No qualifying bean of type question

No qualifying bean of type problem solving ideas

To solve the problem of No qualifying bean of type, there are currently two reasons for the error:

1. Annotations
2. Configuration (scanning packages, nacos, class names, etc.)

1. Comments

• Check if the annotations corresponding to controller, service and mapper are correct
• Such as: @Controller  @Service  @Component   @Repository

2. Configuration

1. Configure whether nacos is used, and you need to configure database information, etc.

• 

2. Whether the scan package is used

• 
  or use @MapperScan(value="com.*** ")

 

Annotation Extension

• what: special tag in code
• where: can be placed on a method or a class

1. How does the front-end code link use annotations?

1. If the annotation is on the method, you can write the annotation of the method in the link
   

• If the annotation is on the class, you need to write the annotation of the class + method in the link
  

2. Annotation attribute:

• path: Specifies the requested URL
• (commonly used) value has the same function as path, you can add a path, use value can be omitted, just write the path directly
• (commonly used) method: specify the request method of this method
• headers: Specify conditions to limit request headers-
• params: conditions for restricting request parameters
  – the key and value are the same
  – case 1: only limit the parameters passed, not what the parameters are specific
  – case 2: the parameters must be consistent

3. Common Notes

@RequestParam

• Role: Assign the parameter with the specified name in the request to the formal parameter in the controller
• Attribute:
  –value: parameter name
  –required: whether this parameter must be filled in
• Example

@RequestBody

• Role: used to get the content of the request body
• Attribute: required
• Scope: Asynchronous (used when asynchronous)
• Example
  

@PathVariable

• Function: placeholder for binding url
  
li>
• Benefits: restful programming style
• The original way – add the root path to each path
  
• restful method: use get, post, put to distinguish the path
  –localhost:8080/user/10 get——this is the http request indicating that the request method is get and the parameter id
  

@RequestHeader: not commonly used

@CookieValue

• Role: Pass the value of the specified cookie name into the controller method parameter

@ModelAttribute

• Function: Modify methods and parameters
• how: This modification is executed first

@SessionAttributes

• Function: used for parameter sharing between multiple execution controller methods
• attributes
  –value
  –type-stored data type