JSP定制标记——用“脚本编程变量”取代bean来进行遍历

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Tag13.java

package tag13;

import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.BodyTagSupport;
import java.io.IOException;
import java.util.List;
import java.util.Iterator;

public class Tag13 extends BodyTagSupport {
    private List lists;
    private Iterator iters;
    public void setLists(List lists){
        this.lists = lists;
    }
    public int doStartTag() throws JspException {
        return EVAL_BODY_BUFFERED;
    }
    public void doInitBody() throws JspException {
        if (lists.size() <= 0) return;
        iters = lists.iterator();
        pageContext.setAttribute(this.id, iters.next());
    }
    public int doAfterBody() throws JspException {
        if (iters.hasNext()) {
            pageContext.setAttribute(this.id, iters.next());
            return EVAL_BODY_AGAIN;
        } else {
            try {
                bodyContent.writeOut(this.getPreviousOut());
            } catch (IOException ioe) {
                throw new JspException(ioe.getMessage());
            }
        }
        return SKIP_BODY;
    }
}

Info13.java

package tag13;

import javax.servlet.jsp.tagext.TagData;
import javax.servlet.jsp.tagext.TagExtraInfo;
import javax.servlet.jsp.tagext.VariableInfo;

public class Info13 extends TagExtraInfo {
    public VariableInfo[] getVariableInfo(TagData data) {
        return new VariableInfo[] {
            new VariableInfo(data.getId(),
            "java.lang.Object",
            true,
            VariableInfo.NESTED)
            };
    }
}

tag13.tld

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE taglib PUBLIC '-//Sun Microsystems, Inc.//DTD JSP Tag Library 1.2//EN' 'http://java.sun.com/dtd/web-jsptaglibrary_1_2.dtd'>

<taglib>
    <tlib-version>1.2</tlib-version>
    <jsp-version>1.2</jsp-version>
    <short-name>aaaaaaaaaaaaaaa</short-name>
    <info>aaaaaaaaaa</info>
    <tag>
        <name>tag13</name>
        <tag-class>tag13.Tag13</tag-class>
        <tei-class>tag13.Info13</tei-class>
        <body-content>JSP</body-content>
        <attribute>
            <name>id</name>
            <required>true</required>
            <rtexprvalue>true</rtexprvalue>
        </attribute>
        <attribute>
            <name>lists</name>
            <required>true</required>
            <rtexprvalue>true</rtexprvalue>
        </attribute>
    </tag>
</taglib>

tag13.jsp

<%@ page contentType="text/html;charset=GBK" %>
<%@ taglib prefix="tag" uri="tag13.tld" %>
<%@ page import="java.util.List,
java.util.ArrayList"
%>

结果：

aaaaaaaaaaaaaaabbbbbbbbbbbbbbbbbbbbbbbbbbbbbcccccccccccccccccccccccccccccccccccdddddddddddddddddddddddddddddddddddddddddddd

分析：

1、在标记类中每次计算Body时，以标记类的ID为key保存bean到PageContext中，然后在JSP页面中直接访问这个bean。

2、由于标记类的ID属性由TagSupport类和BodyTagSupport类进行维护，因此程序员在自己定制的标记类中无须另设定一个ID属性。