Friday Repost: Easy file uploading in Grails

The Friday Repost series are copies from my earlier writings. Since I don’t want to loose them, and they might prove useful to others, I’m reposting them on this blog.

If you want to upload files with Grails, there are multiple ways of doing so. However, there’s at least one way which makes it really easy do so, while keeping the code as clean as possible. This blog describes the steps to take to get the file upload to work, while maintaining a very clean codebase.

To get started, first create a new Grails application by running the following command:

grails create-app imageupload

After you have created your application, create a new file called ‘UploadImageCommand.groovy’ in the src/groovy/com/example/command directory

The UploadImageCommand.groovy should look like this:

Using commands for all changes in the system is usually a good thing. This prevents any malicious code from entering the system, and also describes the
intent of the system by using sensible naming for the commands, in this case ‘Upload Image’.

Now we need two more things: the persistent object (the Domain Object) and the Controller. Actually, I would recommend using a Service for all state changes
of the system, because of the transactional support in services and for providing a uniform way of state changes. However, that’s beyond the scope of this blog, so we’ll
leave it for later and focus on the image uploading for now!

The domain class

To create the domain class, typing in the following:

grails create-domain-class com.example.domain.Image

This creates an Image.groovy file in the grails-app/domain folder. Open the file, and type in the following contents:

Also, create a controller:

grails create-controller com.example.controller.Image

This creates an ImageController.groovy file in the grails-app/controllers folder. Open the file, and type in the following contents:

Now, all you need is a simple form which will upload your image (or actually any kind of document). The easiest way to do this is create a new file called
upload.gsp and place it in the web-app directory . Make the file look like this:

Now, type grails run-app

And browse to http://localhost:8080/imageupload/upload.gsp. When you upload a file there, you will see the counter increase in the log file. Clean, fast and easy!

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