jstl c:choose>、<c:when>和<c:otherwise>标签的自定义开发

<c:choose>
<c:when test="${param.age>24}">大学毕业</c:when>
<c:when test="${param.age>20}">高中毕业</c:when>
<c:otherwise>高中以下学历</c:otherwise>
</c:choose>

》开发三个标签 choose when otherwise

》其中when标签中有一个Boolean类型的属性：test

》choose是when和otherwise的父标签，when在otherwise之前使用

》在父标签中定义一个“全局”的Boolean类型的flag：用于判断子标签在满足条件的情况下是否执行

      >若when的test为true，且when的父标签flag也为true，则执行when的标签体（正常输出标签体内容）同时将flag设置为false

      >若when的test为true，且when的父标签flag为false，则不执行标签体

      >若flag为true，otherwise执行标签体

choose类

public class ChooseTag extends SimpleTagSupport {
    private boolean flag = true;
    public void setFlag(boolean flag) {
        this.flag = flag;
    }
    public boolean isFlag() {
        return flag;
    }
    @Override
    public void doTag() throws JspException, IOException {
        getJspBody().invoke(null);
    }

when类

public class WhenTag extends SimpleTagSupport {
    private boolean test;
    public void setTest(boolean test) {
        this.test = test;
    }
    @Override
    public void doTag() throws JspException, IOException {
        if(test){
            //得到父标签的引用
            ChooseTag chooseTag = (ChooseTag) getParent();
            Boolean flag = chooseTag.isFlag();
            if(flag){
                getJspBody().invoke(null);
                chooseTag.setFlag(false);
            }
        }
    }

otherwise类

public class OtherWiseTag extends SimpleTagSupport {
    @Override
    public void doTag() throws JspException, IOException {
        ChooseTag chooseTag = (ChooseTag) getParent();
        if(chooseTag.isFlag()){
            getJspBody().invoke(null);
        }
    }

test.jsp

<!-- 导入标签库文件(自定义) -->
<%@taglib uri="http://www.wlc.com/myTag/core" prefix="wlc"%>

<wlc:choose>
        <wlc:when test="${param.age>24}">大学毕业</wlc:when>
        <wlc:when test="${param.age>20}">高中毕业</wlc:when>
        <wlc:otherwise>高中以下学历</wlc:otherwise>
    </wlc:choose>

tld文件

<tag>
        <name>choose</name>
        <tag-class>cn.stud.wlc.tag.ChooseTag</tag-class>
        <body-content>scriptless</body-content>
    </tag>

    <tag>
        <name>when</name>
        <tag-class>cn.stud.wlc.tag.WhenTag</tag-class>
        <body-content>scriptless</body-content>
        <attribute>
            <name>test</name>
            <required>true</required>
            <rtexprvalue>true</rtexprvalue>
        </attribute>
    </tag>

    <tag>
        <name>otherwise</name>
        <tag-class>cn.stud.wlc.tag.OtherWiseTag</tag-class>
        <body-content>scriptless</body-content>
    </tag>