一、分析
二、
1.OGNL
在访问action前，要经过各种intercepter,其中ParameterFilterInterceptor会把各咱参数放到ValueStack里，从而使OGNL可以访问这些参数，而ValueStack里包含对象stack和map
(1)map
赋值：ActionContext.getContext().put("roleList", roleList);
取值：在jsp中通过ognl取<s:iterator value="#roleList">或<s:iterator value="%{#roleList}">
注：因为struts标签默认使用ognl表达式，所以可以省略“%{}”，而“#”是表示从map中取值，不会去对象栈中去取
(2)对象stack
压栈：ActionContext.getContext().getValueStack().push(role);
取值：
<table cellpadding="0" cellspacing="0" class="mainForm">
<tr>
<td width="100">岗位名称</td>
<td><s:textfield name="name" cssClass="InputStyle" /> *</td>
</tr>
<tr>
<td>岗位说明</td>
<td><s:textarea name="description" cssClass="TextareaStyle"></s:textarea></td>
</tr>
</table>
struts标签会自动去对象statck中找%{name}、%{description}
2.El表达式
若使用了struts框架，则request会被装饰类StrutsRequestWrapper代换，StrutsRequestWrapper包装了ServletRequest，也提供了访问valuestack的方法，所以使El表达式可以访问request中的值及访问valuestack,
在jsp中写${name}，此时的取值顺序是(1)先以request中取,若取不到就到valuestack取，源码如下：
/*
* $Id$
*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/ package org.apache.struts2.dispatcher; import com.opensymphony.xwork2.ActionContext;
import com.opensymphony.xwork2.util.ValueStack; import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper; import static org.apache.commons.lang3.BooleanUtils.isTrue; /**
* <!-- START SNIPPET: javadoc -->
*
* All Struts requests are wrapped with this class, which provides simple JSTL accessibility. This is because JSTL
* works with request attributes, so this class delegates to the value stack except for a few cases where required to
* prevent infinite loops. Namely, we don't let any attribute name with "#" in it delegate out to the value stack, as it
* could potentially cause an infinite loop. For example, an infinite loop would take place if you called:
* request.getAttribute("#attr.foo").
*
* <!-- END SNIPPET: javadoc -->
*
*/
public class StrutsRequestWrapper extends HttpServletRequestWrapper { private static final String REQUEST_WRAPPER_GET_ATTRIBUTE = "__requestWrapper.getAttribute";
private final boolean disableRequestAttributeValueStackLookup; /**
* The constructor
* @param req The request
*/
public StrutsRequestWrapper(HttpServletRequest req) {
this(req, false);
} /**
* The constructor
* @param req The request
* @param disableRequestAttributeValueStackLookup flag for disabling request attribute value stack lookup (JSTL accessibility)
*/
public StrutsRequestWrapper(HttpServletRequest req, boolean disableRequestAttributeValueStackLookup) {
super(req);
this.disableRequestAttributeValueStackLookup = disableRequestAttributeValueStackLookup;
} /**
* 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); 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;
}
}
例如:
<s:iterator value="#roleList">
${id},
${name},
${description},
<s:a action="role_delete?id=%{id}" onclick="return confirm('确定要删除吗？')">删除</s:a>,
<s:a action="role_editUI?id=%{id}">修改</s:a>
<br/>
</s:iterator>
分析：s:iterator每次循环都会把当前对象压栈，循环结束就弹栈，${id}的访问顺序时先到对象栈里找，再到map里找，所以肯定可以找到
3.ModelDriven
ModelDriven的原理是，访问action前，ModelDrivenInterceptor会把model压到对象栈里，从而页面提交的比如id,name等字段会优先封闭到model里
源码如下：
@Override
public String intercept(ActionInvocation invocation) throws Exception {
Object action = invocation.getAction(); if (action instanceof ModelDriven) {
ModelDriven modelDriven = (ModelDriven) action;
ValueStack stack = invocation.getStack();
Object model = modelDriven.getModel();
if (model != null) {
stack.push(model);
}
if (refreshModelBeforeResult) {
invocation.addPreResultListener(new RefreshModelBeforeResult(modelDriven, model));
}
}
return invocation.invoke();
}
用法如：
<s:form action="role_add">
<s:textfield name="name"></s:textfield>
<s:textarea name="description"></s:textarea>
<s:submit value="提交"></s:submit>
</s:form>
一提交，字段会自动封装到role里去，因为RoleAction实现了ModelDriven
@Override
public String intercept(ActionInvocation invocation) throws Exception {
Object action = invocation.getAction(); if (action instanceof ModelDriven) {
ModelDriven modelDriven = (ModelDriven) action;
ValueStack stack = invocation.getStack();
Object model = modelDriven.getModel();
if (model != null) {
stack.push(model);
}
if (refreshModelBeforeResult) {
invocation.addPreResultListener(new RefreshModelBeforeResult(modelDriven, model));
}
}
return invocation.invoke();
}