RestEasy Interceptor (JAX-RS).Extract current locale from HTTP Request Header : 'Accept-Languages'.

AcceptLanguagesRequestInterceptor.java

package com...rest.support.interceptors;

import java.util.List;
import java.util.Locale;

import javax.ws.rs.WebApplicationException;
import javax.ws.rs.core.HttpHeaders;
import javax.ws.rs.ext.Provider;

import org.jboss.resteasy.annotations.interception.Precedence;
import org.jboss.resteasy.annotations.interception.ServerInterceptor;
import org.jboss.resteasy.core.ResourceMethod;
import org.jboss.resteasy.core.ServerResponse;
import org.jboss.resteasy.spi.Failure;
import org.jboss.resteasy.spi.HttpRequest;
import org.jboss.resteasy.spi.interception.PreProcessInterceptor;

/**
 * Extract current locale from HTTP Request Header : 'Accept-Languages'.
 */
@Provider
@Precedence("CUSTOM-REQUEST-HEADERS")
@ServerInterceptor
public class AcceptLanguagesRequestInterceptor
        implements PreProcessInterceptor
{

    @Override
    public ServerResponse preProcess(HttpRequest request, ResourceMethod method) throws Failure, WebApplicationException
    {
        HttpHeaders httpHeaders = request.getHttpHeaders();
        List<Locale> acceptableLanguages = httpHeaders.getAcceptableLanguages();

        Locale defLocale = (acceptableLanguages.isEmpty() ? Locale.getDefault() : acceptableLanguages.get(0));
        // TODO: store it in ThreadLocal...
        System.out.println("Locale found = " + defLocale.toString());

        return null;
    }

}

LocaleThreadLocal.java

import java.util.Locale;

/**
 ** A {@link ThreadLocal} to store the Locale to be used in the message interpolator.
 */
public class LocaleThreadLocal
{

    public static final ThreadLocal<Locale> THREAD_LOCAL = new ThreadLocal<Locale>();

    public static Locale get()
    {
        return (THREAD_LOCAL.get() == null) ? Locale.getDefault() : THREAD_LOCAL.get();
    }

    public static void set(Locale locale)
    {
        THREAD_LOCAL.set(locale);
    }

    public static void unset()
    {
        THREAD_LOCAL.remove();
    }

}