JavaWeb 自定義标簽&EL自定義函數

原作者:尚矽谷-佟剛

forEach标簽

ForEachTag.java

package com.atweihai.javaweb.mytag;

import java.io.IOException;
import java.util.Collection;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.SimpleTagSupport;

public class ForEachTag extends SimpleTagSupport{

    private Collection<?> item;

    private String var;

    public void setItem(Collection<?> item) {
        this.item = item;
    }

    public void setVar(String var) {
        this.var = var;
    }

    @Override
    public void doTag() throws JspException, IOException {
        //循環周遊集合
         if(item!=null&&item.size()>){
             for(Object obj:item){
                 //放入PageContext對象中,鍵:var 值:每次周遊的對象
                 getJspContext().setAttribute(var,obj);
                 //标簽體解析後輸出
                 getJspBody().invoke(null);
             }
         }
    }
}
           

mytag.tld

<tag>
     <name>forEach</name>
     <tag-class>com.atweihai.javaweb.mytag.ForEachTag</tag-class>
     <!-- tagdependent：标簽體内容直接被寫入BodyContent，由自定義标簽類來進行處理，而不被JSP容器解釋
          JSP：接受所有JSP文法，如定制的或内部的tag、scripts、靜态HTML、腳本元素、JSP指令和動作
          empty：空标記，即起始标記和結束标記之間沒有内容
          scriptless:标簽體可以包含EL表達式和JSP動作元素，但不能包含JSP的腳本元素和表達式元素
     -->
     <body-content>scriptless</body-content>

     <attribute>
        <name>item</name>
        <required>true</required>
        <rtexprvalue>true</rtexprvalue>
     </attribute>

     <attribute>
        <name>var</name>
        <required>true</required>
        <rtexprvalue>false</rtexprvalue>
     </attribute>
  </tag>
           

mytag.jsp

<%@taglib    prefix="atweihai" uri="http://com.atweihai/jsp/mytag/core" %>

  <%
      List<Customer> customers=new ArrayList<Customer>();
      customers.add(new Customer(,"AA",));
      customers.add(new Customer(,"BB",));
      customers.add(new Customer(,"CC",));
      customers.add(new Customer(,"DD",));
      customers.add(new Customer(,"EE",));
      customers.add(new Customer(,"FF",));

      request.setAttribute("customers", customers);
  %>
 <atweihai:forEach item="${requestScope.customers }" var="cust">
          ${cust.id }--${cust.name }--${cust.age }<br>
 </atweihai:forEach>
           

頁面運作效果

choose when otherwise 标簽

ChooseTag.java

package com.atweihai.javaweb.mytag;

import java.io.IOException;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.SimpleTagSupport;

public class ChooseTag extends SimpleTagSupport {

    private boolean flag=true;

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

    public boolean isFlag() {
        return flag;
    }

    @Override
    public void doTag() throws JspException, IOException {
        getJspBody().invoke(null);
    }

}
           

WhenTag.java

package com.atweihai.javaweb.mytag;

import java.io.IOException;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.SimpleTagSupport;

public class WhenTag extends SimpleTagSupport {

    private boolean test;
    public void setTest(boolean test) {
        this.test = test;
    }


    @Override
    public void doTag() throws JspException, IOException {
        if(test){
            ChooseTag parent=(ChooseTag) getParent();
            boolean flag =parent.isFlag();

            if(flag){
                getJspBody().invoke(null);
                parent.setFlag(false);
            }
        }
    }
}
           

OtherwiseTag.java

package com.atweihai.javaweb.mytag;

import java.io.IOException;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.SimpleTagSupport;

public class OtherwiseTag extends SimpleTagSupport {

    @Override
    public void doTag() throws JspException, IOException {
          ChooseTag parent= (ChooseTag) getParent();
          boolean flag=parent.isFlag();

          if(flag){
              getJspBody().invoke(null);
          }
    }

}
           

mytag.tld

<tag>
        <name>choose</name>
        <tag-class>com.atweihai.javaweb.mytag.ChooseTag</tag-class>
        <body-content>scriptless</body-content>
  </tag>

  <tag>
        <name>when</name>
        <tag-class>com.atweihai.javaweb.mytag.WhenTag</tag-class>
        <body-content>scriptless</body-content>

        <attribute>
          <name>test</name>
          <required>true</required>
          <rtexprvalue>true</rtexprvalue>
        </attribute>

  </tag>

  <tag>
       <name>otherwise</name>
       <tag-class>com.atweihai.javaweb.mytag.OtherwiseTag</tag-class>
       <body-content>scriptless</body-content>
  </tag>
           

mytag.jsp

<%@ taglib prefix="atweihai" uri="http://com.atweihai/jsp/mytag/core" %>

  <atweihai:choose>
      <atweihai:when test="${param.age > 24}">大學畢業</atweihai:when>
      <atweihai:when test="${param.age > 20}">高中畢業</atweihai:when>
      <atweihai:otherwise>高中以下</atweihai:otherwise>
   </atweihai:choose>
           

頁面運作結果

EL自定義函數 substring(str,beginIndex,length)

substring(“abcdefghijklmn”,3,4) ===>defg

SubString.java

package com.atweihai.javaweb.mytag;

public class SubString {

    public static String substring(String str,int beginIndex,int length){
        return str.substring(beginIndex, beginIndex+length);
    }
}
           

mytag.tld

<function>
         <name>substring</name>
         <function-class>com.atweihai.javaweb.mytag.SubString</function-class>
         <function-signature>java.lang.String substring (java.lang.String,int,int)</function-signature>
  </function>
           

mytag.jsp

<%@ taglib prefix="atweihai" uri="http://com.atweihai/jsp/mytag/core" %>
 ${atweihai:substring("abcdefghijklmn",,) }
           

頁面運作結果