jsp自定义标签
1.生命周期图:
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
2. 自定义标签开发步骤
1.1 助手类
1.2 tld
1.3 taglib
3.标签类别：
- UI标签:out,select
- 控制标签:if,foreach
- 数据标签:set
4.自定义标签 set、out、if、foreach、select 代码：
teacher实体类
package xiaoyi.entity;
public class Teacher {
private String tid;
private String tname;
public String getTid() {
return tid;
}
public void setTid(String tid) {
this.tid = tid;
}
public String getTname() {
return tname;
}
public void setTname(String tname) {
this.tname = tname;
}
@Override
public String toString() {
return "Teacher [tid=" + tid + ", tname=" + tname + "]";
}
public Teacher(String tid, String tname) {
super();
this.tid = tid;
this.tname = tname;
}
public Teacher() {
super();
}
}
setTag
package com.xiaoyi.jsp.tag;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.BodyTagSupport;
/**
*set标签属于数据标签 不需要展示内容
*作用：是将value赋值给var
*
*/
public class SetTag extends BodyTagSupport {
private static final long serialVersionUID = -3333181484204403802L;
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);
return SKIP_BODY;//跳过主体，不需要展示内容
}
}
outTag
package com.xiaoyi.jsp.tag;
import java.io.IOException;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.BodyTagSupport;
/**
*把set用out来打印出来
*out属于ui标签 (需要展示效果，是依靠属标签性展示页面效果)
*jspWriter对象(流)
*/
public class OutTag extends BodyTagSupport {
private static final long serialVersionUID = -3333181484204403802L;
private Object value;
public Object getValue() {
return value;
}
public void setValue(Object value) {
this.value = value;
}
@Override
public int doStartTag() throws JspException {
JspWriter out= pageContext.getOut();
try {
out.print(value);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return super.doStartTag();
}
}
ifTag
package com.xiaoyi.jsp.tag;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.BodyTagSupport;
/**
*if属于控制标签（页面展示效果依赖的是标签体）
*/
public class ifTag extends BodyTagSupport {
private static final long serialVersionUID = -3333181484204403802L;
private boolean test;
public boolean isTest() {
return test;
}
public void setTest(boolean test) {
this.test = test;
}
@Override
public int doStartTag() throws JspException {
return test? EVAL_BODY_INCLUDE :SKIP_BODY;//为true计算标签体，为false跳过标签体
}
}
foreachTag
package com.xiaoyi.jsp.tag;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.BodyTagSupport;
public class ForeachTag extends BodyTagSupport {
private static final long serialVersionUID = -3333181484204403802L;
private String var;
private List<Object>items=new ArrayList<Object>();
public String getVar() {
return var;
}
public void setVar(String var) {
this.var = var;
}
public List<Object> getItems() {
return items;
}
public void setItems(List<Object> items) {
this.items = items;
}
@Override
public int doStartTag() throws JspException {
Iterator<Object>it= items.iterator();//迭代器遍历
pageContext.setAttribute(var, it.next());//指针往下移
pageContext.setAttribute("it", it);//当前迭代器遍历的状态传到下一个方法
return EVAL_BODY_INCLUDE;
}
@Override
public int doAfterBody() throws JspException {
//获取原来状态的迭代器，而并非新创建一个迭代器.it不同的引用 同一个对象，指向也是同一个
Iterator<Object>it=(Iterator<Object>) pageContext.getAttribute("it");//拿到上面迭代器的状态
if(it.hasNext()) {//有下一个就跳
pageContext.setAttribute(var, it.next());//先输出新的主体
pageContext.setAttribute("it", it);//保存到下一次循环中
return EVAL_BODY_AGAIN;//就一直循环
}else {
return EVAL_PAGE;//为false就结束
}
}
}
selectTag
package com.xiaoyi.jsp.tag;
import java.io.IOException;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
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.PropertyUtils;
/**
* 自定义select标签应具备的功能
* 1.新增查询页面，只要通过一个标签就可以完成数据的绑定，而并非使用c:foreach绑定
* 2.修改页面，同样通过一个自定义标签完成数据的遍历的展示，以及默认选中指定项
*
* 思考：
* 1.要往后台传值 id,name
* 2.定义数据库存储的对应的标签属性，前台页面展示的标签属性 textKey,textVal
* 3.定义下拉框的默认值headerTextKey,headTextVal
* 4.下拉框需要加载数据 items
* 5.属性值接受数据库中保存的value值 selectedVal
*
* 属于UI标签
*
*
*/
public class SelectTag extends BodyTagSupport{
private static final long serialVersionUID = -3333181484204403802L;
private String id;
private String name;
private List<Object> items = new ArrayList<>();
private String textKey;
private String textVal;
private String headerTextKey;
private String headerTextVal;
private String selectedVal;
@Override
public int doStartTag() throws JspException {
JspWriter out= pageContext.getOut();//获取流对象
try {
//之所以能够在页面上看到 select下拉框的效果原因在于后台做了html代码的拼接
out.print(toHTML());
} catch (IOException | NoSuchFieldException | SecurityException | IllegalArgumentException | IllegalAccessException | InvocationTargetException | NoSuchMethodException e) {
e.printStackTrace();
}
return super.doStartTag();
}
private String toHTML() throws NoSuchFieldException, SecurityException, IllegalArgumentException, IllegalAccessException, InvocationTargetException, NoSuchMethodException {
StringBuilder sb=new StringBuilder();
String value="";
String html="";
sb.append("<select id='"+id+"' name='"+name+"'>");
if(!(headerTextKey==null || "".equals(headerTextKey)||headerTextVal==null ||"".equals(headerTextVal))) {
//默认选中第一行
sb.append("<option selected value='"+headerTextKey+"'>"+headerTextVal+"</option>");
}
//items=teas,textKey=tid,textVal=tname
for (Object obj : items) {
//一种方法：底层代码
Field f=obj.getClass().getDeclaredField(textKey);
f.setAccessible(true);//设置访问条件
value=(String) f.get(obj);
//第二种方法：第三方工具包
html=(String) PropertyUtils.getProperty(obj, textVal);
//考虑如果是修改界面需要下拉框回选所存储的值
if(value.equals(selectedVal)) {//为空不是修改界面
sb.append("<option selected value='"+value+"'>"+html+"</option>");
}else {//反之修改界面
sb.append("<option value='"+value+"'>"+html+"</option>");
}
}
sb.append("</select>");
return sb.toString();
}
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 getHeaderTextKey() {
return headerTextKey;
}
public void setHeaderTextKey(String headerTextKey) {
this.headerTextKey = headerTextKey;
}
public String getHeaderTextVal() {
return headerTextVal;
}
public void setHeaderTextVal(String headerTextVal) {
this.headerTextVal = headerTextVal;
}
public String getSelectedVal() {
return selectedVal;
}
public void setSelectedVal(String selectedVal) {
this.selectedVal = selectedVal;
}
}
x.tld
<?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>xy 1.1 core library</description>
<display-name>xy core</display-name>
<tlib-version>1.1</tlib-version>
<short-name>c</short-name>
<uri>/xy</uri>
<tag>
<!-- 填写的是标签库中的标签 -->
<name>demo</name>
<!-- 标签对应的后台助手类 -->
<tag-class>com.xiaoyi.jsp.tag.DemoTag</tag-class>
<!-- 标签类别 -->
<body-content>JSP</body-content>
<attribute>
<!-- 自定义标签中的属性 -->
<name>test</name>
<!-- 属性值是否必填 -->
<required>true</required>
<!-- 是否支持表达式EL表达式/ognl表达式 -->
<rtexprvalue>false</rtexprvalue>
</attribute>
</tag>
<!-- set标签 -->
<tag>
<name>set</name>
<tag-class>com.xiaoyi.jsp.tag.SetTag</tag-class>
<body-content>JSP</body-content>
<attribute>
<name>var</name>
<required>true</required>
<rtexprvalue>false</rtexprvalue>
</attribute>
<attribute>
<name>value</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
</tag>
<!-- out标签 -->
<tag>
<name>out</name>
<tag-class>com.xiaoyi.jsp.tag.OutTag</tag-class>
<body-content>JSP</body-content>
<attribute>
<name>value</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
</tag>
<!-- if标签 -->
<tag>
<name>if</name>
<tag-class>com.xiaoyi.jsp.tag.ifTag</tag-class>
<body-content>JSP</body-content>
<attribute>
<name>test</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
</tag>
<!-- foreach标签 -->
<tag>
<name>foreach</name>
<tag-class>com.xiaoyi.jsp.tag.ForeachTag</tag-class>
<body-content>JSP</body-content>
<attribute>
<name>var</name>
<required>true</required>
<rtexprvalue>false</rtexprvalue>
</attribute>
<attribute>
<name>items</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
</tag>
<!-- select标签 -->
<tag>
<name>select</name>
<tag-class>com.xiaoyi.jsp.tag.SelectTag</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>headerTextKey</name>
<required>false</required>
<rtexprvalue>false</rtexprvalue>
</attribute>
<attribute>
<name>headerTextVal</name>
<required>false</required>
<rtexprvalue>false</rtexprvalue>
</attribute>
<attribute>
<name>selectedVal</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
</tag>
</taglib>
Demo2
<%@page import="xiaoyi.entity.Teacher"%>
<%@page import="java.util.ArrayList"%>
<%@page import="java.util.List"%>
<%@ page language="java" contentType="text/html; charset=utf-8"
pageEncoding="utf-8"%>
<%@taglib uri="/xy" prefix="x"%>
<!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>jsp第二堂课的案例</title>
</head>
<body>
<h2>out标签输出</h2>
<x:set var="name" value="zs"></x:set>
<x:out value="${name }"></x:out>
<h2>if标签</h2>
<x:if test="true">haha</x:if>
<x:if test="false">hehe</x:if>
<hr>
<%
List l=new ArrayList();
l.add(new Teacher("1","鸵"));
l.add(new Teacher("2","鸟"));
l.add(new Teacher("3","蛋"));
pageContext.setAttribute("teas", l);
%>
<h2>foreach标签</h2>
<x:foreach items="${teas }" var="t">
${t.tid},${t.tname}<br>
</x:foreach>
<%-- <x:select ></x:select> --%>
<h2>select标签 新增查询页面下拉框</h2>
<x:select textVal="tname" items="${teas}" textKey="tid"></x:select>
<hr>
<x:select headerTextKey="-1" headerTextVal="==请选择==" textVal="tname" items="${teas}" textKey="tid"></x:select>
<h2>修改页面下拉框</h2>
<x:select headerTextKey="-1" headerTextVal="==请选择==" textVal="tname" items="${teas}" textKey="tid" selectedVal="3"></x:select>
</body>
</html>
展示的效果
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