Servlet.init() and Filter.init() call sequence

java servlets jakarta-ee servlet-filters
martsraits picture martsraits · May 25, 2010 · Viewed 17.5k times · Source

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?

Answer

BalusC picture BalusC · May 25, 2010

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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