Question

I coded my own Spring filter in order to encode in UTF-8 all the responses except for images:

package my.local.package.filter;

public class CharacterEncodingFilter extends org.springframework.web.filter.CharacterEncodingFilter
{

    protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain) throws IOException, ServletException
    {
        if(!request.getRequestURI().endsWith("jpg") &&
                !request.getRequestURI().endsWith("png") &&
                !request.getRequestURI().endsWith("gif") &&
                !request.getRequestURI().endsWith("ico"))
        {
            super.doFilterInternal(request, response, filterChain);
        }

        filterChain.doFilter(request, response);
    }
}

I’m referencing it in the web.xml:

<filter>
    <filter-name>CharacterEncodingFilter</filter-name>
    <filter-class>my.local.package.filter.CharacterEncodingFilter</filter-class>
    <init-param>
        <param-name>encoding</param-name>
        <param-value>UTF-8</param-value>
    </init-param>
    <init-param>
        <param-name>forceEncoding</param-name>
        <param-value>true</param-value>
    </init-param>
</filter>

<filter-mapping>
    <filter-name>CharacterEncodingFilter</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

Everything works as expected, jpg/png/gif/ico files are not encoded in UTF-8 while all the other files are.

I’m now trying to code a simple controller which has to return a 404 error under certain conditions:

@Controller
public class Avatar
{
    @RequestMapping("/images/{width}x{height}/{subject}.jpg")
    public void avatar(HttpServletResponse response,
                       @PathVariable("width") String width,
                       @PathVariable("height") String height,
                       @PathVariable("subject") String subject) throws IOException
    {
        ...

        // if(error)
        // {
            response.sendError(HttpServletResponse.SC_NOT_FOUND, "Not found");
            return;
        // }

        ...
    }
}

But when requesting, for example, /images/52×52/1.jpg i get a page containing this error:

java.lang.IllegalStateException: Cannot call sendError() after the response has been committed

I think I coded the filter in a wrong way (I’m not experienced with Spring), because if I specify org.springframework.web.filter.CharacterEncodingFilter instead of my.local.package.filter.CharacterEncodingFilter in the web.xml file, it works perfectly.

Can someone help me?

Thank you.

Answer 1

You are calling filterChain.doFilter(request, response); twice. Once in your code and once in super.doFilterInternal(request, response, filterChain);

To fix this, simply put your doFilter in the else clause to your if.