首先强调一下struts2的线程程安全，在Struts2中大量采用ThreadLocal线程局部变量的方法来保证线程的安全,像Dispatcher等都是通过ThreadLocal来保存变量值,使得每个线程都有自己独立的实例变量,互不相干.
接下来就从Dispatcher开始看起，先看其构造函数：
//创建Dispatcher，此类是一个Delegate，它是真正完成根据url解析转向，读取对应Action的地方 public Dispatcher(ServletContext servletContext, Map<String, String> initParams) { this.servletContext = servletContext; //配置在web.xml中的param参数 this.initParams = initParams; }
我们再看在FilterDispatcher创建Dispatcher的:
protected Dispatcher createDispatcher(FilterConfig filterConfig) { Map<String, String> params = new HashMap<String, String>(); for (Enumeration e = filterConfig.getInitParameterNames(); e.hasMoreElements();) { String name = (String) e.nextElement(); String value = filterConfig.getInitParameter(name); params.put(name, value); } //都可以从FilterConfig中得到 return new Dispatcher(filterConfig.getServletContext(), params); }
创建Dispatcher之后,来看init()方法init()方法是用来Load用户配置文件,资源文件以及默认的配置文件.
主要分七步走,看下面注释
public void init() { if (configurationManager == null) { //设置ConfigurationManager的defaultFrameworkBeanName. //这里DEFAULT_BEAN_NAME为struts,这是xwork框架的内容,Framework可以是xwork,struts,webwork等 configurationManager = new ConfigurationManager(BeanSelectionProvider.DEFAULT_BEAN_NAME); } //读取properties信息,默认的default.properties, init_DefaultProperties(); // [1] //读取xml配置文件 init_TraditionalXmlConfigurations(); // [2] //读取用户自定义的struts.properties init_LegacyStrutsProperties(); // [3] //自定义的configProviders init_CustomConfigurationProviders(); // [5] //载入FilterDispatcher传进来的initParams init_FilterInitParameters() ; // [6] //将配置文件中的bean与具体的类映射 init_AliasStandardObjects() ; // [7] //构建一个用于依赖注射的Container对象 //在这里面会循环调用上面七个ConfigurationProvider的register方法 //其中的重点就是DefaultConfiguration的#reload()方法 Container container = init_PreloadConfiguration(); container.inject(this); init_CheckConfigurationReloading(container); init_CheckWebLogicWorkaround(container); if (!dispatcherListeners.isEmpty()) { for (DispatcherListener l : dispatcherListeners) { l.dispatcherInitialized(this); } } }
分七步载入各种配置属性,都是通过ConfigurationProvider接口进行的,这个接口提供init(),destroy(),register()等方法.将各种ConfigurationProvider初始化之后将实例添加到ConfigurationManager的List里面.最后通过循环调用List里的这些destroy(),register()等方法实现对配置文件的属性进行注册和销毁等功能.下面将分析这七层功夫是怎样一步步练成的.
首先是init_DefaultProperties()
private void init_DefaultProperties() { configurationManager.addConfigurationProvider(new DefaultPropertiesProvider()); } //直接来看DefaultPropertiesProvider好了,DefaultPropertiesProvider实际上只是实现了register()方法 public void register(ContainerBuilder builder, LocatableProperties props) throws ConfigurationException { Settings defaultSettings = null; try { defaultSettings = new PropertiesSettings("org/apache/struts2/default"); } catch (Exception e) { throw new ConfigurationException("Could not find or error in org/apache/struts2/default.properties", e); } loadSettings(props, defaultSettings); }//PropertiesSettings构造方法 //读取org/apache/struts2/default.properties的配置信息，如果项目中需要覆盖，可以在classpath里的struts.properties里覆写 public PropertiesSettings(String name) { URL settingsUrl = ClassLoaderUtils.getResource(name + ".properties", getClass()); if (settingsUrl == null) { LOG.debug(name + ".properties missing"); settings = new LocatableProperties(); return; } settings = new LocatableProperties(new LocationImpl(null, settingsUrl.toString())); // Load settings InputStream in = null; try { in = settingsUrl.openStream(); settings.load(in); } catch (IOException e) { throw new StrutsException("Could not load " + name + ".properties:" + e, e); } finally { if(in != null) { try { in.close(); } catch(IOException io) { LOG.warn("Unable to close input stream", io); } } } } //loadSettings主要是将progerty的value和Locale从上面PropertiesSettings中取得并存放到LocatableProperties props //这个props是register的一个入参. protected void loadSettings(LocatableProperties props, final Settings settings) { // We are calling the impl methods to get around the single instance of Settings that is expected for (Iterator i = settings.listImpl(); i.hasNext(); ) { String name = (String) i.next(); props.setProperty(name, settings.getImpl(name), settings.getLocationImpl(name)); } }
再来看第二步：init_TraditionalXmlConfigurations()
private void init_TraditionalXmlConfigurations() { //首先读取web.xml中的config初始参数值 //如果没有配置就使用默认的DEFAULT_CONFIGURATION_PATHS:"struts-default.xml,struts-plugin.xml,struts.xml"， //这儿就可以看出为什么默认的配置文件必须取名为这三个名称了 //如果不想使用默认的名称，直接在web.xml中配置config初始参数即可 String configPaths = initParams.get("config"); if (configPaths == null) { configPaths = DEFAULT_CONFIGURATION_PATHS; } String[] files = configPaths.split("\\s*[,]\\s*"); for (String file : files) { if (file.endsWith(".xml")) { if ("xwork.xml".equals(file)) { //XmlConfigurationProvider负责解析xwork.xml configurationManager.addConfigurationProvider(new XmlConfigurationProvider(file, false)); } else { //其它xml都是由StrutsXmlConfigurationProvider来解析 configurationManager.addConfigurationProvider(new StrutsXmlConfigurationProvider(file, false, servletContext)); } } else { throw new IllegalArgumentException("Invalid configuration file name"); } } }
对于其它配置文件只用StrutsXmlConfigurationProvider，此类继承XmlConfigurationProvider，而XmlConfigurationProvider又实现ConfigurationProvider接口。类XmlConfigurationProvider负责配置文件的读取和解析，首先通过init()中的loadDocuments(configFileName);利用DomHelper中的public static Document parse(InputSource inputSource, Map<String, String> dtdMappings) 将configFileName配置文件通过SAX解析方式按照DtdMappings解析成Document对象.然后通过Provider的register()方法加载"bean"和"constant"属性,再通过loadPackages()加载package及package中的属性addAction()方法负责读取<action>标签，并将数据保存在ActionConfig中；addResultTypes()方法负责将<result-type>标签转化为ResultTypeConfig对象；loadInterceptors()方法负责将<interceptor>标签转化为InterceptorConfi对象；loadInterceptorStack()方法负责将<interceptor-ref>标签转化为InterceptorStackConfig对象；loadInterceptorStacks()方法负责将<interceptor-stack>标签转化成InterceptorStackConfig对象。而上面的方法最终会被addPackage()方法调用,addPackage又会被Provider的loadPackages()调用，将所读取到的数据汇集到PackageConfig对象中。
protected PackageConfig addPackage(Element packageElement) throws ConfigurationException { PackageConfig.Builder newPackage = buildPackageContext(packageElement); if (newPackage.isNeedsRefresh()) { return newPackage.build(); } // add result types (and default result) to this package addResultTypes(newPackage, packageElement); // load the interceptors and interceptor stacks for this package loadInterceptors(newPackage, packageElement); // load the default interceptor reference for this package loadDefaultInterceptorRef(newPackage, packageElement); // load the default class ref for this package loadDefaultClassRef(newPackage, packageElement); // load the global result list for this package loadGlobalResults(newPackage, packageElement); // load the global exception handler list for this package loadGobalExceptionMappings(newPackage, packageElement); // get actions NodeList actionList = packageElement.getElementsByTagName("action"); for (int i = 0; i < actionList.getLength(); i++) { Element actionElement = (Element) actionList.item(i); addAction(actionElement, newPackage); } // load the default action reference for this package loadDefaultActionRef(newPackage, packageElement); PackageConfig cfg = newPackage.build(); configuration.addPackageConfig(cfg.getName(), cfg); return cfg; } //loadConfigurationFiles解析读取xml中的内容 private List<Document> loadConfigurationFiles(String fileName, Element includeElement) { ... //通过DomHelper调用SAX进行解析xml doc = DomHelper.parse(in, dtdMappings); ... Element rootElement = doc.getDocumentElement(); NodeList children = rootElement.getChildNodes(); int childSize = children.getLength(); for (int i = 0; i < childSize; i++) { Node childNode = children.item(i); if (childNode instanceof Element) { Element child = (Element) childNode; final String nodeName = child.getNodeName(); if ("include".equals(nodeName)) { String includeFileName = child.getAttribute("file"); //解析每个action配置是，对于include文件可以使用通配符*来进行配置 //如Struts.xml中可配置成<include file="actions_*.xml"/> if (includeFileName.indexOf('*') != -1) { ClassPathFinder wildcardFinder = new ClassPathFinder(); wildcardFinder.setPattern(includeFileName); Vector<String> wildcardMatches = wildcardFinder.findMatches(); for (String match : wildcardMatches) { //递归Load子file中的<include/> docs.addAll(loadConfigurationFiles(match, child)); } } else { docs.addAll(loadConfigurationFiles(includeFileName, child)); } } } } docs.add(doc); loadedFileUrls.add(url.toString()); ... return docs; }
