Taglib原理和实现之El表达式和JSTL标签
时间:2010-12-14
1、问题：你想和jstl共同工作。比如，在用自己的标签处理一些逻辑之后，让jstl处理余下的工作。
2、看这个jsp例子：
....
<%
String name="diego";
request.setAttribute("name",name);
%>
<c:out value="${name}"/>
......
许多jstl标签支持El表达式，所以，只要你在自己的标签内部把值塞进request，其他jstl标签就能使用它们
3、下面这个例子，从request里面取得对象，找到它属性的值，塞到request里去。
package diegoyun;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.TagSupport;
import org.apache.commons.beanutils.PropertyUtils;
import org.apache.taglibs.standard.lang.support.ExpressionEvaluatorManager;
public class SetVarTag extends TagSupport
{
private Object value = null;
private String property = null;
private String var = null;
public void setVar(String var)
{
this.var = var;
}
public void setProperty(String property)
{
this.property = property;
}
public void setValue(Object value)throws JspException{
this.value = ExpressionEvaluatorManager.evaluate("value", value.toString(), Object.class, this, pageContext);
}
public int doEndTag() throws JspException{
Object propertyValue = null;
try{
propertyValue = PropertyUtils.getProperty(value, property);
}
catch (Exception e) {
throw new JspException(e);
}
pageContext.setAttribute(var,propertyValue);
return EVAL_PAGE;
}
}
Taglib?-àíoíêμ????El±í′?ê?oíJSTL±ê??(2)
ê±??:2010-12-14
±àD′tld
<!--SetVarTag-->
<tag>
??<name>set</name>
??<tag-class>diegoyun.SetVarTag</tag-class>
??<body-content>empty</body-content>
??<attribute>
????<name>value</name>
????<required>true</required>
????<rtexprvalue>true</rtexprvalue>
??</attribute>
??<attribute>
????<name>property</name>
????<required>false</required>
????<rtexprvalue>false</rtexprvalue>
??</attribute>
??<attribute>
????<name>var</name>
????<required>false</required>
????<rtexprvalue>false</rtexprvalue>
??</attribute>
</tag>
±àD′jsp
<%@ page language="java" %>
<%@ page import="diegoyun.vo.*"%>
<%@ taglib uri="/WEB-INF/tlds/diego.tld" prefix="diego"%>
<%@ taglib uri="/WEB-INF/tlds/c.tld" prefix="c"%>
<html>
<body bgcolor="#FFFFFF">
<%
??Man man = new Man();
??man.setName("diego");
??request.setAttribute("man",man);
%>
Get value from request and set it''s property value into request:<br>
<diego:set value="${man}" property="name" var="myname"/>
now use OutTag of jstl taglib to get the name:<br>
value is : <c:out value="${myname}" />
</body>
</html>
??DD￡?D§1?è???￡o
Get value from request and set it''s property value into request:
now use OutTag of jstl taglib to get the name:
value is : diego
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