Resolving spring i18n messages from extjs files

Question

Spring has its strategy to make the internationalisation in our spring project by declaring its beans. to access the messages from jsp files we use

<spring:message code="messages.field">

Thats ok for jsp files but what about extjs(javascript) files ?

for example I have login.js must use the i18n messages:

items: [ {
        fieldLabel: **// here I must get the field messages.username//**,
        name: 'j_username',
        allowBlank: false,
        listeners: {
            specialkey: function(field, e) {
                if (e.getKey() == e.ENTER) {
                    submitForm();
                }
            }
        }
    },

Temporarily, I created my own solution without using spring i18n beans and may it will be helpfully as a solution if we don't have an approch to implement i18n with spring from extjs.however it's not to say that my solution don't present some disadvantages that I will list them at the end of this post.

first create a controller I18nController.java, this controller will be the target of the incoming requests that have the pattern /i18n.js, its responsibility to create a javascript variable i18n and return the response as a contentType = javascript.

@RequestMapping(value = "/i18n.js", method = RequestMethod.GET)
public void i18n(HttpServletResponse response, Locale locale) throws JsonGenerationException, JsonMappingException,
        IOException {

    response.setContentType("application/javascript;charset=UTF-8");

    byte[] output = buildResponse(locale);
    response.setContentLength(output.length);

    ServletOutputStream out = response.getOutputStream();
    out.write(output);
    out.flush();
}
private byte[] buildResponse(Locale locale) {
    ResourceBundle rb = ResourceBundle.getBundle("i18n/messages", locale);

    Map<String, String> messages = Maps.newHashMap();
    Enumeration<String> e = rb.getKeys();
    while (e.hasMoreElements()) {
        String key = e.nextElement();
        messages.put(key, rb.getString(key));
    }

    String output =  "var i18n = "+ jsonHandler.writeValueAsString(messages) + ";";

Second, in any jsp/html files I just use :

<script src ="i18n.js"></script>

So by that I can access to my variable from any extjs files and resolve the i18n messages:

items: [ {
        fieldLabel: i18n.user_username,
        name: 'j_username',
        allowBlank: false,
        listeners: {
            specialkey: function(field, e) {
                if (e.getKey() == e.ENTER) {
                    submitForm();
                }
            }
        }
    }
    return output.getBytes(StandardCharsets.UTF_8);
}

disadvantages:

1. why using my own solution whereas spring give the classes to implements the same solution(make the project totally spring)
2. If my propoerties file messages_en.preoperties has a huge entries and lets say that the js file will use only 2 fields, here, i loaded the full entries :( ==> bad performance.

So then, how can I resolve i18n messages from extjs and using spring without using my solution ?

Thanks.