什么时候在Spring MVC中不需要@RequestParam注释？

Question

I'm looking through some Spring 3 MVC controller code and I see that @RequestParam is used for some parameters and not for others. Example where it is not being used:

@RequestMapping(value = "/experiments", method = RequestMethod.GET)
public String getExperimentsPage(ExperimentSearchCriteria criteria, Map<String, Object> model) {
    // method body here
}

When is @RequestParam (or similar parameter-specifying annotation) not needed?

Answer 1

Good question, I have been wondering this too until I found it being mentioned in the doc:

Note that use of @RequestParam is optional, eg to set its attributes. By default any argument that is a simple value type, as determined by BeanUtils#isSimpleProperty, and is not resolved by any other argument resolver, is treated as if it was annotated with @RequestParam.

https://docs.spring.io/spring/docs/current/spring-framework-reference/web.html#mvc-ann-requestparam

Most of time, I don't specify this unless my method parameter name is different with request parameter, or, if the value is optional, I will need to use required=false .

Answer 2

I'm not really sure about your question, but you only need @RequestParam when you want to bind a method argument with a parameter held by the request.

I think this is pretty clear here .

Answer 3

@RequestParam is used to pass query parameters.

Example: http://localhost:8080/employee/get?status=ACTIVE

Here we can get status with below code

@RequestParam(value="status") String status

We have some properties like required, defaultValue etc. If you provide required=false as mentioned in below line of code, the status parameter is not mandatory in URL

@RequestParam(value="status",required=false)

The URL will be like http://localhost:8080/employee/get