struts2的ActionContext源代码解析

ActionContext.getContext().put("name","liming");和Map request = (Map)ActionContext.getContext().get("request");request.put("name","liming");设置name变量，当需要在jsp中显示时，可以通过OGNL读取。

ActionContext（com.opensymphony.xwork.ActionContext）是Action执行时的上下文，上下文可以看作是一个容器（其实我们这里的容器就是一个Map而已），它存放放的是Action在执行时需要用到的对象，比如：在使用WebWork时，我们的上下文放有请求的参数（Parameter）、会话(Session)、Servlet上下文（ServletContext）、本地化（Locale）信息等，补充说明application和ServletContext在本2.3.1.2中是一样的（可以参看下面2.3.1.2ActionContext的getApplication()方法上的注释）。

在每次执行Action之前都会创建新的ActionContext，ActionContext是线程安全的，也就是说在同一个线程里ActionContext里的属性是唯一的，这样我的Action就可以在多线程中使用。

我们可以通过ActionContext的静态方法：ActionContext.getContext()来取得当前的ActionContext对象，我们看看这段代码：

      public static ActionContext getContext() {
        return (ActionContext) actionContext.get();

        // Don't do lazy context creation, as it requires container; the creation of which may
        // precede the context creation
        //if (context == null) {
        //    ValueStack vs = ValueStackFactory.getFactory().createValueStack();
        //    context = new ActionContext(vs.getContext());
        //    setContext(context);
        //}

    }

   public static void setContext(ActionContext context) {
        actionContext.set(context);
    }

    public void setContextMap(Map<String, Object> contextMap) {
        getContext().context = contextMap;
    }

      public Map<String, Object> getContextMap() {
        return context;
    }

参考struts2ActionContext源代码（struts2.3.1.2版本官方源代码）

/*
 * Copyright 2002-2006,2009 The Apache Software Foundation.
 *
 * Licensed 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 com.opensymphony.xwork2;

import com.opensymphony.xwork2.inject.Container;
import com.opensymphony.xwork2.util.ValueStack;

import java.io.Serializable;
import java.util.HashMap;
import java.util.Locale;
import java.util.Map;

/**
 * The ActionContext is the context in which an {@link Action} is executed. Each context is basically a
 * container of objects an action needs for execution like the session, parameters, locale, etc. <p>
 * <p/>
 * The ActionContext is thread local which means that values stored in the ActionContext are
 * unique per thread. See the {@link ThreadLocal} class for more information. The benefit of
 * this is you don't need to worry about a user specific action context, you just get it:
 * <p/>
 * <ul><code>ActionContext context = ActionContext.getContext();</code></ul>
 * <p/>
 * Finally, because of the thread local usage you don't need to worry about making your actions thread safe.
 *
 * @author Patrick Lightbody
 * @author Bill Lynch (docs)
 */
public class ActionContext implements Serializable {
    static ThreadLocal actionContext = new ThreadLocal();

    /**
     * Constant that indicates the action is running under a "development mode".
     * This mode provides more feedback that is useful for developers but probably
     * too verbose/error prone for production.
     */
    //public static final String DEV_MODE = "__devMode";

    /**
     * Constant for the name of the action being executed.
     */
    public static final String ACTION_NAME = "com.opensymphony.xwork2.ActionContext.name";

    /**
     * Constant for the {@link com.opensymphony.xwork2.util.ValueStack OGNL value stack}.
     */
    public static final String VALUE_STACK = ValueStack.VALUE_STACK;

    /**
     * Constant for the action's session.
     */
    public static final String SESSION = "com.opensymphony.xwork2.ActionContext.session";

    /**
     * Constant for the action's application context.
     */
    public static final String APPLICATION = "com.opensymphony.xwork2.ActionContext.application";

    /**
     * Constant for the action's parameters.
     */
    public static final String PARAMETERS = "com.opensymphony.xwork2.ActionContext.parameters";

    /**
     * Constant for the action's locale.
     */
    public static final String LOCALE = "com.opensymphony.xwork2.ActionContext.locale";

    /**
     * Constant for the action's type converter.
     */
    public static final String TYPE_CONVERTER = "com.opensymphony.xwork2.ActionContext.typeConverter";

    /**
     * Constant for the action's {@link com.opensymphony.xwork2.ActionInvocation invocation} context.
     */
    public static final String ACTION_INVOCATION = "com.opensymphony.xwork2.ActionContext.actionInvocation";

    /**
     * Constant for the map of type conversion errors.
     */
    public static final String CONVERSION_ERRORS = "com.opensymphony.xwork2.ActionContext.conversionErrors";

    /**
     * Constant for the container
     */
    public static final String CONTAINER = "com.opensymphony.xwork2.ActionContext.container";
   
    Map<String, Object> context;

    /**
     * Creates a new ActionContext initialized with another context.
     *
     * @param context a context map.
     */
    public ActionContext(Map<String, Object> context) {
        this.context = context;
    }

    /**
     * Sets the action invocation (the execution state).
     *
     * @param actionInvocation the action execution state.
     */
    public void setActionInvocation(ActionInvocation actionInvocation) {
        put(ACTION_INVOCATION, actionInvocation);
    }

    /**
     * Gets the action invocation (the execution state).
     *
     * @return the action invocation (the execution state).
     */
    public ActionInvocation getActionInvocation() {
        return (ActionInvocation) get(ACTION_INVOCATION);
    }

    /**
     * Sets the action's application context.
     *
     * @param application the action's application context.
     */
    public void setApplication(Map<String, Object> application) {
        put(APPLICATION, application);
    }

    /**
     * Returns a Map of the ServletContext when in a servlet environment or a generic application level Map otherwise.
     *
     * @return a Map of ServletContext or generic application level Map
     */
    public Map<String, Object> getApplication() {
        return (Map<String, Object>) get(APPLICATION);
    }

    /**
     * Sets the action context for the current thread.
     *
     * @param context the action context.
     */
    public static void setContext(ActionContext context) {
        actionContext.set(context);
    }

    /**
     * Returns the ActionContext specific to the current thread.
     *
     * @return the ActionContext for the current thread, is never <tt>null</tt>.
     */
    public static ActionContext getContext() {
        return (ActionContext) actionContext.get();

        // Don't do lazy context creation, as it requires container; the creation of which may
        // precede the context creation
        //if (context == null) {
        //    ValueStack vs = ValueStackFactory.getFactory().createValueStack();
        //    context = new ActionContext(vs.getContext());
        //    setContext(context);
        //}

    }

    /**
     * Sets the action's context map.
     *
     * @param contextMap the context map.
     */
    public void setContextMap(Map<String, Object> contextMap) {
        getContext().context = contextMap;
    }

    /**
     * Gets the context map.
     *
     * @return the context map.
     */
    public Map<String, Object> getContextMap() {
        return context;
    }

    /**
     * Sets conversion errors which occurred when executing the action.
     *
     * @param conversionErrors a Map of errors which occurred when executing the action.
     */
    public void setConversionErrors(Map<String, Object> conversionErrors) {
        put(CONVERSION_ERRORS, conversionErrors);
    }

    /**
     * Gets the map of conversion errors which occurred when executing the action.
     *
     * @return the map of conversion errors which occurred when executing the action or an empty map if
     *         there were no errors.
     */
    public Map<String, Object> getConversionErrors() {
        Map<String, Object> errors = (Map) get(CONVERSION_ERRORS);

        if (errors == null) {
            errors = new HashMap<String, Object>();
            setConversionErrors(errors);
        }

        return errors;
    }

    /**
     * Sets the Locale for the current action.
     *
     * @param locale the Locale for the current action.
     */
    public void setLocale(Locale locale) {
        put(LOCALE, locale);
    }

    /**
     * Gets the Locale of the current action. If no locale was ever specified the platform's
     * {@link java.util.Locale#getDefault() default locale} is used.
     *
     * @return the Locale of the current action.
     */
    public Locale getLocale() {
        Locale locale = (Locale) get(LOCALE);

        if (locale == null) {
            locale = Locale.getDefault();
            setLocale(locale);
        }

        return locale;
    }

    /**
     * Sets the name of the current Action in the ActionContext.
     *
     * @param name the name of the current action.
     */
    public void setName(String name) {
        put(ACTION_NAME, name);
    }

    /**
     * Gets the name of the current Action.
     *
     * @return the name of the current action.
     */
    public String getName() {
        return (String) get(ACTION_NAME);
    }

    /**
     * Sets the action parameters.
     *
     * @param parameters the parameters for the current action.
     */
    public void setParameters(Map<String, Object> parameters) {
        put(PARAMETERS, parameters);
    }

    /**
     * Returns a Map of the HttpServletRequest parameters when in a servlet environment or a generic Map of
     * parameters otherwise.
     *
     * @return a Map of HttpServletRequest parameters or a multipart map when in a servlet environment, or a
     *         generic Map of parameters otherwise.
     */
    public Map<String, Object> getParameters() {
        return (Map<String, Object>) get(PARAMETERS);
    }

    /**
     * Sets a map of action session values.
     *
     * @param session  the session values.
     */
    public void setSession(Map<String, Object> session) {
        put(SESSION, session);
    }

    /**
     * Gets the Map of HttpSession values when in a servlet environment or a generic session map otherwise.
     *
     * @return the Map of HttpSession values when in a servlet environment or a generic session map otherwise.
     */
    public Map<String, Object> getSession() {
        return (Map<String, Object>) get(SESSION);
    }

    /**
     * Sets the OGNL value stack.
     *
     * @param stack the OGNL value stack.
     */
    public void setValueStack(ValueStack stack) {
        put(VALUE_STACK, stack);
    }

    /**
     * Gets the OGNL value stack.
     *
     * @return the OGNL value stack.
     */
    public ValueStack getValueStack() {
        return (ValueStack) get(VALUE_STACK);
    }
   
    /**
     * Gets the container for this request
     *
     * @param cont The container
     */
    public void setContainer(Container cont) {
        put(CONTAINER, cont);
    }
   
    /**
     * Sets the container for this request
     *
     * @return The container
     */
    public Container getContainer() {
        return (Container) get(CONTAINER);
    }
   
    public <T> T getInstance(Class<T> type) {
        Container cont = getContainer();
        if (cont != null) {
            return cont.getInstance(type);
        } else {
            throw new XWorkException("Cannot find an initialized container for this request.");
        }
    }

    /**
     * Returns a value that is stored in the current ActionContext by doing a lookup using the value's key.
     *
     * @param key the key used to find the value.
     * @return the value that was found using the key or <tt>null</tt> if the key was not found.
     */
    public Object get(String key) {
        return context.get(key);
    }

    /**
     * Stores a value in the current ActionContext. The value can be looked up using the key.
     *
     * @param key   the key of the value.
     * @param value the value to be stored.
     */
    public void put(String key, Object value) {
        context.put(key, value);
    }
}