Servlet for serving static content

Bruno_De_Fraine_6918 0
Viewed 178420

I deploy a webapp on two different containers (Tomcat and Jetty), but their default servlets for serving the static content have a different way of handling the URL structure I want to use (details).

I am therefore looking to include a small servlet in the webapp to serve its own static content (images, CSS, etc.). The servlet should have the following properties:

  • No external dependencies
  • Simple and reliable
  • Support for If-Modified-Since header (i.e. custom getLastModified method)
  • (Optional) support for gzip encoding, etags,...

Is such a servlet available somewhere? The closest I can find is example 4-10 from the servlet book.

Update: The URL structure I want to use - in case you are wondering - is simply:

    <servlet-mapping>
            <servlet-name>main</servlet-name>
            <url-pattern>/*</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
            <servlet-name>default</servlet-name>
            <url-pattern>/static/*</url-pattern>
    </servlet-mapping>

So all requests should be passed to the main servlet, unless they are for the static path. The problem is that Tomcat's default servlet does not take the ServletPath into account (so it looks for the static files in the main folder), while Jetty does (so it looks in the static folder).

jakarta-ee servlets jsp java
14 Answers

There is no need for completely custom implementation of the default servlet in this case, you can use this simple servlet to wrap request to the container's implementation:


package com.example;

import java.io.*;

import javax.servlet.*;
import javax.servlet.http.*;

public class DefaultWrapperServlet extends HttpServlet
{   
    public void doGet(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException
    {
        RequestDispatcher rd = getServletContext().getNamedDispatcher("default");

        HttpServletRequest wrapped = new HttpServletRequestWrapper(req) {
            public String getServletPath() { return ""; }
        };

        rd.forward(wrapped, resp);
    }
}
user_1031540

I ended up rolling my own StaticServlet. It supports If-Modified-Since, gzip encoding and it should be able to serve static files from war-files as well. It is not very difficult code, but it is not entirely trivial either.

The code is available: StaticServlet.java. Feel free to comment.

Update: Khurram asks about the ServletUtils class which is referenced in StaticServlet. It is simply a class with auxiliary methods that I used for my project. The only method you need is coalesce (which is identical to the SQL function COALESCE). This is the code:

public static <T> T coalesce(T...ts) {
    for(T t: ts)
        if(t != null)
            return t;
    return null;
}
Bruno_De_Fraine_69180
user_2796380

I had the same problem and I solved it by using the code of the 'default servlet' from the Tomcat codebase.

https://github.com/apache/tomcat/blob/master/java/org/apache/catalina/servlets/DefaultServlet.java

The DefaultServlet is the servlet that serves the static resources (jpg,html,css,gif etc) in Tomcat.

This servlet is very efficient and has some the properties you defined above.

I think that this source code, is a good way to start and remove the functionality or depedencies you don't need.

  • References to the org.apache.naming.resources package can be removed or replaced with java.io.File code.
  • References to the org.apache.catalina.util package are propably only utility methods/classes that can be duplicated in your source code.
  • References to the org.apache.catalina.Globals class can be inlined or removed.
user_193310

Use org.mortbay.jetty.handler.ContextHandler. You don't need additional components like StaticServlet.

At the jetty home,

$ cd contexts

$ cp javadoc.xml static.xml

$ vi static.xml

...

<Configure class="org.mortbay.jetty.handler.ContextHandler">
<Set name="contextPath">/static</Set>
<Set name="resourceBase"><SystemProperty name="jetty.home" default="."/>/static/</Set>
<Set name="handler">
  <New class="org.mortbay.jetty.handler.ResourceHandler">
    <Set name="cacheControl">max-age=3600,public</Set>
  </New>
 </Set>
</Configure>

Set the value of contextPath with your URL prefix, and set the value of resourceBase as the file path of the static content.

It worked for me.

yogman_243490
user_1297600
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