Struts2源码分析(三) 绘制Struts2执行的核心流程时序图并分析

末蓝、 2022-07-26 11:11 177阅读 0赞

前一篇博客中根据Struts2的官方架构图简单的描绘了Struts2运行流程，并解释了一下Struts2中一些核心类的用途。现在我们从源码的角度分析Struts2的核心流程。

首先根据一个Struts2的HelloWorld绘制出Struts2的启动时的时序图:  
![这里写图片描述][20160410085323013]  
备注:由于这个图非常大，所以这里放置了一个缩图。文章的最后我会给出这个时序图的下载地址。

把核心流程分为16步。接下来一步步的分析:

#### 一.请求URL时执行StrutsPrepareAndExecuteFilter的doFilter() ####

public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
    
            HttpServletRequest request = (HttpServletRequest) req;
            HttpServletResponse response = (HttpServletResponse) res;
    
            try {
                if (excludedPatterns != null && prepare.isUrlExcluded(request, excludedPatterns)) {
                    chain.doFilter(request, response);
                } else {
                    prepare.setEncodingAndLocale(request, response);
                    prepare.createActionContext(request, response);
                    prepare.assignDispatcherToThread();
                    request = prepare.wrapRequest(request);
                    ActionMapping mapping = prepare.findActionMapping(request, response, true);
                    if (mapping == null) {
                        boolean handled = execute.executeStaticResourceRequest(request, response);
                        if (!handled) {
                            chain.doFilter(request, response);
                        }
                    } else {
                        execute.executeAction(request, response, mapping);
                    }
                }
            } finally {
                prepare.cleanupRequest(request);
            }
        }

#### 二.执行PrepareOperations的setEncodingAndLocale设置编码 ####

prepare.setEncodingAndLocale(request, response);

PrepareOperations中调用Dispatcher中的prepare()方法

public void setEncodingAndLocale(HttpServletRequest request, HttpServletResponse response) {
            dispatcher.prepare(request, response);
        }

在Dispatcher中的prepare中则通过依赖注入在default.properties中的定义的STRUTS\_I18N\_ENCODING

public void prepare(HttpServletRequest request, HttpServletResponse response) {
            String encoding = null;
            if (defaultEncoding != null) {
                encoding = defaultEncoding;
            }
            // check for Ajax request to use UTF-8 encoding strictly http://www.w3.org/TR/XMLHttpRequest/#the-send-method
            if ("XMLHttpRequest".equals(request.getHeader("X-Requested-With"))) {
                encoding = "UTF-8";
            }
    
            Locale locale = null;
            if (defaultLocale != null) {
                locale = LocalizedTextUtil.localeFromString(defaultLocale, request.getLocale());
            }
    
            if (encoding != null) {
                applyEncoding(request, encoding);
            }
    
            if (locale != null) {
                response.setLocale(locale);
            }
    
            if (paramsWorkaroundEnabled) {
                request.getParameter("foo"); // simply read any parameter (existing or not) to "prime" the request
            }
        }

#### 三.通过执行PrepareOperations的createActionContext设置一个ActionContext (Action上下文) ####

prepare.createActionContext(request, response);

#### 四.在PrepareOperations的createActionContext中从当前线程中获取ActionContext ####

public ActionContext createActionContext(HttpServletRequest request, HttpServletResponse response) {
            ActionContext ctx;
            Integer counter = 1;
            Integer oldCounter = (Integer) request.getAttribute(CLEANUP_RECURSION_COUNTER);
            if (oldCounter != null) {
                counter = oldCounter + 1;
            }
    
            ActionContext oldContext = ActionContext.getContext();
            if (oldContext != null) {
                // detected existing context, so we are probably in a forward
                ctx = new ActionContext(new HashMap<String, Object>(oldContext.getContextMap()));
            } else {
                ValueStack stack = dispatcher.getContainer().getInstance(ValueStackFactory.class).createValueStack();
                stack.getContext().putAll(dispatcher.createContextMap(request, response, null));
                ctx = new ActionContext(stack.getContext());
            }
            request.setAttribute(CLEANUP_RECURSION_COUNTER, counter);
            ActionContext.setContext(ctx);
            return ctx;
        }

**Struts先调用ActionContext类的静态方法getContext()中其实是从ThreadLocal中获取一个ActionContext实例。ThreadLoacl是从当前线程中获取ActionContext的**

#### 五,六,七 当从ThreadLoacl中获取到的ActionContext为null创建ValueStack ####

先通过dispatcher获取到Container。然后获取到ValueStackFactory并创建ValueStack

ValueStack stack = dispatcher.getContainer().getInstance(ValueStackFactory.class).createValueStack();

#### 八.在OgnlContext给ValueStack的Map栈赋值 ####

ValueStack stack = dispatcher.getContainer().getInstance(ValueStackFactory.class).createValueStack();
    
    stack.getContext().putAll(dispatcher.createContextMap(request, response, null));

把request,session,application等域对象封装成map,再把各个map放入到valueStack的map栈中。该方法的作用就是初始化valueStack中的map栈中的request,session,application….

#### 九.把ValueStack中的map栈赋值给了ActionContext中的context:Map ####

ActionContext oldContext = ActionContext.getContext();
            if (oldContext != null) {
                // detected existing context, so we are probably in a forward
                ctx = new ActionContext(new HashMap<String, Object>(oldContext.getContextMap()));
            } else {
                ValueStack stack = dispatcher.getContainer().getInstance(ValueStackFactory.class).createValueStack();
                stack.getContext().putAll(dispatcher.createContextMap(request, response, null));
                ctx = new ActionContext(stack.getContext());
      }

注意观察如上代码:  
现在我们可以总结一下:Struts先从当前线程中获取一个ActionContext:

**如果该ActionContext为null。则创建一个新的ValueStack并将域对象设置给ValueStack的Map栈中，接着创建一个ActionContext，然后把ValueStack的Map栈赋值给ActionContext中的context:Map`<`String,Object`>`。**

**如果该ActionContext不为null。则依然创建一个新的ActionContext。并把旧的ActionContext中的中的context:Map`<`String,Object`>`赋值给新的**

#### 十.将当前的acitonContext对象设置到ThreadLoacl(当前线程)中 ####

ActionContext.setContext(ctx);

该方法调用的ThreadLoacl的set方法来设置ActionContext到当前线程中。

#### 十一.执行ExecuteOperations的executeAction ####

protected ExecuteOperations execute;
    ActionMapping mapping = prepare.findActionMapping(request, response, true);
    if(mapping!=null){
       ....
    }else{
       execute.executeAction(request, response, mapping);
    }

观察如上代码:  
**StrutsPrepareAndExecuteFilter通过ActionMapper来获取一个ActionMapping对象,当ActionMapping对象不为Null。则调用executeAction**

#### 十二.执行Dispatcher的serviceAction ####

public void executeAction(HttpServletRequest request, HttpServletResponse response, ActionMapping mapping) throws ServletException {
            dispatcher.serviceAction(request, response, mapping);
        }

#### 十三，十四.在Dispatcher的serviceAction方法中获取ValueStack创建ActionProxy ####

public void serviceAction(HttpServletRequest request, HttpServletResponse response, ActionMapping mapping)
                throws ServletException {
    
            Map<String, Object> extraContext = createContextMap(request, response, mapping);
    
            // If there was a previous value stack, then create a new copy and pass it in to be used by the new Action
            ValueStack stack = (ValueStack) request.getAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY);
            boolean nullStack = stack == null;
            if (nullStack) {
                ActionContext ctx = ActionContext.getContext();
                if (ctx != null) {
                    stack = ctx.getValueStack();
                }
            }
            if (stack != null) {
                extraContext.put(ActionContext.VALUE_STACK, valueStackFactory.createValueStack(stack));
            }
    
            String timerKey = "Handling request from Dispatcher";
            try {
                UtilTimerStack.push(timerKey);
                String namespace = mapping.getNamespace();
                String name = mapping.getName();
                String method = mapping.getMethod();
    
                ActionProxy proxy = getContainer().getInstance(ActionProxyFactory.class).createActionProxy(
                        namespace, name, method, extraContext, true, false);
    
                request.setAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY, proxy.getInvocation().getStack());
    
                // if the ActionMapping says to go straight to a result, do it!
                if (mapping.getResult() != null) {
                    Result result = mapping.getResult();
                    result.execute(proxy.getInvocation());
                } else {
                    proxy.execute();
                }
    
                // If there was a previous value stack then set it back onto the request
                if (!nullStack) {
                    request.setAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY, stack);
                }
            } catch (ConfigurationException e) {
                logConfigurationException(request, e);
                sendError(request, response, HttpServletResponse.SC_NOT_FOUND, e);
            } catch (Exception e) {
                if (handleException || devMode) {
                    sendError(request, response, HttpServletResponse.SC_INTERNAL_SERVER_ERROR, e);
                } else {
                    throw new ServletException(e);
                }
            } finally {
                UtilTimerStack.pop(timerKey);
            }
        }

#### 十五.通过DefaultActionInvocation的init()方法将Action压入值栈栈定 ####

ActionProxy proxy = getContainer().getInstance(ActionProxyFactory.class).createActionProxy(
                        namespace, name, method, extraContext, true, false);

在ActionProxyFactory的createActionProxy方法中:

public ActionProxy createActionProxy(String namespace, String actionName, String methodName, Map<String, Object> extraContext, boolean executeResult, boolean cleanupContext) {
             ActionInvocation inv = new DefaultActionInvocation(extraContext, true);
            container.inject(inv);
            return createActionProxy(inv, namespace, actionName, methodName, executeResult, cleanupContext);
        }

createActionProxy有很多个重载方法,最终会调用:

public ActionProxy createActionProxy(ActionInvocation inv, String namespace, String actionName, String methodName, boolean executeResult, boolean cleanupContext) {
    
            DefaultActionProxy proxy = new DefaultActionProxy(inv, namespace, actionName, methodName, executeResult, cleanupContext);
            container.inject(proxy);
            proxy.prepare();
            return proxy;
        }

而在DefaultActionProxy的prepare方法中:

invocation.init(this);

DefaultActionInvocation的init()方法

public void init(ActionProxy proxy) {
            this.proxy = proxy;
            Map<String, Object> contextMap = createContextMap();
    
            // Setting this so that other classes, like object factories, can use the ActionProxy and other
            // contextual information to operate
            ActionContext actionContext = ActionContext.getContext();
    
            if (actionContext != null) {
                actionContext.setActionInvocation(this);
            }
    
            createAction(contextMap);
    
            if (pushAction) {
                stack.push(action);
                contextMap.put("action", action);
            }
    
            invocationContext = new ActionContext(contextMap);
            invocationContext.setName(proxy.getActionName());
    
            // get a new List so we don't get problems with the iterator if someone changes the list
            List<InterceptorMapping> interceptorList = new ArrayList<InterceptorMapping>(proxy.getConfig().getInterceptors());
            interceptors = interceptorList.iterator();
        }

可以看到，通过当前的ActionProxy获取到Action对象后，Action对象就被压入Struts值栈栈顶。此时同时获取了拦截器的迭代器

这块比较复杂，简单总结一下:

> 1、调用createAction方法创建action  
> 2、调用stack.push(action);方法把action  
> 放入到栈顶  
> 3、调用contextMap.put(“action”, action);  
> 把action放入到map栈中  
> 4、获取当前请求的经过的所有的拦截器  
> 并且返回拦截器的迭代器的形式

#### 十六.执行ActionProxy的execute()方法 ####

DefaultActionProxy的execute()方法源码:

public String execute() throws Exception {
            ActionContext nestedContext = ActionContext.getContext();
            ActionContext.setContext(invocation.getInvocationContext());
    
            String retCode = null;
    
            String profileKey = "execute: ";
            try {
                UtilTimerStack.push(profileKey);
    
                retCode = invocation.invoke();
            } finally {
                if (cleanupContext) {
                    ActionContext.setContext(nestedContext);
                }
                UtilTimerStack.pop(profileKey);
            }

#### 十七.执行DefaultActionInvocation的invoke方法 ####

invoke方法是整个Struts框架最精华的地方.主要分为如下几步:

> 1、按照顺序的方式执行所有的拦截器  
> 2、执行action方法获取返回值  
> 3、执行结果集  
> 4、按照倒叙的方式执行拦截器

观察源代码:

public String invoke() throws Exception {
            String profileKey = "invoke: ";
            try {
                UtilTimerStack.push(profileKey);
    
                if (executed) {
                    throw new IllegalStateException("Action has already executed");
                }
    
                if (interceptors.hasNext()) {
                    final InterceptorMapping interceptor = interceptors.next();
                    String interceptorMsg = "interceptor: " + interceptor.getName();
                    UtilTimerStack.push(interceptorMsg);
                    try {
                                    resultCode = interceptor.getInterceptor().intercept(DefaultActionInvocation.this);
                                }
                    finally {
                        UtilTimerStack.pop(interceptorMsg);
                    }
                } else {
                    resultCode = invokeActionOnly();
                }
    
                // this is needed because the result will be executed, then control will return to the Interceptor, which will
                // return above and flow through again
                if (!executed) {
                    if (preResultListeners != null) {
                        for (Object preResultListener : preResultListeners) {
                            PreResultListener listener = (PreResultListener) preResultListener;
    
                            String _profileKey = "preResultListener: ";
                            try {
                                UtilTimerStack.push(_profileKey);
                                listener.beforeResult(this, resultCode);
                            }
                            finally {
                                UtilTimerStack.pop(_profileKey);
                            }
                        }
                    }
    
                    // now execute the result, if we're supposed to
                    if (proxy.getExecuteResult()) {
                        executeResult();
                    }
    
                    executed = true;
                }
    
                return resultCode;
            }
            finally {
                UtilTimerStack.pop(profileKey);
            }
        }

#### 十八.最后执行PrepareOperations的cleanupRequest方法 ####

**清空actionContext中的所有的数据**

public void cleanupDispatcher() {
            if (dispatcher == null) {
                throw new StrutsException("Something is seriously wrong, Dispatcher is not initialized (null) ");
            } else {
                try {
                    dispatcher.cleanup();
                } finally {
                    ActionContext.setContext(null);
                }
            }
        }

时序图下载:  
[http://download.csdn.net/detail/canot/9486379][http_download.csdn.net_detail_canot_9486379]

[20160410085323013]: /images/20220724/80225dff35014f1c87a2b47b06a602a4.png
[http_download.csdn.net_detail_canot_9486379]: http://download.csdn.net/detail/canot/9486379