download process, and continue to download, the server caused less pressure.
Load file list, displayed in the download list
The back-end code logic is mostly the same and currently supports MySQL,Oracle, and SQL. Need to configure the database before using, can refer to me to write this article: blog.ncmem.com/wordpress/2… Welcome to join the group to discuss “374992201”