jsp中自定义标签用法实例分析
编程学习 2021-07-05 11:23www.dzhlxh.cn编程入门
这篇文章主要介绍了jsp中自定义标签用法,以实例形式较为详细的分析了jsp自定义标签的功能、定义及具体实现技巧,具有一定参考借鉴价值,需要的朋友可以参考下
本文实例讲述了jsp中自定义标签用法。分享给大家供大家参考。具体如下：
这里简单的写了一个自定义标签，自己定义标签的好处就是在jsp页面中可以使用自己定义的功能，完全与Java代码分离
1. tld文件如下：
首先是要写×.tld文件，当项目随着服务器启动的时候，会检查项目中有没有*tld文件。
写的tld文件
<?xml version="1.0" encoding="UTF-8" ?>
<taglib xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-jsptaglibrary_2_1.xsd"
version="2.1">
<!-- 定义版本 -->
<tlib-version>1.0</tlib-version>
<!-- 定义名字 -->
<short-name>apsliyuan</short-name>
<!-- 定义uri -->
<uri>http://my.oschina.net/aps</uri>
<!-- 定义自己的类 -->
<tag>
<!-- name 就是在jsp中显示的标签名字，<aps:hellowTag/> -->
<name>hellowTag</name>
<!-- 自己写的标签类的完整路径 -->
<tag-class>cn.itcast.apsliyuan.tag.HellowtTag</tag-class>
<!-- jsp中主题中是不是要显示内容，有四个属性， 如果为empty的话。在jsp页面中标签就不能定义自己的内容了，否则会报 Servlet.service()
for servlet jsp threw exception org.apache.jasper.JasperException: /index.jsp(12,8)
According to TLD, tag aps:hellowTag must be empty, but is not 异常
-->
<body-content>JSP</body-content>
</tag>
<!--
这里没有写属性，有时间补上
-->
<tag>
<name>ApsliyuanTag</name>
<tag-class>cn.itcast.apsliyuan.tag.ApsliyuanTag</tag-class>
<body-content>JSP</body-content>
</tag>
</taglib>
2. 自定义标签类java代码如下：
//自定义标签的类
package cn.itcast.apsliyuan.tag;
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Date;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.TagSupport;
public class HellowtTag extends TagSupport{
/**
*
*/
private static final long serialVersionUID = 1781703371130382609L;
@Override
public int doStartTag() throws JspException {
// TODO Auto-generated method stub
JspWriter out = pageContext.getOut();
SimpleDateFormat format=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
try {
out.print(format.format(new Date()));
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return EVAL_BODY_INCLUDE;
}
@Override
public int doEndTag() throws JspException {
// TODO Auto-generated method stub
JspWriter out = pageContext.getOut();
try {
out.print("<br/> <hr/>标签执行完毕了");
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return EVAL_PAGE;
}
}
3. jsp引入自己定义标签代码如下：
//jsp中引入自己定义的标签 <%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%> <%@taglib uri="http://my.oschina.net/aps" prefix="aps" %> <%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%> <!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>index.jsp</title> </head> <body> 现在的时间是：<aps:hellowTag> </aps:hellowTag><br/> <hr/> 我爱的人是： <aps:ApsliyuanTag/> </body> </html>
4. TagSupport代码如下：
//看看TagSupport中的源代码， 这个是适配器模式
public class TagSupport implements IterationTag, Serializable {
public static final Tag findAncestorWithClass(Tag from,
// TCK signature test fails with generics
@SuppressWarnings("unchecked")
Class klass) {
boolean isInterface = false;
if (from == null ||
klass == null ||
(!Tag.class.isAssignableFrom(klass) &&
!(isInterface = klass.isInterface()))) {
return null;
}
for (;;) {
Tag tag = from.getParent();
if (tag == null) {
return null;
}
if ((isInterface && klass.isInstance(tag)) ||
klass.isAssignableFrom(tag.getClass()))
return tag;
else
from = tag;
}
}
/**
* Default constructor, all subclasses are required to define only
* a public constructor with the same signature, and to call the
* superclass constructor.
*
* This constructor is called by the code generated by the JSP
* translator.
*/
public TagSupport() { }
/**
* Default processing of the start tag, returning SKIP_BODY.
*
* @return SKIP_BODY
* @throws JspException if an error occurs while processing this tag
*
* @see Tag#doStartTag()
*/
public int doStartTag() throws JspException {
return SKIP_BODY;
}
/**
* Default processing of the end tag returning EVAL_PAGE.
*
* @return EVAL_PAGE
* @throws JspException if an error occurs while processing this tag
*
* @see Tag#doEndTag()
*/
public int doEndTag() throws JspException {
return EVAL_PAGE;
}
/**
* Default processing for a body.
*
* @return SKIP_BODY
* @throws JspException if an error occurs while processing this tag
*
* @see IterationTag#doAfterBody()
*/
public int doAfterBody() throws JspException {
return SKIP_BODY;
}
// Actions related to body evaluation
/**
* Release state.
*
* @see Tag#release()
*/
public void release() {
parent = null;
id = null;
if( values != null ) {
values.clear();
}
values = null;
}
/**
* Set the nesting tag of this tag.
*
* @param t The parent Tag.
* @see Tag#setParent(Tag)
*/
public void setParent(Tag t) {
parent = t;
}
/**
* The Tag instance most closely enclosing this tag instance.
* @see Tag#getParent()
*
* @return the parent tag instance or null
*/
public Tag getParent() {
return parent;
}
/**
* Set the id attribute for this tag.
*
* @param id The String for the id.
*/
public void setId(String id) {
this.id = id;
}
/**
* The value of the id attribute of this tag; or null.
*
* @return the value of the id attribute, or null
*/
public String getId() {
return id;
}
/**
* Set the page context.
*
* @param pageContext The PageContext.
* @see Tag#setPageContext
*/
public void setPageContext(PageContext pageContext) {
this.pageContext = pageContext;
}
/**
* Associate a value with a String key.
*
* @param k The key String.
* @param o The value to associate.
*/
public void setValue(String k, Object o) {
if (values == null) {
values = new Hashtable<String, Object>();
}
values.put(k, o);
}
/**
* Get a the value associated with a key.
*
* @param k The string key.
* @return The value associated with the key, or null.
*/
public Object getValue(String k) {
if (values == null) {
return null;
} else {
return values.get(k);
}
}
/**
* Remove a value associated with a key.
*
* @param k The string key.
*/
public void removeValue(String k) {
if (values != null) {
values.remove(k);
}
}
/**
* Enumerate the keys for the values kept by this tag handler.
*
* @return An enumeration of all the keys for the values set,
* or null or an empty Enumeration if no values have been set.
*/
public Enumeration<String> getValues() {
if (values == null) {
return null;
}
return values.keys();
}
// private fields
private Tag parent;
private Hashtable<String, Object> values;
/**
* The value of the id attribute of this tag; or null.
*/
protected String id;
// protected fields
/**
* The PageContext.
*/
protected PageContext pageContext;
}
doStartTag的返回值
在doStartTag返回的值决定的body部分的数据如何显示。
两个返回值：
0 – SKIP_BODY – 常量。不显示body。
1－EVAN_BODY_INCLUDE ;包含body部分的数据，正常显示。
3：在doEndTag也有两个返回值
决定后面的页面部分是否显示：
SKIP_PAGE : 不再显示后面的页面部分。
EVAL_PAGE : 显示后面的page部分。
希望本文所述对大家的JSP程序设计有所帮助。