structs2源码分析

一、到网上下载struts2的源代码：

http://mirrors.cnnic.cn/apache//struts/source/struts-2.3.16.3-src.zip

我把项目的源码路径定向到下载到的源代码：

这份是webwork的核心源码，读取配置文件的核心代码就在于此：

二、下面是struts本尊，基本实现的就是请求的分发：

二、从项目本身去做分析：

好多大牛大师傅都不断强调，去看源码分析源码，但是却从来很少人，告诉你怎么去看，经过多年的摸索我总算找到一个分析源代码的套路，特别对于java工程项目而已，一般来说这些类似于struts这类型的开源项目都会将源代码给开放出去，如果单单打开那些包去看源码哪怕你看个半天其他没啥实际效果，因为没有形成应用场景，例如，没有将请求到处理的执行流程都在脑中思考过一篇，去看人家的源码分析其实尼玛的就是把概念念一遍；

好啦，废话不多讲，上源码分析：

目前我本身的应用使用jetty作为应用服务器：

来看看这部分的代码：

protected void setupWebContext(WebAppContext webapp) {
    webapp.addFilter(UrlRewriteFilter.class, "/*", FilterMapping.DEFAULT);
    webapp.addFilter(StrutsPrepareAndExecuteFilter.class, "/*", FilterMapping.FORWARD |  FilterMapping.REQUEST);
}

说明：webapp是接收请求上下文的对象，请求过来必须经过webapp的filter；

webapp.addFilter(StrutsPrepareAndExecuteFilter.class, "/*", FilterMapping.FORWARD |  FilterMapping.REQUEST);

这段代码实现拦截请求处理并转发的功能，也就是说请求必将经过

StrutsPrepareAndExecuteFilter类的处理：

StrutsPrepareAndExecuteFilter.java代码如下：

/*
 * $Id: DefaultActionSupport.java 651946 2008-04-27 13:41:38Z apetrelli $
 *
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *  http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.struts2.dispatcher.ng.filter;

import org.apache.struts2.StrutsStatics;
import org.apache.struts2.dispatcher.Dispatcher;
import org.apache.struts2.dispatcher.mapper.ActionMapping;
import org.apache.struts2.dispatcher.ng.ExecuteOperations;
import org.apache.struts2.dispatcher.ng.InitOperations;
import org.apache.struts2.dispatcher.ng.PrepareOperations;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.List;
import java.util.regex.Pattern;

/**
 * Handles both the preparation and execution phases of the Struts dispatching process.  This filter is better to use
 * when you don‘t have another filter that needs access to action context information, such as Sitemesh.
 */
public class StrutsPrepareAndExecuteFilter implements StrutsStatics, Filter {
    protected PrepareOperations prepare;
    protected ExecuteOperations execute;
    protected List<Pattern> excludedPatterns = null;

    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();
        }
    }

    /**
     * Callback for post initialization
     */
    protected void postInit(Dispatcher dispatcher, FilterConfig filterConfig) {
    }

    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);
        }
    }

    public void destroy() {
        prepare.cleanupDispatcher();
    }

}

可以得到的一些有用的信息，这个类是实现了：StrutsStatics, Filter这两个接口；

1、init实现初始化配置信息；

2、doFilter处理请求、过滤请求；

3、destroy负责清空分发器；

我们再细心点观察思考，就会发现一个比较重要的对象：Dispatcher，在init的时候我们将其填充完成

我们来看看Dispather这个类：

/*
 * $Id$
 *
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *  http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.struts2.dispatcher;

import com.opensymphony.xwork2.ActionContext;
import com.opensymphony.xwork2.ActionProxy;
import com.opensymphony.xwork2.ActionProxyFactory;
import com.opensymphony.xwork2.FileManager;
import com.opensymphony.xwork2.FileManagerFactory;
import com.opensymphony.xwork2.LocaleProvider;
import com.opensymphony.xwork2.ObjectFactory;
import com.opensymphony.xwork2.Result;
import com.opensymphony.xwork2.config.Configuration;
import com.opensymphony.xwork2.config.ConfigurationException;
import com.opensymphony.xwork2.config.ConfigurationManager;
import com.opensymphony.xwork2.config.ConfigurationProvider;
import com.opensymphony.xwork2.config.FileManagerFactoryProvider;
import com.opensymphony.xwork2.config.FileManagerProvider;
import com.opensymphony.xwork2.config.entities.InterceptorMapping;
import com.opensymphony.xwork2.config.entities.InterceptorStackConfig;
import com.opensymphony.xwork2.config.entities.PackageConfig;
import com.opensymphony.xwork2.config.providers.XmlConfigurationProvider;
import com.opensymphony.xwork2.inject.Container;
import com.opensymphony.xwork2.inject.ContainerBuilder;
import com.opensymphony.xwork2.inject.Inject;
import com.opensymphony.xwork2.interceptor.Interceptor;
import com.opensymphony.xwork2.util.ClassLoaderUtil;
import com.opensymphony.xwork2.util.LocalizedTextUtil;
import com.opensymphony.xwork2.util.ValueStack;
import com.opensymphony.xwork2.util.ValueStackFactory;
import com.opensymphony.xwork2.util.location.LocatableProperties;
import com.opensymphony.xwork2.util.location.Location;
import com.opensymphony.xwork2.util.location.LocationUtils;
import com.opensymphony.xwork2.util.logging.Logger;
import com.opensymphony.xwork2.util.logging.LoggerFactory;
import com.opensymphony.xwork2.util.profiling.UtilTimerStack;
import freemarker.template.Template;
import org.apache.struts2.ServletActionContext;
import org.apache.struts2.StrutsConstants;
import org.apache.struts2.StrutsException;
import org.apache.struts2.StrutsStatics;
import org.apache.struts2.config.DefaultBeanSelectionProvider;
import org.apache.struts2.config.DefaultPropertiesProvider;
import org.apache.struts2.config.PropertiesConfigurationProvider;
import org.apache.struts2.config.StrutsXmlConfigurationProvider;
import org.apache.struts2.dispatcher.mapper.ActionMapping;
import org.apache.struts2.dispatcher.multipart.MultiPartRequest;
import org.apache.struts2.dispatcher.multipart.MultiPartRequestWrapper;
import org.apache.struts2.util.AttributeMap;
import org.apache.struts2.util.ObjectFactoryDestroyable;
import org.apache.struts2.util.fs.JBossFileManager;
import org.apache.struts2.views.freemarker.FreemarkerManager;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.File;
import java.io.IOException;
import java.io.StringWriter;
import java.io.Writer;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.CopyOnWriteArrayList;

/**
 * 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>();

    /**
     * Store ConfigurationManager instance, set on init.
     */
    private ConfigurationManager configurationManager;

    /**
     * Store state of StrutsConstants.STRUTS_DEVMODE setting.
     */
    private boolean devMode;

    /**
     * Store state of StrutsConstants.DISABLE_REQUEST_ATTRIBUTE_VALUE_STACK_LOOKUP setting.
     */
    private boolean disableRequestAttributeValueStackLookup;

    /**
     * Store state of StrutsConstants.STRUTS_I18N_ENCODING setting.
     */
    private String defaultEncoding;

    /**
     * Store state of StrutsConstants.STRUTS_LOCALE setting.
     */
    private String defaultLocale;

    /**
     * Store state of StrutsConstants.STRUTS_MULTIPART_SAVEDIR setting.
     */
    private String multipartSaveDir;

    /**
     * Stores the value of {@link StrutsConstants#STRUTS_MULTIPART_PARSER} setting
     */
    private String multipartHandlerName;

    /**
     * Provide list of default configuration files.
     */
    private static final String DEFAULT_CONFIGURATION_PATHS = "struts-default.xml,struts-plugin.xml,struts.xml";

    /**
     * Store state of STRUTS_DISPATCHER_PARAMETERSWORKAROUND.
     * <p/>
     * The workaround is for WebLogic.
     * We try to autodect WebLogic on Dispatcher init.
     * The workaround can also be enabled manually.
     */
    private boolean paramsWorkaroundEnabled = false;

    /**
     * Indicates if Dispatcher should handle exception and call sendError()
     * Introduced to allow integration with other frameworks like Spring Security
     */
    private boolean handleException;

    /**
     * Provide the dispatcher instance for the current thread.
     *
     * @return The dispatcher instance
     */
    public static Dispatcher getInstance() {
        return instance.get();
    }

    /**
     * Store the dispatcher instance for this thread.
     *
     * @param instance The instance
     */
    public static void setInstance(Dispatcher instance) {
        Dispatcher.instance.set(instance);
    }

    /**
     * Add a dispatcher lifecycle listener.
     *
     * @param listener The listener to add
     */
    public static void addDispatcherListener(DispatcherListener listener) {
        dispatcherListeners.add(listener);
    }

    /**
     * Remove a specific dispatcher lifecycle listener.
     *
     * @param listener The listener
     */
    public static void removeDispatcherListener(DispatcherListener listener) {
        dispatcherListeners.remove(listener);
    }

    private ServletContext servletContext;
    private Map<String, String> initParams;

    private ValueStackFactory valueStackFactory;

    /**
     * Create the Dispatcher instance for a given ServletContext and set of initialization parameters.
     *
     * @param servletContext Our servlet context
     * @param initParams The set of initialization parameters
     */
    public Dispatcher(ServletContext servletContext, Map<String, String> initParams) {
        this.servletContext = servletContext;
        this.initParams = initParams;
    }

    /**
     * Modify state of StrutsConstants.STRUTS_DEVMODE setting.
     * @param mode New setting
     */
    @Inject(StrutsConstants.STRUTS_DEVMODE)
    public void setDevMode(String mode) {
        devMode = "true".equals(mode);
    }

    /**
     * Modify state of StrutsConstants.DISABLE_REQUEST_ATTRIBUTE_VALUE_STACK_LOOKUP setting.
     * @param disableRequestAttributeValueStackLookup New setting
     */
    @Inject(value=StrutsConstants.STRUTS_DISABLE_REQUEST_ATTRIBUTE_VALUE_STACK_LOOKUP, required=false)
    public void setDisableRequestAttributeValueStackLookup(String disableRequestAttributeValueStackLookup) {
        this.disableRequestAttributeValueStackLookup = "true".equalsIgnoreCase(disableRequestAttributeValueStackLookup);
    }

    /**
     * Modify state of StrutsConstants.STRUTS_LOCALE setting.
     * @param val New setting
     */
    @Inject(value=StrutsConstants.STRUTS_LOCALE, required=false)
    public void setDefaultLocale(String val) {
        defaultLocale = val;
    }

    /**
     * Modify state of StrutsConstants.STRUTS_I18N_ENCODING setting.
     * @param val New setting
     */
    @Inject(StrutsConstants.STRUTS_I18N_ENCODING)
    public void setDefaultEncoding(String val) {
        defaultEncoding = val;
    }

    /**
     * Modify state of StrutsConstants.STRUTS_MULTIPART_SAVEDIR setting.
     * @param val New setting
     */
    @Inject(StrutsConstants.STRUTS_MULTIPART_SAVEDIR)
    public void setMultipartSaveDir(String val) {
        multipartSaveDir = val;
    }

    @Inject(StrutsConstants.STRUTS_MULTIPART_PARSER)
    public void setMultipartHandler(String val) {
        multipartHandlerName = val;
    }

    @Inject
    public void setValueStackFactory(ValueStackFactory valueStackFactory) {
        this.valueStackFactory = valueStackFactory;
    }

    @Inject(StrutsConstants.STRUTS_HANDLE_EXCEPTION)
    public void setHandleException(String handleException) {
        this.handleException = Boolean.parseBoolean(handleException);
    }

    /**
     * Releases all instances bound to this dispatcher instance.
     */
    public void cleanup() {

        // clean up ObjectFactory
        ObjectFactory objectFactory = getContainer().getInstance(ObjectFactory.class);
        if (objectFactory == null) {
            if (LOG.isWarnEnabled()) {
            LOG.warn("Object Factory is null, something is seriously wrong, no clean up will be performed");
            }
        }
        if (objectFactory instanceof ObjectFactoryDestroyable) {
            try {
                ((ObjectFactoryDestroyable)objectFactory).destroy();
            }
            catch(Exception e) {
                // catch any exception that may occurred during destroy() and log it
                LOG.error("exception occurred while destroying ObjectFactory [#0]", e, objectFactory.toString());
            }
        }

        // clean up Dispatcher itself for this thread
        instance.set(null);

        // clean up DispatcherListeners
        if (!dispatcherListeners.isEmpty()) {
            for (DispatcherListener l : dispatcherListeners) {
                l.dispatcherDestroyed(this);
            }
        }

        // clean up all interceptors by calling their destroy() method
        Set<Interceptor> interceptors = new HashSet<Interceptor>();
        Collection<PackageConfig> packageConfigs = configurationManager.getConfiguration().getPackageConfigs().values();
        for (PackageConfig packageConfig : packageConfigs) {
            for (Object config : packageConfig.getAllInterceptorConfigs().values()) {
                if (config instanceof InterceptorStackConfig) {
                    for (InterceptorMapping interceptorMapping : ((InterceptorStackConfig) config).getInterceptors()) {
                        interceptors.add(interceptorMapping.getInterceptor());
                    }
                }
            }
        }
        for (Interceptor interceptor : interceptors) {
            interceptor.destroy();
        }

        // Clear container holder when application is unloaded / server shutdown
        ContainerHolder.clear();

        //cleanup action context
        ActionContext.setContext(null);

        // clean up configuration
        configurationManager.destroyConfiguration();
        configurationManager = null;
    }

    private void init_FileManager() throws ClassNotFoundException {
        if (initParams.containsKey(StrutsConstants.STRUTS_FILE_MANAGER)) {
            final String fileManagerClassName = initParams.get(StrutsConstants.STRUTS_FILE_MANAGER);
            final Class<FileManager> fileManagerClass = (Class<FileManager>) Class.forName(fileManagerClassName);
            if (LOG.isInfoEnabled()) {
                LOG.info("Custom FileManager specified: #0", fileManagerClassName);
            }
            configurationManager.addContainerProvider(new FileManagerProvider(fileManagerClass, fileManagerClass.getSimpleName()));
        } else {
            // add any other Struts 2 provided implementations of FileManager
            configurationManager.addContainerProvider(new FileManagerProvider(JBossFileManager.class, "jboss"));
        }
        if (initParams.containsKey(StrutsConstants.STRUTS_FILE_MANAGER_FACTORY)) {
            final String fileManagerFactoryClassName = initParams.get(StrutsConstants.STRUTS_FILE_MANAGER_FACTORY);
            final Class<FileManagerFactory> fileManagerFactoryClass = (Class<FileManagerFactory>) Class.forName(fileManagerFactoryClassName);
            if (LOG.isInfoEnabled()) {
                LOG.info("Custom FileManagerFactory specified: #0", fileManagerFactoryClassName);
            }
            configurationManager.addContainerProvider(new FileManagerFactoryProvider(fileManagerFactoryClass));
        }
    }

    private void init_DefaultProperties() {
        configurationManager.addContainerProvider(new DefaultPropertiesProvider());
    }

    private void init_LegacyStrutsProperties() {
        configurationManager.addContainerProvider(new PropertiesConfigurationProvider());
    }

    private void init_TraditionalXmlConfigurations() {
        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)) {
                    configurationManager.addContainerProvider(createXmlConfigurationProvider(file, false));
                } else {
                    configurationManager.addContainerProvider(createStrutsXmlConfigurationProvider(file, false, servletContext));
                }
            } else {
                throw new IllegalArgumentException("Invalid configuration file name");
            }
        }
    }

    protected XmlConfigurationProvider createXmlConfigurationProvider(String filename, boolean errorIfMissing) {
        return new XmlConfigurationProvider(filename, errorIfMissing);
    }

    protected XmlConfigurationProvider createStrutsXmlConfigurationProvider(String filename, boolean errorIfMissing, ServletContext ctx) {
        return new StrutsXmlConfigurationProvider(filename, errorIfMissing, ctx);
    }

    private void init_CustomConfigurationProviders() {
        String configProvs = initParams.get("configProviders");
        if (configProvs != null) {
            String[] classes = configProvs.split("\\s*[,]\\s*");
            for (String cname : classes) {
                try {
                    Class cls = ClassLoaderUtil.loadClass(cname, this.getClass());
                    ConfigurationProvider prov = (ConfigurationProvider)cls.newInstance();
                    configurationManager.addContainerProvider(prov);
                } catch (InstantiationException e) {
                    throw new ConfigurationException("Unable to instantiate provider: "+cname, e);
                } catch (IllegalAccessException e) {
                    throw new ConfigurationException("Unable to access provider: "+cname, e);
                } catch (ClassNotFoundException e) {
                    throw new ConfigurationException("Unable to locate provider class: "+cname, e);
                }
            }
        }
    }

    private void init_FilterInitParameters() {
        configurationManager.addContainerProvider(new ConfigurationProvider() {
            public void destroy() {
            }

            public void init(Configuration configuration) throws ConfigurationException {
            }

            public void loadPackages() throws ConfigurationException {
            }

            public boolean needsReload() {
                return false;
            }

            public void register(ContainerBuilder builder, LocatableProperties props) throws ConfigurationException {
                props.putAll(initParams);
            }
        });
    }

    private void init_AliasStandardObjects() {
        configurationManager.addContainerProvider(new DefaultBeanSelectionProvider());
    }

    private Container init_PreloadConfiguration() {
        Configuration config = configurationManager.getConfiguration();
        Container container = config.getContainer();

        boolean reloadi18n = Boolean.valueOf(container.getInstance(String.class, StrutsConstants.STRUTS_I18N_RELOAD));
        LocalizedTextUtil.setReloadBundles(reloadi18n);

        ContainerHolder.store(container);

        return container;
    }

    private void init_CheckWebLogicWorkaround(Container container) {
        // test whether param-access workaround needs to be enabled
        if (servletContext != null && servletContext.getServerInfo() != null
                && servletContext.getServerInfo().contains("WebLogic")) {
            if (LOG.isInfoEnabled()) {
            LOG.info("WebLogic server detected. Enabling Struts parameter access work-around.");
            }
            paramsWorkaroundEnabled = true;
        } else {
            paramsWorkaroundEnabled = "true".equals(container.getInstance(String.class,
                    StrutsConstants.STRUTS_DISPATCHER_PARAMETERSWORKAROUND));
        }
    }

    /**
     * Load configurations, including both XML and zero-configuration strategies,
     * and update optional settings, including whether to reload configurations and resource files.
     */
    public void init() {

        if (configurationManager == null) {
            configurationManager = createConfigurationManager(DefaultBeanSelectionProvider.DEFAULT_BEAN_NAME);
        }

        try {
            init_FileManager();
            init_DefaultProperties(); // [1]
            init_TraditionalXmlConfigurations(); // [2]
            init_LegacyStrutsProperties(); // [3]
            init_CustomConfigurationProviders(); // [5]
            init_FilterInitParameters() ; // [6]
            init_AliasStandardObjects() ; // [7]

            Container container = init_PreloadConfiguration();
            container.inject(this);
            init_CheckWebLogicWorkaround(container);

            if (!dispatcherListeners.isEmpty()) {
                for (DispatcherListener l : dispatcherListeners) {
                    l.dispatcherInitialized(this);
                }
            }
        } catch (Exception ex) {
            if (LOG.isErrorEnabled())
                LOG.error("Dispatcher initialization failed", ex);
            throw new StrutsException(ex);
        }
    }

    protected ConfigurationManager createConfigurationManager(String name) {
        return new ConfigurationManager(name);
    }

    /**
     * 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) {
            logConfigurationException(request, 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);
        }
    }

    /**
     * Performs logging of missing action/result configuration exception
     *
     * @param request current {@link HttpServletRequest}
     * @param e {@link ConfigurationException} that occurred
     */
    protected void logConfigurationException(HttpServletRequest request, ConfigurationException e) {
        // WW-2874 Only log error if in devMode
        String uri = request.getRequestURI();
        if (request.getQueryString() != null) {
            uri = uri + "?" + request.getQueryString();
        }
        if (devMode) {
            LOG.error("Could not find action or result\n#0", e, uri);
        } else if (LOG.isWarnEnabled()) {
            LOG.warn("Could not find action or result: #0", e, uri);
        }
    }

    /**
     * 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;
    }

    /**
     * Merge all application and servlet attributes into a single <tt>HashMap</tt> to represent the entire
     * <tt>Action</tt> context.
     *
     * @param requestMap     a Map of all request attributes.
     * @param parameterMap   a Map of all request parameters.
     * @param sessionMap     a Map of all session attributes.
     * @param applicationMap a Map of all servlet context attributes.
     * @param request        the HttpServletRequest object.
     * @param response       the HttpServletResponse object.
     * @param servletContext the ServletContextmapping object.
     * @return a HashMap representing the <tt>Action</tt> context.
     */
    public HashMap<String,Object> createContextMap(Map requestMap,
                                    Map parameterMap,
                                    Map sessionMap,
                                    Map applicationMap,
                                    HttpServletRequest request,
                                    HttpServletResponse response,
                                    ServletContext servletContext) {
        HashMap<String,Object> extraContext = new HashMap<String,Object>();
        extraContext.put(ActionContext.PARAMETERS, new HashMap(parameterMap));
        extraContext.put(ActionContext.SESSION, sessionMap);
        extraContext.put(ActionContext.APPLICATION, applicationMap);

        Locale locale;
        if (defaultLocale != null) {
            locale = LocalizedTextUtil.localeFromString(defaultLocale, request.getLocale());
        } else {
            locale = request.getLocale();
        }

        extraContext.put(ActionContext.LOCALE, locale);
        //extraContext.put(ActionContext.DEV_MODE, Boolean.valueOf(devMode));

        extraContext.put(StrutsStatics.HTTP_REQUEST, request);
        extraContext.put(StrutsStatics.HTTP_RESPONSE, response);
        extraContext.put(StrutsStatics.SERVLET_CONTEXT, servletContext);

        // helpers to get access to request/session/application scope
        extraContext.put("request", requestMap);
        extraContext.put("session", sessionMap);
        extraContext.put("application", applicationMap);
        extraContext.put("parameters", parameterMap);

        AttributeMap attrMap = new AttributeMap(extraContext);
        extraContext.put("attr", attrMap);

        return extraContext;
    }

    /**
     * Return the path to save uploaded files to (this is configurable).
     *
     * @return the path to save uploaded files to
     * @param servletContext Our ServletContext
     */
    private String getSaveDir(ServletContext servletContext) {
        String saveDir = multipartSaveDir.trim();

        if (saveDir.equals("")) {
            File tempdir = (File) servletContext.getAttribute("javax.servlet.context.tempdir");
            if (LOG.isInfoEnabled()) {
            LOG.info("Unable to find ‘struts.multipart.saveDir‘ property setting. Defaulting to javax.servlet.context.tempdir");
            }

            if (tempdir != null) {
                saveDir = tempdir.toString();
                setMultipartSaveDir(saveDir);
            }
        } else {
            File multipartSaveDir = new File(saveDir);

            if (!multipartSaveDir.exists()) {
                if (!multipartSaveDir.mkdirs()) {
                    String logMessage;
                    try {
                        logMessage = "Could not find create multipart save directory ‘" + multipartSaveDir.getCanonicalPath() + "‘.";
                    } catch (IOException e) {
                        logMessage = "Could not find create multipart save directory ‘" + multipartSaveDir.toString() + "‘.";
                    }
                    if (devMode) {
                        LOG.error(logMessage);
                    } else {
                        if (LOG.isWarnEnabled()) {
                            LOG.warn(logMessage);
                        }
                    }
                }
            }
        }

        if (LOG.isDebugEnabled()) {
            LOG.debug("saveDir=" + saveDir);
        }

        return saveDir;
    }

    /**
     * Prepare a request, including setting the encoding and locale.
     *
     * @param request The request
     * @param response The response
     */
    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
        }
    }

    private void applyEncoding(HttpServletRequest request, String encoding) {
        try {
            if (!encoding.equals(request.getCharacterEncoding())) {
                // if the encoding is already correctly set and the parameters have been already read
                // do not try to set encoding because it is useless and will cause an error
                request.setCharacterEncoding(encoding);
            }
        } catch (Exception e) {
            LOG.error("Error setting character encoding to ‘" + encoding + "‘ - ignoring.", e);
        }
    }

    /**
     * Wrap and return the given request or return the original request object.
     * </p>
     * This method transparently handles multipart data as a wrapped class around the given request.
     * Override this method to handle multipart requests in a special way or to handle other types of requests.
     * Note, {@link org.apache.struts2.dispatcher.multipart.MultiPartRequestWrapper} is
     * flexible - look first to that object before overriding this method to handle multipart data.
     *
     * @param request the HttpServletRequest object.
     * @param servletContext Our ServletContext object
     * @return a wrapped request or original request.
     * @see org.apache.struts2.dispatcher.multipart.MultiPartRequestWrapper
     * @throws java.io.IOException on any error.
     */
    public HttpServletRequest wrapRequest(HttpServletRequest request, ServletContext servletContext) throws IOException {
        // don‘t wrap more than once
        if (request instanceof StrutsRequestWrapper) {
            return request;
        }

        String content_type = request.getContentType();
        if (content_type != null && content_type.contains("multipart/form-data")) {
            MultiPartRequest mpr = getMultiPartRequest();
            LocaleProvider provider = getContainer().getInstance(LocaleProvider.class);
            request = new MultiPartRequestWrapper(mpr, request, getSaveDir(servletContext), provider);
        } else {
            request = new StrutsRequestWrapper(request, disableRequestAttributeValueStackLookup);
        }

        return request;
    }

    /**
     * On each request it must return a new instance as implementation could be not thread safe
     * and thus ensure of resource clean up
     *
     * @return
     */
    protected MultiPartRequest getMultiPartRequest() {
        MultiPartRequest mpr = null;
        //check for alternate implementations of MultiPartRequest
        Set<String> multiNames = getContainer().getInstanceNames(MultiPartRequest.class);
        for (String multiName : multiNames) {
            if (multiName.equals(multipartHandlerName)) {
                mpr = getContainer().getInstance(MultiPartRequest.class, multiName);
            }
        }
        if (mpr == null ) {
            mpr = getContainer().getInstance(MultiPartRequest.class);
        }
        return mpr;
    }

    /**
     * Removes all the files created by MultiPartRequestWrapper.
     *
     * @param request the HttpServletRequest object.
     * @see org.apache.struts2.dispatcher.multipart.MultiPartRequestWrapper
     */
    public void cleanUpRequest(HttpServletRequest request) {
        ContainerHolder.clear();
        if (!(request instanceof MultiPartRequestWrapper)) {
            return;
        }
        MultiPartRequestWrapper multiWrapper = (MultiPartRequestWrapper) request;
        multiWrapper.cleanUp();
    }

    /**
     * Send an HTTP error response code.
     *
     * @param request  the HttpServletRequest object.
     * @param response the HttpServletResponse object.
     * @param code     the HttpServletResponse error code (see {@link javax.servlet.http.HttpServletResponse} for possible error codes).
     * @param e        the Exception that is reported.
     * @param ctx      the ServletContext object.
     */
    public void sendError(HttpServletRequest request, HttpServletResponse response, ServletContext ctx, int code, Exception e) {
        Boolean devModeOverride = FilterDispatcher.getDevModeOverride();
        if (devModeOverride != null ? devModeOverride : devMode) {
            if (LOG.isDebugEnabled()) {
                LOG.debug("Exception occurred during processing request: #0", e, e.getMessage());
            }
            try {
                FreemarkerManager mgr = getContainer().getInstance(FreemarkerManager.class);

                freemarker.template.Configuration config = mgr.getConfiguration(ctx);
                Template template = config.getTemplate("/org/apache/struts2/dispatcher/error.ftl");

                List<Throwable> chain = new ArrayList<Throwable>();
                Throwable cur = e;
                chain.add(cur);
                while ((cur = cur.getCause()) != null) {
                    chain.add(cur);
                }

                HashMap<String,Object> data = new HashMap<String,Object>();
                data.put("exception", e);
                data.put("unknown", Location.UNKNOWN);
                data.put("chain", chain);
                data.put("locator", new Locator());

                Writer writer = new StringWriter();
                template.process(data, writer);

                response.setContentType("text/html");
                response.getWriter().write(writer.toString());
                response.getWriter().close();
            } catch (Exception exp) {
                try {
                    if (LOG.isDebugEnabled()) {
                        LOG.debug("Cannot show problem report!", exp);
                    }
                    response.sendError(code, "Unable to show problem report:\n" + exp + "\n\n" + LocationUtils.getLocation(exp));
                } catch (IOException ex) {
                    // we‘re already sending an error, not much else we can do if more stuff breaks
                }
            }
        } else {
            try {
                // WW-1977: Only put errors in the request when code is a 500 error
                if (code == HttpServletResponse.SC_INTERNAL_SERVER_ERROR) {
                    // WW-4103: Only logs error when application error occurred, not Struts error
                    if (LOG.isErrorEnabled()) {
                        LOG.error("Exception occurred during processing request: #0", e, e.getMessage());
                    }
                    // send a http error response to use the servlet defined error handler
                    // make the exception availible to the web.xml defined error page
                    request.setAttribute("javax.servlet.error.exception", e);

                    // for compatibility
                    request.setAttribute("javax.servlet.jsp.jspException", e);
                }

                // send the error response
                response.sendError(code, e.getMessage());
            } catch (IOException e1) {
                // we‘re already sending an error, not much else we can do if more stuff breaks
            }
        }
    }

    /**
     * Cleanup any resources used to initialise Dispatcher
     */
    public void cleanUpAfterInit() {
        if (LOG.isDebugEnabled()) {
            LOG.debug("Cleaning up resources used to init Dispatcher");
        }
        ContainerHolder.clear();
    }

    /**
     * Provide an accessor class for static XWork utility.
     */
    public static class Locator {
        public Location getLocation(Object obj) {
            Location loc = LocationUtils.getLocation(obj);
            if (loc == null) {
                return Location.UNKNOWN;
            }
            return loc;
        }
    }

    /**
     * Expose the ConfigurationManager instance.
     *
     * @return The instance
     */
    public ConfigurationManager getConfigurationManager() {
        return configurationManager;
    }

    /**
     * Modify the ConfigurationManager instance
     *
     * @param mgr The configuration manager
     * @deprecated should be removed as is used only in tests
     */
    public void setConfigurationManager(ConfigurationManager mgr) {
        ContainerHolder.clear();
        this.configurationManager = mgr;
    }

    /**
     * Expose the dependency injection container.
     * @return Our dependency injection container
     */
    public Container getContainer() {
        if (ContainerHolder.get() != null) {
            return ContainerHolder.get();
        }
        ConfigurationManager mgr = getConfigurationManager();
        if (mgr == null) {
            throw new IllegalStateException("The configuration manager shouldn‘t be null");
        } else {
            Configuration config = mgr.getConfiguration();
            if (config == null) {
                throw new IllegalStateException("Unable to load configuration");
            } else {
                Container container = config.getContainer();
                ContainerHolder.store(container);
                return container;
            }
        }
    }

}

注意到下面的实现：

 /**
     * Create the Dispatcher instance for a given ServletContext and set of initialization parameters.
     *
     * @param servletContext Our servlet context
     * @param initParams The set of initialization parameters
     */
    public Dispatcher(ServletContext servletContext, Map<String, String> initParams) {
        this.servletContext = servletContext;
        this.initParams = initParams;
}

说明：servletContext就是servlet请求上下文

   protected XmlConfigurationProvider createStrutsXmlConfigurationProvider(String filename, boolean errorIfMissing, ServletContext ctx) {
        return new StrutsXmlConfigurationProvider(filename, errorIfMissing, ctx);
}

这里面创建StrutsXmlConfigurationProvider；

这个类做了些什么呢？

在看：

/*
 * $Id$
 *
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *  http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.struts2.config;

import java.io.File;
import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

import javax.servlet.ServletContext;

import com.opensymphony.xwork2.ActionContext;
import com.opensymphony.xwork2.config.ConfigurationException;
import com.opensymphony.xwork2.config.providers.XmlConfigurationProvider;
import com.opensymphony.xwork2.inject.ContainerBuilder;
import com.opensymphony.xwork2.inject.Context;
import com.opensymphony.xwork2.inject.Factory;
import com.opensymphony.xwork2.util.location.LocatableProperties;
import com.opensymphony.xwork2.util.logging.Logger;
import com.opensymphony.xwork2.util.logging.LoggerFactory;

/**
 * Override Xwork class so we can use an arbitrary config file
 */
public class StrutsXmlConfigurationProvider extends XmlConfigurationProvider {

    private static final Logger LOG = LoggerFactory.getLogger(StrutsXmlConfigurationProvider.class);
    private File baseDir = null;
    private String filename;
    private String reloadKey;
    private ServletContext servletContext;

    /**
     * Constructs the configuration provider
     *
     * @param errorIfMissing If we should throw an exception if the file can‘t be found
     */
    public StrutsXmlConfigurationProvider(boolean errorIfMissing) {
        this("struts.xml", errorIfMissing, null);
    }

    /**
     * Constructs the configuration provider
     *
     * @param filename The filename to look for
     * @param errorIfMissing If we should throw an exception if the file can‘t be found
     * @param ctx Our ServletContext
     */
    public StrutsXmlConfigurationProvider(String filename, boolean errorIfMissing, ServletContext ctx) {
        super(filename, errorIfMissing);
        this.servletContext = ctx;
        this.filename = filename;
        reloadKey = "configurationReload-"+filename;
        Map<String,String> dtdMappings = new HashMap<String,String>(getDtdMappings());
        dtdMappings.put("-//Apache Software Foundation//DTD Struts Configuration 2.0//EN", "struts-2.0.dtd");
        dtdMappings.put("-//Apache Software Foundation//DTD Struts Configuration 2.1//EN", "struts-2.1.dtd");
        dtdMappings.put("-//Apache Software Foundation//DTD Struts Configuration 2.1.7//EN", "struts-2.1.7.dtd");
        dtdMappings.put("-//Apache Software Foundation//DTD Struts Configuration 2.3//EN", "struts-2.3.dtd");
        setDtdMappings(dtdMappings);
        File file = new File(filename);
        if (file.getParent() != null) {
            this.baseDir = file.getParentFile();
        }
    }

    /* (non-Javadoc)
     * @see com.opensymphony.xwork2.config.providers.XmlConfigurationProvider#register(com.opensymphony.xwork2.inject.ContainerBuilder, java.util.Properties)
     */
    @Override
    public void register(ContainerBuilder containerBuilder, LocatableProperties props) throws ConfigurationException {
        if (servletContext != null && !containerBuilder.contains(ServletContext.class)) {
            containerBuilder.factory(ServletContext.class, new Factory<ServletContext>() {
                public ServletContext create(Context context) throws Exception {
                    return servletContext;
                }
            });
        }
        super.register(containerBuilder, props);
    }

    /* (non-Javadoc)
     * @see com.opensymphony.xwork2.config.providers.XmlConfigurationProvider#init(com.opensymphony.xwork2.config.Configuration)
     */
    @Override
    public void loadPackages() {
        ActionContext ctx = ActionContext.getContext();
        ctx.put(reloadKey, Boolean.TRUE);
        super.loadPackages();
    }

    /**
     * Look for the configuration file on the classpath and in the file system
     *
     * @param fileName The file name to retrieve
     * @see com.opensymphony.xwork2.config.providers.XmlConfigurationProvider#getConfigurationUrls
     */
    @Override
    protected Iterator<URL> getConfigurationUrls(String fileName) throws IOException {
        URL url = null;
        if (baseDir != null) {
            url = findInFileSystem(fileName);
            if (url == null) {
                return super.getConfigurationUrls(fileName);
            }
        }
        if (url != null) {
            List<URL> list = new ArrayList<URL>();
            list.add(url);
            return list.iterator();
        } else {
            return super.getConfigurationUrls(fileName);
        }
    }

    protected URL findInFileSystem(String fileName) throws IOException {
        URL url = null;
        File file = new File(fileName);
        if (LOG.isDebugEnabled()) {
            LOG.debug("Trying to load file " + file);
        }

        // Trying relative path to original file
        if (!file.exists()) {
            file = new File(baseDir, fileName);
        }
        if (file.exists()) {
            try {
                url = file.toURI().toURL();
            } catch (MalformedURLException e) {
                throw new IOException("Unable to convert "+file+" to a URL");
            }
        }
        return url;
    }

    /**
     * Overrides needs reload to ensure it is only checked once per request
     */
    @Override
    public boolean needsReload() {
        ActionContext ctx = ActionContext.getContext();
        if (ctx != null) {
            return ctx.get(reloadKey) == null && super.needsReload();
        } else {
            return super.needsReload();
        }

    }

    public String toString() {
        return ("Struts XML configuration provider ("+filename+")");
    }
}

注意到里面的：

  public StrutsXmlConfigurationProvider(boolean errorIfMissing) {
        this("struts.xml", errorIfMissing, null);
    }

我相信大多数人看到这里应该已经明白读取struts配置的真是这个类；

再来注意下：

private ConfigurationManager configurationManager;

实际上ConfigurationManager 就是整个项目的配置管理类，struts读取到文件系统的东西都是放到ConfigurationManager 所管理的内存区内；

doFilter负责处理请求的过滤，

我们来看看其处理的逻辑：

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);
                }

也就是说它是要找到符合findActionMapping的一个map路由，然后executeAction，然后里面在执行serviceAction

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

我们看到proxy.execute();就是说代理然后再执行对对应的action：

网上有一张图，能够比较清晰的表达：

依照上图，我们可以看出一个请求在struts的处理大概有如下步骤：

　　1、客户端初始化一个指向Servlet容器的请求；

　　2、这个请求经过一系列的过滤器（Filter）（这些过滤器中有一个叫做ActionContextCleanUp的可选过滤器，这个过滤器对于Struts2和其他框架的集成很有帮助，例如：SiteMesh Plugin）；

　　3、接着StrutsPrepareAndExecuteFilter被调用，StrutsPrepareAndExecuteFilter询问ActionMapper来决定这个请求是否需要调用某个Action；

　　4、如果ActionMapper决定需要调用某个Action，FilterDispatcher把请求的处理交给ActionProxy；

　　5、ActionProxy通过Configuration Manager询问框架的配置文件，找到需要调用的Action类；

　　6、ActionProxy创建一个ActionInvocation的实例。

　　7、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（Intercepter）的调用。

8、一旦Action执行完毕，ActionInvocation负责根据struts.xml中的配置找到对应的返回结果。返回结果通常是（但不总是，也可能是另外的一个Action链）一个需要被表示的JSP或者FreeMarker的模版。在表示的过程中可以使用Struts2 框架中继承的标签。在这个过程中需要涉及到ActionMapper。

Struts2的包结构：

以下是包说明：

根目录下的5个文件说明：