Have you ever encounter with the limit
of JSP file or exception when you try to add even single line in JSP file? In my
experience there was such challenging and interesting work to write few lines
in JSP page. The funny thing was the contents of JSP were too large to add even
single line. Before explaining how I handled this problem let me tell you what
happens when you write a code in JSP file.
All of you know that the code written
in JSP file using JSP directive <% %> it goes inside _jspService method. But
I’d like to add one more point here, though its goes to _jspService method but
inside single try catch block, this is the point where there is twist on the
tail.
Let’s
take a look.
<%@
page language="java" contentType="text/html;
charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<!DOCTYPE
html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta
http-equiv="Content-Type" content="text/html;
charset=ISO-8859-1">
<title>Test1</title>
<script
type="text/javascript">
function sayHello(name){
alert("Welcome " + name);
}
function sayThank(){
alert("Thanks..");
}
</script>
</head>
<body>
<script
type="text/javascript">
sayHello('shail');
sayThank();
</script>
</body>
</html>
Now
when you deploy this JSP in web container and call, this file get converted in
pure java file which will have _jspService method as below
public void
_jspService(final javax.servlet.http.HttpServletRequest request, final
javax.servlet.http.HttpServletResponse response)
throws java.io.IOException,
javax.servlet.ServletException {
final javax.servlet.jsp.PageContext
pageContext;
javax.servlet.http.HttpSession session =
null;
final javax.servlet.ServletContext
application;
final javax.servlet.ServletConfig config;
javax.servlet.jsp.JspWriter out = null;
final java.lang.Object page = this;
javax.servlet.jsp.JspWriter _jspx_out =
null;
javax.servlet.jsp.PageContext
_jspx_page_context = null;
try {
response.setContentType("text/html;
charset=ISO-8859-1");
pageContext =
_jspxFactory.getPageContext(this, request, response,
null,
true, 8192, true);
_jspx_page_context = pageContext;
application =
pageContext.getServletContext();
config = pageContext.getServletConfig();
session = pageContext.getSession();
out = pageContext.getOut();
_jspx_out = out;
out.write("\r\n");
out.write("<!DOCTYPE html PUBLIC
\"-//W3C//DTD HTML 4.01 Transitional//EN\" \"http://www.w3.org/TR/html4/loose.dtd\">\r\n");
out.write("<html>\r\n");
out.write("<head>\r\n");
out.write("<meta
http-equiv=\"Content-Type\" content=\"text/html;
charset=ISO-8859-1\">\r\n");
out.write("<title>Test1</title>\r\n");
out.write("<script
type=\"text/javascript\">\r\n");
out.write("\tfunction
sayHello(name){\r\n");
out.write("\t\talert(\"Welcome \" +
name);\r\n");
out.write("\t\t\r\n");
out.write("\t}\r\n");
out.write("\tfunction
sayThank(){\r\n");
out.write("\t\talert(\"Thanks..\");\r\n");
out.write("\t}\r\n");
out.write("</script>\r\n");
out.write("</head>\r\n");
out.write("<body>\r\n");
out.write("\t<script
type=\"text/javascript\">\r\n");
out.write("\t\tsayHello('shail');\r\n");
out.write("\t\tsayThank();\r\n");
out.write("\t</script>\r\n");
out.write("</body>\r\n");
out.write("</html>");
} catch (java.lang.Throwable t) {
if (!(t instanceof
javax.servlet.jsp.SkipPageException)){
out = _jspx_out;
if (out != null &&
out.getBufferSize() != 0)
try { out.clearBuffer(); } catch
(java.io.IOException e) {}
if (_jspx_page_context != null)
_jspx_page_context.handlePageException(t);
else throw new ServletException(t);
}
} finally {
_jspxFactory.releasePageContext(_jspx_page_context);
}
}
Now
if you count how many out.write
statements are inside try block? You will find 23. Specially look immediate
after yellow marked line. You will find there is one empty line in JSP file
which has taken a line in java file marked in Red Color. Let’s look at another program with same functionality.
<%@
page language="java" contentType="text/html;
charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<!DOCTYPE
html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta
http-equiv="Content-Type" content="text/html;
charset=ISO-8859-1">
<title>Test2</title>
<script
type="text/javascript" src="js/j1.js"></script>
</head>
<body>
<script
type="text/javascript">
sayHello('shail');
sayThank();
</script>
</body>
</html>
and
JS folder have js1.js file which contents are as below
function
sayHello(name){
alert("Welcome " + name);
alert("wait..");
}
function
sayThank(){
alert("Thanks..");
}
Now
when you deploy this file and run it, this will be converted in Java file as
below
public void
_jspService(final javax.servlet.http.HttpServletRequest request, final
javax.servlet.http.HttpServletResponse response)
throws java.io.IOException,
javax.servlet.ServletException {
final javax.servlet.jsp.PageContext
pageContext;
javax.servlet.http.HttpSession session =
null;
final javax.servlet.ServletContext
application;
final javax.servlet.ServletConfig config;
javax.servlet.jsp.JspWriter out = null;
final java.lang.Object page = this;
javax.servlet.jsp.JspWriter _jspx_out =
null;
javax.servlet.jsp.PageContext
_jspx_page_context = null;
try {
response.setContentType("text/html;
charset=ISO-8859-1");
pageContext =
_jspxFactory.getPageContext(this, request, response,
null,
true, 8192, true);
_jspx_page_context = pageContext;
application =
pageContext.getServletContext();
config = pageContext.getServletConfig();
session = pageContext.getSession();
out = pageContext.getOut();
_jspx_out = out;
out.write("\r\n");
out.write("<!DOCTYPE html PUBLIC
\"-//W3C//DTD HTML 4.01 Transitional//EN\" \"http://www.w3.org/TR/html4/loose.dtd\">\r\n");
out.write("<html>\r\n");
out.write("<head>\r\n");
out.write("<meta
http-equiv=\"Content-Type\" content=\"text/html;
charset=ISO-8859-1\">\r\n");
out.write("<title>Test2</title>\r\n");
out.write("<script
type=\"text/javascript\"
src=\"js/j1.js\"></script>\r\n");
out.write("</head>\r\n");
out.write("<body>\r\n");
out.write("\t<script
type=\"text/javascript\">\r\n");
out.write("\t\tsayHello('shail');\r\n");
out.write("\t\tsayThank();\r\n");
out.write("\t</script>\r\n");
out.write("</body>\r\n");
out.write("</html>");
} catch (java.lang.Throwable t) {
if (!(t instanceof
javax.servlet.jsp.SkipPageException)){
out = _jspx_out;
if (out != null &&
out.getBufferSize() != 0)
try { out.clearBuffer(); } catch
(java.io.IOException e) {}
if (_jspx_page_context != null)
_jspx_page_context.handlePageException(t);
else throw new ServletException(t);
}
} finally {
_jspxFactory.releasePageContext(_jspx_page_context);
}
}
Now if you count how many out.write statements are inside above
try block? You will find 15 and total difference between Test1_jsp.java and Test2_jsp.java
are 8 lines. If you see closely, you will find there are much empty lines in JS file than Test1.jsp but converted java file has no such line.
Is it matter? My answer
will be Yes. When you write as much
as line in JSP file inside <% %> it goes to single try-catch block of
_jspService method. Do you know there is a size limit of try-catch block i.e.
32K. So before writing code inside JSP, you should be careful.
Use following tips to avoid
limit error
Ø Write all java script in
different file and instead of including this file use
<script
type="text/javascript" src="js/j1.js"></script>
Ø If there are a large volume
of java code inside JSP. Create different method using <%!
%> block,
so that a separate method will be created and you can call this method.
<%!
public
void go(){
System.out.println("Hello");
}
%>
Ø Avoid empty line in JSP
file.
Ø Small html tag can be
combined in single line.
That’s all,
Thanks J
