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\apps\struts2-blank.war解压；
3、取出\struts2-blank\WEB-INF\lib下的所有jar包到Struts_01\WebContent\WEB-INF\lib下；
4、\struts2-blank\WEB-INF\src\java下的struts.xml、log4j2.xml、velocity.properties拷贝到Struts_01\WebContent\src；
5、拷贝\struts2-blank\WEB-INF\web.xml到Struts_01\WebContent\WEB-INF\web.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";
}
}
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>
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>
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。
/*
* 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> 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);
} /**
* 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.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);
}
}
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，
/*
* 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.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; /**
* Ognl implementation of a value stack that allows for dynamic Ognl expressions to be evaluated against it. When evaluating an expression,
* 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
* for the given property or a method of the given name (depending on the expression being evaluated).
*
* @author Patrick Lightbody
* @author tm_jee
* @version $Date$ $Id$
*/
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 root;
transient Map<String, Object> context;
Class defaultType;
Map<Object, Object> overrides;
transient OgnlUtil ognlUtil;
transient SecurityMemberAccess securityMemberAccess;
private transient XWorkConverter converter; 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;
securityMemberAccess.setExcludedClasses(ognlUtil.getExcludedClasses());
securityMemberAccess.setExcludedPackageNamePatterns(ognlUtil.getExcludedPackageNamePatterns());
securityMemberAccess.setExcludedPackageNames(ognlUtil.getExcludedPackageNames());
} 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);
} /** /**
* @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) {
Map<String, Object> context = getContext();
try {
trySetValue(expr, value, throwExceptionOnFailure, context);
} 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) 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);
} 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 [#0] with expression [#1]", re, value.toString(), expr);
}
}
} private void handleOgnlException(String expr, Object value, boolean throwExceptionOnFailure, OgnlException e) {
boolean shouldLog = shouldLogMissingPropertyWarning(e);
String msg = null;
if (throwExceptionOnFailure || shouldLog) {
msg = ErrorMessageBuilder.create()
.errorSettingExpressionWithValue(expr, value)
.build();
}
if (shouldLog) {
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) {
final Object value = handleOgnlException(expr, throwExceptionOnFailure, e);
return converter.convertValue(getContext(), value, asType);
} catch (Exception e) {
final Object value = handleOtherException(expr, throwExceptionOnFailure, e);
return converter.convertValue(getContext(), value, asType);
} 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 (shouldLogMissingPropertyWarning(e)) {
LOG.warn("Could not find property [#0]!", e, expr);
}
if (throwExceptionOnFailure) {
throw new XWorkException(e);
}
}
return ret;
} private boolean shouldLogMissingPropertyWarning(OgnlException e) {
return (e instanceof NoSuchPropertyException || e instanceof MethodFailedException)
&& 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);
return converter.convertValue(getContext(), value, asType);
}
} 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, XWorkConstants.ALLOW_STATIC_METHOD_ACCESS));
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 setExcludeProperties(Set<Pattern> excludeProperties) {
securityMemberAccess.setExcludeProperties(excludeProperties);
} @Inject
public void setXWorkConverter(final XWorkConverter converter) {
this.converter = converter;
}
}
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
/*
* 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.util; import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CopyOnWriteArrayList; /**
* A Stack that is implemented using a List.
*
* @author plightbo
* @version $Revision$
*/
public class CompoundRoot extends CopyOnWriteArrayList<Object> { private static final long serialVersionUID = 8563229069192473995L; public CompoundRoot() {
} public CompoundRoot(List<?> list) {
super(list);
} public CompoundRoot cutStack(int index) {
return new CompoundRoot(subList(index, size()));
} public Object peek() {
return get(0);
} public Object pop() {
return remove(0);
} public void push(Object o) {
add(0, o);
}
}
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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