Dinesh on Java

In spring the @RequestParam annotation is used to bind request parameter values to the handler method arguments in controller. Let’s see use of it with example in this article.

@Target(value=PARAMETER)
@Retention(value=RUNTIME)
@Documented
public @interface RequestParam

• defaultValue– It is String type attribute and the default value to use as a fallback when the request parameter is not provided or has an empty value.
• name– It is String type attribute and name of the request parameter to bind to.
• required– It is Boolean type attribute whether the parameter is required.
• value– It is String type attribute and it is alias for name attribute.

The ‘defaultValue’ attribute of @RequestParam
It is String type attribute and the default value to use as a fallback when the request parameter is not provided or has an empty value. Providing a default value implicitly sets ‘required’ to false.

@RequestParam(defaultValue="www.dineshonjava.com") String siteName

The ‘required’ attribute of @RequestParam
It is Boolean type attribute whether the parameter is required. The default is true. If parameter is missing in the request then it will be returned status code 400. We can override this to false if the parameter is not present in the request.

Following will be mapped with both /tutorials/bookmark?siteName=dineshonjava and /tutorials/bookmark

@Controller
public class TutorialController {

    @RequestMapping(value = "/tutorials/bookmark")
    public String bookMarkTutorial (
        @RequestParam(required = false) String siteName,
              Model model) {
        model.addAttribute("I have bookmarked tutorial : " + siteName);
        return "success";
    }
}

Using @RequestParam with value and without value attribute

Using ‘value’ element of @RequestParam
It is String type attribute and it is alias for name attribute. ‘value’ attribute of @RequestParam is used to specify URL query param name. Following handler method will be mapped with the request /tutorials/bookmark?site=dineshonjava :

Controller
public class TutorialController {

    @RequestMapping(value = "/tutorials/bookmark")
    public String bookMarkTutorial (
        @RequestParam("site") String siteName,Model map) {
        model.addAttribute("I have bookmarked tutorial : " + siteName);
        return "success";
    }
}

@RequestParam without ‘value’ element
We could skip the ‘value’ attribute of @RequestParam annotation if variable name of handler method is same as request parameter name.
Following handler will be mapped with /tutorials/bookmark?siteName=dineshonjava:

@Controller
public class TutorialController {

    @RequestMapping(value = "/tutorials/bookmark")
    public String bookMarkTutorial (
        @RequestParam String siteName,
              Model model) {
        model.addAttribute("I have bookmarked tutorial : " + siteName);
        return "success";
    }
}

Using multiple @RequestParam annotations
A handler method can have any number of @RequestParam annotations, it depended on the request parameters we are passing to the handler method. Following handler will be mapped with
/tutorials/bookmark?siteName=dineshonjava&author=dinesh:

@Controller
public class TutorialController {

    @RequestMapping(value = "/tutorials/bookmark")
    public String bookMarkTutorial (
        @RequestParam String siteName,
 @RequestParam String author,
              Model model) {
        model.addAttribute("I have bookmarked tutorial : " + siteName+" Author : "+author);
        return "success";
    }
}

Using Map with @RequestParam for multiple params
Spring provide support for bind the request parameters to the Map and MultiValueMap. All query string names and values are populated to the Map. Following will be mapped with /tutorials/bookmark?siteName=dineshonjava&author=dinesh:

@Controller
public class TutorialController {

    @RequestMapping(value = "/tutorials/bookmark")
    public String bookMarkTutorial (
        @RequestParam Map queryMap
              Model model) {
        model.addAttribute("I have bookmarked tutorial : " + queryMap.get("siteName")+
 " Author : "+queryMap.get("author"));
        return "success";
    }
}

Summary
In Spring @RequestParam annotation we can use for bind the request parameters to the handler method arguments. It provides auto-type conversion by default for parameters like int, float, String, Date etc. We can also override the default behavior of this annotation like required attribute set false to non mandatory request parameters.