Taglib原理和实现：El和JSTL标签

＜%
String name="diego";
request.setAttribute("name",name);
%＞
＜c:out value="${name}"/＞
......

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;
}
}

＜!--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＞

＜%@ 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＞