JavaWeb学习记录（十九）——开发JSTL自定义标签

一、防盗链标签

import javax.servlet.http.HttpServletResponse;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.PageContext;
import javax.servlet.jsp.tagext.JspFragment;
import javax.servlet.jsp.tagext.SimpleTagSupport;

public class RefererTag extends SimpleTagSupport{
   private String name;
   private String page;
   public void setName(String name) {
       this.name = name;
   }
   public void setPage(String page) {
       this.page = page;
   }

   @Override
   public void doTag() throws JspException, IOException {
       PageContext pageContext=(PageContext) this.getJspContext();
       HttpServletRequest request=(HttpServletRequest) pageContext.getRequest();
       String referer=request.getHeader("Referer");
       JspFragment jf=this.getJspBody();
       System.out.println(name);
       System.out.println(referer);
       if(referer==null||!referer.startsWith(name)){
           HttpServletResponse response=(HttpServletResponse) pageContext.getResponse();
           response.sendRedirect("page");
       }else{

       }
   }
}

<tag>
        <description>description</description>
        <name>referer</name>
        <tag-class>web17.tag.RefererTag</tag-class>
       <body-content>scriptless</body-content>
       
       <attribute>
           <name>name</name>
           <required>true</required>
           <rtexprvalue>true</rtexprvalue>
       </attribute>
       <attribute>
           <name>page</name>
           <required>true</required>
           <rtexprvalue>true</rtexprvalue>
       </attribute>
    </tag>

　　测试

二、if标签

<tag>
        <description>description</description>
        <name>if</name>
        <tag-class>web17.tag.IfTag</tag-class>
       <body-content>scriptless</body-content>
       
       <attribute>
           <name>test</name>
           <required>true</required>
           <rtexprvalue>true</rtexprvalue>
       </attribute>
    </tag>

　　测试

　　<c:if test="${1==1 }">1==1为真执行</c:if>
<c:if test="${1>=2 }">1>=2为真执行</c:if>

三、选择（if-else）标签

　　package web17.tag;

import java.io.IOException;

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

public class ChooseTag extends SimpleTagSupport{
   private boolean isOk;

   public boolean isOk(){
       return isOk;
   }
   public void setOk(boolean isOk){
       this.isOk=isOk;
   }
   @Override
   public void doTag() throws JspException, IOException {
       JspFragment jf=this.getJspBody();
       jf.invoke(null);
   }
}
　　package web17.tag;

import java.io.IOException;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.JspFragment;
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 {
       JspFragment jf=this.getJspBody();
       if(test){
           jf.invoke(null);
       }else{

       }
   }
}

　　package web17.tag;

import java.io.IOException;

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

public class OtherWiseTag extends SimpleTagSupport{
   @Override
   public void doTag() throws JspException, IOException {
       ChooseTag ct=(ChooseTag) this.getParent();
       JspFragment jf=this.getJspBody();
       if(ct.isOk()){
           jf.invoke(null);
       }else{

       }
   }
}

<tag>
        <description>description</description>
        <name>choose</name>
        <tag-class>web17.tag.ChooseTag</tag-class>
       <body-content>scriptless</body-content>
    </tag>
   <tag>
        <description>description</description>
        <name>when</name>
        <tag-class>web17.tag.WhenTag</tag-class>
       <body-content>scriptless</body-content>
       
       <attribute>
           <name>test</name>
           <required>true</required>
           <rtexprvalue>true</rtexprvalue>
       </attribute>
    </tag>
    <tag>
        <description>description</description>
        <name>otherwise</name>
        <tag-class>web17.tag.OtherWiseTag</tag-class>
       <body-content>scriptless</body-content>
    </tag>

　　测试

四、迭代标签

　　package web17.tag;

import java.io.IOException;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

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

public class ForEachTag extends SimpleTagSupport{
   private String var;
   private Object items;

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

   public void setItems(Object items) {
       this.items = items;
   }

   @Override
   public void doTag() throws JspException, IOException {
       JspFragment jf=this.getJspBody();
       if(items!=null){
           if(items instanceof List){
               List item=(List)items;
               for(int i=0;i<item.size();i++){
                   Object v=item.get(i);
                   this.getJspContext().setAttribute(var, v);
                   jf.invoke(null);
               }
           }else if(items instanceof Set){
               Set set=(Set)items;
               Iterator<Set> it=set.iterator();
               while(it.hasNext()){
                   Object v=it.next();
                   this.getJspContext().setAttribute(var, v);
                   jf.invoke(null);
               }
           }else if(items instanceof Map){
               Map map=(Map)items;
               Set<Map.Entry> set=map.entrySet();
               Iterator<Entry> it=set.iterator();
               while(it.hasNext()){
                   Entry entry=it.next();
                   this.getJspContext().setAttribute(var, entry);
                   jf.invoke(null);
               }
           }else if(items instanceof int[]){
               int arr[]=(int[]) items;
               for(int i=0;i<arr.length;i++){
                   this.getJspContext().setAttribute(var, arr[i]);
                   jf.invoke(null);
               }
           }
       }
   }
}

<tag>
        <description>description</description>
        <name>forEach</name>
        <tag-class>web17.tag.ForEachTag</tag-class>
       <body-content>scriptless</body-content>
       
       <attribute>
           <name>var</name>
           <required>true</required>
           <rtexprvalue>true</rtexprvalue>
       </attribute>
       
       <attribute>
           <name>items</name>
           <required>true</required>
           <rtexprvalue>true</rtexprvalue>
       </attribute>
    </tag>

　　测试

　　<%
       List<String> list=new ArrayList<String>();
       list.add("zsf1");
       list.add("zsf2");
       list.add("zsf3");
       pageContext.setAttribute("list", list);
   %>
   <br/>
   <c:forEach items="${list}" var="x">
      ${x }
   </c:forEach>


   <%
       Set<String> set=new HashSet<String>();
       set.add("zsf11");
       set.add("zsf22");
       set.add("zsf33");
       pageContext.setAttribute("set", set);
   %>
   <br/>
   <c:forEach items="${set}" var="x">
      ${x }
   </c:forEach>


   <%
       Map<String,String> map=new HashMap<String,String>();
       map.put("name1","zsf111");
       map.put("name2","zsf222");
       map.put("name3","zsf333");
       pageContext.setAttribute("map", map);
   %>
   <br/>
   <c:forEach items="${map}" var="x">
      ${x.key }
      ${x.value }
   </c:forEach>
   <br/>
   <%
      int[] arr={1,2,3,4};
      pageContext.setAttribute("arr", arr);
      %>
      <c:forEach items="${arr }" var="r">${r }</c:forEach>

五、html转义标签

　　package web17.util;

public class HtmlFilter {
   public static String htmlFilter(String content) {
       //定义字符数组
       char chars[]=new char[content.length()];
       //把字符串直接复制到chars[]数组中
       content.getChars(0, content.length(), chars, 0);
       StringBuffer sb=new StringBuffer();
       for(int index=0;index<chars.length;index++){
           char c=chars[index];
           switch (c) {
           case '>':
               sb.append(">");
               break;
           case '<':
               sb.append("<");
               break;
           default:
               sb.append(c);
               break;
           }
       }
       return sb.toString();
   }
}

　　package web17.tag;

import java.io.IOException;
import java.io.StringWriter;

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

import web17.util.HtmlFilter;

public class EscapeTag extends SimpleTagSupport {
   @Override
   public void doTag() throws JspException, IOException {
       //获取操作对象
       JspFragment jf=this.getJspBody();
       //写到流中
       StringWriter sw=new StringWriter();
       //写入该流
       jf.invoke(sw);
       //获取这个内容
       String content=sw.getBuffer().toString();
       String sb = HtmlFilter.htmlFilter(content);
       //输出
       JspWriter out=this.getJspContext().getOut();
       //写出
       out.println(sb);
   }


}

　　<tag>
        <description>description</description>
        <name>escape</name>
        <tag-class>web17.tag.EscapeTag</tag-class>
       <body-content>scriptless</body-content>
    </tag>

　　测试

　　<c:escape>
<a href="">点点</a>
</c:escape>