Struts2中的ActionContext和ValueStack详解

ActionContext

我们知道Servlet是单例多线程的，容器会在线程池中为每一次请求分配一个线程。而在struts2中，每个线程会创建一个Action上下文即ActionContext，它由当前线程创建并与线程绑定在一起,也就是说依赖于请求，所以在请求未发生时，里面时没有储存信息的。作为Servlet Api的封装，ActionContext以Map容器的结构储存了哪些信息,又是怎样获取的呢？

 

一.获取ActionContext和存取信息

ActionContext如同一个Map类型的数据中心，不管是在jsp  Action类还是非Action类均可非常方便的获取ActionContext  

1）在jsp中

在jsp中无需获得ActionContext,将字符串"amy"存入ActionContext,key是"myKey"：<s:set  value=%{"amy"} var="myKey"/>

取出这个字符串：<s:property  value="#myKey"/>

将java对象存入ActionContext,key是"myObject" :<s:bean name=%{"com.my.User"}  var="myObject"/>（当OGNL表达式不能解析时使用%{ }）

取出这个对象：<s:property  value="#myObject"/>

 

其中有一些对象是由容器存入的如（这些对象是Map类型）：

<s:property  value="#request"/>

<s:property  value="#session"/>

<s:property  value="#application"/>

<s:property  value="#params"/>

2）Action中

由拦截器注入或ActionContext.getContext()获得

         // 存入值  
        Person person = new Person();//
        ActionContext.getContext().put("person", person);  
        // 获取值  
        Object object =  ActionContext.getContext().get("person");   

3）过滤器中

publicclass MyInterceptor extends AbstractInterceptor {  
 
    public String intercept(ActionInvocation invocation) throws Exception {  
        // 获得ActionContext  
        ActionContext actionContext = invocation.getInvocationContext();  
        // 存入值  
        Person person = new Person();  
        actionContext.put("person", person);  
        // 获取值  
        Object value = actionContext.get("person");  
        // 获取HttpServletRequest  
        HttpServletRequest request = (HttpServletRequest) actionContext.get(StrutsStatics.HTTP_REQUEST);  
        // 获取request的Map，即HttpServletRequest.getAttribute(...)和HttpServletRequest.setAttribute(...)所操作的值 
        Map requestMap = (Map) actionContext.get("request");  
        // 其他代码  
        // ......  
        return invocation.invoke();  
    }  
}  

二，ActionContext中的提供方法

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;

public class ActionContext implements Serializable {

    static ThreadLocal<ActionContext> actionContext = new ThreadLocal<ActionContext>();

    /**
     * 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";
    
    private 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);
    }

    /**
     * 获得当前action的代理
     *
     * @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);
    }

    /**
     * 获得Map类型的application
     *
     * @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.get();
    }

    /**
     * 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);
    }
}

1)get方法

ActionContext actionContext=ActionContext.getContext(); //提供静态的方法获得实例对象，保证一次请求中数据同步，线程安全。

get（"key"）可以获取开发者放入的String 或自定义类型的数据，也可以获取容器已经放入的范围对象和容器。

Map类型的"范围对象"：

Map<String,Object> requestMap=(Map<String,Object>)actionContext.get("request");

Map<String,Object> sessionMap=(Map<String,Object>)actionContext.get("session");

HttpServlet原生的范围对象：

HttpServletRequest request=(HttpServletRequest)actionContext.get(StrutsStatics.HTTP_REQUEST);

requestMap是Struts对request的封装，request方法setAttribute(key,vakue)对应的值放入requestMap中，实现对Servlet的解耦。除此之外他们的作用范围和生命周期是相同的。类似的还有HttpServletSession类型的session 和Map类型的sessionMap  HttpServletContext类型的context和Map类型的applicationMap  request.getParameter("")获得的参数和paramters类型的Map

2）public ActionInvocation getActionInvocation()

获得当前Action的代理对象，其底层也是get方法实现的，其中的参数是事先定好的常量。

3）public Map<String, Object> getApplication()

底层实现：(Map<String, Object>) get(APPLICATION)

4）public Map<String, Object> getContextMap()

获得上下文对应的容器

5） public Locale getLocale() { //获得本地对象
        Locale locale = (Locale) get(LOCALE);

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

6）  public Container getContainer() {   //获得请求容器
        return (Container) get(CONTAINER);
    }

7）public Map<String, Object> getParameters() {
        return (Map<String, Object>) get(PARAMETERS);
    }

由请求参数和请求值封装而成的Map容器。

8）public Map<String, Object> getSession()

同上

9） public ValueStack getValueStack() {  return (ValueStack) get(VALUE_STACK); }

获得值栈对象

10） public String getName() { return (String) get(ACTION_NAME);}

获得当前action的名字

 三，ValueStack

ValueStack是struts的栈值对象接口。在发生请求时随Action的创建而产生，每一个Action对应一个ValueStack，在Action移除时消失。他的作用是储存数据，一个变量对应一个值（这里先不讨论他的实现类）

1,获得当前ValueStack的方法

1)jsp中：无需获取，直接使用标签即可

2）在java代码中，ValueSatck valueStack=ActionContext.getContext().getValueStack();

2，提供的方法

 public abstract String findString(String expr);//利用默认的搜索规则，根据路径表达式获取key值
    public abstract String findString(String expr, boolean throwExceptionOnFailure);

    /**
     * Find a value by evaluating the given expression against the stack in the default search order.
     *
     * @param expr the expression giving the path of properties to navigate to find the property value to return
     * @return the result of evaluating the expression
     */
    public abstract Object findValue(String expr); //利用默认的搜索规则，根据路径表达式获取值

    public abstract Object findValue(String expr, boolean throwExceptionOnFailure); //

    /**
     * Find a value by evaluating the given expression against the stack in the default search order.
     *
     * @param expr   the expression giving the path of properties to navigate to find the property value to return
     * @param asType the type to convert the return value to
     * @return the result of evaluating the expression
     */
    public abstract Object findValue(String expr, Class asType);//利用默认的搜索规则，根据路径表达式和类型获取值
    public abstract Object findValue(String expr, Class asType,  boolean throwExceptionOnFailure);

    /**
     * Get the object on the top of the stack <b>without</b> changing the stack.
     *
     * @return the object on the top.
     * @see CompoundRoot#peek()
     */
    public abstract Object peek();//获取栈顶的元素（不改变原栈值对象）

    /**
     * Get the object on the top of the stack and <b>remove</b> it from the stack.
     *
     * @return the object on the top of the stack
     * @see CompoundRoot#pop()
     */
    public abstract Object pop();//移除并返回栈顶的元素

    /**
     * Put this object onto the top of the stack
     *
     * @param o the object to be pushed onto the stack
     * @see CompoundRoot#push(Object)
     */
    public abstract void push(Object o);//将对象压入栈内

    /**
     * Sets an object on the stack with the given key
     * so it is retrievable by {@link #findValue(String)}, {@link #findValue(String, Class)}
     *
     * @param key  the key
     * @param o    the object
     */
    public abstract void set(String key, Object o);//给栈内的元素设置值

    /**
     * Get the number of objects in the stack
     *
     * @return the number of objects in the stack
     */
    public abstract int size();//返回元素数量

3，默认实现类OGNLValueStack

OGNLValueStack是ValueStack的默认实现类，Struts2根据OGNL表达式语言，利用栈值的形式在界面和后台之间传递数据，另外提供诸如集合的投影和过滤以及lambda表达式等。OGNLValueStack在OGNL基础上对对象属性的存取做的些许改动。

package com.opensymphony.xwork2.ognl;  
  
import com.opensymphony.xwork2.ActionContext;  
import com.opensymphony.xwork2.TextProvider;  
import com.opensymphony.xwork2.XWorkConstants;  
import com.opensymphony.xwork2.XWorkException;  
import com.opensymphony.xwork2.conversion.impl.XWorkConverter;  
import com.opensymphony.xwork2.inject.Container;  
import com.opensymphony.xwork2.inject.Inject;  
import com.opensymphony.xwork2.ognl.accessor.CompoundRootAccessor;  
import com.opensymphony.xwork2.util.ClearableValueStack;  
import com.opensymphony.xwork2.util.CompoundRoot;  
import com.opensymphony.xwork2.util.MemberAccessValueStack;  
import com.opensymphony.xwork2.util.ValueStack;  
import com.opensymphony.xwork2.util.logging.Logger;  
import com.opensymphony.xwork2.util.logging.LoggerFactory;  
import com.opensymphony.xwork2.util.logging.LoggerUtils;  
import com.opensymphony.xwork2.util.reflection.ReflectionContextState;  
import ognl.*;  
  
import java.io.Serializable;  
import java.util.HashMap;  
import java.util.Map;  
import java.util.Set;  
import java.util.regex.Pattern;  
  
public class OgnlValueStack implements Serializable, ValueStack, ClearableValueStack, MemberAccessValueStack {  
  
    public static final String THROW_EXCEPTION_ON_FAILURE = OgnlValueStack.class.getName() + ".throwExceptionOnFailure";  
  
    private static final long serialVersionUID = 370737852934925530L;  
  
    private static final String MAP_IDENTIFIER_KEY = "com.opensymphony.xwork2.util.OgnlValueStack.MAP_IDENTIFIER_KEY";  
    private static final Logger LOG = LoggerFactory.getLogger(OgnlValueStack.class);  
      
    //CompoundRoot继承了ArraryList，提供了额外的方法：push()和pop()方法，所以它相当于栈结构  
    <span style="color:#FF0000;">CompoundRoot root;  
    transient Map<String, Object> context;  
    Class defaultType;  
    Map<Object, Object> overrides;  
    transient OgnlUtil ognlUtil;  
    transient SecurityMemberAccess securityMemberAccess;</span>  
  
    private boolean devMode;  
    private boolean logMissingProperties;  
  
    protected OgnlValueStack(XWorkConverter xworkConverter, CompoundRootAccessor accessor, TextProvider prov, boolean allowStaticAccess) {  
        setRoot(xworkConverter, accessor, new CompoundRoot(), allowStaticAccess);  
        push(prov);  
    }  
  
    protected OgnlValueStack(ValueStack vs, XWorkConverter xworkConverter, CompoundRootAccessor accessor, boolean allowStaticAccess) {  
        setRoot(xworkConverter, accessor, new CompoundRoot(vs.getRoot()), allowStaticAccess);  
    }  
  
    @Inject  
    public void setOgnlUtil(OgnlUtil ognlUtil) {  
        this.ognlUtil = ognlUtil;  
    }  
  
    protected void setRoot(XWorkConverter xworkConverter, CompoundRootAccessor accessor, CompoundRoot compoundRoot,  
                           boolean allowStaticMethodAccess) {  
        this.root = compoundRoot;  
        this.securityMemberAccess = new SecurityMemberAccess(allowStaticMethodAccess);  
        this.context = Ognl.createDefaultContext(this.root, accessor, new OgnlTypeConverterWrapper(xworkConverter), securityMemberAccess);  
        context.put(VALUE_STACK, this);  
        Ognl.setClassResolver(context, accessor);  
        ((OgnlContext) context).setTraceEvaluations(false);  
        ((OgnlContext) context).setKeepLastEvaluation(false);  
    }  
  
    @Inject(XWorkConstants.DEV_MODE)  
    public void setDevMode(String mode) {  
        devMode = "true".equalsIgnoreCase(mode);  
    }  
  
    @Inject(value = "logMissingProperties", required = false)  
    public void setLogMissingProperties(String logMissingProperties) {  
        this.logMissingProperties = "true".equalsIgnoreCase(logMissingProperties);  
    }  
  
    /** 
     * @see com.opensymphony.xwork2.util.ValueStack#getContext() 
     */  
    public Map<String, Object> getContext() {  
        return context;  
    }  
  
    /** 
     * @see com.opensymphony.xwork2.util.ValueStack#setDefaultType(java.lang.Class) 
     */  
    public void setDefaultType(Class defaultType) {  
        this.defaultType = defaultType;  
    }  
  
    /** 
     * @see com.opensymphony.xwork2.util.ValueStack#setExprOverrides(java.util.Map) 
     */  
    public void setExprOverrides(Map<Object, Object> overrides) {  
        if (this.overrides == null) {  
            this.overrides = overrides;  
        } else {  
            this.overrides.putAll(overrides);  
        }  
    }  
  
    /** 
     * @see com.opensymphony.xwork2.util.ValueStack#getExprOverrides() 
     */  
    public Map<Object, Object> getExprOverrides() {  
        return this.overrides;  
    }  
  
    /** 
     * @see com.opensymphony.xwork2.util.ValueStack#getRoot() 
     */  
    public CompoundRoot getRoot() {  
        return root;  
    }  
  
    /** 
     * @see com.opensymphony.xwork2.util.ValueStack#setParameter(String, Object) 
     */  
    public void setParameter(String expr, Object value) {  
        setValue(expr, value, devMode, false);  
    }  
  
    /** 
 
    /** 
     * @see com.opensymphony.xwork2.util.ValueStack#setValue(java.lang.String, java.lang.Object) 
     */  
    public void setValue(String expr, Object value) {  
        setValue(expr, value, devMode);  
    }  
  
    /** 
     * @see com.opensymphony.xwork2.util.ValueStack#setValue(java.lang.String, java.lang.Object, boolean) 
     */  
    public void setValue(String expr, Object value, boolean throwExceptionOnFailure) {  
        setValue(expr, value, throwExceptionOnFailure, true);  
    }  
  
    private void setValue(String expr, Object value, boolean throwExceptionOnFailure, boolean evalExpression) {  
        Map<String, Object> context = getContext();  
        try {  
            trySetValue(expr, value, throwExceptionOnFailure, context, evalExpression);  
        } catch (OgnlException e) {  
            handleOgnlException(expr, value, throwExceptionOnFailure, e);  
        } catch (RuntimeException re) { //XW-281  
            handleRuntimeException(expr, value, throwExceptionOnFailure, re);  
        } finally {  
            cleanUpContext(context);  
        }  
    }  
  
    private void trySetValue(String expr, Object value, boolean throwExceptionOnFailure, Map<String, Object> context, boolean evalExpression) throws OgnlException {  
        context.put(XWorkConverter.CONVERSION_PROPERTY_FULLNAME, expr);  
        context.put(REPORT_ERRORS_ON_NO_PROP, (throwExceptionOnFailure) ? Boolean.TRUE : Boolean.FALSE);  
        ognlUtil.setValue(expr, context, root, value, evalExpression);  
    }  
  
    private void cleanUpContext(Map<String, Object> context) {  
        ReflectionContextState.clear(context);  
        context.remove(XWorkConverter.CONVERSION_PROPERTY_FULLNAME);  
        context.remove(REPORT_ERRORS_ON_NO_PROP);  
    }  
  
    private void handleRuntimeException(String expr, Object value, boolean throwExceptionOnFailure, RuntimeException re) {  
        if (throwExceptionOnFailure) {  
            String message = ErrorMessageBuilder.create()  
                    .errorSettingExpressionWithValue(expr, value)  
                    .build();  
            throw new XWorkException(message, re);  
        } else {  
            if (LOG.isWarnEnabled()) {  
                LOG.warn("Error setting value", re);  
            }  
        }  
    }  
  
    private void handleOgnlException(String expr, Object value, boolean throwExceptionOnFailure, OgnlException e) {  
        String msg = "Error setting expression '" + expr + "' with value '" + value + "'";  
        if (LOG.isWarnEnabled()) {  
            LOG.warn(msg, e);  
        }  
        if (throwExceptionOnFailure) {  
            throw new XWorkException(msg, e);  
        }  
    }  
  
    /** 
     * @see com.opensymphony.xwork2.util.ValueStack#findString(java.lang.String) 
     */  
    public String findString(String expr) {  
        return (String) findValue(expr, String.class);  
    }  
  
    public String findString(String expr, boolean throwExceptionOnFailure) {  
        return (String) findValue(expr, String.class, throwExceptionOnFailure);  
    }  
  
    /** 
     * @see com.opensymphony.xwork2.util.ValueStack#findValue(java.lang.String) 
     */  
    public Object findValue(String expr, boolean throwExceptionOnFailure) {  
        try {  
            setupExceptionOnFailure(throwExceptionOnFailure);  
            return tryFindValueWhenExpressionIsNotNull(expr);  
        } catch (OgnlException e) {  
            return handleOgnlException(expr, throwExceptionOnFailure, e);  
        } catch (Exception e) {  
            return handleOtherException(expr, throwExceptionOnFailure, e);  
        } finally {  
            ReflectionContextState.clear(context);  
        }  
    }  
  
    private void setupExceptionOnFailure(boolean throwExceptionOnFailure) {  
        if (throwExceptionOnFailure) {  
            context.put(THROW_EXCEPTION_ON_FAILURE, true);  
        }  
    }  
  
    private Object tryFindValueWhenExpressionIsNotNull(String expr) throws OgnlException {  
        if (expr == null) {  
            return null;  
        }  
        return tryFindValue(expr);  
    }  
  
    private Object handleOtherException(String expr, boolean throwExceptionOnFailure, Exception e) {  
        logLookupFailure(expr, e);  
  
        if (throwExceptionOnFailure)  
            throw new XWorkException(e);  
  
        return findInContext(expr);  
    }  
  
    private Object tryFindValue(String expr) throws OgnlException {  
        Object value;  
        expr = lookupForOverrides(expr);  
        if (defaultType != null) {  
            value = findValue(expr, defaultType);  
        } else {  
            value = getValueUsingOgnl(expr);  
            if (value == null) {  
                value = findInContext(expr);  
            }  
        }  
        return value;  
    }  
  
    private String lookupForOverrides(String expr) {  
        if ((overrides != null) && overrides.containsKey(expr)) {  
            expr = (String) overrides.get(expr);  
        }  
        return expr;  
    }  
  
    private Object getValueUsingOgnl(String expr) throws OgnlException {  
        try {  
            return ognlUtil.getValue(expr, context, root);  
        } finally {  
            context.remove(THROW_EXCEPTION_ON_FAILURE);  
        }  
    }  
  
    public Object findValue(String expr) {  
        return findValue(expr, false);  
    }  
  
    /** 
     * @see com.opensymphony.xwork2.util.ValueStack#findValue(java.lang.String, java.lang.Class) 
     */  
    public Object findValue(String expr, Class asType, boolean throwExceptionOnFailure) {  
        try {  
            setupExceptionOnFailure(throwExceptionOnFailure);  
            return tryFindValueWhenExpressionIsNotNull(expr, asType);  
        } catch (OgnlException e) {  
            return handleOgnlException(expr, throwExceptionOnFailure, e);  
        } catch (Exception e) {  
            return handleOtherException(expr, throwExceptionOnFailure, e);  
        } finally {  
            ReflectionContextState.clear(context);  
        }  
    }  
  
    private Object tryFindValueWhenExpressionIsNotNull(String expr, Class asType) throws OgnlException {  
        if (expr == null) {  
            return null;  
        }  
        return tryFindValue(expr, asType);  
    }  
  
    private Object handleOgnlException(String expr, boolean throwExceptionOnFailure, OgnlException e) {  
        Object ret = findInContext(expr);  
        if (ret == null) {  
            if (shouldLogNoSuchPropertyWarning(e)) {  
                LOG.warn("Could not find property [" + ((NoSuchPropertyException) e).getName() + "]");  
            }  
            if (throwExceptionOnFailure) {  
                throw new XWorkException(e);  
            }  
        }  
        return ret;  
    }  
  
    private boolean shouldLogNoSuchPropertyWarning(OgnlException e) {  
        return e instanceof NoSuchPropertyException && devMode && logMissingProperties;  
    }  
  
    private Object tryFindValue(String expr, Class asType) throws OgnlException {  
        Object value = null;  
        try {  
            expr = lookupForOverrides(expr);  
            value = getValue(expr, asType);  
            if (value == null) {  
                value = findInContext(expr);  
            }  
        } finally {  
            context.remove(THROW_EXCEPTION_ON_FAILURE);  
        }  
        return value;  
    }  
  
    private Object getValue(String expr, Class asType) throws OgnlException {  
        return ognlUtil.getValue(expr, context, root, asType);  
    }  
  
    private Object findInContext(String name) {  
        return getContext().get(name);  
    }  
  
    public Object findValue(String expr, Class asType) {  
        return findValue(expr, asType, false);  
    }  
  
    /** 
     * Log a failed lookup, being more verbose when devMode=true. 
     * 
     * @param expr The failed expression 
     * @param e    The thrown exception. 
     */  
    private void logLookupFailure(String expr, Exception e) {  
        String msg = LoggerUtils.format("Caught an exception while evaluating expression '#0' against value stack", expr);  
        if (devMode && LOG.isWarnEnabled()) {  
            LOG.warn(msg, e);  
            LOG.warn("NOTE: Previous warning message was issued due to devMode set to true.");  
        } else if (LOG.isDebugEnabled()) {  
            LOG.debug(msg, e);  
        }  
    }  
  
    /** 
     * @see com.opensymphony.xwork2.util.ValueStack#peek() 
     */  
    public Object peek() {  
        return root.peek();  
    }  
  
    /** 
     * @see com.opensymphony.xwork2.util.ValueStack#pop() 
     */  
    public Object pop() {  
        return root.pop();  
    }  
  
    /** 
     * @see com.opensymphony.xwork2.util.ValueStack#push(java.lang.Object) 
     */  
    public void push(Object o) {  
        root.push(o);  
    }  
  
    /** 
     * @see com.opensymphony.xwork2.util.ValueStack#set(java.lang.String, java.lang.Object) 
     */  
    public void set(String key, Object o) {  
        //set basically is backed by a Map pushed on the stack with a key being put on the map and the Object being the value  
        Map setMap = retrieveSetMap();  
        setMap.put(key, o);  
    }  
  
    private Map retrieveSetMap() {  
        Map setMap;  
        Object topObj = peek();  
        if (shouldUseOldMap(topObj)) {  
            setMap = (Map) topObj;  
        } else {  
            setMap = new HashMap();  
            setMap.put(MAP_IDENTIFIER_KEY, "");  
            push(setMap);  
        }  
        return setMap;  
    }  
  
    /** 
     * check if this is a Map put on the stack  for setting if so just use the old map (reduces waste) 
     */  
    private boolean shouldUseOldMap(Object topObj) {  
        return topObj instanceof Map && ((Map) topObj).get(MAP_IDENTIFIER_KEY) != null;  
    }  
  
    /** 
     * @see com.opensymphony.xwork2.util.ValueStack#size() 
     */  
    public int size() {  
        return root.size();  
    }  
  
    private Object readResolve() {  
        // TODO: this should be done better  
        ActionContext ac = ActionContext.getContext();  
        Container cont = ac.getContainer();  
        XWorkConverter xworkConverter = cont.getInstance(XWorkConverter.class);  
        CompoundRootAccessor accessor = (CompoundRootAccessor) cont.getInstance(PropertyAccessor.class, CompoundRoot.class.getName());  
        TextProvider prov = cont.getInstance(TextProvider.class, "system");  
        boolean allow = "true".equals(cont.getInstance(String.class, "allowStaticMethodAccess"));  
        OgnlValueStack aStack = new OgnlValueStack(xworkConverter, accessor, prov, allow);  
        aStack.setOgnlUtil(cont.getInstance(OgnlUtil.class));  
        aStack.setRoot(xworkConverter, accessor, this.root, allow);  
  
        return aStack;  
    }  
  
  
    public void clearContextValues() {  
        //this is an OGNL ValueStack so the context will be an OgnlContext  
        //it would be better to make context of type OgnlContext  
        ((OgnlContext) context).getValues().clear();  
    }  
  
    public void setAcceptProperties(Set<Pattern> acceptedProperties) {  
        securityMemberAccess.setAcceptProperties(acceptedProperties);  
    }  
  
    public void setPropertiesJudge(PropertiesJudge judge) {  
        securityMemberAccess.setPropertiesJudge(judge);  
    }  
  
    public void setExcludeProperties(Set<Pattern> excludeProperties) {  
        securityMemberAccess.setExcludeProperties(excludeProperties);  
    }  
  
}  

OGNLValueStack分为两部分，分别是Map形式的OGNLContext和ArrayList形式的CompoundRoot

其中CompoundRoot为根元素（Struts2中为当前Action）,直接访问路径

 1 public UserAction extends ActionSupport{
 2     private String name;
 3     private int age;
 4     private Adress adress;
 5 
 6     public String excute(){
 7         //.....其他代码
 8         return SUCCESS;
 9     }
10     public void setName(String name){
11         this.name=name;
12     }
13     public void setAge(int age){
14         this.age=age;
15     }
16     public void setAdress(Adress adress){
17         this.adress=adress;
18     }
19     public String getName(){
20         return name;
21     }
22     public String getAge(){
23         return age;
24     }public String geAdress(){
25         return adress;
26     }
　　　　class Adress{
         private String phone;
         private String adressName;
         public void setPhone(String phone){
             this.phone=phone;
         }
         public void setAdressName(String adressName){
             this.adressName=adressName;
         }
         public String getPhone(){

             return phone;
         }

        public String getAdressName(){

             return AdressName;
         }
      }
27 }

 

ValueStack valueStack=ActionContext.getContext().getValueStack()；

存入值

valueStack.setValue("name","amy");

valueStack.setValue("age",24);

Adress adress=new Adress();

valueStack.setValue("adress","adress");

valueStack.setValue("adress.phone","123645789");

valueStack.setValue("adress.adressName,"**********");取值

valueStack.findValue("name");

valueStack.findValue("age");

valueStack.findValue("adress");

valueStack.findValue("adress.phone");

valueStack.findValue("adress.adressName");

 

OGNLContext部分，访问路径前加#

（Map）valueStack.findValue("#request");

（Map）valueStack.findValue("#session");

（Map）valueStack.findValue("#application");

（Map）valueStack.findValue("#parameters");

四 , ActionContext和OGNLValueStack的关系