struts2配置文件加载流程分析

 【IT168 技术文档】

首先org.apache.struts2.dispatcher. FilterDispatcher.java 中的init（）方法，
 

  public void init(FilterConfig filterConfig) throws ServletException {this.filterConfig = filterConfig;String param = filterConfig.getInitParameter("packages");//由此可以看出可以增加参数packages       String packages = "org.apache.struts2.static template org.apache.struts2.interceptor.debugging";if (param != null) {packages = param + " " + packages;}this.pathPrefixes = parse(packages);dispatcher = new Dispatcher(filterConfig.getServletContext());}

org.apache.struts2.dispatcher. Dispatcher.java
首先执行静态代码块：

  static {ObjectFactory.setObjectFactory(new StrutsObjectFactory());ActionProxyFactory.setFactory(new StrutsActionProxyFactory());}

 
执行构造方法
   public Dispatcher(ServletContext servletContext) {
       init(servletContext);
}
然后执行init()方法：

boolean reloadi18n = Boolean.valueOf(
(String) Settings.get(StrutsConstants.STRUTS_I18N_RELOAD)).booleanValue();
上面的语句读取了properties文件。


读取properties文件的流程：
首先执行Org.apache.struts2.dispatcher.Dispatcher.java 类的方法init()中的语句
       boolean reloadi18n = Boolean.valueOf((String)
Settings.get(StrutsConstants.STRUTS_I18N_RELOAD)).booleanValue();

然后执行了org.apacher.struts2.config.Setting.java类中的方法
   public static String get(String name) throws IllegalArgumentException {
       String val = getInstance().getImpl(name);
       return val;
   }
然后执行了
   public static Settings getInstance() {
       return (settingsImpl == null) ? getDefaultInstance() : settingsImpl;
}
然后执行了

   private static Settings getDefaultInstance() {if (defaultImpl == null) {// Create bootstrap implementation           defaultImpl = new DefaultSettings(); //产生了一个DefaultSettings对象// Create default implementation           try {String className = get(StrutsConstants.STRUTS_CONFIGURATION);if (!className.equals(defaultImpl.getClass().getName())) {try {// singleton instances shouldn't be built accessing request or session-specific context data                       defaultImpl = (Settings) ObjectFactory.getObjectFactory().buildBean(Thread.currentThread().getContextClassLoader().loadClass(className), null);} catch (Exception e) {LOG.error("Could not instantiate settings", e);}}} catch (IllegalArgumentException ex) {// ignore           }}return defaultImpl;}

然后首先执行了语句defaultImpl = new DefaultSettings();

   public DefaultSettings() {// Create default implementations// Use default properties and struts.properties       ArrayList list = new ArrayList();try {list.add(new PropertiesSettings("struts"));//从这里加载struts.properties文件       } catch (Exception e) {log.warn("Could not find or error in struts.properties", e);}try {list.add(new PropertiesSettings("org/apache/struts2/default")); //加载默认的defualt.properties文件       } catch (Exception e) {log.error("Could not find org/apache/struts2/default.properties", e);}Settings[] configList = new Settings[list.size()];//定义了Settings对象数组       config = new DelegatingSettings((Settings[]) list.toArray(configList));// Add list of additional properties settingss       try {StringTokenizer configFiles = new StringTokenizer((String) config.getImpl(StrutsConstants.STRUTS_CUSTOM_PROPERTIES), ",");加载了用户自己定义的properties文件。while (configFiles.hasMoreTokens()) {String name = configFiles.nextToken();try {list.add(new PropertiesSettings(name));} catch (Exception e) {log.error("Could not find " + name + ".properties. Skipping");}}configList = new Settings[list.size()];config = new DelegatingSettings((Settings[]) list.toArray(configList));} catch (IllegalArgumentException e) {// thrown when Settings is unable to find a certain property// eg. struts.custom.properties in default.properties which is commented// out       }// Add additional list of i18n global resource bundles       try {LocalizedTextUtil.addDefaultResourceBundle("org/apache/struts2/struts-messages");StringTokenizer bundleFiles = new StringTokenizer((String) config.getImpl(StrutsConstants.STRUTS_CUSTOM_I18N_RESOURCES), ", ");while (bundleFiles.hasMoreTokens()) {String name = bundleFiles.nextToken();try {log.info("Loading global messages from " + name);LocalizedTextUtil.addDefaultResourceBundle(name);} catch (Exception e) {log.error("Could not find " + name + ".properties. Skipping");}}} catch (IllegalArgumentException e) {// struts.custom.i18n.resources wasn't provided       }}

看看org.apache.struts2.config.DelegatingSettings.java下面的方法。

 /*** Gets the specified property - calls getImpl(String) method on config objects in config list* until successful.** @see #get(String)*/   public String getImpl(String name) throws IllegalArgumentException {// Delegate to the other settings       IllegalArgumentException e = null;for (int i = 0; i < configList.length; i++) {try {return configList[i].getImpl(name);} catch (IllegalArgumentException ex) {e = ex;// Try next config           }}throw e;}

小结：
    通过上面的代码分析，大家就可以明白为什么struts.properties中的配置项会自动覆盖default.properties中的属性，而不会配用户自定义的配置文件覆盖