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In which order are Servlet.init() and Filter.init() methods called in java web application? Which one is called first? Are all Servlet.init() methods called before than any Filter.doFilter method?
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Q 20 - When init method of filter gets called? A - The init method is called by the web container to indicate to a filter that it is being placed into service.
Every filter must implement the three methods in the Filter interface: init(), doFilter(), and destroy(). When the Container decides to instantiate a filter, the init() method is your chance to do any set-up tasks before the filter is called.
The doFilter method of the Filter is called by the container each time a request/response pair is passed through the chain due to a client request for a resource at the end of the chain. The FilterChain passed in to this method allows the Filter to pass on the request and response to the next entity in the chain.
init. Called by the servlet container to indicate to a servlet that the servlet is being placed into service. The servlet container calls the init method exactly once after instantiating the servlet. The init method must complete successfully before the servlet can receive any requests.
The filters are always initialized during webapp's startup in the order as they are defined in the web.xml.
The servlets are by default initialized during the first HTTP request on their url-pattern only. But you can configure them as well to initialize during webapp's startup using the <load-on-startup> entries wherein you can specify their priority. They will then be loaded in the priority order.
E.g.
<servlet> <servlet-name>myServlet</servlet-name> <servlet-class>mypackage.MyServlet</servlet-class> <load-on-startup>1</load-on-startup> </servlet> If there are more servlets with the same priority order, then the loading order for those servlets is unspecified and may be arbitrary. Servlets are however in any way initialized after the initialization of filters, but before invocation of the filters.
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