how counter variable works in jsp
harish goyal
Ranch Hand
Posts: 51
posted 11 years ago
<html>
<body>
<%! int i =1; %>
<%= i++ %>
</html>
</body>
output: 1 (at every refresh value is increasing)
________________________________________________________
<html>
<body>
<% int i =1; %>
<%= i++ %>
</html>
</body>
output: 1 (constant value not changing on refresh)
can anyone explain this behavior
<body>
<%! int i =1; %>
<%= i++ %>
</html>
</body>
output: 1 (at every refresh value is increasing)
________________________________________________________
<html>
<body>
<% int i =1; %>
<%= i++ %>
</html>
</body>
output: 1 (constant value not changing on refresh)
can anyone explain this behavior
Chetan Parekh
Ranch Hand
Posts: 3640
Vishnu Prakash
Ranch Hand
Posts: 1026
Sravan Kumar
Ranch Hand
Posts: 121
posted 11 years ago
This declares an instance variable 'i' in the generated servlet. This variable is common to all requests that hit this servlet and hence the page count is increased.
This declares a variable 'i' inside _jspService method that is run in a separate Thread for every request. So this variable is initialized to 1 for every request and printed as 1.
Please note variables declared inside <%! .. %> are not thread-safe.
[ October 04, 2005: Message edited by: Sravan Kumar ]
This declares an instance variable 'i' in the generated servlet. This variable is common to all requests that hit this servlet and hence the page count is increased.
This declares a variable 'i' inside _jspService method that is run in a separate Thread for every request. So this variable is initialized to 1 for every request and printed as 1.
Please note variables declared inside <%! .. %> are not thread-safe.
[ October 04, 2005: Message edited by: Sravan Kumar ]
keep smilin :: sravan<br /><a href="http://sravanpens.blogspot.com" target="_blank" rel="nofollow">I scribble here</a>
harish goyal
Ranch Hand
Posts: 51
posted 11 years ago
<%! int i =1; %>
This declares an instance variable 'i' in the generated servlet.
This variable is common to all requests that hit this servlet
and hence the page count is increased.
--------------------------------------------------
so in jsp we can consider instance variable as static variable
which is common for all requests
and
<%! int i =1; %> is not thread safe
<%! int i =1; %>
This declares an instance variable 'i' in the generated servlet.
This variable is common to all requests that hit this servlet
and hence the page count is increased.
--------------------------------------------------
so in jsp we can consider instance variable as static variable
which is common for all requests
and
<%! int i =1; %> is not thread safe
Sravan Kumar
Ranch Hand
Posts: 121
posted 11 years ago
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It is not static unless you declare it so. It is an instance variable. Since there will be only one instance of a servlet and that will be accessed by all threads that process a request to this servlet, it is not thread-safe.
Whereas, a variable declared in <% .. %> [scriptlet] lands up inside the _jspService method and hence every thread has its own copy. So, it is thread-safe.
It is not static unless you declare it so. It is an instance variable. Since there will be only one instance of a servlet and that will be accessed by all threads that process a request to this servlet, it is not thread-safe.
Whereas, a variable declared in <% .. %> [scriptlet] lands up inside the _jspService method and hence every thread has its own copy. So, it is thread-safe.
keep smilin :: sravan<br /><a href="http://sravanpens.blogspot.com" target="_blank" rel="nofollow">I scribble here</a>
harish goyal
Ranch Hand
Posts: 51
Sravan Kumar
Ranch Hand
Posts: 121
posted 11 years ago
There is no effect in a servlet environment because there will be only one instance of a servlet per JVM. But, this variable will not be bound to this instance, but to the Class.
keep smilin :: sravan<br /><a href="http://sravanpens.blogspot.com" target="_blank" rel="nofollow">I scribble here</a>
harish goyal
Ranch Hand
Posts: 51
Sravan Kumar
Ranch Hand
Posts: 121
posted 11 years ago
1. You should not use SingleThreadModel. It doesn't solve thread related problems like it appears to, and has been deprecated.
2. There is no need of declaring the counter variable static. It works without it.
If you use SingleThreadModel, different instances of the Servlet are created / used for different requests and in that case, to update the number of Servlet hits, you need to declare the counter variable as static. But, the bible says not to use it !!
2. There is no need of declaring the counter variable static. It works without it.
If you use SingleThreadModel, different instances of the Servlet are created / used for different requests and in that case, to update the number of Servlet hits, you need to declare the counter variable as static. But, the bible says not to use it !!
keep smilin :: sravan<br /><a href="http://sravanpens.blogspot.com" target="_blank" rel="nofollow">I scribble here</a>
posted 11 years ago
That is one of the big differences between declaring an instance static and not. Even with SingleThreadModel, instance variables declared static will be shared among servlets.
Originally posted by harish goyal:
if we use single thread model
than we can use static variable
am i right
That is one of the big differences between declaring an instance static and not. Even with SingleThreadModel, instance variables declared static will be shared among servlets.
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