Extending @oopbase's answer with return;
statement.
Let's consider a use case of traditional authentication system where we store login information into the session. On each page we check for active session like,
/* Some Import Statements here. */
if(null == session || !session.getAttribute("is_login").equals("1")) {
response.sendRedirect("http://domain.com/login");
}
// ....
session.getAttribute("user_id");
// ....
/* Some More JSP+Java+HTML code here */
It looks fine at first glance however; It has one issue. If your server has expired session due to time limit and user is trying to access the page he might get error if you have not written your code in try..catch
block or handled if(null != session.getAttribute("attr_name"))
everytime.
So by putting a return;
statement I stopped further execution and forced to redirect page to certain location.
if(null == session || !session.getAttribute("is_login").equals("1")) {
response.sendRedirect("http://domain.com/login");
return;
}
Note that Use of redirection may vary based on the requirements. Nowadays people don't use such authentication system. (Modern approach - Token Based Authentication) It's just an simple example to understand where and how to place redirection(s).