java.util.ResourceBundle
java.text.MessageFormat

// 加载资源文件
ResourceBundle resource = ResourceBundle.getBundle("messages");
// 获取资源文件中的信息
String driverName = resource.getString("database.driver");

Locale locale1 = new Locale("zh", "CN");
ResourceBundle resb1 = ResourceBundle.getBundle("myres", locale1);resb1.getString("aaa");

String pig = "{0}{1}{2}{3}{4}{5}{6}{7}{8}{9}{10}{11}{12}{13}{14}{15}{16}";
Object[] array = new Object[]{"A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q"};
String value = MessageFormat.format(pig, array);
System.out.println(value);  //最终结果是：ABCDEFGHIJKLMNOPQ

database.driver=com.mysql.jdbc.Drvier
database.url=jdbc:mysql://localhost:3306:test
database.user={0}
database.pass={0}

public class ResourceBundleTest {public static void main(String[] args) {// 指明包路径和文件名即可ResourceBundle resource = ResourceBundle.getBundle("code.stu.ResourceBundle.myResources");String driverName = resource.getString("database.driver");String url = resource.getString("database.url");Object[] array1 = new Object[]{"root"};Object[] array2 = new Object[]{"test"};// 取得字符串，直接格式化String user = MessageFormat.format(resource.getString("database.user"), new Object[]{"root"});String pass = MessageFormat.format(resource.getString("database.pass"), new Object[]{"test"});System.out.println(driverName + url + user + pass);//结果：com.mysql.jdbc.Drvierjdbc:mysql://localhost:3306:testroottest
    }
}

package org.apache.catalina.util;import java.text.MessageFormat;
import java.util.Hashtable;
import java.util.Locale;
import java.util.MissingResourceException;
import java.util.ResourceBundle;
import java.net.URLClassLoader;public class StringManager {// ResourceBundle用于读取properties文件private ResourceBundle bundle;private static org.apache.juli.logging.Log log=org.apache.juli.logging.LogFactory.getLog( StringManager.class );// 私有的构造方法能够保证外界无法实例化自己，这也是单例实现的关键步骤private StringManager(String packageName) {// properties文件所在的package+“.LocalStrings”// 所有tomcat的日志使用的properties文件都依照这个形式来命名的String bundleName = packageName + ".LocalStrings";try {// 根据bundleName取得解析资源文件的实例bundle = ResourceBundle.getBundle(bundleName);return;} catch( MissingResourceException ex ) {// 好吧，异常就先不管了。// Try from the current loader ( that's the case for trusted apps )ClassLoader cl=Thread.currentThread().getContextClassLoader();if( cl != null ) {try {bundle=ResourceBundle.getBundle(bundleName, Locale.getDefault(), cl);return;} catch(MissingResourceException ex2) {}}if( cl==null )cl=this.getClass().getClassLoader();if (log.isDebugEnabled())log.debug("Can't find resource " + bundleName +" " + cl);if( cl instanceof URLClassLoader ) {if (log.isDebugEnabled()) log.debug( ((URLClassLoader)cl).getURLs());}}}/*** Get a string from the underlying resource bundle.** @param key The resource name*/public String getString(String key) {return MessageFormat.format(getStringInternal(key), (Object [])null);}protected String getStringInternal(String key) {// key 还是要保证不是nullif (key == null) {String msg = "key is null";throw new NullPointerException(msg);}// 返回stringString str = null;if( bundle==null )return key;try {// 资源文件里去查有没有对应的内容str = bundle.getString(key);} catch (MissingResourceException mre) {str = "Cannot find message associated with key '" + key + "'";}return str;}public String getString(String key, Object[] args) {String iString = null;String value = getStringInternal(key);// this check for the runtime exception is some pre 1.1.6// VM's don't do an automatic toString() on the passed in// objects and barf outtry {// ensure the arguments are not null so pre 1.2 VM's don't barfObject nonNullArgs[] = args;for (int i=0; i<args.length; i++) {if (args[i] == null) {if (nonNullArgs==args) nonNullArgs=(Object[])args.clone();nonNullArgs[i] = "null";}}// 格式化，就是把一些变化的参数插入到value这个string中去，格式化成一个新的最终的stringiString = MessageFormat.format(value, nonNullArgs);} catch (IllegalArgumentException iae) {StringBuffer buf = new StringBuffer();buf.append(value);for (int i = 0; i < args.length; i++) {buf.append(" arg[" + i + "]=" + args[i]);}iString = buf.toString();}return iString;}// 下面四个getString方法，最终都需要调用getString(String key, Object[] args)public String getString(String key, Object arg) {Object[] args = new Object[] {arg};return getString(key, args);}public String getString(String key, Object arg1, Object arg2) {Object[] args = new Object[] {arg1, arg2};return getString(key, args);}public String getString(String key, Object arg1, Object arg2,Object arg3) {Object[] args = new Object[] {arg1, arg2, arg3};return getString(key, args);}public String getString(String key, Object arg1, Object arg2,Object arg3, Object arg4) {Object[] args = new Object[] {arg1, arg2, arg3, arg4};return getString(key, args);}// Hashtable维护整个tomcat的StringManagerprivate static Hashtable managers = new Hashtable();// 保证一个包一个StringManager，私有化构造函数+Hashtable维护实现（值得学习）// 从而避免大量的StringManager实例化和销毁的操作,毕竟写日志属于比较频繁的操作。public synchronized static StringManager getManager(String packageName) {// 用一个Hashtable来管理控制，保证每个包提供一个StringManagerStringManager mgr = (StringManager)managers.get(packageName);// 属于这个包的Manager有了吗if (mgr == null) {mgr = new StringManager(packageName);// 实例化好后，把它放进Hashtable里去，下次就不用实例化了
            managers.put(packageName, mgr);}return mgr;}
}