OA学习笔记-010-Struts部分源码分析、Intercepter、ModelDriver、OGNL、EL

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();
     }