本文執行個體講述了jsp中自訂標籤用法。分享給大家供大家參考。具體如下：
這裡簡單的寫了一個自訂標籤，自己定義標籤的好處就是在jsp頁面中可以使用自己定義的功能，完全與Java代碼分離
1. tld檔案如下：
首先是要寫×.tld檔案，當項目隨著伺服器啟動的時候，會檢查項目中有沒有*tld檔案。
寫的tld檔案
<?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"> <!-- 定義版本 --> <tlib-version>1.0</tlib-version> <!-- 定義名字 --> <short-name>apsliyuan</short-name> <!-- 定義uri --> <uri>http://my.oschina.net/aps</uri> <!-- 定義自己的類 --> <tag> <!-- name 就是在jsp中顯示的標籤名字，<aps:hellowTag/> --> <name>hellowTag</name> <!-- 自己寫的標籤類的完整路徑 --> <tag-class>cn.itcast.apsliyuan.tag.HellowtTag</tag-class> <!-- jsp中主題中是不是要顯示內容，有四個屬性， 如果為empty的話。在jsp頁面中標籤就不能定義自己的內容了，否則會報 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 異常 --> <body-content>JSP</body-content> </tag><!-- 這裡沒有寫屬性，有時間補上 --> <tag> <name>ApsliyuanTag</name> <tag-class>cn.itcast.apsliyuan.tag.ApsliyuanTag</tag-class> <body-content>JSP</body-content> </tag></taglib>
2. 自訂標籤類java代碼如下：
//自訂標籤的類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/>標籤執行完畢了"); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } return EVAL_PAGE; }}
3. jsp引入自己定義標籤代碼如下：
//jsp中引入自己定義的標籤<%@ 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> 現在的時間是：<aps:hellowTag> </aps:hellowTag><br/> <hr/> 我愛的人是： <aps:ApsliyuanTag/></body></html>
4. TagSupport代碼如下：
//看看TagSupport中的原始碼， 這個是適配器模式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的傳回值
在doStartTag返回的值決定的body部分的資料如何顯示。
兩個傳回值：
0 – SKIP_BODY – 常量。不顯示body。
1－EVAN_BODY_INCLUDE ;包含body部分的資料，正常顯示。
3：在doEndTag也有兩個傳回值
決定後面的頁面部分是否顯示：
SKIP_PAGE : 不再顯示後面的頁面部分。
EVAL_PAGE : 顯示後面的page部分。
希望本文所述對大家的JSP程式設計有所協助。
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