    001// Copyright 2006, 2007, 2012 The Apache Software Foundation
    002//
    003// Licensed under the Apache License, Version 2.0 (the "License");
    004// you may not use this file except in compliance with the License.
    005// You may obtain a copy of the License at
    006//
    007//     http://www.apache.org/licenses/LICENSE-2.0
    008//
    009// Unless required by applicable law or agreed to in writing, software
    010// distributed under the License is distributed on an "AS IS" BASIS,
    011// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    012// See the License for the specific language governing permissions and
    013// limitations under the License.
    014
    015package org.apache.tapestry5.commons;
    016
    017import java.util.Set;
    018
    019/**
    020 * Provides access to a messages catalog, a set of properties files that provide localized messages for a particular
    021 * locale. The message catalog consists of keys and values and follows the semantics of a Java {@link
    022 * java.util.ResourceBundle} with some changes.
    023 */
    024public interface Messages
    025{
    026    /**
    027     * Returns true if the bundle contains the named key.
    028     */
    029    boolean contains(String key);
    030
    031    /**
    032     * Returns the localized message for the given key. If catalog does not contain such a key, then a modified version
    033     * of the key is returned (converted to upper case and enclosed in brackets).
    034     *
    035     * @param key
    036     * @return localized message for key, or placeholder
    037     */
    038    String get(String key);
    039
    040    /**
    041     * Returns a formatter for the message, which can be used to substitute arguments (as per {@link
    042     * java.util.Formatter}).
    043     *
    044     * @param key
    045     * @return formattable object
    046     */
    047    MessageFormatter getFormatter(String key);
    048
    049    /**
    050     * Convenience for accessing a formatter and formatting a localized message with arguments.
    051     */
    052    String format(String key, Object... args);
    053
    054    /**
    055     * Returns a set of all the keys for which this instance may provide a value.
    056     *
    057     * @return set of keys
    058     * @since 5.4
    059     */
    060    Set<String> getKeys();
    061}