Create a simple REST application with Spark Micro framework

Spark is the quickest and easiest way to start a simple web server and expose some resources. A simple one-liner can get the job done with spark. It’s that easy!

All you need to get started are the spark binaries in your classpath. As I’m using gradle for build management, all I have to do is add the following line in my build.gradle file.

With that, you are all set to use spark. Let’s get started.

Open a Java class file and follow along. I’m creating a class called Server with the main method inside it.

Add a import for all the static methods in spark with spark.Spark.*. This keeps the very readable.

Let’s start with a simple rest endpoint. A GET on /hello should return Hello World. Pretty simple, right? With any other framework you might use, there would be atleast a couple of lines. But not with spark. All you need to add is,

Now, if you want to pass a path parameter to the above get request after /hello, say a name, i.e., /hello/selena or /hello/taylor, it cab be done with /hello/:name. The :name becomes the path parameter here and you can access the variable passed in with request.params(:name).

Alright, Now that you’ve got your feet wet in Spark, it is time to take a leap and swim. Let’s build an application through which you can upload and download files.

These are the four endpoints I want to create.

To store the files, I will create a directory called storage and add all the uploaded files to that.

And I’ve setup the endpoints like this:

From each endpoint, I call a method with the required parameters. downloadFile() and deleteFile() only need the file name. countFiles() doesn't need any argument and uploadFile() would need the full req object.

Let’s see the methods now:

I have put effort in making sure that the methods are well-readable on their own. And any lingering doubts should be taken care of by the comments. But of-course, you can always reach out on twitter for any queries.

I’m uploading a LICENSE file and as you see, it is successfully uploaded.

Let’s confirm that with the count endpoint.

And we have 1 file which is the LICENSE file we just uploaded.

Now, Let’s try downloading the LICENSE file.

And we have downloaded the file. One thing you’d notice is that we’re getting all of the file text as a single line. This is of course to be expected, as in the downloadFile() method I have .collect(Collectors.joining()) which joins all the lines together with out adding anything between them. And that is why we get everything in a single line. If you want the line separator character between the lines, then put that in the joining() method.

And finally let’s test the delete endpoint.

And the file is deleted. To confirm this let’s run the count once more.

And we’ve got zero indicating that the file is indeed deleted.

And with that, we have all of our endpoints working as expected.

The full code is available as gist at

Thanks for reading. See you again in the next article.

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