@RequestParam omitted but mapping is still done correctly

Question

I just found that even if I omit the @RequestParam annotation on the organization parameter, Spring is still able to bind it.

@RequestMapping(value="", method = RequestMethod.POST)
@ResponseBody
public String save(String organization){
    logger.info(organization); // it works
}

Can anyone points to the documentation that clarifies this behaviour? I have always though that @RequestParam was mandatory for binding to work.

Thanks

Answer 1

Take a look at https://reversecoding.net/spring-mvc-requestparam-binding-request-parameters/ There is an explanation:

Examples without @RequestParam

Based on the list of HandlerMethodArgumentResolver configured in your application, @RequestParam can also be omitted. If you have a look at the code of method getDefaultArgumentResolvers() of RequestMappingHandlerAdapter there is the following piece of code at the end:

// Catch-all resolvers.add(new RequestParamMethodArgumentResolver(getBeanFactory(), true));

resolvers.add(new ServletModelAttributeMethodProcessor(true));

// Catch-all resolvers.add(new RequestParamMethodArgumentResolver(getBeanFactory(), true));

resolvers.add(new ServletModelAttributeMethodProcessor(true));

Basically, it's added to the resolvers a RequestParamMethodArgumentResolver with useDefaultResolution set to true. Looking at the documentation we can see that this means that method argument that is a simple type, as defined in BeanUtils.isSimpleProperty(java.lang.Class), is treated as a request parameter even if it isn't annotated. The request parameter name is derived from the method parameter name.

Answer 2

Your resolvers do it automatically. When you pass the HandlerMethodArgumentResolver bean to your resolver, the BeanUtil checks if the parameter is a primitive value or a simple String . If so, it does the binding itself.

Answer 3

@RequestMapping(value = "/rest")
@ResponseBody
public String save(String username, String password) {
    return String.format("username=%s  password=%s", username, password);
}

Hit the service http://localhost:8080/rest?username=mypwd&password=uname

You will be able to see the result given below.

Output: username=pwd password=uname

Answer 4

here I have some examples for the @RequestParam to provide you,hope they can help you: @RequestMapping(value = "/selection/findByField", method = RequestMethod.POST) public @ResponseBody List<selectionsDO> add(@RequestParam(value = "field", required = true) String field,@RequestParam(value = "value", required = true) String value) { return mongoService.findByField(field,value); } @RequestMapping(value = "/selection/findByField", method = RequestMethod.POST) public @ResponseBody List<selectionsDO> add(@RequestParam(value = "field", required = true) String field,@RequestParam(value = "value", required = true) String value) { return mongoService.findByField(field,value); }

The words "required = true" means that this field must submit at request.