JSP2.0中Simple Tag介绍

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JSP Servlet XML Web SUN

JSP2.0中为了简化标签的复杂性，增加了制作Simple Tag的标签类SimpleTagSupport类。SimpleTagSupport类是实现SimpleTag接口的。它只需要实现一个doTag()方法即可，而不需要一堆回传值。

举例说明：
例1：HelloSimpleTag标签

第一步：制作标签处理类
AddSimpleTag.java

package com.newould.taglib;

import java.io.*;
import javax.servlet.jsp.*;
import javax.servlet.jsp.tagext.*;

public class AddSimpleTag extends SimpleTagSupport {

private int num1 = 0;
private int num2 = 0;

public void setNum1(int num1) {
this.num1 = num1;
}

public void setNum2(int num2) {
this.num2 = num2;
}

public void doTag() throws JspException, IOException {

JspContext ctx = getJspContext();
JspWriter out = ctx.getOut();

int sum = num1 + num2;
ctx.setAttribute("sum", Integer.toString(sum));

out.println(num1 + " + " + num2 + " = " + sum);
}
}

第二步：编写标签性质文件
MyTaglib.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 web-jsptaglibrary_2_0.xsd"
version="2.0">

<description>My Taglib by JavaWorld.com.tw</description>
<tlib-version>1.0</tlib-version>
<jsp-version>2.0</jsp-version>
<short-name>Mytaglib</short-name>
<uri></uri>
......

<tag>
<description>Add Simple Tag</description>
<name>Add</name>
<tag-class>com.newould.taglib.AddSimpleTag</tag-class>
<body-content>empty</body-content>

<attribute>
<name>num1</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
</attribute>

第三步：编写Jsp网页
HelloSimpleTag.jsp

<%@ page contentType="text/html;charset=GB2312" %>
<%@ taglib uri="/WEB-INF/tlds/MyTaglib.tld" prefix="mytag" %>

<html>
<head>
<title>HelloSimpleTag.jsp</title>
</head>
<body>

<h2>Simple Tag 标签</h2>

</body>
</html>

例2：AddSimpleTag标签
第一步：制作标签处理类
HelloSimpleTag.java

package com.newould.taglib;

import java.io.*;
import javax.servlet.jsp.*;
import javax.servlet.jsp.tagext.*;

public class HelloSimpleTag extends SimpleTagSupport {

public void doTag() throws JspException, IOException {

JspWriter out = getJspContext().getOut();
out.println("Hello Simple Tag");
}
}

第二步：编写标签性质文件
MyTaglib.tld

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

<tag>
<description>Hello Simple Tag</description>
<name>HelloSimpleTag</name>
<tag-class>com.newould.taglib.HelloSimpleTag</tag-class>
<body-content>empty</body-content>
</tag>
</taglib>

第三步：编写Jsp网页
AddSimpleTag.jsp

%@ page contentType="text/html;charset=GB2312" %>
<%@ taglib uri="/WEB-INF/tlds/MyTaglib.tld" prefix="mytag" %>

<html>
<head>
<title>AddSimpleTag.jsp</title>
</head>
<body>

<h2>AddSimpleTag 标签</h2>

最后结果：${sum}

</body>
</html>

例3 RepeatSimpleTag标签
RepeatSimpleTag标签主要是用来重复显示某段文字。
这个例子在处理上与前两个例子有点不同

第一步：制作标签处理类
RepeatSimpleTag.java

package com.newould.taglib;

import java.io.*;
import javax.servlet.jsp.*;
import javax.servlet.jsp.tagext.*;

public class RepeatSimpleTag extends SimpleTagSupport {

private int count = 0;//重复的次数
private JspFragment fragment;//重复的内容

public void setCount(int count) {
this.count = count;
}

public void setFragment(JspFragment fragment) {
this.fragment = fragment;
}

public void doTag() throws JspException, IOException {

JspContext ctx = getJspContext();
JspWriter out = ctx.getOut();

for(int i=0 ; i<count ; i++) {
fragment.invoke(null);//表示将fragment的内容显示出来
}
}
}

第二步：编写标签性质文件
MyTaglib.tld

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

<tag>
<description>Repeate Simple Tag</description>
<name>Repeat</name>
<tag-class>com.newould.taglib.RepeatSimpleTag</tag-class>
<body-content>empty</body-content>

<attribute>
<name>count</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
</attribute>

<attribute>
<name>fragment</name>
<required>true</required>
<fragment>true</fragment>
</attribute>
</tag>

</taglib>

注意：<fragment>true</fragment>，一定要这样设定fragment属性。

第三步：编写Jsp网页
RepeatSimpleTag.jsp

<%@ page contentType="text/html;charset=GB2312" %>
<%@ taglib uri="/WEB-INF/tlds/MyTaglib.tld" prefix="mytag" %>

<html>
<head>
<title>RepeatSimpleTag.jsp</title>
</head>
<body>

<h2>RepeatSimpleTag 标签</h2>

<mytag:Repeat count="5" >
<jsp:attribute name="fragment">
重复执行 ....<br>
</jsp:attribute>
</mytag:Repeat>
</body>
</html>

DynamicAttributes接口
只要制作的标签实现了DynamicAttributes接口就有动态属性的功能。
例如:我们要做多个数的累加运算,则AddSimpleTag标签就可以通过实现DynamicAttributes接口就可以实现了.

实现DynamicAttributes接口,必须实现setDynamicAttributes()方法,此方法用来接收动态属性.

举例:第一步：制作标签处理类

package com.newould.taglib;

import java.io.*;
import java.util.*;
import javax.servlet.jsp.*;
import javax.servlet.jsp.tagext.*;

public class DynamicAdd extends SimpleTagSupport implements DynamicAttributes {

//用来接收动态属性
private ArrayList keys = new ArrayList();
private ArrayList values = new ArrayList();

public void doTag() throws JspException, IOException {

JspContext ctx = getJspContext();
JspWriter out = ctx.getOut();

float num = 0;
float sum = Float.parseFloat((String)values.get(0));
out.print(sum);

for (int i = 1 ; i < keys.size() ; i++) {
String temp = (String)values.get(i);
num = Float.parseFloat(temp);
sum = sum + num;
out.print(" + " + num);
}

out.print(" = " + sum);
ctx.setAttribute("sum", Float.toString(sum));

}

public void setDynamicAttribute(String uri, String name, Object value) throws JspException {
keys.add(name);
values.add(value);
}
}

第二步：编写标签性质文件
<tag>
<description>DynamicAttribute</description>
<name>DynAdd</name>
<tag-class>com.newould.taglib.DynamicAdd</tag-class>
<body-content>empty</body-content>

<dynamic-attributes>true</dynamic-attributes>
</tag>

第三步：编写Jsp网页
<%@ page contentType="text/html;charset=GB2312" %>
<%@ taglib prefix="JSPBook" tagdir="/WEB-INF/tags/" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

<html>
<head>
<title>CH16 - DynAdd.jsp</title>
</head>
<body>

<JSPBook:DynAdd num1="111" num2="222" num3="444" >

<jsp:attribute name="great">
<font color="red">SUM：${sum} ...</red>
</jsp:attribute>
<jsp:attribute name="less">
<font color="blue">SUM：${sum} ...</red>
</jsp:attribute>
</JSPBook:DynAdd>

</body>
</html>

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2007-01-24 02:40
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