TranslationBundle.java

/*
 * Copyright (C) 2010, Sasa Zivkov <sasa.zivkov@sap.com> and others
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Distribution License v. 1.0 which is available at
 * https://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

package org.eclipse.jgit.nls;

import java.lang.reflect.Field;
import java.util.Locale;
import java.util.MissingResourceException;
import java.util.ResourceBundle;

import org.eclipse.jgit.errors.TranslationBundleLoadingException;
import org.eclipse.jgit.errors.TranslationStringMissingException;

/**
 * Base class for all translation bundles that provides injection of translated
 * texts into public String fields.
 *
 * <p>
 * The usage pattern is shown with the following example. First define a new
 * translation bundle:
 *
 * <pre>
 * public class TransportText extends TranslationBundle {
 *  public static TransportText get() {
 *      return NLS.getBundleFor(TransportText.class);
 *  }
 *
 *  public String repositoryNotFound;
 *
 *  public String transportError;
 * }
 * </pre>
 *
 * Second, define one or more resource bundle property files.
 *
 * <pre>
 * TransportText_en_US.properties:
 *      repositoryNotFound=repository {0} not found
 *      transportError=unknown error talking to {0}
 * TransportText_de.properties:
 *      repositoryNotFound=repository {0} nicht gefunden
 *      transportError=unbekannter Fehler während der Kommunikation mit {0}
 * ...
 * </pre>
 *
 * Then make use of it:
 *
 * <pre>
 * NLS.setLocale(Locale.GERMAN); // or skip this call to stick to the JVM default locale
 * ...
 * throw new TransportException(uri, TransportText.get().transportError);
 * </pre>
 *
 * The translated text is automatically injected into the public String fields
 * according to the locale set with
 * {@link org.eclipse.jgit.nls.NLS#setLocale(Locale)}. However, the
 * {@link org.eclipse.jgit.nls.NLS#setLocale(Locale)} method defines only
 * prefered locale which will be honored only if it is supported by the provided
 * resource bundle property files. Basically, this class will use
 * {@link java.util.ResourceBundle#getBundle(String, Locale)} method to load a
 * resource bundle. See the documentation of this method for a detailed
 * explanation of resource bundle loading strategy. After a bundle is created
 * the {@link #effectiveLocale()} method can be used to determine whether the
 * bundle really corresponds to the requested locale or is a fallback.
 *
 * <p>
 * To load a String from a resource bundle property file this class uses the
 * {@link java.util.ResourceBundle#getString(String)}. This method can throw the
 * {@link java.util.MissingResourceException} and this class is not making any
 * effort to catch and/or translate this exception.
 *
 * <p>
 * To define a concrete translation bundle one has to:
 * <ul>
 * <li>extend this class
 * <li>define a public static get() method like in the example above
 * <li>define public static String fields for each text message
 * <li>make sure the translation bundle class provide public no arg constructor
 * <li>provide one or more resource bundle property files in the same package
 * where the translation bundle class resides
 * </ul>
 */
public abstract class TranslationBundle {

    private Locale effectiveLocale;
    private ResourceBundle resourceBundle;

    /**
     * Get the locale used for loading the resource bundle from which the field
     * values were taken.
     *
     * @return the locale used for loading the resource bundle from which the
     *         field values were taken.
     */
    public Locale effectiveLocale() {
        return effectiveLocale;
    }

    /**
     * Get the resource bundle on which this translation bundle is based.
     *
     * @return the resource bundle on which this translation bundle is based.
     */
    public ResourceBundle resourceBundle() {
        return resourceBundle;
    }

    /**
     * Injects locale specific text in all instance fields of this instance.
     * Only public instance fields of type <code>String</code> are considered.
     * <p>
     * The name of this (sub)class plus the given <code>locale</code> parameter
     * define the resource bundle to be loaded. In other words the
     * <code>this.getClass().getName()</code> is used as the
     * <code>baseName</code> parameter in the
     * {@link ResourceBundle#getBundle(String, Locale)} parameter to load the
     * resource bundle.
     * <p>
     *
     * @param locale
     *            defines the locale to be used when loading the resource bundle
     * @exception TranslationBundleLoadingException
     *                see {@link TranslationBundleLoadingException}
     * @exception TranslationStringMissingException
     *                see {@link TranslationStringMissingException}
     */
    void load(Locale locale)
            throws TranslationBundleLoadingException {
        Class bundleClass = getClass();
        try {
            resourceBundle = ResourceBundle.getBundle(bundleClass.getName(),
                    locale, bundleClass.getClassLoader());
        } catch (MissingResourceException e) {
            throw new TranslationBundleLoadingException(bundleClass, locale, e);
        }
        this.effectiveLocale = resourceBundle.getLocale();

        for (Field field : bundleClass.getFields()) {
            if (field.getType().equals(String.class)) {
                try {
                    String translatedText = resourceBundle.getString(field.getName());
                    field.set(this, translatedText);
                } catch (MissingResourceException e) {
                    throw new TranslationStringMissingException(bundleClass, locale, field.getName(), e);
                } catch (IllegalArgumentException | IllegalAccessException e) {
                    throw new Error(e);
                }
            }
        }
    }
}