Relatively Ignorant Blog

I was interested to read Bill de hÓra’s question about whether servlets and JSP can be used to create a RESTful application without resorting to RPC-style URIs like:

http://www.innoq.com/blog/entry.jsp?id=java_web_frameworks

Absolutely yes! A beauty for me of the web side of Java EE is that the URI can take any format you like. So, to use a URI like:

http://www.innoq.com/blog/st/2007/08/15/java_web_frameworks.html

we could work as follows.

1. The externally facing URI is probably mapped by a reverse proxy or content switch (or the like) to the blogging application on a Java EE application server. The internal URI might be something like:

   http://s012.innoq.com/javablog/blog/st/2007/08/15/java_web_frameworks.html

2. The application server might interpret the URI like this:

   /javablog: Root web context of the Java blogging application.

   /blog: Part of the URI that maps to a servlet for serving all blog pages. In web.xml it may be mapped with:

   <servlet>
      <servlet-name>BloggingServlet</servlet-name>
      <servlet-class>com.innoq.blogging.web.BloggingServlet</servlet-class>
      ...
   </servlet>
   <servlet-mapping>
      <servlet-name>BloggingServlet</servlet-name>
      <url-pattern>/blog*</url-pattern>
      ...
   </servlet-mapping>
   

   Further work continues in the servlet’s doGet method.

   /st/2007/08/15/java_web_frameworks.html: This string is available to the servlet using request.getPathInfo().

3. The servlet tokenises the string and works with the information. For example st is used to brand the blog as belonging to Stefan Tilkov, 2007, 08 and 15 are date identifiers and java_web_frameworks is the post slug, with .html to indicate that the content type of the response is text/html.
4. The servlet uses that information to retrieve the post from the persistence store and assembles request-scope objects that will be used by the JSP.
5. The servlet forwards to the JSP, which templates the HTML response. For example:

   request.getRequestDispatcher("/WEB-INF/jsp/blog_post.jsp").
forward(request, response);

   The JSP is never called via a URI that maps to its directory structure. It can (as in this example) reside under the WEB-INF directory, which cannot be mapped to a URI path.

Caching? That can be done by the servlet or by the application server or somewhere in front of that. Or publishing a post may result in the creation of an HTML file on disk in a directory structure that maps directly to the URI.