java 自定义标签（二）-优快云博客

本文介绍了一种使用Java实现自定义JSP标签的方法，通过继承SimpleTagSupport类并实现DynamicAttributes接口来创建一个下拉选择框标签。文章详细展示了如何在Java类中设置属性，并在JSP页面中应用该标签。

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java 自定义标签（二）

2012-03-20 13:49

继承SimpleTagSupport 类实现 DynamicAttributes接口

主要步骤

1.java类

package MyTag;

import java.io.IOException;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.PageContext;
import javax.servlet.jsp.tagext.DynamicAttributes;
import javax.servlet.jsp.tagext.SimpleTagSupport;

public class Tag2 extends SimpleTagSupport implements DynamicAttributes {

private static final String ATTR_TEMPLATE = "%s='%s'";
private static final String OPTION_TEMPLATE = "<option value='%1$s'>%1$s</option>";
private List optionsList;
private String name;
private String size;
private Map<String, Object> tagAttrs = new HashMap<String, Object>();

public void setName(String name) {
this.name = name;
}

public void setSize(String size) {
this.size = size;
}

public void setOptionsList(List optionsList) {
this.optionsList = optionsList;
}

@Override
public void doTag() throws JspException, IOException {
   PageContext pageContext = (PageContext) getJspContext();
   JspWriter out = pageContext.getOut();
   out.print("<select ");
   out.print(String.format(ATTR_TEMPLATE, "name", this.name));
   out.print(String.format(ATTR_TEMPLATE, "size", this.size));
   for (String attrName : tagAttrs.keySet()) {
    String attrDefinition = String.format(ATTR_TEMPLATE, attrName, tagAttrs.get(attrName));
    out.print(attrDefinition);
   }
   out.print(">");

for (Object option : this.optionsList) {

    String optionTag = String.format(OPTION_TEMPLATE, option.toString());
    out.println(optionTag);
   }
   out.println("</select>");
}

@Override
public void setDynamicAttribute(String uri, String name, Object value) throws JspException {

//动态加载标签的其他属性（tld文件未定义属性）例如 style="width:140px" name 为style value 为 width:140px 若存在过个其他属性时

//循环此方法
tagAttrs.put(name, value);
}
}

2.jsp文件

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
    <%@ page import="java.util.*" %>
     <%@ taglib uri="/mytag2" prefix="formTags" %>
<!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=ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
<%
List<String> colorList = new ArrayList<String>();
    colorList.add("red");
    colorList.add("blue");
    colorList.add("white");
    request.setAttribute("colorList",colorList);
%>
<form action="" method="post">
<formTags:select name="color" size="1" optionsList="${requestScope.colorList}" style="width:140px"/>
</form>
</body>
</html>

3.tld文件

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

<taglib xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3g.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee web-jsptaglibrary_2_0.xsd"
version="2.0">
<tlib-version>1.2</tlib-version>
<jsp-version>1.2</jsp-version>
<short-name>Forms Taglib</short-name>
<uri>MyTagLib2</uri>
<description>
An example tab library of replacements for the html form tags.
</description>

<tag>
<name>select</name>
<tag-class>MyTag.Tag2</tag-class>
<body-content>empty</body-content>

<attribute>
   <name>optionsList</name>
   <required>true</required>
   <rtexprvalue>true</rtexprvalue>
   <type>java.util.List</type>
</attribute>

<attribute>
   <name>name</name>
   <required>true</required>
</attribute>

<attribute>
   <name>size</name>
   <required>true</required>
</attribute>
<dynamic-attributes>true</dynamic-attributes>  //动态加载其他属性例如 style="width:140px
</tag>
</taglib>
4.web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
<display-name>MyProject</display-name>
<welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
</welcome-file-list>
<jsp-config>
    <taglib>
  <taglib-uri>/mytag2</taglib-uri>
  <taglib-location>/WEB-INF/tlds/tagLib2.tld</taglib-location>
</taglib>

</jsp-config>
</web-app>