Struts2执行流程

来源：互联网发布：js图片轮播和点击切换编辑：程序博客网时间：2024/06/05 22:18

1. 请求示意图

2. 一个请求在Struts2框架中的处理步骤：

1. 客户端初始化一个指向Servlet容器的请求

2. 根据web.xml配置，请求先经过ActionContextCleanUp过滤器，主要清理当前线程中ActionContext和Dispatcher

3. 请求经过插件过滤器（该步可以略过）

4. 请求经过StrutsPrepareAndExecuteFilter核心过滤器，执行doFilter方法，在该方法中，询问ActionMapper来决定这个请求是否需要调用Action

5. 如果ActionMapper决定调用某个Action，则ActionMapper会返回一个ActionMapping实例（存储Action的配置文件），并创建ActionProxy（Action代理）对象，将请求交给代理对象继续处理

6. ActionProxy对象根据ActionMapping和Configuration Manager询问框架的配置文件，找到需要调用的Action类

7. ActionProxy对象创建时，会同时创建一个ActionInvocation的实例

8. ActionInvocation实例使用命名模式来调用，在调用Action的过程前后，涉及到相关拦截器的调用

9. 一旦Action执行完毕，ActionInvocation实例负责struts.xml中的配置创建并返回到result结果视图，result通常是一个需要被表示的JSP或者FreeMarker的模板，也可能是另外的一个Action链

10. 如果要在返回result之前做些什么，可以实现PreResultListener接口，PreResultListener可以在Interceptor中实现，也可以在Action中实现

11. 根据Result对象信息，生成用户响应信息response

3. 源码分析阶段

3.1 服务器启动阶段

1. 服务器启动后，进入web.xml，跳进配置的核心过滤器StrutsPrepareAndExecuteFilter

2. 类内部首先是三个变量的声明

    protected PrepareOperations prepare;
    protected ExecuteOperations execute;
    protected List<Pattern> excludedPatterns = null;

3. 进入到init方法

public void init(FilterConfig filterConfig) throws ServletException {
        InitOperations init = new InitOperations();
        Dispatcher dispatcher = null;
        try {
            FilterHostConfig config = new FilterHostConfig(filterConfig);
            init.initLogging(config);
            dispatcher = init.initDispatcher(config);
            init.initStaticContentLoader(config, dispatcher);
            prepare = new PrepareOperations(filterConfig.getServletContext(), dispatcher);
            execute = new ExecuteOperations(filterConfig.getServletContext(), dispatcher);
            this.excludedPatterns = init.buildExcludedPatternsList(dispatcher);
            postInit(dispatcher, filterConfig);
        } finally {
            if (dispatcher != null) {
                dispatcher.cleanUpAfterInit();
            }
            init.cleanup();
        }
    }

4.对于第5行

 FilterHostConfig config = new FilterHostConfig(filterConfig);

进入到FilterHostConfig内部查看，发现FilterHostConfig主要是用来获取Servlet上下文、web.xml中的init-param配置的param-name获取param-value的值

public class FilterHostConfig implements HostConfig {
    private FilterConfig config;
    public FilterHostConfig(FilterConfig config) {
        this.config = config;
    }
    public String getInitParameter(String key) {
        return config.getInitParameter(key);
    }
    public Iterator<String> getInitParameterNames() {
        return MakeIterator.convert(config.getInitParameterNames());
    }
    public ServletContext getServletContext() {
        return config.getServletContext();
    }
}

dispatcher中serviceAction方法

/**
     * Load Action class for mapping and invoke the appropriate Action method, or go directly to the Result.
加载Action类用于映射，执行相应的Action方法，或者直接转到Result视图
     * <p/>
     * This method first creates the action context from the given parameters,
这个方法首先从给定的参数创建action上下文
     * and then loads an <tt>ActionProxy</tt> from the given action name and namespace.
然后，从给定的action名和名称空间中加载一个ActionProxy
     * After that, the Action method is executed and output channels through the response object.
之后，action方法被执行以及通过响应对象输出通道
     * Actions not found are sent back to the user via the {@link Dispatcher#sendError} method,
Action如果没有发现，将通过sendError方法返回用户提示
     * using the 404 return code.
使用404返回代码
     * All other errors are reported by throwing a ServletException.
其他的错误将被抛出ServletException异常
     *
     * @param request  HttpServletRequest 对象
     * @param response HttpServletResponse对象
     * @param mapping  ActionMapping对象
     * @throws ServletException when an unknown error occurs (not a 404, but typically something that
     *                          would end up as a 5xx by the servlet container)
     * @param context Our ServletContext object
     */
    public void serviceAction(HttpServletRequest request, HttpServletResponse response, ServletContext context,
                              ActionMapping mapping) throws ServletException {
        Map<String, Object> extraContext = createContextMap(request, response, mapping, context);
        // If there was a previous value stack, then create a new copy and pass it in to be used by the new Action
//如果先前有一个值栈，那么创建一个新的副本，并传递给新的Action使用
//从request中获取到ValueStack对象
        ValueStack stack = (ValueStack) request.getAttribute(ServletActionContext.STRUTS_VALUESTACK_KEY);
//判断ValueStack是否为空
        boolean nullStack = stack == null;
        if (nullStack) {
//为空，获取ActionContext
            ActionContext ctx = ActionContext.getContext();
            if (ctx != null) {
//如果ActionContext不为空，通过ActionContext获取ValueStack---通过查看ActionContext，发现ActionContext包含ValueStack，
                stack = ctx.getValueStack();
            }
        }
        if (stack != null) {
//把ValueStack放入ActionContext中
            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();
            Configuration config = configurationManager.getConfiguration();
//加载ActionProxy
            ActionProxy proxy = config.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!
//如果ActionMapping决定直接返回到结果视图，完成
            if (mapping.getResult() != null) {
                Result result = mapping.getResult();
                result.execute(proxy.getInvocation());
            } else {
//否则往下执行
                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) {
        // WW-2874 Only log error if in devMode
            if (devMode) {
                String reqStr = request.getRequestURI();
                if (request.getQueryString() != null) {
                    reqStr = reqStr + "?" + request.getQueryString();
                }
                LOG.error("Could not find action or result\n" + reqStr, e);
            } else {
                if (LOG.isWarnEnabled()) {
                    LOG.warn("Could not find action or result", e);
                }
            }
            sendError(request, response, context, HttpServletResponse.SC_NOT_FOUND, e);
        } catch (Exception e) {
            if (handleException || devMode) {
                sendError(request, response, context, HttpServletResponse.SC_INTERNAL_SERVER_ERROR, e);
            } else {
                throw new ServletException(e);
            }
        } finally {
            UtilTimerStack.pop(timerKey);
        }
    }