JSP教程-在JSP中使用自定义标签进行迭代
我们可以使用IterationTag接口的doAfterBody()方法来迭代任何标签的体内容。
在这里，我们将使用实现IterationTag接口的TagSupport类。为了迭代体内容，我们需要在doAfterBody()方法中使用EVAL_BODY_AGAIN常量。
使用JSP自定义标签进行迭代的示例
在这个例子中，我们将使用自定义标签中的属性，该属性返回任何给定数字的幂。我们在这里创建了三个文件：
- index.jsp
- PowerNumber.java
- mytags.tld
index.jsp
<%@ taglib uri="WEB-INF/mytags.tld" prefix="m" %>
3 ^ 5 = <m:power number="3" power="5">
body
</m:power> PowerNumber.java
package cn.javatiku.taghandler;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.TagSupport;
public class PowerNumber extends TagSupport{
private int number;
private int power;
private static int counter;
private static int result=1;
public void setPower(int power) {
this.power = power;
}
public void setNumber(int number) {
this.number = number;
}
public int doStartTag() throws JspException {
return EVAL_BODY_INCLUDE;
}
public int doAfterBody() {
counter++;
result *= number;
if (counter==power)
return SKIP_BODY;
else
return EVAL_BODY_AGAIN;
}
public int doEndTag() throws JspException {
JspWriter out=pageContext.getOut();
try{
out.print(result);
}catch(Exception e){e.printStackTrace();}
return EVAL_PAGE;
}
} mytags.tld
<?xml version="1.0" encoding="ISO-8859-1" ?>
<!DOCTYPE taglib
PUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag Library 1.2//EN"
"http://java.sun.com/j2ee/dtd/web-jsptaglibrary_1_2.dtd">
<taglib>
<tlib-version>1.0</tlib-version>
<jsp-version>1.2</jsp-version>
<short-name>simple</short-name>
<uri>http://tomcat.apache.org/example-taglib</uri>
<description>A simple tab library for the examples</description>
<tag>
<name>power</name>
<tag-class>cn.javatiku.taghandler.PowerNumber</tag-class>
<attribute>
<name>number</name>
<required>true</required>
</attribute>
<attribute>
<name>power</name>
<required>true</required>
</attribute>
</tag>
</taglib> 创建循环标签（为循环创建标签）
我们创建一个循环标签，该标签迭代此标签的体内容。
index.jsp
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title>Insert title here</title>
</head>
<body>
<%@taglib prefix="m" uri="sssuri" %>
<m:loop end="5" start="1">
<p>My Name is khan</p>
</m:loop>
</body>
</html> mytags.tld
<?xml version="1.0" encoding="ISO-8859-1" ?>
<!DOCTYPE taglib
PUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag Library 1.2//EN"
"http://java.sun.com/j2ee/dtd/web-jsptaglibrary_1_2.dtd">
<taglib>
<tlib-version>1.0</tlib-version>
<jsp-version>1.2</jsp-version>
<short-name>abc</short-name>
<uri>sssuri</uri>
<tag>
<name>loop</name>
<tag-class>cn.javatiku.customtag.Loop</tag-class>
<attribute>
<name>start</name>
<required>true</required>
</attribute>
<attribute>
<name>end</name>
<required>true</required>
</attribute>
</tag>
</taglib> Loop.java
package cn.javatiku.customtag;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.TagSupport;
public class Loop extends TagSupport{
private int start=0;
private int end=0;
public void setStart(int start) {
this.start = start;
}
public void setEnd(int end) {
this.end = end;
}
@Override
public int doStartTag() throws JspException {
return EVAL_BODY_INCLUDE;
}
@Override
public int doAfterBody() throws JspException {
if(start<end){
start++;
return EVAL_BODY_AGAIN;
}else{
return SKIP_BODY;
}
}
} 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">
<jsp-config>
<taglib>
<taglib-uri>sssuri</taglib-uri>
<taglib-location>/WEB-INF/mytags.tld</taglib-location>
</taglib>
</jsp-config>
</web-app> 输出
