CODEWITHSUNDEEP
javaspringspring-mvclocale
AndreaNobili
AndreaNobili

Reputation: 42957

Parameter of a controller method in Spring MVC

I am quite new in Spring MVC World and I a question for you.

I have created a new Spring MVC project by the STS template.

So now I have a minimal project that, once that is executed, show an Hello World message with the current date and time shown

This is the code of the only controller class of this project:

package org.gnagna.bla;

import java.text.DateFormat;
import java.util.Date;
import java.util.Locale;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

/**
 * Handles requests for the application home page.
 */
@Controller
public class HomeController {

private static final Logger logger = LoggerFactory.getLogger(HomeController.class);

/**
 * Simply selects the home view to render by returning its name.
 */
@RequestMapping(value = "/", method = RequestMethod.GET)
public String home(Locale locale, Model model) {
    logger.info("Welcome home! The client locale is {}.", locale);

    Date date = new Date();
    DateFormat dateFormat = DateFormat.getDateTimeInstance(DateFormat.LONG, DateFormat.LONG, locale);

    String formattedDate = dateFormat.format(date);

    model.addAttribute("serverTime", formattedDate );

    return "home";
}

}

So there is only one method called called home that handled HTTP GET Call toward the "/" URL, ok this is clear for me.

The thing that this is not clead is about the input parameter of this method, as you can see this method receives two input parameter:

1) The model

2) A Locale object that contain some information about the user

But: who create this Locale object and when this is passed as input parameter in my controller?

Tnx

Andrea

Upvotes: 2

Views: 6053

Answers (2)

Sazzadur Rahaman
Sazzadur Rahaman

Reputation: 7116

In your GET request you can send locale information to the server by using special paramerter of that request like, ?language=en. But the question is how your servlet container knows that the language parameter is the parameter bearing your locale information. To let the Spring MVC container know about this special locale parameter, you need two add the special interceptor in your targer-servlet.xml like bellow:

    <bean id="localeChangeInterceptor"
    class="org.springframework.web.servlet.i18n.LocaleChangeInterceptor">
    <property name="paramName" value="language" />
</bean>

<bean class="org.springframework.web.servlet.mvc.support.ControllerClassNameHandlerMapping" >
    <property name="interceptors">
       <list>
        <ref bean="localeChangeInterceptor" />
        </list>
    </property>
</bean>

The thing is now, your servlet container knows the value of the locale parameter passed with your GET request. But still you need someone to change the locale based on the selected language link and display the message from properties file accordingly. A special bean named localeResolver comes to the rescue to do the job, like bellow:

    <bean id="localeResolver"
    class="org.springframework.web.servlet.i18n.SessionLocaleResolver">
    <property name="defaultLocale" value="en" />
</bean>

Now if you like to use the locale object in your GET request handler method, you write the method signature like public String home(Locale locale, Model model)(like, what you have done). Then your servlet container gets an extra job of putting that locale object as your method parameter before invoking it and you get it inside your method like magic!

Upvotes: 1

Francisco Paulo
Francisco Paulo

Reputation: 6322

A LocaleResolver is doing that.

One such resolver is eventually used by the HandlerMethodInvokere to inspect the parameters of the @RequestMapping method that you are invoking (the "home" method in your case). When it comes across a Locale parameter it simply uses the locale resolver to fetch a Locale object to pass as argument there.

You can see more information about it here: http://static.springsource.org/spring/docs/3.0.0.M3/reference/html/ch16s06.html

http://templth.wordpress.com/2010/07/21/configuring-locale-switching-with-spring-mvc-3/

http://www.mkyong.com/spring-mvc/spring-mvc-internationalization-example/

Upvotes: 4

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