doFilter called twice, intended behaviour?

Question

I'm working through the Java EE servlet tutorial and tried the mood example. I noticed the doFilter is getting called twice, once the servlet call is in the chain and the second time it isnt.

I added some printlns in the TimeOfDayFilter.java and in the MoodServlet.java to show this.

TimeOfDayFilter.java:

    ...
    System.out.println("TimeOfDay before"); //added
    chain.doFilter(req, res);
    System.out.println("TimeOfDay after"); //added
    ...

MoodServlet.java:

    ...
    response.setContentType("text/html;charset=UTF-8");

    System.out.println("MoodServlet"); //added

    PrintWriter out = response.getWriter();
    ...

The result from the glassfish server (3.1) window when calling the servlet is the following:

    INFO: mood was successfully deployed in 406 milliseconds.
    INFO: TimeOfDay before
    INFO: MoodServlet
    INFO: TimeOfDay after
    INFO: TimeOfDay before
    INFO: TimeOfDay after

Is this intended behaviour? If so, what is the reason for the extra call?

Just do `System.out.println(request.getRequestURI())` to learn which request exactly hit the filter. And, press F12 in webbrowser to track all fired HTTP requests. — BalusC, Jan 16 '16 at 11:59
For me, the extra request came out to be a request to get the `favicon.ico` file, Phew! that wasn't visible in the chrome's network capture, I saw it in Fiddler. I double verified it as @BalusC has said here, it was indeed the case. I think it is the browser behavior. — Paramvir Singh Karwal, Jul 20 '19 at 18:29
@ParamvirSinghKarwal: modern browsers will implicitly request favicon.ico and use it as "bookmark icon" which you usually see on left hand side of document title in browser tab or address bar, depending on the browser make/version. For example, for Stack Overflow, this image will be used: https://stackoverflow.com/favicon.ico — BalusC, Jul 21 '19 at 23:12

sebasbad · Answer 1 · 2018-07-20T18:32:08.183

The Filter.doFilter method is called once per request. You can execute some code before other filters in the chain are called and also afterwards (in the order specified in the filter chain, as per the web.xml filter-mapping order), something like the following example:

public MyFilter implements Filter {
    public void doFilter(ServletRequest request, ServletResponse response,
           FilterChain chain) 
           throws IOException, ServletException
    {
        codeToExecuteBeforeOtherFiltersInTheChain(request, response);

        chain.doFilter(request, response);

        codeToExecuteAfterOtherFiltersInTheChain(request, response);

    }
}

If your filter is configured to dispatch REQUEST and FORWARD requests, then the MyFilter.doFilter method will be called once for the original request and once if the request has been forwarded:

Configure filter mapping using web.xml file:

...
<filter-mapping>
      <filter-name>MyFilter</filter-name>
      <url-pattern>/*</url-pattern>
      <dispatcher>REQUEST</dispatcher>
      <dispatcher>FORWARD</dispatcher>
</filter-mapping>
...

Configure filter mapping using @WebFilter annotation:

@WebFilter(urlPatterns = "/*", dispatcherTypes = {
    DispatcherType.REQUEST, DispatcherType.FORWARD
}) public MyFilter implements Filter {
    ...
}

To be able to check if the request has been forwarded, you can use the request attribute described here: How to know when the request is forwarded in a RequestWrapper object

For details about filters see: https://docs.oracle.com/cd/B32110_01/web.1013/b28959/filters.htm

score 3 · Answer 2 · answered Apr 02 '15 at 10:46

chain.doFilter(request,response);

This will pass the control to the servlet the filter is associated with. But after the corresponding servlet is executed, the control comes back at the end of the above line and all the lines thereafter in the current doFilter() is executed.

If you want to pass the control permanently to the servlet and not letting it return to the filter, just add a

return;

at the end of chain.doFilter(request,response) line in the current filter.

This answer doesn't explain the symptoms described in the question in any way. — BalusC, Jan 16 '16 at 12:00

score 2 · Answer 3 · edited Aug 28 '18 at 02:30

2

I solved the same issue after removing @Component in CustomFilter class.

edited Aug 28 '18 at 02:30

Pang

9,564
146
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answered Aug 28 '18 at 02:24

Mohan Pinapatruni

33
3

2

I dont think @Component has to do anything with this. – Tomas Bisciak May 07 '19 at 19:13
worked for me as well. But can somebody explain the logic behind the same. Thanks in advance! – Kusum Feb 10 '20 at 08:16
Yes. worked fine for me too. But please somebody can explain it? – Udeesha Induwara Feb 28 '20 at 06:29
Maybe you registered the filter elsewhere and also the Spring registered the filter automatically since it was annotated as @Component. Check if the init is called twitce. – Adam Mar 24 '20 at 16:14
Check this filter documentation https://www.baeldung.com/spring-boot-add-filter – edison gudiño Aug 22 '21 at 22:15

Zeeshan Bilal · Answer 4 · 2017-01-20T07:24:35.010

1

Yes it is, Filter is executed twice in the life cycle, first calls when request from client come to servlet and second time when response is served to the client after execution of servlet.

The order of execution is somehow looks like this.

edited Jan 20 '17 at 07:24

answered May 20 '13 at 09:58

Zeeshan Bilal

1,147
1
8
22

2

Thanks for the answer, but a few more questions: - One could also interpret the reponse arrows as being the code that happens after the chain.doFilter call (as in the line of my code snippet which prints "TimeOfDay after"), but it is really a fresh call of the filters DoFilter method? - Is there a way to determine if it is the first or the second time that its called (request or response part)? - Is there a way not to have the call on the way back? – user1348661 May 20 '13 at 10:51
1

Following topic on servlet documentation explains the whole concept in detail, [Understanding and Using Servlet Filters](http://sqltech.cl/doc/oas10gR3/web.1013/b14426/filters.htm) You can use some request parameter or use following `if` statement for that `if(res instanceof HttpServletResponse)` to defreetiate – Zeeshan Bilal May 20 '13 at 12:15
Ok, I get the picture (but the if statement doesnt work with me, always returns true, I'll dive into it). Thx – user1348661 May 20 '13 at 18:07
Maybe the second set of 'TimeofDay before' and 'TimeofDay after' were triggered by a request that does not go to the servlet. Like a request for a static image or css or js file? – septerr Jul 02 '14 at 16:45
4

@Zeeshan Bilal: I think your answer is wrong. For each request, the method doFilter is called once. The statements in doFilter are executed until "chain.doFilter(req, resp)" is reached. "chain.doFilter(req, resp)" causes the execution to be continued in the next filter in chain or in the servlet. After the sequence of filters and the servlet is executed, the doFilter-Method is continued after "chain.doFilter(req, resp)". – JimHawkins Jun 03 '15 at 09:20
@septerr I experienced this behaviour, when the client processed a XML document which contained an URL to a xsd file. – JimHawkins Jun 03 '15 at 09:22
13

This answer is pure nonsense. Please fix or delete it. All those upvotes generated by ignorant nitwits are misleading to future readers. – BalusC Jan 16 '16 at 11:58
check it now... sorry for inconvenience. – Zeeshan Bilal Jan 20 '17 at 07:28

SilverFox · Answer 5 · 2016-01-16T10:30:48.997

The reason why the filter is called twice are the images used in the response creation, as for instance

out.println("<img src=\"resources/images/duke.snooze.gif\" alt=\"Duke sleeping\"/><br/>");

Please see the log output

2016-01-16T11:25:34.894+0100|Info: TimeOfDay doFilter method before sending to chain

2016-01-16T11:25:34.895+0100|Info: MoodServlet get method called

2016-01-16T11:25:34.895+0100|Info: TimeOfDay doFilter method after sending to chain

2016-01-16T11:25:34.942+0100|Info: TimeOfDay doFilter method before sending to chain

2016-01-16T11:25:34.942+0100|Info: TimeOfDay doFilter method after sending to chain

src in img tag is nothing else than the second request for server to take care of. Please notice the url pattern used in the @WebFilter

@WebFilter(filterName = "TimeOfDayFilter",
urlPatterns = {"/*"},
initParams = {
    @WebInitParam(name = "mood", value = "awake")})

It will intercept all the requests coming into mood application. As an exercise simply try to remove images from the response or change url pattern to intercept only requests ending up in MoodServlet

@WebFilter(filterName = "TimeOfDayFilter",
urlPatterns = {"/report"},
initParams = {
    @WebInitParam(name = "mood", value = "awake")})

Both will result in one call of doFilter as you originally expected

2016-01-16T11:28:53.485+0100|Info: TimeOfDay doFilter method before sending to chain

2016-01-16T11:28:53.486+0100|Info: MoodServlet get method called

2016-01-16T11:28:53.487+0100|Info: TimeOfDay doFilter method after sending to chain

1) HTML in Servlet is bad practice. HTML belongs in JSP. JSP is a tool much more suitable for defining HTML code which should be emitted. You do not need to fuzz with double quotes at all. 2) It are not necessarily only images. Any asset/resource whose URL matches the filter's URL pattern could be a candidate (CSS, JS, favicons, etc). — BalusC, Jan 16 '16 at 12:02
Hi BalusC, thanks for additional in deep and handy ideas, as usually. The whole example is from the official Java EE 7 tutorial I went through today and it made me ask the very same question which I found here :) It is only a basic showcase of servlet, filter and listener tutorial creators have used. Creation of html response in servlet is there only for simplicity of course. — SilverFox, Jan 16 '16 at 13:35
(Yes, technically also jsp turns into servlet, but you understand my point :) ) — SilverFox, Jan 16 '16 at 13:43
Nope. I'm outputting `(HttpServletRequest)servletRequest).getRequestURL()` and that's not the case. The filter is called twice. — isapir, Sep 05 '16 at 20:47

score 1 · Answer 6 · answered Jun 16 '19 at 16:25

As Mohan has stated, @Component will make your filter be called twice if you have it already registered in you Application class, like this:

resources.add(new MyFilter());

If that's the case you have to choose between annotating it or registering it. But this is only valid for JAX-RS applications that use Spring. Not the topic of this question.

score 0 · Answer 7 · answered May 02 '19 at 04:55

I came across the same issue when the doFilter is called twice (or multiple times). The problem was that the filter handles every request including css, js, image and all other files while I expected one request for each page, so I solved the issue by adding the following code:

@WebFilter(filterName = "MyCustomFilter")
public class MyCustomFilter implements Filter {

  public void doFilter(ServletRequest request,ServletResponse response,
          FilterChain chain) throws IOException, ServletException {
    HttpServletRequest httpRequest = (HttpServletRequest) request;
    String accept = httpRequest.getHeader("accept");

    // Since the filter handles every request
    // we have to ensure that the request is asking for text/html
    if (accept == null || !accept.toLowerCase().startsWith("text/html")) {
      chain.doFilter(request, response);
      return;
    }

    // your code goes here

Hope this will help people like me who googled this question .

but in this case also request comes to doFilter handle, which we don't want. — Kusum, Feb 10 '20 at 07:59

score 0 · Answer 8 · answered Mar 06 '20 at 05:03

As @BalusC said, in my case the browser was requesting the favicon.ico by default, so there was an error in the browser's console

Failed to load resource: the server responded with a status of 404 (Not Found)

So I followed this answer and the error dissapeared but then I got the filter to get called twice.

MY SOLUTION

I replaced

<link rel="shortcut icon" href="#" />

For this:

<link rel="shortcut icon" href="../assets/img/valid_icon.png" />

doFilter called twice, intended behaviour?

8 Answers8

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