Source Taste: Struts 2 org.apache.struts2.dispatcher.Dispatcher

PART 1:

/**
 * A utility class the actual dispatcher delegates most of its tasks to. Each instance
 * of the primary dispatcher holds an instance of this dispatcher to be shared for
 * all requests.
 *
 * @see org.apache.struts2.dispatcher.FilterDispatcher
 */
public class Dispatcher {

    /**
     * Provide a logging instance.
     */
    private static final Logger LOG = LoggerFactory.getLogger(Dispatcher.class);

    /**
     * Provide a thread local instance.
     */
    private static ThreadLocal<Dispatcher> instance = new ThreadLocal<Dispatcher>();

    /**
     * Store list of DispatcherListeners.
     */
    private static List<DispatcherListener> dispatcherListeners =
        new CopyOnWriteArrayList<DispatcherListener>();

Notice that

1. the ThreadLocal and theCopyOnWriteArrayList, both for concurrency scenarios.

2. This is a util class, rather than an interface.

PART 2:

/**
     * Create a context map containing all the wrapped request objects
     *
     * @param request The servlet request
     * @param response The servlet response
     * @param mapping The action mapping
     * @param context The servlet context
     * @return A map of context objects
     */
    public Map<String,Object> createContextMap(HttpServletRequest request, HttpServletResponse response,
            ActionMapping mapping, ServletContext context) {

        // request map wrapping the http request objects
        Map requestMap = new RequestMap(request);

        // parameters map wrapping the http parameters.  ActionMapping parameters are now handled and applied separately
        Map params = new HashMap(request.getParameterMap());

        // session map wrapping the http session
        Map session = new SessionMap(request);

        // application map wrapping the ServletContext
        Map application = new ApplicationMap(context);

        Map<String,Object> extraContext = createContextMap(requestMap, params, session, application, request, response, context);

        if (mapping != null) {
            extraContext.put(ServletActionContext.ACTION_MAPPING, mapping);
        }
        return extraContext;
    }

Noteworthy:

1. RequestMap/SessionMap/ApplicationMap.

2. appliation map wrapping the ServletContext.

PART 3:

/**
     * Load Action class for mapping and invoke the appropriate Action method, or go directly to the Result.
     * <p/>
     * This method first creates the action context from the given parameters,
     * and then loads an <tt>ActionProxy</tt> from the given action name and namespace.
     * After that, the Action method is executed and output channels through the response object.
     * Actions not found are sent back to the user via the {@link Dispatcher#sendError} method,
     * using the 404 return code.
     * All other errors are reported by throwing a ServletException.
     *
     * @param request  the HttpServletRequest object
     * @param response the HttpServletResponse object
     * @param mapping  the action mapping object
     * @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
        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();

            Configuration config = configurationManager.getConfiguration();
            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!
            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) {
        	// 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);
        }
    }