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Struts（九）：值栈（OGNL）

引言

在我们开发过程中，往往会使用一个对像传递到一个具体的action中，之后到跳转页面中访问对应对象的具体的参数。

比如：我们搭建一个struts2项目：

回顾下如何搭建strut2：

1、下载的struts2开发包（struts-2.3.31-all.zip）；

2、解压struts-2.3.31-all.zip,并把appsstruts2-blank.war解压；

3、取出struts2-blankWEB-INFlib下的所有jar包到Struts_01WebContentWEB-INFlib下；

4、struts2-blankWEB-INFsrcjava下的struts.xml、log4j2.xml、velocity.properties拷贝到Struts_01WebContentsrc；

5、拷贝struts2-blankWEB-INFweb.xml到Struts_01WebContentWEB-INFweb.xml下；

6、创建包com.dx.struts2.valuestack，并在包下创建Product.java。

package com.dx.struts2.valuestack;

public class Product {
    private Integer productId;
    private String productName;
    private String productDesc;
    private Double productPrice;
    
    public Integer getProductId() {
        return productId;
    }
    public void setProductId(Integer productId) {
        this.productId = productId;
    }
    public String getProductName() {
        return productName;
    }
    public void setProductName(String productName) {
        this.productName = productName;
    }
    public String getProductDesc() {
        return productDesc;
    }
    public void setProductDesc(String productDesc) {
        this.productDesc = productDesc;
    }
    public Double getProductPrice() {
        return productPrice;
    }
    public void setProductPrice(Double productPrice) {
        this.productPrice = productPrice;
    }
    
    public String save(){
        System.out.println("save");
        return "success";
    }
}

View Code

7、修改web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app id="WebApp_9" version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">

    <display-name>Struts 01</display-name>

    <filter>
        <filter-name>struts2</filter-name>
        <filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter</filter-class>
    </filter>

    <filter-mapping>
        <filter-name>struts2</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

    <welcome-file-list>
        <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>

    <!-- Restricts access to pure JSP files - access available only via Struts 
        action <security-constraint> <display-name>No direct JSP access</display-name> 
        <web-resource-collection> <web-resource-name>No-JSP</web-resource-name> <url-pattern>*.jsp</url-pattern> 
        </web-resource-collection> <auth-constraint> <role-name>no-users</role-name> 
        </auth-constraint> </security-constraint> <security-role> <description>Don't 
        assign users to this role</description> <role-name>no-users</role-name> </security-role> -->
</web-app>

View Code

8、修改struts.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE struts PUBLIC
    "-//Apache Software Foundation//DTD Struts Configuration 2.3//EN"
    "http://struts.apache.org/dtds/struts-2.3.dtd">

<struts>
    <!-- <constant name="struts.action.extension" value="action" /> -->
    <constant name="struts.enable.DynamicMethodInvocation" value="false" />
    <constant name="struts.devMode" value="false" />

    <package name="default" namespace="/" extends="struts-default">
        <action name="product-save" class="com.dx.struts2.valuestack.Product"
            method="save">
            <result>/details.jsp</result>
        </action>
    </package>

    <!-- Add packages here -->

</struts>

View Code

9、添加页面index.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ taglib prefix="s" uri="/struts-tags"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    <s:form action="product-save">
        product name: 
        <input name="productName" />
        <br />
        product description: 
        <input name="productDesc" />
        <br />
        product price: 
        <input name="productPrice" />
        <br />
        <s:submit name="method:save.do" value="提交"></s:submit>
    </s:form>
</body>
</html>

10、添加details.jsp页面

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
${productName}<br/>
request.getAttribute("productName"):<%=request.getAttribute("productName") %><br/>
${productDesc}<br/>
${productPrice}<br/>

<%=request %>
</body>
</html>

运行发现request对象不是HttpRequestWrapper。

跟踪调试：

从“引言”的代码运行结果中发现request是org.apache.struts2.dispatcher.StrutsRequestWrapper类型。那就说明一个问题，这里边的${productName}和<%=request.getAttribute("productName")%>都是通过调用StrutsRequestWrapper(Ctrl+T会弹出窗口，输入StrutsRequestWrapper会自动索引到源代码)的getAttribute(String key)函数：

/**
     * Gets the object, looking in the value stack if not found
     *
     * @param key The attribute key
     */
    public Object getAttribute(String key) {
        if (key == null) {
            throw new NullPointerException("You must specify a key value");
        }

        if (disableRequestAttributeValueStackLookup || key.startsWith("javax.servlet")) {
            // don't bother with the standard javax.servlet attributes, we can short-circuit this
            // see WW-953 and the forums post linked in that issue for more info
            return super.getAttribute(key);
        }

        ActionContext ctx = ActionContext.getContext();
        Object attribute = super.getAttribute(key); //supper->HttpRequestWrapper

        if (ctx != null && attribute == null) {
            boolean alreadyIn = isTrue((Boolean) ctx.get(REQUEST_WRAPPER_GET_ATTRIBUTE));

            // note: we don't let # come through or else a request for
            // #attr.foo or #request.foo could cause an endless loop
            if (!alreadyIn && !key.contains("#")) {
                try {
                    // If not found, then try the ValueStack
                    ctx.put(REQUEST_WRAPPER_GET_ATTRIBUTE, Boolean.TRUE);
                    ValueStack stack = ctx.getValueStack();
                    if (stack != null) {
                        attribute = stack.findValue(key);
                    }
                } finally {
                    ctx.put(REQUEST_WRAPPER_GET_ATTRIBUTE, Boolean.FALSE);
                }
            }
        }
        return attribute;
    }

如果debug的话，可以从代码跟踪中找到上边的Product对象的参数是存储到哪里。

付截图：

从上边截图中我们发现Product对象是存储到ValueStack（值栈）中,而并不是在请求域中真的存在这样的一个值。

查看ActionContext源码，发现里边存储了Application/Seesion/Parameter等。

  1 /*
  2  * Copyright 2002-2006,2009 The Apache Software Foundation.
  3  * 
  4  * Licensed under the Apache License, Version 2.0 (the "License");
  5  * you may not use this file except in compliance with the License.
  6  * You may obtain a copy of the License at
  7  * 
  8  *      http://www.apache.org/licenses/LICENSE-2.0
  9  * 
 10  * Unless required by applicable law or agreed to in writing, software
 11  * distributed under the License is distributed on an "AS IS" BASIS,
 12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 13  * See the License for the specific language governing permissions and
 14  * limitations under the License.
 15  */
 16 package com.opensymphony.xwork2;
 17 
 18 import com.opensymphony.xwork2.inject.Container;
 19 import com.opensymphony.xwork2.util.ValueStack;
 20 
 21 import java.io.Serializable;
 22 import java.util.HashMap;
 23 import java.util.Locale;
 24 import java.util.Map;
 25 
 26 
 27 /**
 28  * The ActionContext is the context in which an {@link Action} is executed. Each context is basically a
 29  * container of objects an action needs for execution like the session, parameters, locale, etc. <p>
 30  * <p/>
 31  * The ActionContext is thread local which means that values stored in the ActionContext are
 32  * unique per thread. See the {@link ThreadLocal} class for more information. The benefit of
 33  * this is you don't need to worry about a user specific action context, you just get it:
 34  * <p/>
 35  * <ul><code>ActionContext context = ActionContext.getContext();</code></ul>
 36  * <p/>
 37  * Finally, because of the thread local usage you don't need to worry about making your actions thread safe.
 38  *
 39  * @author Patrick Lightbody
 40  * @author Bill Lynch (docs)
 41  */
 42 public class ActionContext implements Serializable {
 43 
 44     static ThreadLocal<ActionContext> actionContext = new ThreadLocal<ActionContext>();
 45 
 46     /**
 47      * Constant for the name of the action being executed.
 48      */
 49     public static final String ACTION_NAME = "com.opensymphony.xwork2.ActionContext.name";
 50 
 51     /**
 52      * Constant for the {@link com.opensymphony.xwork2.util.ValueStack OGNL value stack}.
 53      */
 54     public static final String VALUE_STACK = ValueStack.VALUE_STACK;
 55 
 56     /**
 57      * Constant for the action's session.
 58      */
 59     public static final String SESSION = "com.opensymphony.xwork2.ActionContext.session";
 60 
 61     /**
 62      * Constant for the action's application context.
 63      */
 64     public static final String APPLICATION = "com.opensymphony.xwork2.ActionContext.application";
 65 
 66     /**
 67      * Constant for the action's parameters.
 68      */
 69     public static final String PARAMETERS = "com.opensymphony.xwork2.ActionContext.parameters";
 70 
 71     /**
 72      * Constant for the action's locale.
 73      */
 74     public static final String LOCALE = "com.opensymphony.xwork2.ActionContext.locale";
 75 
 76     /**
 77      * Constant for the action's type converter.
 78      */
 79     public static final String TYPE_CONVERTER = "com.opensymphony.xwork2.ActionContext.typeConverter";
 80 
 81     /**
 82      * Constant for the action's {@link com.opensymphony.xwork2.ActionInvocation invocation} context.
 83      */
 84     public static final String ACTION_INVOCATION = "com.opensymphony.xwork2.ActionContext.actionInvocation";
 85 
 86     /**
 87      * Constant for the map of type conversion errors.
 88      */
 89     public static final String CONVERSION_ERRORS = "com.opensymphony.xwork2.ActionContext.conversionErrors";
 90 
 91 
 92     /**
 93      * Constant for the container
 94      */
 95     public static final String CONTAINER = "com.opensymphony.xwork2.ActionContext.container";
 96     
 97     private Map<String, Object> context;
 98 
 99     /**
100      * Creates a new ActionContext initialized with another context.
101      *
102      * @param context a context map.
103      */
104     public ActionContext(Map<String, Object> context) {
105         this.context = context;
106     }
107 
108 
109     /**
110      * Sets the action invocation (the execution state).
111      *
112      * @param actionInvocation the action execution state.
113      */
114     public void setActionInvocation(ActionInvocation actionInvocation) {
115         put(ACTION_INVOCATION, actionInvocation);
116     }
117 
118     /**
119      * Gets the action invocation (the execution state).
120      *
121      * @return the action invocation (the execution state).
122      */
123     public ActionInvocation getActionInvocation() {
124         return (ActionInvocation) get(ACTION_INVOCATION);
125     }
126 
127     /**
128      * Sets the action's application context.
129      *
130      * @param application the action's application context.
131      */
132     public void setApplication(Map<String, Object> application) {
133         put(APPLICATION, application);
134     }
135 
136     /**
137      * Returns a Map of the ServletContext when in a servlet environment or a generic application level Map otherwise.
138      *
139      * @return a Map of ServletContext or generic application level Map
140      */
141     public Map<String, Object> getApplication() {
142         return (Map<String, Object>) get(APPLICATION);
143     }
144 
145     /**
146      * Sets the action context for the current thread.
147      *
148      * @param context the action context.
149      */
150     public static void setContext(ActionContext context) {
151         actionContext.set(context);
152     }
153 
154     /**
155      * Returns the ActionContext specific to the current thread.
156      *
157      * @return the ActionContext for the current thread, is never <tt>null</tt>.
158      */
159     public static ActionContext getContext() {
160         return actionContext.get();
161     }
162 
163     /**
164      * Sets the action's context map.
165      *
166      * @param contextMap the context map.
167      */
168     public void setContextMap(Map<String, Object> contextMap) {
169         getContext().context = contextMap;
170     }
171 
172     /**
173      * Gets the context map.
174      *
175      * @return the context map.
176      */
177     public Map<String, Object> getContextMap() {
178         return context;
179     }
180 
181     /**
182      * Sets conversion errors which occurred when executing the action.
183      *
184      * @param conversionErrors a Map of errors which occurred when executing the action.
185      */
186     public void setConversionErrors(Map<String, Object> conversionErrors) {
187         put(CONVERSION_ERRORS, conversionErrors);
188     }
189 
190     /**
191      * Gets the map of conversion errors which occurred when executing the action.
192      *
193      * @return the map of conversion errors which occurred when executing the action or an empty map if
194      *         there were no errors.
195      */
196     public Map<String, Object> getConversionErrors() {
197         Map<String, Object> errors = (Map) get(CONVERSION_ERRORS);
198 
199         if (errors == null) {
200             errors = new HashMap<String, Object>();
201             setConversionErrors(errors);
202         }
203 
204         return errors;
205     }
206 
207     /**
208      * Sets the Locale for the current action.
209      *
210      * @param locale the Locale for the current action.
211      */
212     public void setLocale(Locale locale) {
213         put(LOCALE, locale);
214     }
215 
216     /**
217      * Gets the Locale of the current action. If no locale was ever specified the platform's
218      * {@link java.util.Locale#getDefault() default locale} is used.
219      *
220      * @return the Locale of the current action.
221      */
222     public Locale getLocale() {
223         Locale locale = (Locale) get(LOCALE);
224 
225         if (locale == null) {
226             locale = Locale.getDefault();
227             setLocale(locale);
228         }
229 
230         return locale;
231     }
232 
233     /**
234      * Sets the name of the current Action in the ActionContext.
235      *
236      * @param name the name of the current action.
237      */
238     public void setName(String name) {
239         put(ACTION_NAME, name);
240     }
241 
242     /**
243      * Gets the name of the current Action.
244      *
245      * @return the name of the current action.
246      */
247     public String getName() {
248         return (String) get(ACTION_NAME);
249     }
250 
251     /**
252      * Sets the action parameters.
253      *
254      * @param parameters the parameters for the current action.
255      */
256     public void setParameters(Map<String, Object> parameters) {
257         put(PARAMETERS, parameters);
258     }
259 
260     /**
261      * Returns a Map of the HttpServletRequest parameters when in a servlet environment or a generic Map of
262      * parameters otherwise.
263      *
264      * @return a Map of HttpServletRequest parameters or a multipart map when in a servlet environment, or a
265      *         generic Map of parameters otherwise.
266      */
267     public Map<String, Object> getParameters() {
268         return (Map<String, Object>) get(PARAMETERS);
269     }
270 
271     /**
272      * Sets a map of action session values.
273      *
274      * @param session  the session values.
275      */
276     public void setSession(Map<String, Object> session) {
277         put(SESSION, session);
278     }
279 
280     /**
281      * Gets the Map of HttpSession values when in a servlet environment or a generic session map otherwise.
282      *
283      * @return the Map of HttpSession values when in a servlet environment or a generic session map otherwise.
284      */
285     public Map<String, Object> getSession() {
286         return (Map<String, Object>) get(SESSION);
287     }
288 
289     /**
290      * Sets the OGNL value stack.
291      *
292      * @param stack the OGNL value stack.
293      */
294     public void setValueStack(ValueStack stack) {
295         put(VALUE_STACK, stack);
296     }
297 
298     /**
299      * Gets the OGNL value stack.
300      *
301      * @return the OGNL value stack.
302      */
303     public ValueStack getValueStack() {
304         return (ValueStack) get(VALUE_STACK);
305     }
306     
307     /**
308      * Gets the container for this request
309      * 
310      * @param cont The container
311      */
312     public void setContainer(Container cont) {
313         put(CONTAINER, cont);
314     }
315     
316     /**
317      * Sets the container for this request
318      * 
319      * @return The container
320      */
321     public Container getContainer() {
322         return (Container) get(CONTAINER);
323     }
324     
325     public <T> T getInstance(Class<T> type) {
326         Container cont = getContainer();
327         if (cont != null) {
328             return cont.getInstance(type);
329         } else {
330             throw new XWorkException("Cannot find an initialized container for this request.");
331         }
332     }
333 
334     /**
335      * Returns a value that is stored in the current ActionContext by doing a lookup using the value's key.
336      *
337      * @param key the key used to find the value.
338      * @return the value that was found using the key or <tt>null</tt> if the key was not found.
339      */
340     public Object get(String key) {
341         return context.get(key);
342     }
343 
344     /**
345      * Stores a value in the current ActionContext. The value can be looked up using the key.
346      *
347      * @param key   the key of the value.
348      * @param value the value to be stored.
349      */
350     public void put(String key, Object value) {
351         context.put(key, value);
352     }
353 }

View Code

继续调试，我来看下是ValueStack是怎么存储数据的。

我们发现ValueStack是：com.opensymphony.xwork2.ognl.OgnlValueStack，

  1 /*
  2  * Copyright 2002-2006,2009 The Apache Software Foundation.
  3  * 
  4  * Licensed under the Apache License, Version 2.0 (the "License");
  5  * you may not use this file except in compliance with the License.
  6  * You may obtain a copy of the License at
  7  * 
  8  *      http://www.apache.org/licenses/LICENSE-2.0
  9  * 
 10  * Unless required by applicable law or agreed to in writing, software
 11  * distributed under the License is distributed on an "AS IS" BASIS,
 12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 13  * See the License for the specific language governing permissions and
 14  * limitations under the License.
 15  */
 16 package com.opensymphony.xwork2.ognl;
 17 
 18 import com.opensymphony.xwork2.ActionContext;
 19 import com.opensymphony.xwork2.TextProvider;
 20 import com.opensymphony.xwork2.XWorkConstants;
 21 import com.opensymphony.xwork2.XWorkException;
 22 import com.opensymphony.xwork2.conversion.impl.XWorkConverter;
 23 import com.opensymphony.xwork2.inject.Container;
 24 import com.opensymphony.xwork2.inject.Inject;
 25 import com.opensymphony.xwork2.ognl.accessor.CompoundRootAccessor;
 26 import com.opensymphony.xwork2.util.ClearableValueStack;
 27 import com.opensymphony.xwork2.util.CompoundRoot;
 28 import com.opensymphony.xwork2.util.MemberAccessValueStack;
 29 import com.opensymphony.xwork2.util.ValueStack;
 30 import com.opensymphony.xwork2.util.logging.Logger;
 31 import com.opensymphony.xwork2.util.logging.LoggerFactory;
 32 import com.opensymphony.xwork2.util.logging.LoggerUtils;
 33 import com.opensymphony.xwork2.util.reflection.ReflectionContextState;
 34 import ognl.*;
 35 
 36 import java.io.Serializable;
 37 import java.util.HashMap;
 38 import java.util.Map;
 39 import java.util.Set;
 40 import java.util.regex.Pattern;
 41 
 42 /**
 43  * Ognl implementation of a value stack that allows for dynamic Ognl expressions to be evaluated against it. When evaluating an expression,
 44  * the stack will be searched down the stack, from the latest objects pushed in to the earliest, looking for a bean with a getter or setter
 45  * for the given property or a method of the given name (depending on the expression being evaluated).
 46  *
 47  * @author Patrick Lightbody
 48  * @author tm_jee
 49  * @version $Date$ $Id$
 50  */
 51 public class OgnlValueStack implements Serializable, ValueStack, ClearableValueStack, MemberAccessValueStack {
 52 
 53     public static final String THROW_EXCEPTION_ON_FAILURE = OgnlValueStack.class.getName() + ".throwExceptionOnFailure";
 54 
 55     private static final long serialVersionUID = 370737852934925530L;
 56 
 57     private static final String MAP_IDENTIFIER_KEY = "com.opensymphony.xwork2.util.OgnlValueStack.MAP_IDENTIFIER_KEY";
 58     private static final Logger LOG = LoggerFactory.getLogger(OgnlValueStack.class);
 59 
 60     CompoundRoot root;
 61     transient Map<String, Object> context;
 62     Class defaultType;
 63     Map<Object, Object> overrides;
 64     transient OgnlUtil ognlUtil;
 65     transient SecurityMemberAccess securityMemberAccess;
 66     private transient XWorkConverter converter;
 67 
 68     private boolean devMode;
 69     private boolean logMissingProperties;
 70 
 71     protected OgnlValueStack(XWorkConverter xworkConverter, CompoundRootAccessor accessor, TextProvider prov, boolean allowStaticAccess) {
 72         setRoot(xworkConverter, accessor, new CompoundRoot(), allowStaticAccess);
 73         push(prov);
 74     }
 75 
 76     protected OgnlValueStack(ValueStack vs, XWorkConverter xworkConverter, CompoundRootAccessor accessor, boolean allowStaticAccess) {
 77         setRoot(xworkConverter, accessor, new CompoundRoot(vs.getRoot()), allowStaticAccess);
 78     }
 79 
 80     @Inject
 81     public void setOgnlUtil(OgnlUtil ognlUtil) {
 82         this.ognlUtil = ognlUtil;
 83         securityMemberAccess.setExcludedClasses(ognlUtil.getExcludedClasses());
 84         securityMemberAccess.setExcludedPackageNamePatterns(ognlUtil.getExcludedPackageNamePatterns());
 85         securityMemberAccess.setExcludedPackageNames(ognlUtil.getExcludedPackageNames());
 86     }
 87 
 88     protected void setRoot(XWorkConverter xworkConverter, CompoundRootAccessor accessor, CompoundRoot compoundRoot,
 89                            boolean allowStaticMethodAccess) {
 90         this.root = compoundRoot;
 91         this.securityMemberAccess = new SecurityMemberAccess(allowStaticMethodAccess);
 92         this.context = Ognl.createDefaultContext(this.root, accessor, new OgnlTypeConverterWrapper(xworkConverter), securityMemberAccess);
 93         context.put(VALUE_STACK, this);
 94         Ognl.setClassResolver(context, accessor);
 95         ((OgnlContext) context).setTraceEvaluations(false);
 96         ((OgnlContext) context).setKeepLastEvaluation(false);
 97     }
 98 
 99     @Inject(XWorkConstants.DEV_MODE)
100     public void setDevMode(String mode) {
101         devMode = "true".equalsIgnoreCase(mode);
102     }
103 
104     @Inject(value = "logMissingProperties", required = false)
105     public void setLogMissingProperties(String logMissingProperties) {
106         this.logMissingProperties = "true".equalsIgnoreCase(logMissingProperties);
107     }
108 
109     /**
110      * @see com.opensymphony.xwork2.util.ValueStack#getContext()
111      */
112     public Map<String, Object> getContext() {
113         return context;
114     }
115 
116     /**
117      * @see com.opensymphony.xwork2.util.ValueStack#setDefaultType(java.lang.Class)
118      */
119     public void setDefaultType(Class defaultType) {
120         this.defaultType = defaultType;
121     }
122 
123     /**
124      * @see com.opensymphony.xwork2.util.ValueStack#setExprOverrides(java.util.Map)
125      */
126     public void setExprOverrides(Map<Object, Object> overrides) {
127         if (this.overrides == null) {
128             this.overrides = overrides;
129         } else {
130             this.overrides.putAll(overrides);
131         }
132     }
133 
134     /**
135      * @see com.opensymphony.xwork2.util.ValueStack#getExprOverrides()
136      */
137     public Map<Object, Object> getExprOverrides() {
138         return this.overrides;
139     }
140 
141     /**
142      * @see com.opensymphony.xwork2.util.ValueStack#getRoot()
143      */
144     public CompoundRoot getRoot() {
145         return root;
146     }
147 
148     /**
149      * @see com.opensymphony.xwork2.util.ValueStack#setParameter(String, Object)
150      */
151     public void setParameter(String expr, Object value) {
152         setValue(expr, value, devMode);
153     }
154 
155     /**
156 
157     /**
158      * @see com.opensymphony.xwork2.util.ValueStack#setValue(java.lang.String, java.lang.Object)
159      */
160     public void setValue(String expr, Object value) {
161         setValue(expr, value, devMode);
162     }
163 
164     /**
165      * @see com.opensymphony.xwork2.util.ValueStack#setValue(java.lang.String, java.lang.Object, boolean)
166      */
167     public void setValue(String expr, Object value, boolean throwExceptionOnFailure) {
168         Map<String, Object> context = getContext();
169         try {
170             trySetValue(expr, value, throwExceptionOnFailure, context);
171         } catch (OgnlException e) {
172             handleOgnlException(expr, value, throwExceptionOnFailure, e);
173         } catch (RuntimeException re) { //XW-281
174             handleRuntimeException(expr, value, throwExceptionOnFailure, re);
175         } finally {
176             cleanUpContext(context);
177         }
178     }
179 
180     private void trySetValue(String expr, Object value, boolean throwExceptionOnFailure, Map<String, Object> context) throws OgnlException {
181         context.put(XWorkConverter.CONVERSION_PROPERTY_FULLNAME, expr);
182         context.put(REPORT_ERRORS_ON_NO_PROP, (throwExceptionOnFailure) ? Boolean.TRUE : Boolean.FALSE);
183         ognlUtil.setValue(expr, context, root, value);
184     }
185 
186     private void cleanUpContext(Map<String, Object> context) {
187         ReflectionContextState.clear(context);
188         context.remove(XWorkConverter.CONVERSION_PROPERTY_FULLNAME);
189         context.remove(REPORT_ERRORS_ON_NO_PROP);
190     }
191 
192     private void handleRuntimeException(String expr, Object value, boolean throwExceptionOnFailure, RuntimeException re) {
193         if (throwExceptionOnFailure) {
194             String message = ErrorMessageBuilder.create()
195                     .errorSettingExpressionWithValue(expr, value)
196                     .build();
197             throw new XWorkException(message, re);
198         } else {
199             if (LOG.isWarnEnabled()) {
200                 LOG.warn("Error setting value [#0] with expression [#1]", re, value.toString(), expr);
201             }
202         }
203     }
204 
205     private void handleOgnlException(String expr, Object value, boolean throwExceptionOnFailure, OgnlException e) {
206         boolean shouldLog = shouldLogMissingPropertyWarning(e);
207         String msg = null;
208         if (throwExceptionOnFailure || shouldLog) {
209             msg = ErrorMessageBuilder.create()
210                     .errorSettingExpressionWithValue(expr, value)
211                     .build();
212         }
213         if (shouldLog) {
214             LOG.warn(msg, e);
215         }
216         
217         if (throwExceptionOnFailure) {
218             throw new XWorkException(msg, e);
219         }
220     }
221 
222     /**
223      * @see com.opensymphony.xwork2.util.ValueStack#findString(java.lang.String)
224      */
225     public String findString(String expr) {
226         return (String) findValue(expr, String.class);
227     }
228 
229     public String findString(String expr, boolean throwExceptionOnFailure) {
230         return (String) findValue(expr, String.class, throwExceptionOnFailure);
231     }
232 
233     /**
234      * @see com.opensymphony.xwork2.util.ValueStack#findValue(java.lang.String)
235      */
236     public Object findValue(String expr, boolean throwExceptionOnFailure) {
237         try {
238             setupExceptionOnFailure(throwExceptionOnFailure);
239             return tryFindValueWhenExpressionIsNotNull(expr);
240         } catch (OgnlException e) {
241             return handleOgnlException(expr, throwExceptionOnFailure, e);
242         } catch (Exception e) {
243             return handleOtherException(expr, throwExceptionOnFailure, e);
244         } finally {
245             ReflectionContextState.clear(context);
246         }
247     }
248 
249     private void setupExceptionOnFailure(boolean throwExceptionOnFailure) {
250         if (throwExceptionOnFailure) {
251             context.put(THROW_EXCEPTION_ON_FAILURE, true);
252         }
253     }
254 
255     private Object tryFindValueWhenExpressionIsNotNull(String expr) throws OgnlException {
256         if (expr == null) {
257             return null;
258         }
259         return tryFindValue(expr);
260     }
261 
262     private Object handleOtherException(String expr, boolean throwExceptionOnFailure, Exception e) {
263         logLookupFailure(expr, e);
264 
265         if (throwExceptionOnFailure)
266             throw new XWorkException(e);
267 
268         return findInContext(expr);
269     }
270 
271     private Object tryFindValue(String expr) throws OgnlException {
272         Object value;
273         expr = lookupForOverrides(expr);
274         if (defaultType != null) {
275             value = findValue(expr, defaultType);
276         } else {
277             value = getValueUsingOgnl(expr);
278             if (value == null) {
279                 value = findInContext(expr);
280             }
281         }
282         return value;
283     }
284 
285     private String lookupForOverrides(String expr) {
286         if ((overrides != null) && overrides.containsKey(expr)) {
287             expr = (String) overrides.get(expr);
288         }
289         return expr;
290     }
291 
292     private Object getValueUsingOgnl(String expr) throws OgnlException {
293         try {
294             return ognlUtil.getValue(expr, context, root);
295         } finally {
296             context.remove(THROW_EXCEPTION_ON_FAILURE);
297         }
298     }
299 
300     public Object findValue(String expr) {
301         return findValue(expr, false);
302     }
303 
304     /**
305      * @see com.opensymphony.xwork2.util.ValueStack#findValue(java.lang.String, java.lang.Class)
306      */
307     public Object findValue(String expr, Class asType, boolean throwExceptionOnFailure) {
308         try {
309             setupExceptionOnFailure(throwExceptionOnFailure);
310             return tryFindValueWhenExpressionIsNotNull(expr, asType);
311         } catch (OgnlException e) {
312             final Object value = handleOgnlException(expr, throwExceptionOnFailure, e);
313             return converter.convertValue(getContext(), value, asType);
314         } catch (Exception e) {
315             final Object value = handleOtherException(expr, throwExceptionOnFailure, e);
316             return converter.convertValue(getContext(), value, asType);
317         } finally {
318             ReflectionContextState.clear(context);
319         }
320     }
321 
322     private Object tryFindValueWhenExpressionIsNotNull(String expr, Class asType) throws OgnlException {
323         if (expr == null) {
324             return null;
325         }
326         return tryFindValue(expr, asType);
327     }
328 
329     private Object handleOgnlException(String expr, boolean throwExceptionOnFailure, OgnlException e) {
330         Object ret = findInContext(expr);
331         if (ret == null) {
332             if (shouldLogMissingPropertyWarning(e)) {
333                 LOG.warn("Could not find property [#0]!", e, expr);
334             }
335             if (throwExceptionOnFailure) {
336                 throw new XWorkException(e);
337             }
338         }
339         return ret;
340     }
341 
342     private boolean shouldLogMissingPropertyWarning(OgnlException e) {
343         return (e instanceof NoSuchPropertyException || e instanceof MethodFailedException)
344                 && devMode && logMissingProperties;
345     }
346 
347     private Object tryFindValue(String expr, Class asType) throws OgnlException {
348         Object value = null;
349         try {
350             expr = lookupForOverrides(expr);
351             value = getValue(expr, asType);
352             if (value == null) {
353                 value = findInContext(expr);
354                 return converter.convertValue(getContext(), value, asType);
355             }
356         } finally {
357             context.remove(THROW_EXCEPTION_ON_FAILURE);
358         }
359         return value;
360     }
361 
362     private Object getValue(String expr, Class asType) throws OgnlException {
363         return ognlUtil.getValue(expr, context, root, asType);
364     }
365 
366     private Object findInContext(String name) {
367         return getContext().get(name);
368     }
369 
370     public Object findValue(String expr, Class asType) {
371         return findValue(expr, asType, false);
372     }
373 
374     /**
375      * Log a failed lookup, being more verbose when devMode=true.
376      *
377      * @param expr The failed expression
378      * @param e    The thrown exception.
379      */
380     private void logLookupFailure(String expr, Exception e) {
381         String msg = LoggerUtils.format("Caught an exception while evaluating expression '#0' against value stack", expr);
382         if (devMode && LOG.isWarnEnabled()) {
383             LOG.warn(msg, e);
384             LOG.warn("NOTE: Previous warning message was issued due to devMode set to true.");
385         } else if (LOG.isDebugEnabled()) {
386             LOG.debug(msg, e);
387         }
388     }
389 
390     /**
391      * @see com.opensymphony.xwork2.util.ValueStack#peek()
392      */
393     public Object peek() {
394         return root.peek();
395     }
396 
397     /**
398      * @see com.opensymphony.xwork2.util.ValueStack#pop()
399      */
400     public Object pop() {
401         return root.pop();
402     }
403 
404     /**
405      * @see com.opensymphony.xwork2.util.ValueStack#push(java.lang.Object)
406      */
407     public void push(Object o) {
408         root.push(o);
409     }
410 
411     /**
412      * @see com.opensymphony.xwork2.util.ValueStack#set(java.lang.String, java.lang.Object)
413      */
414     public void set(String key, Object o) {
415         //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
416         Map setMap = retrieveSetMap();
417         setMap.put(key, o);
418     }
419 
420     private Map retrieveSetMap() {
421         Map setMap;
422         Object topObj = peek();
423         if (shouldUseOldMap(topObj)) {
424             setMap = (Map) topObj;
425         } else {
426             setMap = new HashMap();
427             setMap.put(MAP_IDENTIFIER_KEY, "");
428             push(setMap);
429         }
430         return setMap;
431     }
432 
433     /**
434      * check if this is a Map put on the stack  for setting if so just use the old map (reduces waste)
435      */
436     private boolean shouldUseOldMap(Object topObj) {
437         return topObj instanceof Map && ((Map) topObj).get(MAP_IDENTIFIER_KEY) != null;
438     }
439 
440     /**
441      * @see com.opensymphony.xwork2.util.ValueStack#size()
442      */
443     public int size() {
444         return root.size();
445     }
446 
447     private Object readResolve() {
448         // TODO: this should be done better
449         ActionContext ac = ActionContext.getContext();
450         Container cont = ac.getContainer();
451         XWorkConverter xworkConverter = cont.getInstance(XWorkConverter.class);
452         CompoundRootAccessor accessor = (CompoundRootAccessor) cont.getInstance(PropertyAccessor.class, CompoundRoot.class.getName());
453         TextProvider prov = cont.getInstance(TextProvider.class, "system");
454         boolean allow = "true".equals(cont.getInstance(String.class, XWorkConstants.ALLOW_STATIC_METHOD_ACCESS));
455         OgnlValueStack aStack = new OgnlValueStack(xworkConverter, accessor, prov, allow);
456         aStack.setOgnlUtil(cont.getInstance(OgnlUtil.class));
457         aStack.setRoot(xworkConverter, accessor, this.root, allow);
458 
459         return aStack;
460     }
461 
462 
463     public void clearContextValues() {
464         //this is an OGNL ValueStack so the context will be an OgnlContext
465         //it would be better to make context of type OgnlContext
466         ((OgnlContext) context).getValues().clear();
467     }
468 
469     public void setAcceptProperties(Set<Pattern> acceptedProperties) {
470         securityMemberAccess.setAcceptProperties(acceptedProperties);
471     }
472 
473     public void setExcludeProperties(Set<Pattern> excludeProperties) {
474         securityMemberAccess.setExcludeProperties(excludeProperties);
475     }
476 
477     @Inject
478     public void setXWorkConverter(final XWorkConverter converter) {
479         this.converter = converter;
480     }
481 }

View Code

继续调试查看ValueStack属性，context是ognl.OgnlContext也是一个Map类型，Root类型是一个ValueStack类型。

这里我们看以看出Root是一个CompoundRoot类型

 1 /*
 2  * Copyright 2002-2006,2009 The Apache Software Foundation.
 3  * 
 4  * Licensed under the Apache License, Version 2.0 (the "License");
 5  * you may not use this file except in compliance with the License.
 6  * You may obtain a copy of the License at
 7  * 
 8  *      http://www.apache.org/licenses/LICENSE-2.0
 9  * 
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 package com.opensymphony.xwork2.util;
17 
18 import java.util.ArrayList;
19 import java.util.List;
20 import java.util.concurrent.CopyOnWriteArrayList;
21 
22 
23 /**
24  * A Stack that is implemented using a List.
25  * 
26  * @author plightbo
27  * @version $Revision$
28  */
29 public class CompoundRoot extends CopyOnWriteArrayList<Object> {
30 
31     private static final long serialVersionUID = 8563229069192473995L;
32 
33     public CompoundRoot() {
34     }
35 
36     public CompoundRoot(List<?> list) {
37         super(list);
38     }
39 
40 
41     public CompoundRoot cutStack(int index) {
42         return new CompoundRoot(subList(index, size()));
43     }
44 
45     public Object peek() {
46         return get(0);
47     }
48 
49     public Object pop() {
50         return remove(0);
51     }
52 
53     public void push(Object o) {
54         add(0, o);
55     }
56 }

View Code

从源代码中我们可以看出CompoundRoot是一个通过List实现的栈，而结合测试我们可以知道Product对象就是存储到root对象中。

在数据查找时，如果都存储在值栈中的话，会先从值栈中第一个元素查找，如果第一个元素的属性不包含要找的对象，就从第二元素找。

总结：

ValueStack（值栈）：贯穿整个Action的生命周期（每个Action类的对象实例都拥有一个ValueStack对象），相当于一个数据的中转站，在其中保存当前Action对象和其他相关对象。

Struts框架把ValueStack对象保存在名为"struts.valueStack"的请求属性中。

在值栈对象的内部有两个逻辑部分：

1、ContextMap:Struts把各种各样的映射关系（一些Map类型的对象）压入ContextMap中。实际上就是对ActionContext的引用。Struts会把下面这些映射压入ContextMap对中：

parameters:该Map中包含当请求的请求参数

request:该Map中包含当前request对象中的所有属性

session：该Map中包含当前session对象中所有属性

application：该Map中包含当前application对象中的所有属性

attr:该Map中按如下顺序来检索某个属性：request,session,application

2、ObjectStack：Struts把Action和相关对象压入ObjectStack中。

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原文地址：https://www.cnblogs.com/yy3b2007com/p/6497599.html