Tomcat中的ResourceBundle国际化解析

一、ResourceBundle 简介:

资源束(ResourceBundle)是一个本地化对象。它封装了适用于本地环境的资源; 这个类主要用来解决国际化和本地化问题。国际化和本地化可不是两个概念，两者都是一起出现的。可以说，国际化的目的就是为了实现本地化。

比如对于“取消”，中文中我们使用“取消”来表示，而英文中我们使用“cancel”。若我们的程序是面向国际的（这也是软件发展的一个趋势），那么使用的人群必然是多语言环境的，实现国际化就非常有必要。而ResourceBundle可以帮助我们轻松完成这个任务：当程序需要一个特定于语言环境的资源时（如 String），程序可以从适合当前用户语言环境的资源包（大多数情况下也就是.properties文件）中加载它。这样可以编写很大程度上独立于用户语言环境的程序代码，它将资源包中大部分（即便不是全部）特定于语言环境的信息隔离开来。

这使编写的程序可以：

轻松地本地化或翻译成不同的语言
一次处理多个语言环境
以后可以轻松进行修改，以便支持更多的语言环境

说的简单点，这个类的作用就是读取资源属性文件（properties），然后根据.properties文件的名称信息（本地化信息），匹配当前系统的国别语言信息（也可以程序指定），然后获取相应的properties文件的内容。使用这个类，properties需要遵循一定的命名规范，一般的命名规范是： 自定义名_语言代码_国别代码.properties(LocalStrings_zh_CN.properties)，如果是默认的，直接写为：自定义名.properties(LocalStrings.properties)

当在中文操作系统下，如果LocalStrings_zh_CN.properties、LocalStrings.properties两个文件都存在，则优先会使用LocalStrings_zh_CN.properties，当LocalStrings_zh_CN.properties不存在时候，会使用默认的myres.properties。在没有提供语言和地区的资源文件时使用的是系统默认的资源文件。

资源文件都必须是ISO-8859-1编码，因此，对于所有非西方语系的处理，都必须先将之转换为Java Unicode Escape格式。转换方法是通过JDK自带的工具native2ascii; 所以在中文资源文件中最好把中文转换为unicode, 否则可能会因为编译软件编码格式不一致而出现乱码问题

例如:

userConfig.start=\u7528\u6237\u914d\u7f6e\uff1a\u5904\u7406\u5f00\u59cb

二、ResourceBundle的使用

PropertyResourceBundle将本地化的文本存储于Java property文件中。

从ResourceBundle中获取值

获取ResourceBundle实例后可以通过下面的方法获得本地化值。
getObject(String key);
getString(String key);
getStringArray(String key);
还可以通过keySet()方法获取所有的key。Set keys = bundle.keySet();
其它ResourceBundle 方法可以通过查看文档获得。

使用示例:

(1) 新建4个属性文件

my_en_US.properties：cancelKey=cancelmy_zh_CN.properties：cancelKey=\u53D6\u6D88（取消）my_zh.properties：cancelKey=\u53D6\u6D88zh（取消zh）my.properties：cancelKey=\u53D6\u6D88default（取消default）

(2) 获取bundle

ResourceBundle bundle = ResourceBundle.getBundle("res", new Locale("zh", "CN"));

注意: 其中new Locale(“zh”, “CN”)提供本地化信息，上面这行代码，程序会首先在classpath下寻找my_zh_CN.properties文件，若my_zh_CN.properties文件不存在，则取找my_zh.properties，如还是不存在，继续寻找my.properties,若都找不到就抛出异常。

(3) Test示例

import javax.annotation.Resource;
import java.util.Locale;
import java.util.ResourceBundle;/*** @author OovEver* 2018/1/14 22:12*/
public class Main {public static void main(String args[]) {ResourceBundle bundle = ResourceBundle.getBundle("my", new Locale("zh", "CN"));String cancel = bundle.getString("cancelKey");System.out.println(cancel);bundle = ResourceBundle.getBundle("my", Locale.US);cancel = bundle.getString("cancelKey");System.out.println(cancel);bundle = ResourceBundle.getBundle("my", Locale.getDefault());cancel = bundle.getString("cancelKey");System.out.println(cancel);bundle = ResourceBundle.getBundle("my", Locale.GERMAN);cancel = bundle.getString("cancelKey");System.out.println(cancel);bundle = ResourceBundle.getBundle("my");for (String key : bundle.keySet()) {System.out.println(bundle.getString(key));}}
}

(4) 输出结果

取消
cancel
取消
取消
取消

(5) 分析

前面三个分别按照zh_CN,US,默认的结果输出，第四个由于我们未定义GERMAN属性文件，这时ResourceBundle为我们提供了一个fallback（也就是一个备用方案），这个备用方案就是根据当前系统的语言环境来得到的本地化信息。所以若是找不到GERMAN的，之后就会去找CHINA了，所以找到了res_zh_CH.properties这个资源包。最后一个是若有多个属性文件，可以按照Map的形式遍历，获得属性文件内的各个值。

三、Tomcat中的ResourceBundle使用

Tomcat 的国际化管理是根据java文件包分类的; (比如操作系统为中文，那么通ResourceBundle.getBundle(org.apache.XXXX)所得到的本地资源束所指向的文件既是org.apaceh包下的XXXX_CN.properties)

Tomcat 维护了一个StringManager的集合。Tomcat将国际化资源信息存储在相应的包中。

(1) StringManager类中维护了一个StringManager集合

private static Hashtable managers = new Hashtable();

(2) StringManager类实现了对ResourceBundle资源束的管理，是ResourceBundle的封装

private final ResourceBundle bundle;

(3) 构造方法中实现了通过包名来取得本地环境指定包下的bundle

private StringManager(String packageName, Locale locale) {
String bundleName = packageName + ".LocalStrings";
ResourceBundle bnd = null;
try {
if (locale.getLanguage().equals(Locale.ENGLISH.getLanguage())) {
locale = Locale.ROOT;
}
bnd = ResourceBundle.getBundle(bundleName, locale);
} catch (MissingResourceException ex) {
. . .
}
bundle = bnd;
if (bundle != null) {
Locale bundleLocale = bundle.getLocale();
if (bundleLocale.equals(Locale.ROOT)) {
this.locale = Locale.ENGLISH;
} else {
this.locale = bundleLocale;
}
} else {
this.locale = null;
}
}

(4) 最后通过bundle.getString(key);方法，即可得到本地资源信息

public String getString(final String key, final Object... args) {
String value = getString(key);
if (value == null) {
value = key;
}

MessageFormat mf = new MessageFormat(value);
mf.setLocale(locale);
return mf.format(args, new StringBuffer(), null).toString();
}

StringManager类:

package org.apache.tomcat.util.res;import java.text.MessageFormat;
import java.util.Enumeration;
import java.util.Hashtable;
import java.util.LinkedHashMap;
import java.util.Locale;
import java.util.Map;
import java.util.MissingResourceException;
import java.util.ResourceBundle;public class StringManager {private static int LOCALE_CACHE_SIZE = 10;//此StringManager的ResourceBundleprivate final ResourceBundle bundle;private final Locale locale;/*** Creates a new StringManager for a given package. This is a* private method and all access to it is arbitrated by the* static getManager method call so that only one StringManager* per package will be created.** @param packageName Name of package to create StringManager for.*/private StringManager(String packageName, Locale locale) {String bundleName = packageName + ".LocalStrings";ResourceBundle bnd = null;try {// The ROOT Locale uses English. If English is requested, force the// use of the ROOT Locale else incorrect results may be obtained if// the system default locale is not English and translations are// available for the system default locale.if (locale.getLanguage().equals(Locale.ENGLISH.getLanguage())) {locale = Locale.ROOT;}  bnd = ResourceBundle.getBundle(bundleName, locale);} catch (MissingResourceException ex) {// Try from the current loader (that's the case for trusted apps)// Should only be required if using a TC5 style classloader structure// where common != shared != serverClassLoader cl = Thread.currentThread().getContextClassLoader();if (cl != null) {try {bnd = ResourceBundle.getBundle(bundleName, locale, cl);} catch (MissingResourceException ex2) {// Ignore}}}bundle = bnd;// Get the actual locale, which may be different from the requested oneif (bundle != null) {Locale bundleLocale = bundle.getLocale();if (bundleLocale.equals(Locale.ROOT)) {this.locale = Locale.ENGLISH;} else {this.locale = bundleLocale;}} else {this.locale = null;}}/*** Get a string from the underlying resource bundle or return null if the* String is not found.** @param key to desired resource String** @return resource String matching <i>key</i> from underlying bundle or*         null if not found.** @throws IllegalArgumentException if <i>key</i> is null*/public String getString(String key) {if (key == null){String msg = "key may not have a null value";throw new IllegalArgumentException(msg);}String str = null;try {// Avoid NPE if bundle is null and treat it like an MREif (bundle != null) {str = bundle.getString(key);}} catch (MissingResourceException mre) {//bad: shouldn't mask an exception the following way://   str = "[cannot find message associated with key '" + key +//         "' due to " + mre + "]";//     because it hides the fact that the String was missing//     from the calling code.//good: could just throw the exception (or wrap it in another)//      but that would probably cause much havoc on existing//      code.//better: consistent with container pattern to//      simply return null.  Calling code can then do//      a null check.str = null;}return str;}/*** Get a string from the underlying resource bundle and format* it with the given set of arguments.** @param key  The key for the required message* @param args The values to insert into the message** @return The request string formatted with the provided arguments or the*         key if the key was not found.*/public String getString(final String key, final Object... args) {String value = getString(key);if (value == null) {value = key;}MessageFormat mf = new MessageFormat(value);mf.setLocale(locale);return mf.format(args, new StringBuffer(), null).toString();}/*** Identify the Locale this StringManager is associated with.** @return The Locale associated with the StringManager*/public Locale getLocale() {return locale;}// --------------------------------------------------------------// STATIC SUPPORT METHODS// --------------------------------------------------------------private static final Map<String, Map<Locale,StringManager>> managers =new Hashtable<>();/*** Get the StringManager for a given class. The StringManager will be* returned for the package in which the class is located. If a manager for* that package already exists, it will be reused, else a new* StringManager will be created and returned.** @param clazz The class for which to retrieve the StringManager** @return The instance associated with the package of the provide class*/public static final StringManager getManager(Class<?> clazz) {return getManager(clazz.getPackage().getName());}/*** Get the StringManager for a particular package. If a manager for* a package already exists, it will be reused, else a new* StringManager will be created and returned.** @param packageName The package name** @return The instance associated with the given package and the default*         Locale*/public static final StringManager getManager(String packageName) {return getManager(packageName, Locale.getDefault());}/*** Get the StringManager for a particular package and Locale. If a manager* for a package/Locale combination already exists, it will be reused, else* a new StringManager will be created and returned.** @param packageName The package name* @param locale      The Locale** @return The instance associated with the given package and Locale*/public static final synchronized StringManager getManager(String packageName, Locale locale) {Map<Locale,StringManager> map = managers.get(packageName);if (map == null) {/** Don't want the HashMap to be expanded beyond LOCALE_CACHE_SIZE.* Expansion occurs when size() exceeds capacity. Therefore keep* size at or below capacity.* removeEldestEntry() executes after insertion therefore the test* for removal needs to use one less than the maximum desired size**/map = new LinkedHashMap<Locale,StringManager>(LOCALE_CACHE_SIZE, 1, true) {private static final long serialVersionUID = 1L;@Overrideprotected boolean removeEldestEntry(Map.Entry<Locale,StringManager> eldest) {if (size() > (LOCALE_CACHE_SIZE - 1)) {return true;}return false;}};managers.put(packageName, map);}StringManager mgr = map.get(locale);if (mgr == null) {mgr = new StringManager(packageName, locale);map.put(locale, mgr);}return mgr;}/*** Retrieve the StringManager for a list of Locales. The first StringManager* found will be returned.** @param packageName      The package for which the StringManager was*                         requested* @param requestedLocales The list of Locales** @return the found StringManager or the default StringManager*/public static StringManager getManager(String packageName,Enumeration<Locale> requestedLocales) {while (requestedLocales.hasMoreElements()) {Locale locale = requestedLocales.nextElement();StringManager result = getManager(packageName, locale);if (result.getLocale().equals(locale)) {return result;}}// Return the defaultreturn getManager(packageName);}
}