Is there a way to check whether a variable exists, like isset() in php

[jdbolt]

I want to check to see if a variable on an include page exists, is there an easy way to do this? at the oment I have:

						<%
						 if (pageHeader != null) {
						 %>
						 	<%= pageHeader %>
						 <%
						 } else {
						 %>
							 Doc ID Tool
						 <%
						 }
						%>

 

[jdbolt]

Sorry to bump but does anyone have anyone have any ideas? I am really stuck on this one. Basically I have a page include below a String declaration. In the page include (the common head file) I output the string delaration in the header tab. But I need a way to see if the String variable exists, if it doesnt, output a generic header title.

Thanks!

 

[sedj]

You cannot check if a variable exists in Java - its not a scripting langauge, but a compiled language - so if your String variable does not exist when you attempt to reference it, your JSP will not compile.

--------------------------------------------------
Free Java/J2EE Database Connection Pooling Software

http://www.primrose.org.uk

 

[sedj]

One way to achieve what you want is to do something like :

<%
String blah = null;
%>

<%@ include file="header.inc" %>

<%
if (blah != null) {
  out.println(blah);
} else {
   out.println("Hello");
}
%>

However, in header.inc, you would have do replace :

String blah = "something";

with

bla = "something";

in order to avoid compilation errors (redefining a variable name).

You would also have to make sure that in all JSPs that used that header, that they declared 'String blah = null;' before including the page.

--------------------------------------------------
Free Java/J2EE Database Connection Pooling Software

http://www.primrose.org.uk

 

[sedj]

Or actually, a sneakier way would be :

In header.inc, do not actually use a declared variable, but use the session object ...

Instead of

String bla = "something";

say :

session.setAttribute("blah", "something");

Then in your JSP :

                        <%
                         String blah = session.getAttribute("blah");
                         if (blah != null) {
                         %>
                             <%= blah %>
                         <%
                         } else {
                         %>
                             Doc ID Tool
                         <%
                         }
                        %>

--------------------------------------------------
Free Java/J2EE Database Connection Pooling Software

http://www.primrose.org.uk

 

[jdbolt]

When I do this:

<%
if (blah != null) {
  out.println(blah);
} else {
   out.println("Hello");
}
%>

I get the following :

org.apache.jasper.JasperException: Unable to compile class for JSP

An error occurred at line: 71 in the jsp file: /includes/common/header.jsp

Generated servlet error:
    [javac] Compiling 1 source file

C:\Program Files\Apache Software Foundation\Tomcat 5.5\work\Catalina\localhost\sqmdocuments\org\apache\jsp\includes\common\header_jsp.java:129: cannot find symbol
symbol  : variable pageHeader
location: class org.apache.jsp.includes.common.header_jsp
						 if (pageHeader != null) {
                                                     ^



An error occurred at line: 71 in the jsp file: /includes/common/header.jsp

Generated servlet error:
C:\Program Files\Apache Software Foundation\Tomcat 5.5\work\Catalina\localhost\sqmdocuments\org\apache\jsp\includes\common\header_jsp.java:130: cannot find symbol
symbol  : variable pageHeader
location: class org.apache.jsp.includes.common.header_jsp
						 	out.print(pageHeader);
                                                                  ^
2 errors


	org.apache.jasper.compiler.DefaultErrorHandler.javacError(DefaultErrorHandler.java:128)
	org.apache.jasper.compiler.ErrorDispatcher.javacError(ErrorDispatcher.java:351)
	org.apache.jasper.compiler.Compiler.generateClass(Compiler.java:413)
	org.apache.jasper.compiler.Compiler.compile(Compiler.java:453)
	org.apache.jasper.compiler.Compiler.compile(Compiler.java:437)
	org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:555)
	org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:291)
	org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:301)
	org.apache.jasper.servlet.JspServlet.service(JspServlet.java:248)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:802)

 

[sedj]

Whcih solution are you trying ? That error is barfing because there is no variable called "pageHeader" set.

--------------------------------------------------
Free Java/J2EE Database Connection Pooling Software

http://www.primrose.org.uk

 

[jdbolt]

I am trying

<%
	String pageHeader = "Log New Document";
		
%>
<%@ include file="includes/common/header.jsp" %>

Then

						<%
						 if (pageHeader != null) {
						 	out.print(pageHeader);
						 } else {
							out.print("Doc ID Tool");
						 } 
						%>

In the header

 

[Diancecht]

Are both snippets in the same file? Which is its name?

Cheers,
Dian

 

[sedj]

Well I've just tried it and it works fine.

1) page1.jsp :

<%

String pageHeader = null;

%>

<%@ include file="header.inc" %>

<%

if (pageHeader == null) {
	out.println("no header present");
} else {
	out.println(pageHeader);
}
%>

2) header.inc :

<%

pageHeader = "header set in include file";

%>

--------------------------------------------------
Free Java/J2EE Database Connection Pooling Software

http://www.primrose.org.uk

 

[jdbolt]

No, the if is ont he include page:

page1.jsp:

<%

String pageHeader = null;

%>

<%@ include file="header.inc" %>

include.jsp

<%

if (pageHeader == null) {
    out.println("no header present");
} else {
    out.println(pageHeader);
}
%>

 

[Diancecht]

I don't understand

Shouldn't you include include.jsp instead of header.inc?

Cheers,
Dian

 

[venur]

Hi,

What sedj has mentioned works fine. Here is one more example of IF statement in include file. The include file is not a jsp page it is .inc file.

Out put of below code is Hello World!

one.jsp

<html>
  <head>
    <meta http-equiv="Content-Type" content="text/html; charset=windows-1252">
    <title>untitled</title>
  </head>
  <body>
  <%
    String pageHeader = "Hello World!";
  %>
 <%@ include  file="include.inc"%>
  </body>
</html>

include.inc

<%
  if((null != pageHeader) || (!"".equals(pageHeader))){
    out.println(pageHeader);
  }else{
    out.println("No Header");
  }
%>

Cheers
Venu