Struts2源码解析2
Posted shiyuan310
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看了前面一节对Struts2各个模块运行有了大概了解，也对调用的函数有了一定的了解，本节希望打断点跑一个Struts2例子！
还是放在struts2结构图：
一：项目启动后解析web.xml文件，会解析到配置的StrutsPrepareAndExecuteFilter的过滤器。
1 <?xml version="1.0" encoding="UTF-8"?> 2 <web-app id="WebApp_9" version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee" 3 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 4 xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"> 5 6 <display-name>Struts2Demo</display-name> 7 8 <filter> 9 <filter-name>struts2</filter-name> 10 <filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter</filter-class> 11 </filter> 12 13 <filter-mapping> 14 <filter-name>struts2</filter-name> 15 <url-pattern>/*</url-pattern> 16 </filter-mapping> 17 18 <welcome-file-list> 19 <welcome-file>login.jsp</welcome-file> 20 </welcome-file-list> 21 </web-app>
在此研究的是StrutsPrepareAndExecuteFilter。
二：StrutsPrepareAndExecuteFilter
StrutsPrepareAndExecuteFilter中的方法：
| void init(FilterConfig filterConfig) | 继承自Filter，过滤器的初始化 |
| doFilter(ServletRequest req, ServletResponse res, FilterChain chain) | 继承自Filter，执行过滤器 |
| void destroy() | 继承自Filter，用于资源释放 |
| void postInit(Dispatcher dispatcher, FilterConfig filterConfig) | Callback for post initialization（一个空的方法，用于方法回调初始化） |
web容器一启动，就会初始化核心过滤器StrutsPrepareAndExecuteFilter，并执行初始化方法，初始化方法如下：
1 public void init(FilterConfig filterConfig) throws ServletException { 2 InitOperations init = new InitOperations(); 3 Dispatcher dispatcher = null; 4 try { 5 //封装filterConfig，其中有个主要方法getInitParameterNames将参数名字以String格式存储在List 6 FilterHostConfig config = new FilterHostConfig(filterConfig); 7 //初始化struts内部日志 8 init.initLogging(config); 9 //创建dispatcher ，并初始化 10 dispatcher = init.initDispatcher(config); 11 init.initStaticContentLoader(config, dispatcher); 12 //初始化类属性：prepare 、execute 13 prepare = new PrepareOperations(dispatcher); 14 execute = new ExecuteOperations(dispatcher); 15 this.excludedPatterns = init.buildExcludedPatternsList(dispatcher); 16 //回调空的postInit方法 17 postInit(dispatcher, filterConfig); 18 } finally { 19 if (dispatcher != null) { 20 dispatcher.cleanUpAfterInit(); 21 } 22 init.cleanup(); 23 } 24 }
关于封装filterConfig，首先看下FilterHostConfig ，源码如下：
1 public class FilterHostConfig implements HostConfig { 2 3 private FilterConfig config; 4 //构造方法 5 public FilterHostConfig(FilterConfig config) { 6 this.config = config; 7 } 8 //根据init-param配置的param-name获取param-value的值 9 public String getInitParameter(String key) { 10 return config.getInitParameter(key); 11 } 12 //返回初始化参数名的迭代器 13 public Iterator<String> getInitParameterNames() { 14 return MakeIterator.convert(config.getInitParameterNames()); 15 } 16 //返回Servlet上下文 17 public ServletContext getServletContext() { 18 return config.getServletContext(); 19 } 20 }
只有短短的几行代码，getInitParameterNames是这个类的核心，将Filter初始化参数名称有枚举类型转为Iterator。此类的主要作为是对filterConfig 封装。
接下来，看下StrutsPrepareAndExecuteFilter中init方法中dispatcher = init.initDispatcher(config);这是初始化dispatcher的，是通过init对象的initDispatcher方法来初始化的，init是InitOperations类的对象，我们看看InitOperations中initDispatcher方法：
1 public Dispatcher initDispatcher( HostConfig filterConfig ) { 2 Dispatcher dispatcher = createDispatcher(filterConfig); 3 dispatcher.init(); 4 return dispatcher; 5 }
创建Dispatcher，会读取 filterConfig 中的配置信息，将配置信息解析出来，封装成为一个Map，然后根绝servlet上下文和参数Map构造Dispatcher ：
private Dispatcher createDispatcher( HostConfig filterConfig ) { //存放参数的Map Map<String, String> params = new HashMap<String, String>(); //将参数存放到Map，这个地方就用到前面提到FilterHostConfig的转为list功能 for ( Iterator e = filterConfig.getInitParameterNames(); e.hasNext(); ) { String name = (String) e.next(); String value = filterConfig.getInitParameter(name); params.put(name, value); } //根据servlet上下文和参数Map构造Dispatcher return new Dispatcher(filterConfig.getServletContext(), params); }
这样dispatcher对象创建完成，接着就是dispatcher对象的初始化，打开Dispatcher类，看到它的init方法如下：
1 public void init() { 2 3 if (configurationManager == null) { 4 configurationManager = createConfigurationManager(BeanSelectionProvider.DEFAULT_BEAN_NAME); 5 } 6 7 try { 8 init_FileManager(); 9 //加载org/apache/struts2/default.properties 10 init_DefaultProperties(); // [1] 11 //加载struts-default.xml,struts-plugin.xml,struts.xml 12 init_TraditionalXmlConfigurations(); // [2] 13 init_LegacyStrutsProperties(); // [3] 14 //用户自己实现的ConfigurationProviders类 15 init_CustomConfigurationProviders(); // [5] 16 //Filter的初始化参数 17 init_FilterInitParameters() ; // [6] 18 init_AliasStandardObjects() ; // [7] 19 20 Container container = init_PreloadConfiguration(); 21 container.inject(this); 22 init_CheckWebLogicWorkaround(container); 23 24 if (!dispatcherListeners.isEmpty()) { 25 for (DispatcherListener l : dispatcherListeners) { 26 l.dispatcherInitialized(this); 27 } 28 } 29 } catch (Exception ex) { 30 if (LOG.isErrorEnabled()) 31 LOG.error("Dispatcher initialization failed", ex); 32 throw new StrutsException(ex); 33 } 34 }
这里主要是加载一些配置文件的，将按照顺序逐一加载：default.properties，struts-default.xml,struts-plugin.xml,struts.xml，……关于文件是如何加载的，大家可以自己取看源文件，主要是由xwork核心类加载的，代码在xwork-core\\src\\main\\java\\com\\opensymphony\\xwork2\\config\\providers包里面。
现在，我们回到StrutsPrepareAndExecuteFilter类中，刚才我们分析了StrutsPrepareAndExecuteFilter类的init方法，该方法在web容器一启动就会调用的，当用户访问某个action的时候，首先调用核心过滤器StrutsPrepareAndExecuteFilter的doFilter方法，该方法内容如下：
1 public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException { 2 3 HttpServletRequest request = (HttpServletRequest) req; 4 HttpServletResponse response = (HttpServletResponse) res; 5 6 try { 7 if (excludedPatterns != null && prepare.isUrlExcluded(request, excludedPatterns)) { 8 chain.doFilter(request, response); 9 } else { 10 //设置编码和国际化 11 prepare.setEncodingAndLocale(request, response); 12 //创建action上下文 13 prepare.createActionContext(request, response); 14 prepare.assignDispatcherToThread(); 15 request = prepare.wrapRequest(request); 16 ActionMapping mapping = prepare.findActionMapping(request, response, true); 17 //如果mapping为空，则认为不是调用action,会调用下一个过滤器链，直到获取到mapping才调用action 18 if (mapping == null) { 19 boolean handled = execute.executeStaticResourceRequest(request, response); 20 if (!handled) { 21 chain.doFilter(request, response); 22 } 23 } else { 24 execute.executeAction(request, response, mapping); 25 } 26 } 27 } finally { 28 prepare.cleanupRequest(request); 29 } 30 }
下面对doFilter方法中的重点部分一一讲解：
(1)prepare.setEncodingAndLocale(request, response);
第8行是调用prepare对象的setEncodingAndLocale方法，prepare是PrepareOperations类的对象，PrepareOperations类是用来做请求准备工作的。我们看下PrepareOperations类中的setEncodingAndLocale方法：
1 public void setEncodingAndLocale(HttpServletRequest request, HttpServletResponse response) { 2 dispatcher.prepare(request, response); 3 }
在这方法里面我们可以看到它只是调用了dispatcher的prepare方法而已，下面我们看看dispatcher的prepare方法：
1 /** 2 * Prepare a request, including setting the encoding and locale. 3 * 4 * @param request The request 5 * @param response The response 6 */ 7 public void prepare(HttpServletRequest request, HttpServletResponse response) { 8 String encoding = null; 9 if (defaultEncoding != null) { 10 encoding = defaultEncoding; 11 } 12 // check for Ajax request to use UTF-8 encoding strictly http://www.w3.org/TR/XMLHttpRequest/#the-send-method 13 if ("XMLHttpRequest".equals(request.getHeader("X-Requested-With"))) { 14 encoding = "UTF-8"; 15 } 16 17 Locale locale = null; 18 if (defaultLocale != null) { 19 locale = LocalizedTextUtil.localeFromString(defaultLocale, request.getLocale()); 20 } 21 22 if (encoding != null) { 23 applyEncoding(request, encoding); 24 } 25 26 if (locale != null) { 27 response.setLocale(locale); 28 } 29 30 if (paramsWorkaroundEnabled) { 31 request.getParameter("foo"); // simply read any parameter (existing or not) to "prime" the request 32 } 33 }
我们可以看到该方法只是简单的设置了encoding 和locale ，做的只是一些辅助的工作。
(2)prepare.createActionContext(request, response)
我们回到StrutsPrepareAndExecuteFilter的doFilter方法，看到第10行代码：prepare.createActionContext(request, response);这是action上下文的创建，ActionContext是一个容器，这个容器主要存储request、session、application、parameters等相关信 息. ActionContext是一个线程的本地变量，这意味着不同的action之间不会共享ActionContext，所以也不用考虑线程安全问 题。其实质是一个Map，key是标示request、session、……的字符串，值是其对应的对象，我们可以看到com.opensymphony.xwork2.ActionContext类中时如下定义的：
static ThreadLocal<ActionContext> actionContext = new ThreadLocal<ActionContext>();
我们看下PrepareOperations类的createActionContext方法：
1 /** 2 * Creates the action context and initializes the thread local 3 */ 4 public ActionContext createActionContext(HttpServletRequest request, HttpServletResponse response) { 5 ActionContext ctx; 6 Integer counter = 1; 7 Integer oldCounter = (Integer) request.getAttribute(CLEANUP_RECURSION_COUNTER); 8 if (oldCounter != null) { 9 counter = oldCounter + 1; 10 } 11 //此处是从ThreadLocal中获取此ActionContext变量 12 ActionContext oldContext = ActionContext.getContext(); 13 if (oldContext != null) { 14 // detected existing context, so we are probably in a forward 15 ctx = new ActionContext(new HashMap<String, Object>(oldContext.getContextMap())); 16 } else { 17 ValueStack stack = dispatcher.getContainer().getInstance(ValueStackFactory.class).createValueStack(); 18 stack.getContext().putAll(dispatcher.createContextMap(request, response, null)); 19 //stack.getContext()返回的是一个Map<String，Object>，根据此Map构造一个ActionContext
ctx = new ActionContext(stack.getContext()); 20 } 21 request.setAttribute(CLEANUP_RECURSION_COUNTER, counter); 22 ActionContext.setContext(ctx); //将ActionContext存到ThreadLocal 23 return ctx; 24 }
上面第18行代码中dispatcher.createContextMap，如何封装相关参数：
1 /** 2 * Create a context map containing all the wrapped request objects 3 * 4 * @param request The servlet request 5 * @param response The servlet response 6 * @param mapping The action mapping 7 * @return A map of context objects 8 * 9 * @since 2.3.17 10 */ 11 public Map<String,Object> createContextMap(HttpServletRequest request, HttpServletResponse response, 12 ActionMapping mapping) { 13 14 // request map wrapping the http request objects 15 Map requestMap = new RequestMap(request); 16 17 // parameters map wrapping the http parameters. ActionMapping parameters are now handled and applied separately 18 Map params = new HashMap(request.getParameterMap()); 19 20 // session map wrapping the http session 21 Map session = new SessionMap(request); 22 23 // application map wrapping the ServletContext 24 Map application = new ApplicationMap(servletContext); 25 26 Map<String,Object> extraContext = createContextMap(requestMap, params, session, application, request, response); 27 28 if (mapping != null) { 29 extraContext.put(ServletActionContext.ACTION_MAPPING, mapping); 30 } 31 return extraContext; 32 }
(3)request = prepare.wrapRequest(request)
我们再次回到StrutsPrepareAndExecuteFilter的doFilter方法中，看到第15行：request = prepare.wrapRequest(request);这一句是对request进行包装的，我们看下prepare的wrapRequest方法：
1 /** 2 * Wraps the request with the Struts wrapper that handles multipart requests better 3 * @return The new request, if there is one 4 * @throws ServletException 5 */ 6 public HttpServletRequest wrapRequest(HttpServletRequest oldRequest) throws ServletException { 7 HttpServletRequest request = oldRequest; 8 try { 9 // Wrap request first, just in case it is multipart/form-data 10 // parameters might not be accessible through before encoding (ww-1278) 11 request = dispatcher.wrapRequest(request); 12 ServletActionContext.setRequest(request); 13 } catch (IOException e) { 14 throw new ServletException("Could not wrap servlet request with MultipartRequestWrapper!", e); 15 } 16 return request; 17 }
由第11行我们可以看到它里面调用的是dispatcher的wrapRequest方法，我们看下dispatcher的wrapRequest：
1 public HttpServletRequest wrapRequest(HttpServletRequest request) throws IOException { 2 // don\'t wrap more than once 3 if (request instanceof StrutsRequestWrapper) { 4 return request; 5 } 6 7 String content_type = request.getContentType();
//如果content_type是multipart/form-data类型，则将request包装成MultiPartRequestWrapper对象，否则包装成StrutsRequestWrapper对象 8 if (content_type != null && content_type.contains("multipart/form-data")) { 9 MultiPartRequest mpr = getMultiPartRequest(); 10 LocaleProvider provider = getContainer().getInstance(LocaleProvider.class); 11 request = new MultiPartRequestWrapper(mpr, request, getSaveDir(), provider, disableRequestAttributeValueStackLookup); 12 } else { 13 request = new StrutsRequestWrapper(request, disableRequestAttributeValueStackLookup); 14 } 15 16 return request; 17 }
此次包装根据请求内容的类型不同，返回不同的对象，如果为multipart/form-data类型，则返回MultiPartRequestWrapper类型的对象，该对象服务于文件上传，否则返回StrutsRequestWrapper类型的对象，MultiPartRequestWrapper是StrutsRequestWrapper的子类，而这两个类都是HttpServletRequest接口的实现。
(4)ActionMapping mapping = prepare.findActionMapping(request, response, true)
包装request后，通过ActionMapper的getMapping()方法得到请求的Action，Action的配置信息存储在ActionMapping对象中，如StrutsPrepareAndExecuteFilter的doFilter方法中第16行：ActionMapping mapping = prepare.findActionMapping(request, response, true);我们找到prepare对象的findActionMapping方法：
1 public ActionMapping findActionMapping(HttpServletRequest request, HttpServletResponse response, boolean forceLookup) { 2 //首先从request对象中取mapping对象，看是否存在 3 ActionMapping mapping = (ActionMapping) request.getAttribute(STRUTS_ACTION_MAPPING_KEY); 4 //不存在就创建一个 5 if (mapping == null || forceLookup) { 6 try { 7 //首先创建ActionMapper对象，通过ActionMapper对象创建mapping对象 8 mapping = dispatcher.getContainer().getInstance(ActionMapper.class).getMapping(request, dispatcher.getConfigurationManager()); 9 if (mapping != null) { 10 request.setAttribute(STRUTS_ACTION_MAPPING_KEY, mapping); 11 } 12 } catch (Exception ex) { 13 if (dispatcher.isHandleException() || dispatcher.isDevMode()) { 14 dispatcher.sendError(request, response, HttpServletResponse.SC_INTERNAL_SERVER_ERROR, ex); 15 } 16 } 17 } 18 19 return mapping; 20 }
下面是ActionMapper接口的实现类DefaultActionMapper的getMapping()方法的源代码：
1 public ActionMapping getMapping(HttpServletRequest request, ConfigurationManager configManager) { 2 ActionMapping mapping = new ActionMapping(); 3 //获得请求的uri，即请求路径URL中工程名以后的部分，如/userAction.action 4 String uri = RequestUtils.getUri(request); 5 //修正url的带;jsessionid 时找不到的bug 6 int indexOfSemicolon = uri.indexOf(\';\'); 7 uri = (indexOfSemicolon > -1) ? uri.substring(0, indexOfSemicolon) : uri; 8 //删除扩展名，如.action或者.do 9 uri = dropExtension(uri, mapping); 10 if (uri == null) { 11 return null; 12 } 13 //从uri中分离得到请求的action名、命名空间。 14 parseNameAndNamespace(uri, mapping, configManager); 15 //处理特殊的请求参数 16 handleSpecialParameters(request, mapping); 17 //如果允许动态方法调用，即形如/userAction!getAll.action的请求，分离action名和方法名 18 return parseActionName(mapping); 19 }
下面对getMapping方法中的重要部分一一讲解：
①：parseNameAndNamespace(uri, mapping, configManager)
我们主要看下第14行的parseNameAndNamespace(uri, mapping, configManager);这个方法的主要作用是分离出action名和命名空间：
1 protected void parseNameAndNamespace(String uri, ActionMapping mapping, ConfigurationManager configManager) { 2 String namespace, name; 3 int lastSlash = uri.lastIndexOf("/"); //最后的斜杆的位置 4 if (lastSlash == -1) { 5 namespace = ""; 6 name = uri; 7 } else if (lastSlash == 0) { 8 // ww-1046, assume it is the root namespace, it will fallback to 9 // default 10 // namespace anyway if not found in root namespace. 11 namespace = "/"; 12 name = uri.substring(lastSlash + 1); 13 //允许采用完整的命名空间,即设置命名空间是否必须进行精确匹配 14 } else if (alwaysSelectFullNamespace) { 15 // Simply select the namespace as everything before the last slash 16 namespace = uri.substring(0, lastSlash); 17 name = uri.substring(lastSlash + 1); 18 } else { 19 // Try to find the namespace in those defined, defaulting to "" 20 Configuration config = configManager.getConfiguration(); 21 String prefix = uri.substring(0, lastSlash); //临时的命名空间，将会用来进行匹配 22 namespace = "";//将命名空间暂时设为"" 使用eclipse查看源码的方法初识Spring源码 -- doResolveDependency | findAutowireCandidates | @Order@Priority调用排序 | @Autowired注入(代码片段
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