如何在标记中设置JSP变量以使用<％= viewEditPromotionURL>进行读取？

Question

I was thinking such variable can only be set by Java code:

<%
    String viewEditPromotionURL="http://promotion.info";
%>

but I found that it can also be set in custom tag:

<portlet:actionURL name="editPromotion" var="editPromotionURL" />

How tag can set variable visible by <%=...> ?

Can me myself do this? For example:

<%
   String variableName = "myvariable";
   String variableValue = "myvalue";
   // secret part to store myvalue into myvariable
%>

<p>Variable = <%= myvariable%></p>

Is this possible? What to write in the secret part?

Answer 1

If you look at the output from Jasper (the JSP Compiler), the <%= myvariable %> tag is converted to:

javax.servlet.jsp.JspWriter out = pageContext.getOut();
out.print(myvariable);

This means myvariable must be defined somewhere public void _jspService(final javax.servlet.http.HttpServletRequest request, final javax.servlet.http.HttpServletResponse response) can see it. Your only options are either inside the JSP page like your first code snipit, or at the class level using <%! %> <%! %> . In the <portlet:> example you are using a taglib to add variables which you can learn more about here .