Preview Servlet

Purpose of the preview servlet was to serve preview images. Preview images are identified by a bunch of parameters. Type, a versionId and so on. For not writing two or three servlets all preview logic is contained within the servlet.

@Override
public void handleService(HttpServletRequest request, 
    HttpServletResponse response) throws ServletException, 
    IOException
{

	JSPTool jt = new JSPTool(request);

	long id = jt.getInt("id");
	int compilation = jt.getInt("compilation");
	int page = jt.getInt("page");
	String dest = jt.getString("dest");
	String mode = jt.getString("mode");
	String lang = jt.getString("lang");
	String type = jt.getString("type");
	String size = jt.getString("size");

	WebControl web = new WebControl(session, getServiceProvider());
	IScoreControl control = web.getScoreControl();
	m_previewAction.setContext(web);

	try
	{
	        if (type.equals("quickscorepreview") && id != 0)
	        {
	                quickScorePreview(control, request, response, id);
	        }

This snippet shows you the entry point of the servlet. This piece of code retrieves lots of variables in order to decide what to to. Let's improve it using JAX-WS RS, the REST API for Java:

@GET
@Path("score/version/{versionId}.png")
@Produces("image/png")
public Response getScorePreviewpng(@PathParam("versionId") long versionId, 
    @Context HttpServletRequest request) throws Exception
{
    ...
}

@GET
@Path("score/version/{versionId}/{page}/{size}.png")
@Produces("image/png")
public Response getScorePreviewPng(@PathParam("versionId") long versionId, 
    @PathParam("page") int page, @PathParam("size") String size, 
    @Context HttpServletRequest request) throws IOException
{
    ...
}

That code expresses much more what it does. A major change is the descriptive way of the methods. Each method is annotated. To be very honest, there was also one more change: The url pattern changed from something like /Preview?type=quickscorepreview&id=1234
to /preview/score/version/1234.png which is also much easier to read.

Go Servlet

I like simple entry point to applications. And they should be static somehow. This time we're talking about the Go-Servlet. Depending on the url the servlet performs a redirect. If you want to search for something and you want to link it somewhere, you just have to use /go/search/beethoven. The handler behind the url will send you to the correct resource.

As soon as you see the code we'll dig into mud.

@Override
public void handleService(HttpServletRequest request, 
    HttpServletResponse response) throws ServletException, 
    IOException
{
    String url = request.getRequestURI();
    String servlet = request.getServletPath();
    String param = "";
    String cmd = "";
    int index = url.indexOf(servlet);
    
    if (index != -1)
    {
        param = url.substring(index + servlet.length() + 1);
    }

    if (param.length() < 1)
    {
           
		index = param.indexOf('/', 1);

		if (param.length() < index && index != -1)
		{
		    cmd = param.substring(0, index);

Yuck! Lots of substring-ing for resolving the individual pieces. Regex could help here, but would be still hard to read. Let's refactor the servlet to a JAX-WS RS-conform piece of code.

@Path("score/{id}")
@GET
public Response getScore(@PathParam("id") String id, @Context UriInfo uriInfo, 
    @Context HttpServletRequest req) throws IOException, URISyntaxException
{
    ...
}

@Path("search/{id}")
@GET
public Response getSearch(@PathParam("id") String id, @Context UriInfo uriInfo, 
    @Context HttpServletRequest req) throws IOException, URISyntaxException
{
    ...
}

Again we got rid of unnecessary complexity and code. Refactoring of these two took (only the Java side) just 1 or 2 hours. Beneath url and parameter parsing there are a lot more of possibilities which make Java HTTP interfaces fun again:

• AJAX
• JSON data exchange (JAXB/Jackson/Jettison)
• XML data exchange (JAXB)
• Serving real REST resources
• Caching

JSR 311 AX-RS: The JavaTM API for RESTful Web Services

JSR311 describes the REST API within the Java world. It was finally released in Oct 2008. Jersey (Sun Impl of JSR311) was started in early/mid 2007.