Freemarker - compose language switch url

Question

I am using freemarker template engine with Spring and I want to add or replace lang=xxx parameter in the href attribute of link element when rendering page.

The closest solution I have found is following:

<a href="${springMacroRequestContext.getRequestUri()}?lang=en'/>English</a>

But this is not sufficient when I have URL with parameters and fragments because I will miss them. For example http://localhost/sports/search?query=Volleyball&lang=cs#some-fragment results in http://localhost/sports/search?lang=en

How to compose the URL with added or changed lang parameter in freemarker and do not miss any part of requested URL?

Answer 1

I preferred to do it in Java, this simple implementation does not take into account hashes (#) or the presence of the given parameter in the url..

public static String addParamToUrl(String url, String paramName, String paramValue){
    StringBuffer buffer = new StringBuffer(url);
    //adding separator
    if(url.indexOf('?') == -1){
        buffer.append('?');
    }else if(!url.endsWith("?") && !url.endsWith("&")){
        buffer.append('&');
    }        

    buffer.append(paramName);
    if(paramValue != null){
        buffer.append("=");
        buffer.append(URLEncoder.encode(paramValue, "UTF-8"));
    }
    return buffer.toString();
}

Put this method in a Class (i.e:Utils.java) that can be staticly accessed by Freemarker engine and than:

<#assign url = Utils.addParamToUrl(springMacroRequestContext.getRequestUri(), "lang", "en") />

<a href="${url}">English</a>

To expose your Utils class you have to customize FreemarkerManager

public class MyFreemarkerManager extends FreemarkerManager {

    public MyFreemarkerManager(){
        super();
    }

    @Override
    protected void populateContext(ScopesHashModel model, ValueStack stack, Object action, HttpServletRequest request, HttpServletResponse response) {
        super.populateContext(model, stack, action, request, response);

        try {

            BeansWrapper beansWrapper = new BeansWrapperBuilder(Configuration.VERSION_2_3_24).build();
            TemplateHashModel staticModels = beansWrapper.getStaticModels();

            TemplateHashModel utils = (TemplateHashModel)staticModels.get("com.package.Utils");
            model.put("Utils", utils);  

        } catch (TemplateModelException e) {
            //...
        }       

    }
}

Finally you have to tell Spring you are using MyFreemarkerManager as manager for Freemarker.