自定义JSP标签

程序员文章站 2022-05-30 20:53:05

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自定义JSP标签

生命标签图：
自定义JSP标签

1、标签的特点

1.1 标签分两种类型：数据标签和控制标签。
数据标签的特点：存储数据，没有任何的页面效果。标签 set
控制标签的特点：控制的对象是标签体。标签 if foreach

2、自定义标签的开发以及使用步骤

2.1 创建一个标签助手类(继承BodyTagSupport)
标签属性必须助手类的属性对应、且要提供对应get/set方法
rtexprvalue

2.2 创建标签库描述文件(tld)，添加自定义标签的配置
注：tld文件必须保存到WEB-INF目录或其子目录

2.3 在JSP通过taglib指令导入标签库，并通过指定后缀
访问自定义标签

2.4介绍tld自定义标签

<?xml version="1.0" encoding="UTF-8" ?>

<taglib xmlns="http://java.sun.com/xml/ns/j2ee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd"
    version="2.0">

  <description>DZY 1.1 core library</description>
  <display-name>DZY core</display-name>
  <tlib-version>1.1</tlib-version>
  <short-name>c</short-name>
  <uri>http://DZY</uri><!--uri的地址调用  -->

 <tag>
  <!--填写的是标签库中的标签名  -->
    <name>catch</name>
    <!--标签对应后台助手类  -->
    <tag-class>org.apache.taglibs.standard.tag.common.core.CatchTag</tag-class>
    <!-- 标签类别 -->
    <body-content>JSP</body-content>
    <attribute>
    <!--自定义标签中属性  -->
        <name>var</name>
        <!-- 属性值是否必填 -->
        <required>false</required>
        <!--是否支持表达式/ognl表达式  -->
        <rtexprvalue>false</rtexprvalue>
    </attribute>
  </tag>

3、演示自定义JSP标签

SKIP_BODY：跳过主体
EVAL_BODY_INCLUDE：计算标签主体内容并[输出]
EVAL_BODY_BUFFERED：计算标签主体内容并[缓存]
EVAL_PAGE:计算页面的后续部分
SKIP_PAGE:跳过页面的后续部分
EVAL_BODY_AGAIN:再计算主体一次

3.1 set和out的标签操作：
out操作：

package com.DZY.jsp;

import java.io.IOException;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.BodyTagSupport;
/**
 * out类
 * @author Aromanic150
 *
 */
public class OutDemo extends BodyTagSupport {
public Object getValue() {
        return value;
    }
    public void setValue(Object value) {
        this.value = value;
    }
    private Object value;
    @Override
    public int doStartTag() throws JspException {
         JspWriter out=pageContext.getOut();
         try {
            out.write(value.toString());
        } catch (IOException e) {
            // TODO Auto-generated catch block
            throw new RuntimeException(e);
        }
        return SKIP_BODY;
    }
}

set操作：

package com.DZY.jsp;

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

/**
 * set类
 * 
 * @author Aromanic150
 *
 */
public class SetDemo extends BodyTagSupport {
 private static final long serialVersionUID = -123L;
 private String var;
 private Object value;

 public String getVar() {
  return var;
 }

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

 public Object getValue() {
  return value;
 }

 public void setValue(Object value) {
  this.value = value;
 }

 @Override
 public int doStartTag() throws JspException {
  pageContext.setAttribute(var, value);// 将值存入pageContext
  return SKIP_BODY;
 }
}

set和out在tld中自定义

<?xml version="1.0" encoding="UTF-8" ?>

<taglib xmlns="http://java.sun.com/xml/ns/j2ee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd"
    version="2.0">
    
 <description>DZY 1.1 core library</description>
  <display-name>DZY core</display-name>
  <tlib-version>1.1</tlib-version>
  <short-name>c</short-name>
  <uri>http://DZY.set</uri><!--uri的地址调用  -->
<!-- OUT标签 -->
 <tag>
    <name>out</name>
    <tag-class>com.DZY.jsp.OutDemo</tag-class>
    <body-content>empty</body-content>
 <attribute>
     <name>value</name>
     <required>true</required>
     <rtexprvalue>true</rtexprvalue>
 </attribute>
 </tag>

   <!-- SET标签 -->
 <tag>
   <name>set</name>
   <tag-class>com.DZY.jsp.SetDemo</tag-class>
   <body-content>JSP</body-content>
   <attribute>
      <name>var</name>
      <required>false</required>
      <rtexprvalue>true</rtexprvalue>
   </attribute>
    <attribute>
      <name>value</name>
      <required>true</required>
      <rtexprvalue>true</rtexprvalue>
   </attribute>
   </tag>

   </taglib>

在JSP中操作：

<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>
  <%@  taglib   uri="http://DZY.set"   prefix="k"%>//导入地址
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Insert title here</title>
</head>
<body>
 <k:set value="你好"  var="kin"></k:set>
 <k:out value="${kin }"/>
</body>
</html>

显示结果：
自定义JSP标签

3.2 自定义if标签
If的操作:

package com.DZY.jsp;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.BodyTagSupport;
/**
 * if类
 * @author Aromanic150
 *
 */
 public class IfDemo   extends   BodyTagSupport {
    private    boolean  test;
    public boolean isTest() {
  return test;
 }
    public void setTest(boolean test) {
  this.test = test;
 } 
    @Override
    public int doStartTag() throws JspException {
     if(!test) {
      return   SKIP_BODY;//不显示标签中间的内容
     }
     return EVAL_BODY_INCLUDE;//显示标签的内容
    }  
}

tld的操作：
都在一个tld里，我就不放全部了。

<!-- if标签 -->
 <tag>
   <name>if</name>
   <tag-class>com.DZY.jsp.IfDemo</tag-class>
   <body-content>JSP</body-content>
   <attribute>
      <name>test</name>
      <required>true</required>
      <rtexprvalue>true</rtexprvalue>
   </attribute>
   </tag>

在JSP的操作：

 <k:if test="true">你好吗？</k:if>
<k:if test="false">不好</k:if>

显示结果：自定义JSP标签

3.3 自定义Foreach标签
Foreach操作：

package com.DZY.jsp;

import java.util.Iterator;
import java.util.List;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.BodyTagSupport;
import javax.swing.text.html.HTML.Tag;
public class ForeachDemo extends BodyTagSupport{
 //集合
    private List<Object> items;
    //变量的名称
     private String var;
    public List<Object> getItems() {
        return items;
    }
    public void setItems(List<Object> items) {
        this.items = items;
    }
    public String getVar() {
        return var;
    }
    public void setVar(String var) {
        this.var = var;
    }

     @Override
    public int doStartTag() throws JspException {
        // TODO Auto-generated method stub
         if(items==null||items.size()==0) {
             return SKIP_BODY;
         }
         else {
             Iterator<Object> i=items.iterator();
             pageContext.setAttribute("s", i);
             //第一次给变量进行赋值
             pageContext.setAttribute(var, i.next());
        return EVAL_BODY_INCLUDE;
      } 
         }

     @Override
    public int doAfterBody() throws JspException {
         Iterator<Object> it=(Iterator<Object>)pageContext.getAttribute("s");
     while(it.hasNext()) {
         //如何将循环读取出来的数据，显示在页面上
         pageContext.setAttribute(var, it.next());
         return EVAL_BODY_AGAIN;
     }
        return SKIP_BODY;
    }
    }

tid的操作：

   <!--foreach标签  -->
<tag>
 <name>foreach</name>
 <tag-class>com.DZY.jsp.ForeachDemo</tag-class>
 <body-content>JSP</body-content>
 <attribute>
 <name>items</name>
 <required>true</required>
 <rtexprvalue>true</rtexprvalue>
 </attribute>

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

Student类

package com.DZY.jsp;

public class Student {
 private String sid;
 private String sname;
 public Student() {
 }
 public Student(String sid, String sname) {
  this.sid = sid;
  this.sname = sname;
 }
 public String getSid() {
  return sid;
 }
 public void setSid(String sid) {
  this.sid = sid;
 }
 public String getSname() {
  return sname;
 }
 public void setSname(String sname) {
  this.sname = sname;
 }
 }

jsp代码：

  List   kin=new  ArrayList();
  kin.add(new Student("1","qqq"));
  kin.add(new Student("2","www"));
  kin.add(new Student("3","eee"));
  kin.add(new Student("4","rrr"));
  kin.add(new Student("5","ttt"));
  request.setAttribute("kin", kin);
%>
<k:foreach items="${kin}" var="as">
${as.sid} ,   ${as.sname}<br>
</k:foreach>

3.4 自定义Select 标签
Select 操作：

package com.DZY.jsp;

import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.List;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.BodyTagSupport;

import org.apache.commons.beanutils.BeanUtils;

public class SelectDemo extends  BodyTagSupport{
 private static final long serialVersionUID = 1L;
    private String id;
    private String name;
    private List<Object> items = new ArrayList<Object>();
    private String textKey;
    private String textval;
    private String headTextKey;
    private String headTextVal;
    private String selectedval;
    
    public String getId() {
        return id;
    } 
    public void setId(String id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public List<Object> getItems() {
        return items;
    }
    public void setItems(List<Object> items) {
        this.items = items;
    }
    public String getTextKey() {
        return textKey;
    }
    public void setTextKey(String textKey) {
        this.textKey = textKey;
    }
    public String getTextval() {
        return textval;
    }
    public void setTextval(String textval) {
        this.textval = textval;
    }
    public String getHeadTextKey() {
        return headTextKey;
    }
    public void setHeadTextKey(String headTextKey) {
        this.headTextKey = headTextKey;
    }
    public String getHeadTextVal() {
        return headTextVal;
    }
    public void setHeadTextVal(String headTextVal) {
        this.headTextVal = headTextVal;
    }
    public String getSelectedval() {
        return selectedval;
    }
    public void setSelectedval(String selectedval) {
        this.selectedval = selectedval;
    }
    
    @Override
    public int doStartTag() throws JspException {
        JspWriter out = pageContext.getOut();
        try {
            out.write(toHTML());
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return super.doStartTag();
    }
     /**
     * 拼接出下拉列表所对应的select的html代码 
     * <select id='' name=''>
     *  <option value='-1'selected>=======请选择======</option>
     *   </select>
     */
    private String toHTML() throws Exception {
        StringBuilder sb = new StringBuilder();
        sb.append("<select id='" + id + "' name='" + name + "'>");
        if (headTextKey == null || "".equals(headTextKey) || headTextVal == null || "".equals(headTextVal)) {
            sb.append("<option value='" + headTextKey + "' selected>" + headTextVal + "</option>");
        }
        String val;
        String html;
        for (Object obj : items) {
            // 要让学生的id存入数据库，让学生的名字展示在jsp页面
            // <option value='s001'>ls</option>
            // obj sid sname
            Field textKeyField = obj.getClass().getDeclaredField(textKey);
            textKeyField.setAccessible(true);
            val = (String) textKeyField.get(obj);
            html = BeanUtils.getProperty(obj, textval);
            if(val.equals(selectedval)) {
                sb.append(" <option value='"+val+"'selected>"+html+"</option>");
            }else {
                sb.append("<option value='"+val+"'>"+html+"</option>");
            }
        }
        sb.append("</select>");
        return sb.toString();
    }
}

tid的操作

<!--select标签  -->
<tag>
        <name>select</name>
        <tag-class>com.DZY.jsp.SelectDemo</tag-class>
        <body-content>JSP</body-content>
        <attribute>
            <name>id</name>
            <required>false</required>
            <rtexprvalue>false</rtexprvalue>
        </attribute>
        <attribute>
            <name>name</name>
            <required>false</required>
            <rtexprvalue>false</rtexprvalue>
        </attribute>
        <attribute>
            <name>items</name>
            <required>true</required>
            <rtexprvalue>true</rtexprvalue>
        </attribute>
        <attribute>
            <name>textKey</name>
            <required>true</required>
            <rtexprvalue>false</rtexprvalue>
        </attribute>
        <attribute>
            <name>textVal</name>
            <required>true</required>
            <rtexprvalue>false</rtexprvalue>
        </attribute>
        <attribute>
            <name>headTextKey</name>
            <required>false</required>
            <rtexprvalue>false</rtexprvalue>
        </attribute>
        <attribute>
            <name>headTextVal</name>
            <required>false</required>
            <rtexprvalue>false</rtexprvalue>
        </attribute>
        <attribute>
            <name>selectedVal</name>
            <required>false</required>
            <rtexprvalue>true</rtexprvalue>
        </attribute>
    </tag>

jsp代码

<%
  List   kin=new  ArrayList();
  kin.add(new Student("1","qqq"));
  kin.add(new Student("2","www"));
  kin.add(new Student("3","eee"));
  kin.add(new Student("4","rrr"));
  kin.add(new Student("5","ttt"));
  request.setAttribute("kin", kin);
%>
  <k:select textVal="sname" items="sid" textKey="${kin }"></k:select>
 <k:select headTextKey="-1" headTextVal="===请选择学生===" itmes="${kin}"    textKey="sid"   textVal="sname"></k:select>

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