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XWork is an command-pattern framework that is used to power WebWork as well as other applications. XWork provides an Inversion of Control container, a powerful expression language, data type conversion, validation, and pluggable configuration.
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/*
 * Copyright (c) 2002-2006 by OpenSymphony
 * All rights reserved.
 */

package com.opensymphony.xwork2.interceptor;

import com.opensymphony.xwork2.ActionInvocation;
import com.opensymphony.xwork2.util.LocalizedTextUtil;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import java.util.Locale;
import java.util.Map;

/**
 * 
 *
 * An interceptor that handles setting the locale specified in a session as the locale for the current action request.
 * In addition, this interceptor will look for a specific HTTP request parameter and set the locale to whatever value is
 * provided. This means that this interceptor can be used to allow for your application to dynamically change the locale
 * for the user's session. This is very useful for applications that require multi-lingual support and want the user to
 * be able to set his or her language preference at any point. The locale parameter is removed during the execution of
 * this interceptor, ensuring that properties aren't set on an action (such as request_locale) that have no typical
 * corresponding setter in your action.
 *
 * For example, using the default parameter name, a request to foo.action?request_locale=en_US, then the
 * locale for US English is saved in the user's session and will be used for all future requests.
 *
 * 
 *
 * 
 Interceptor parameters:
 *
 * 
 *
 * 

 *
 * parameterName (optional) - the name of the HTTP request parameter that dictates the locale to switch to and save
 * in the session. By default this is request_locale
 *
 * attributeName (optional) - the name of the session key to store the selected locale. By default this is
 * WW_TRANS_I18N_LOCALE
 *
 * 
 *
 * 
 *
 *  Extending the interceptor:
 *
 * 

 *
 * 
 *
 * There are no known extensions points for this interceptor.
 *
 * 
 *
 * 
 Example code:
 *
 * 
 * 
 * <action name="someAction" class="com.examples.SomeAction">
 *     <interceptor-ref name="i18n"/>
 *     <interceptor-ref name="basicStack"/>
 *     <result name="success">good_result.ftl</result>
 * </action>
 * 
 * 
 *
 * @author Aleksei Gopachenko
 */
public class I18nInterceptor extends AbstractInterceptor {
    protected static final Log log = LogFactory.getLog(I18nInterceptor.class);

    public static final String DEFAULT_SESSION_ATTRIBUTE = "WW_TRANS_I18N_LOCALE";
    public static final String DEFAULT_PARAMETER = "request_locale";

    protected String parameterName = DEFAULT_PARAMETER;
    protected String attributeName = DEFAULT_SESSION_ATTRIBUTE;

    public I18nInterceptor() {
        if (log.isDebugEnabled()) {
            log.debug("new I18nInterceptor()");
        }
    }

    public void setParameterName(String parameterName) {
        this.parameterName = parameterName;
    }

    public void setAttributeName(String attributeName) {
        this.attributeName = attributeName;
    }

    public String intercept(ActionInvocation invocation) throws Exception {
        if (log.isDebugEnabled()) {
            log.debug("intercept '"
                    + invocation.getProxy().getNamespace() + "/"
                    + invocation.getProxy().getActionName() + "' { ");
        }
        //get requested locale
        Map params = invocation.getInvocationContext().getParameters();
        Object requested_locale = params.remove(parameterName);
        if (requested_locale != null && requested_locale.getClass().isArray()
                && ((Object[]) requested_locale).length == 1) {
            requested_locale = ((Object[]) requested_locale)[0];
        }

        if (log.isDebugEnabled()) {
            log.debug("requested_locale=" + requested_locale);
        }

        //save it in session
        Map session = invocation.getInvocationContext().getSession();
        if (session != null) {
            if (requested_locale != null) {
                Locale locale = (requested_locale instanceof Locale) ?
                        (Locale) requested_locale : LocalizedTextUtil.localeFromString(requested_locale.toString(), null);
                if (log.isDebugEnabled()) {
                    log.debug("store locale=" + locale);
                }

                if (locale != null) {
                    session.put(attributeName, locale);
                }
            }

            //set locale for action
            Object locale = session.get(attributeName);
            if (locale != null && locale instanceof Locale) {
                if (log.isDebugEnabled()) {
                    log.debug("apply locale=" + locale);
                }

                saveLocale(invocation, (Locale)locale);
            }
        }

        if (log.isDebugEnabled()) {
            log.debug("before Locale=" + invocation.getStack().findValue("locale"));
        }

        final String result = invocation.invoke();
        if (log.isDebugEnabled()) {
            log.debug("after Locale=" + invocation.getStack().findValue("locale"));
        }

        if (log.isDebugEnabled()) {
            log.debug("intercept } ");
        }

        return result;
    }

    /**
     * Save the given locale to the ActionInvocation.
     *
     * @param invocation The ActionInvocation.
     * @param locale The locale to save.
     */
    protected void saveLocale(ActionInvocation invocation, Locale locale) {
        invocation.getInvocationContext().setLocale(locale);
    }

}