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As part of this blog we will look at how to upload and process a file using java Servlet API. I will not be using the Apache File-Upload API.

When defining your servlet determine a folder where you want the temporary file to be downloaded.

you can have the below MultipartConfig annotation as part of the Servlet class file like below.

@MultipartConfig(location="/tmp", fileSizeThreshold=-1L, maxFileSize=10*1024*1024, maxRequestSize=10*1024*1024)
public class FileUploaderServlet extends HttpServlet
{

or you can have it as a configuration as part of the web.xml file.

<multipart-config>
      <location>/tmp</location>
      <max-file-size>10485760</max-file-size>
      <max-request-size>10489760</max-request-size>
      <file-size-threshold>-1L</file-size-threshold>
</multipart-config>

If we are developing a general purpose file up-loader using the configuration in web.xml is the recommended approach. There are default values for all of the above which unlimited for all parameters . In my example my threshold is greater than the max-file-size so everything is instantaneous and in memory.

We are giving a sledge hammer here and the user can provide a large enough file to block the network. I would prefer the file size to be a max of 10 MB which is close to 10% of a Gigabit network traffic for a second. Any amount more than that will have the potential to create issues when more users are trying to download or upload contents to a server which is already processing other requests and potentially bring the server to a crawl for a few seconds.

Now for the code part

The below are the steps performed

• Verify if the request is multipart if not just return.
• Prepare up the metadata information to parse the csv file.
• Use the FilePart from Part to get the inputstream that holds the stream information.
• Always use a BufferedReader on the InputStream as that would further mitigate the load on the network based on the time taken for processing.
• We read through the file untill we get a line that is null(End of File). It is possible to get a null in the beginning so we read the headers inside of the loop.
• Merge the results coming from the file into Banyan.

I had introduced a new set of items IBranch and DataBranch these are the basic building blocks of banyan which is built on top of the ArrayMap interface. Banyan uses a modified version of the above class to upload contents of a csv into the data store. Banyan also supports other formats like JSON but not through this example.