How to output HTML from JSP <%! … %> block?

Question

I just started learning JSP technology, and came across a wall.

How do you output HTML from a method in <%! ... %> JSP declaration block?

This do

Answer 1

You can't use the 'out' variable (nor any of the other "predeclared" scriptlet variables) inside directives.

The JSP page gets translated by your webserver into a Java servlet. Inside tomcats, for instance, everything inside scriptlets (which start "<%"), along with all the static HTML, gets translated into one giant Java method which writes your page, line by line, to a JspWriter instance called "out". This is why you can use the "out" parameter directly in scriptlets. Directives, on the other hand (which start with "<%!") get translated as separate Java methods.

As an example, a very simple page (let's call it foo.jsp):

    
    
        <%!
            String someOutput() {
                return "Some output";
            }
        %>
        <% someOutput(); %>
    

would end up looking something like this (with a lot of the detail ignored for clarity):

public final class foo_jsp
{
    // This is where the request comes in
    public void _jspService(HttpServletRequest request, HttpServletResponse response) 
        throws IOException, ServletException
    {
        // JspWriter instance is gotten from a factory
        // This is why you can use 'out' directly in scriptlets
        JspWriter out = ...; 

        // Snip

        out.write("");
        out.write("");
        out.write("");
        out.write(someOutput()); // i.e. write the results of the method call
        out.write("");
        out.write("");
    }

    // Directive gets translated as separate method - note
    // there is no 'out' variable declared in scope
    private String someOutput()
    {
        return "Some output";
    }
}