Struts2自定义标签3模仿原有的s:if s:elseif s:else自定义自己的if elsif else

第一步：webroot/web-inf下简历str.tld文件

 <?xml version="1.0" encoding="UTF-8"?>
     <!DOCTYPE taglib PUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag Library 1.1//EN" "http://java.sun.com/j2ee/dtds/web-jsptaglibrary_1_1.dtd">
     <taglib>     <!-- 自定义库标签的根 -->
     <tlibversion>1.2</tlibversion>     <!-- 版本号 -->
     <jspversion>1.1</jspversion>       <!-- JSP版本号 -->
     <shortname>stu</shortname>        <!-- prefix="stu"标签名称-->
     <uri>StudentTags</uri>   <!-- uri="StudentTags" 外界导入标签时，认识的名字，很重要。-->  

     <tag>
      <name>selectAll</name>                            <!-- 标签名称 -->
      <tagclass>com.bjsxt.sxf.tag.SeclectAllSt</tagclass>          <!-- 对应的java类的全路径 -->
     </tag>  

     <!-- 有属性的标签，可以有多个属性  <attribute>并列 -->
       <tag>
            <name>selectBySex</name>  <!-- 标签名称 -->
             <tagclass>com.bjsxt.sxf.tag.SeclectStBySex</tagclass>
             <attribute>   <!-- 对应标签的属性。 -->
                  <name>sex</name>
                  <required>true</required>  <!-- 是必需写的属性，即没有写属性标签不能被正常使用 -->
             </attribute>
        </tag>
       <!-- 按班级学生id查询出班级集合，存放到属性var指定的变量中，然后利用s标签的迭代标签，将var指定的变量存放的学生集合遍历出来 -->
        <tag>
                <name>selectByClassId</name> <!-- 标签名称 -->
                <tagclass>com.bjsxt.sxf.tag.MyTag</tagclass> <!-- 对应的java类的全路径 -->
                <body-content>JSP</body-content><!-- 如果不需要标签体则设置empty，反之设定jsp，内部可以运行jsp所有的语法 -->
                <attribute>
                    <name>classId</name><!--指定属性名 和标签java类一致-->
                    <required>true</required><!--该属性是否是必须，如果非必须没设置则为空。 -->
                    <rtexprvalue>true</rtexprvalue><!-- 该属性能不能动态使用表达式为该属性赋值 true可以  false不可以  使用脚本和EL表达式来获取动态的值 -->
                </attribute>
                <attribute>
                    <name>var</name>
                    <required>true</required>
                    <rtexprvalue>false</rtexprvalue>
                </attribute>
                <attribute>
                    <name>num</name>
                    <required>false</required>
                    <rtexprvalue>false</rtexprvalue>
                </attribute>
        </tag>
        <!-- 自定义的myif标签 -->
        <tag>
                <name>myif</name>
                <tagclass>com.bjsxt.sxf.tag.MyIfTag</tagclass>
                <bodycontent>JSP</bodycontent>
                <attribute>
                    <name>flag</name>
                    <required>true</required>
                    <rtexprvalue>true</rtexprvalue>
                </attribute>
                <attribute>
                    <name>condition</name>
                    <required>true</required>
                    <rtexprvalue>true</rtexprvalue>
                </attribute>
        </tag>
        <!-- 自定义的myelseif标签 -->
         <tag>
                <name>myelseif</name>
                <tagclass>com.bjsxt.sxf.tag.MyElseIfTag</tagclass>
                <bodycontent>JSP</bodycontent>
                <attribute>
                    <name>flag</name>
                    <required>true</required>
                    <rtexprvalue>true</rtexprvalue>
                </attribute>
                <attribute>
                    <name>condition</name>
                    <required>true</required>
                    <rtexprvalue>true</rtexprvalue>
                </attribute>
        </tag>
        <!-- 自定义的myelse标签 -->
        <tag>
                <name>myelse</name>
                <tagclass>com.bjsxt.sxf.tag.MyElseTag</tagclass>
                <bodycontent>JSP</bodycontent>
        </tag>

     </taglib>  

第二步：建立标签类

 package com.bjsxt.sxf.tag;

 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;

 import org.apache.struts2.components.Component;
 import org.apache.struts2.views.jsp.ComponentTagSupport;

 import com.bjsxt.sxf.tag.compant.MyIfComponent;
 import com.opensymphony.xwork2.util.ValueStack;
 /**
  * myif的标签类
 * @ClassName: MyIfTag
 * @Description: TODO(这里用一句话描述这个类的作用)
 * @author 尚晓飞
 * @date 2014-10-22 下午3:46:45
 *
  */
 public class MyIfTag extends ComponentTagSupport {
     private String flag;//if判断的标示
     private String condition;//可以传递的多个参数代表

     //生成标签逻辑类的对象。多态。父类引用，指向子类对象
     @Override
     public Component getBean(ValueStack arg0, HttpServletRequest arg1,
             HttpServletResponse arg2) {
         return new MyIfComponent(arg0, arg1,arg2);
     }

     //给逻辑类的属性赋值
     @Override
     protected void populateParams() {
         super.populateParams();
         MyIfComponent myIfComponent=(MyIfComponent) getComponent();
         myIfComponent.setFlag(flag);
         myIfComponent.setCondition(condition);
     }

     public String getFlag() {
         return flag;
     }

     public void setFlag(String flag) {
         this.flag = flag;
     }

     public String getCondition() {
         return condition;
     }

     public void setCondition(String condition) {
         this.condition = condition;
     }

 }

 package com.bjsxt.sxf.tag;

 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;

 import org.apache.struts2.components.Component;
 import org.apache.struts2.views.jsp.ComponentTagSupport;

 import com.bjsxt.sxf.tag.compant.MyElseIfComponent;
 import com.opensymphony.xwork2.util.ValueStack;
 /**
  * myelseif的标签类
 * @ClassName: MyElseIfTag
 * @Description: TODO(这里用一句话描述这个类的作用)
 * @author 尚晓飞
 * @date 2014-10-22 下午3:47:59
 *
  */
 public class MyElseIfTag extends ComponentTagSupport{
     private String flag;//elsif判断的标示
     private String condition;//可以传递的多个参数代表

     //返回该标签逻辑类的对象
     @Override
     public Component getBean(ValueStack arg0, HttpServletRequest arg1,
             HttpServletResponse arg2) {

         return new MyElseIfComponent(arg0, arg1, arg2);
     }

     //给该标签逻辑类对象赋值
     @Override
     protected void populateParams() {
         super.populateParams();
         MyElseIfComponent myElseIfComponent=(MyElseIfComponent) getComponent();
         myElseIfComponent.setFlag(flag);
         myElseIfComponent.setCondition(condition);
     }
     public String getFlag() {
         return flag;
     }
     public void setFlag(String flag) {
         this.flag = flag;
     }
     public String getCondition() {
         return condition;
     }
     public void setCondition(String condition) {
         this.condition = condition;
     }

 }

 package com.bjsxt.sxf.tag;

 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;

 import org.apache.struts2.components.Component;
 import org.apache.struts2.views.jsp.ComponentTagSupport;

 import com.bjsxt.sxf.tag.compant.MyElseComponent;
 import com.opensymphony.xwork2.util.ValueStack;
 /**
  * 自定义的else标签
 * @ClassName: MyElse
 * @Description: TODO(这里用一句话描述这个类的作用)
 * @author 尚晓飞
 * @date 2014-10-22 下午2:24:30
 *
  */
 public class MyElseTag extends ComponentTagSupport{

     @Override
     public Component getBean(ValueStack arg0, HttpServletRequest arg1,
             HttpServletResponse arg2) {
         // TODO Auto-generated method stub
         return new MyElseComponent(arg0, arg1, arg2);
     }

     @Override
     protected void populateParams() {
         // TODO Auto-generated method stub
         super.populateParams();
     }

 }

第三步：建立标签逻辑类

 package com.bjsxt.sxf.tag.compant;

 import java.io.Writer;

 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;

 import org.apache.struts2.components.Component;

 import com.opensymphony.xwork2.util.ValueStack;

 /**
  * myif标签逻辑类 没有@的标签注解，好像不影响，
 * @ClassName: MyIfComponent
 * @Description: TODO(这里用一句话描述这个类的作用)
 * @author 尚晓飞
 * @date 2014-10-22 下午3:49:40
 *
  */
 public class MyIfComponent extends Component {
     protected String flag;
     protected String condition;
     public static final String MyANSWER = "struts.if.answer";
     protected Boolean answer;

     public MyIfComponent(ValueStack stack,HttpServletRequest req,HttpServletResponse resp) {
         super(stack);
     }

     //标签运行开始执行
     @Override
     public boolean start(Writer writer) {
         answer = (Boolean) findValue(flag, Boolean.class);
         if (answer == null) {
                 answer = Boolean.FALSE;
             }

         stack.getContext().put(MyANSWER, answer);
         boolean flg=answer.booleanValue();
         return flg;
     }

     //标签运行结束执行
     @Override
     public boolean end(Writer writer, String body) {
         stack.getContext().put(MyANSWER, answer);
         boolean fd=super.end(writer, body);
         return fd;
     }
     public String getFlag() {
         return flag;
     }

     public void setFlag(String flag) {
         this.flag = flag;
     }

     public String getCondition() {
         return condition;
     }

     public void setCondition(String condition) {
         this.condition = condition;
     }

 }

 package com.bjsxt.sxf.tag.compant;

 import java.io.Writer;
 import java.util.Map;

 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;

 import org.apache.struts2.components.Component;

 import com.opensymphony.xwork2.util.ValueStack;

 /**
  * myelseif的逻辑类
 * @ClassName: MyElseIfComponent
 * @Description: TODO(这里用一句话描述这个类的作用)
 * @author 尚晓飞
 * @date 2014-10-22 下午3:50:49
 *
  */
 public class MyElseIfComponent extends Component {
     protected String flag;
     protected String condition;
     public static final String MyANSWER = "struts.myelseif.answer";
     protected Boolean answer;

     public MyElseIfComponent(ValueStack stack,HttpServletRequest req,HttpServletResponse resp) {
         super(stack);
         // TODO Auto-generated constructor stub
     }

     @Override
     public boolean start(Writer writer) {
         boolean myflag=false;
         //获取值栈
          Map context = stack.getContext();
         //先从值栈中获取if标签的flag的值
          Boolean ifResult = (Boolean) context.get(MyIfComponent.MyANSWER);
         //如果存在elseif 则需要获取该值
          Boolean elseIfResult=(Boolean) context.get(MyElseIfComponent.MyANSWER);
          context.remove(MyIfComponent.MyANSWER);
          context.remove(MyElseIfComponent.MyANSWER);

         //判断是否存在if=true的情况
         if(ifResult!=null&&ifResult==true){
             //if=true
              myflag=false;
         }else{
             //if=false
             //是否存在else if
             if(elseIfResult!=null&&elseIfResult==true){
                 //else if=true;
                 myflag=false;
             }else{
                 //else if=false或者不存在上个else if
                 answer = (Boolean) findValue(flag, Boolean.class);
                 if (answer == null) {
                     answer = Boolean.FALSE;
                 }
                 stack.getContext().put(MyANSWER, answer);
                 myflag=answer.booleanValue();
             }
         }
         return myflag;
     }
     @Override
     public boolean end(Writer writer, String body) {
         stack.getContext().put(MyANSWER, answer);
         return super.end(writer, body);
     }
     public String getFlag() {
         return flag;
     }
     public void setFlag(String flag) {
         this.flag = flag;
     }
     public String getCondition() {
         return condition;
     }
     public void setCondition(String condition) {
         this.condition = condition;
     }
     public Boolean getAnswer() {
         return answer;
     }
     public void setAnswer(Boolean answer) {
         this.answer = answer;
     }

 }

 package com.bjsxt.sxf.tag.compant;

 import java.io.Writer;
 import java.util.Map;

 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;

 import org.apache.struts2.components.Component;

 import com.opensymphony.xwork2.util.ValueStack;

 public class MyElseComponent extends Component{

     /**
      * myelse的逻辑类
      *
      * @Title: EncodingRequestWrapper
      * @Description: 构造函数
      * @param stack
      * @param req
      * @param response
      * @author 尚晓飞
      * @date 2014-10-22 下午3:51:24
      */
     public MyElseComponent(ValueStack stack,HttpServletRequest req,HttpServletResponse response) {
         super(stack);
     }
     //Myelse标签运行开始
     @Override
     public boolean start(Writer writer) {
         boolean myflg=false;
         //获取值栈
          Map context = stack.getContext();
          //获取if的值
          Boolean ifResult = (Boolean) context.get(MyIfComponent.MyANSWER);
          //获取else的值
          Boolean elseifResult=(Boolean) context.get(MyElseIfComponent.MyANSWER);
          //移除值栈中的值
          context.remove(MyIfComponent.MyANSWER);
          context.remove(MyElseIfComponent.MyANSWER);

          //判断是否存在if
          if(ifResult!=null&&ifResult==true){
              //存在if，并且为true;
              myflg=false;
          }else{
              //if为false
              //判断elseif是否存在
              if(elseifResult!=null&&elseifResult==true){
                  //存在elseif标签,且==true
                  myflg=false;
              }else{
                  //不存在elseif标签或者为elseif标签==false或者if标签为false
                  myflg=true;
              }
          }

          return myflg;
     }

     @Override
     public boolean end(Writer writer, String body) {
         // TODO Auto-generated method stub
         boolean d=super.end(writer, body);
         return d;
     }

 }

第四步：测试页面

 <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
 <%@ taglib uri="StudentTags" prefix="stu" %>
 <%@ taglib uri="/struts-tags" prefix="s"%>
 <%
 String path = request.getContextPath();
 String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
 %>

 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
 <html>
   <head>
   </head>

   <body>
     This is my JSP page. <br>
     <a href="<%=request.getContextPath()%>/StudentAction!reportStudent.action">班级表单下载</a>
     <h1>查询出所有学生的标签效果</h1>
        <stu:selectAll></stu:selectAll>
        <h1>查询出指定性别的学生的标签效果</h1>
        <stu:selectBySex sex="男"></stu:selectBySex>
        <h1>查询出指定班级id的学生集合的标签效果</h1>
        <stu:selectByClassId var="students" classId="1" >
            <table border="2">
                <tr>
                    <td>id</td>
                    <td>姓名</td>
                    <td>性别</td>
                    <td>班级</td>
                </tr>
                <s:iterator value="#students" var="stu">
                    <tr>
                        <td><s:property value="#stu.id"/></td>
                        <td><s:property value="#stu.name"/></td>
                        <td><s:property value="#stu.sex"/></td>
                        <td><s:property value="#stu.classRoom.name"/></td>
                    </tr>
                </s:iterator>
            </table>
        </stu:selectByClassId>

        <h1>我是中国人</h1>
        <stu:myif flag="1==3" condition="shangxiaofei">
            <h1>myif是true</h1>
        </stu:myif>
        <stu:myelseif flag="1==2" condition="first">
            <h1>第一个myelseif是false</h1>
        </stu:myelseif>
        <stu:myelseif flag="1==1" condition="sencod">
            <h1>第二个myelseif是true</h1>
        </stu:myelseif>
        <stu:myelse>
            <h1>false</h1>
        </stu:myelse>
   </body>

 </html>

第五步:效果图