Struts2源码阅读(三)_DispatcherConfigurationProvider

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);     }         return new Dispatcher(filterConfig.getServletContext(), params);     
}

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.

XxxProvider类图:

首先是init_DefaultProperties()

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,默认的struts-default.xml,struts-plugin.xml,struts.xml    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);     }     }     }

首先是init_DefaultProperties()

private void init_DefaultProperties() {     configurationManager.addConfigurationProvider(new DefaultPropertiesProvider());     
}     
//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类图：

//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));     }     }

ClassLoaderUtils.getResource( resourceName, callingClass ): 查找指定资源

    public static URL getResource(String resourceName, Class callingClass) {URL url = null;url = Thread.currentThread().getContextClassLoader().getResource(resourceName);if (url == null) {url = ClassLoaderUtils.class.getClassLoader().getResource(resourceName);}if (url == null) {url = callingClass.getClassLoader().getResource(resourceName);}return url;}

为什么要按照这个顺序？前面的加载为什么可能会失败？

LocatableProperties.load( inputStream ): 将文件内容加载到 LocatableProperties 对象内。

    public void load(InputStream in) throws IOException {Reader reader = new InputStreamReader(in);PropertiesReader pr = new PropertiesReader(reader);while (pr.nextProperty()) {String name = pr.getPropertyName();String val = pr.getPropertyValue();int line = pr.getLineNumber();String desc = convertCommentsToString(pr.getCommentLines());Location loc = new LocationImpl(desc, location.getURI(), line, 0);setProperty(name, val, loc);}}

LocatableProperties.setProperty( name, value, location ): 如何实现一个属性名称对应一个属性值，而且有对应一个Location

LocatableProperties 内部有一个Map<String,Location> propLocations;

Properties 类本身又类似一个Map，这样通过两个Map 来实现内部存储。

    public Object setProperty(String key, String value, Object locationObj) {Object obj = super.setProperty(key, value);if (location != null) {Location loc = LocationUtils.getLocation(locationObj);propLocations.put(key, loc);}return obj;}

的十大书店

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;     }