Content-Type：
Used to define how a user’s browser or related device displays data to be loaded, or how to handle data to be loaded.
Content type, generally refers to the content-type that exists in a Web page, and the content-type attribute specifies the HTTP content type of request and response.
If no Content-Type is specified, the default is text/html.
1. text/html：
text/html：Set the Content-Type of the file to the form of text/html, and the browser automatically calls the HTML parser to process the file when it gets the file.
2. text/plain：
text/plain：Set the file to plain text, and browsers do not process it when they get it.
3. application/x-www-form-urlencoded
4. multipart/form-data
5. application/json
6. text/xml