jsp中自定義標簽用法實例分析

2020-07-27 21:30:46

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本文實例講述了jsp中自定義標簽用法。分享給大家供大家參考。具體如下：

這里簡單的寫了一個自定義標簽，自己定義標簽的好處就是在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文件如下：

首先是要寫×.tld文件，當項目隨著服務器啟動的時候，會檢查項目中有沒有*tld文件。
寫的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中顯示的標簽名字，<aps:hellowTag/> -->    <name>hellowTag</name>    <!-- 自己寫的標簽類的完整路徑 -->    <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頁面中標簽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><!--   這里沒有寫屬性，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. 自定義標簽類java代碼如下：

//自定義標簽的類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/>標簽執行完畢了");    } catch (IOException e) {      // TODO Auto-generated catch block      e.printStackTrace();    }    return EVAL_PAGE;  }}

3. jsp引入自己定義標簽代碼如下：

//jsp中引入自己定義的標簽<%@ 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中的源代碼， 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的返回值

在doStartTag返回的值決定的body部分的數據如何顯示。

兩個返回值：

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