Detailed introduction of @RequestParam annotation

@RequestParam (org.springframework.web.bind.annotation.RequestParam) is used to assign the specified request parameter to the formal parameter in the method.

There are three properties:

(1) value: request parameter name (must be configured)

(2) required: Whether it is required, the default is true, that is, this parameter must be included in the request, if not included, an exception will be thrown (optional configuration)

(3) defaultValue: default value, if this value is set, required will be automatically set to false, no matter whether you configure required or not, and what value is configured, it is false (optional configuration)

1 In order to demonstrate the effect, first you need to create a test control class, and then create a test method, _As shown in the figure, add a parameter to the _____ method, ____At this time, the method parameterNo annotations added

1. 

2. Start the web project through the idea tool, and then access the test effect through the browser. If there is no parameter, the obtained parameter is null, but the page can be displayed normally and the request can be executed normally.

   

   After adding the parameters, the parameters can be normal

   

3. Let's compare the effect of adding annotations, but just add @RequestParam without any annotations to set parameters.

   

4. View the effect through the browser again. At this time, the page with the userName parameter can be displayed normally and the result value can be printed out, but as shown in the figure, when the parameter is not used, the page reports an error, returns 400, and promptsuserName does not exist

   

   

5. Of course, such restrictions are optional. Add required=false to @RequestParam to close the restrictions on required parameters, which is the same as the first one without annotations

   

   

6. @RequestParam can also set a default value of a parameter for us when the parameter is empty, as shown in the figure, it can be seen that if there is no parameter, the obtained value is the default value

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7. The key name of the default parameter is the parameter name in the method, but another one can be customized through @RequestParam, because under certain conditions, the method name cannot be modified after being fixed, but the requested parameters need to bePass another parameter key name, so it can be implemented in this way