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This article focuses on the Content-Type explanation of Http requests and its application in Spring MVC

Quote: In Http requests, we use the Content-type every day to specify different formats of request information, but few people fully understand how many values are allowed in the content-type. Here are the available values for the content-type. And how they can be used to map request information in Spring MVC.

1.  Content-Type

MediaType stands for Internet MediaType. Also known as MIME Type, content-Type is used in Http headers to indicate the media Type in a specific request.

Type format: type/subtype(; parameter)? Type Specifies the main type. Any string, such as text, is an asterisk. Subtype, an arbitrary string, such as HTML, if the asterisk represents all; Parameter Specifies some optional parameters, such as the Q parameter of the Accept request header and the Charset parameter of the Content-type.Copy the code

For example, content-type: text/ HTML; charset:utf-8;

Common media format types are as follows:

1. Text/HTML: HTML format
2. Text /plain: plain text format
3. Text/XML: indicates the XML format
4. Image/GIF: indicates the GIF image format
5. Image/JPEG: JPG format
6. Image/PNG: indicates the PNG image format

Media format types beginning with Application:

1. Application/XHTML + XML: XHTML format
2. Application/XML: XML data format
3. Application/Atom + XML: Atom XML aggregation format
4. Application /json: Json data format
5. Application/PDF: in PDF format
6. Application/MSWORD: Word document format
7. Application /octet-stream: binary stream data (e.g. common file downloads)
8. Application/X-www-form-urlencoded: default encType, form form data is coded as key/value format and sent to the server (form default submit data format)

Another common media format is used when uploading files:

Multipart /form-data: This format is used when files need to be uploaded in the form

These are some of the content-Type formats we often use in our daily development.

2. Use of content-type information in Spring MVC

First let’s look at the Class definition in RequestMapping:

@Target({ElementType.METHOD, ElementType.TYPE}) 
@Retention(RetentionPolicy.RUNTIME) 
@Documented 
@Mapping 
public @interface RequestMapping { 
   String[] value() default {}; 
   RequestMethod[] method() default {}; 
   String[] params() default {}; 
   String[] headers() default {}; 
   String[] consumes() default {}; 
   String[] produces() default {}; 
} 

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Value: Specifies the actual address of the request, such as /action/info. Method: specifies the method Type of the requests. GET, POST, PUT and DELETE are the consumes, which are the content-types that handle the requests, for example, application/ JSON and Text/HTML. produces: Params: Specifies that the request must contain some parameter values before this method can handle headers: params: Specifies that the request must contain some parameter values before this method can handle headers: Consumes, Produces uses content-Typ to filter information. As consumes, the method consumes, produces. Content-type can be used to filter and determine headers.

3. Example

  3.1 headers

@RequestMapping(value = "/test", method = RequestMethod.GET, headers="Referer=http://www.ifeng.com/")  
public void testHeaders(@PathVariable String ownerId, @PathVariable String petId) {    
 // implementation omitted  
}  
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Headers matches all Headers, not just the Referer. \

Example 2

@RequestMapping(value = "/response/ContentType", headers = "Accept=application/json")  
public void response2(HttpServletResponse response) throws IOException {  
  // The media type of the content area data representing the response is JSON and encoded in UTF-8 (the client should decode in UTF-8).
  response.setContentType("application/json; charset=utf-8");  
  // Write out the response body
  String jsonData = "{\"username\":\"zhang\", \"password\":\"123\"}";  
  response.getWriter().write(jsonData);  
}  
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The server produces JSON data based on the request header “Accept=application/ JSON”.

When you have the following Accept header, the following rules apply:

1) Accept: Text/HTML, application/XML, application/json will produces the matching in the following order (1) (2) (3) application/application/XML text/HTML json (2) the Accept: application/xml; Q = 0.5, application/json; If q=0.9,text/ HTML will match produces in the following order ①text/ HTML ② Application /json ③ Application/XML is a quality factor of media type, the larger the application, the higher the priority (from 0 to 1) ③Accept: /,text/,text/ HTML will match in the following order ①text/ HTML ②text/ ③*/*

That is, the matching rule is: the most explicit match is preferred.

Part Requests

Responses of

3.2 Examples of Params

@RequestMapping(value = "/test/{userId}", method = RequestMethod.GET, params="myParam=myValue")  
public void findUser(@PathVariable String userId) {    
 // implementation omitted  
}  
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Only requests containing the name “myParam” and the value “myValue” act as a filter.

Consumes 3.3 / produces

@Controller  
@RequestMapping(value = "/users", method = RequestMethod.POST, consumes="application/json", produces="application/json")  
@ResponseBody 
public List<User> addUser(@RequestBody User userl) {    
  // implementation omitted  
  return List<User> users; 
}  

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Produces ==> Handles requests whose Request Content-type is “application/json”. Produces specifies that the Accept header contains “application/json”. It also implies that the content type returned is application/json;

4. To summarize

In this article, we first introduce the main formats supported by content-Type, and then introduce the main usage methods based on the Content of @RequestMapping. Headers, Consumes, and Produces use the various media formats used in the Content-Type. You control access and filter it.

Thank you for reading, I hope I can help you, thank you for your support!