Client

Once the GUI application is loaded, it will send a request (instance/object of Commands class) to server for a list of files from the server's shared directory.Client will write Commands object to ObjectOutputstream. Commands class has to implement Serializable interface as this will be transferred over the network. Commands class will have following value:
- nextCommand value in Commands object will be set to COMMAND_SEND_FILE_LIST
Server

Upon receiving the file list request, the server will read all the files (no directory) in the server's shared directory and wrap each file name and corresponding size in FileInfo object. DirInfo object will have a variable named fileList with type of List(implementation ArrayList). Server will write DirInfo object to socket's ObjectOuputStream so that client can read it from ObjectInputStream.DirInfo and FileInfoclass have to implement Serializable interface as these will be transferred over the network.

Client

Client will read DirInfo object from ObjectInputStream and populate the JList on "Remote File List" panelwith file names. At the same time, each fileName and corresponding fileSize should be saved in a HashMap.Once the JList is loaded and the user double clicks a file name in the JList, client will send a Commands object to server (by writing to ObjectOutputstream) with following values:
- nextCommand value in Commands object will be set to COMMAND_SEND_FILE
- fileName should be set with the double-clicked file name from the JList

Server

Upon receiving send file request (will read Commands object from ObjectInputStream), the server will read the nextCoomand and fileName from Commands object and start transferring the file bytes to client by writing to OutputStream (Could be wrapped into a BufferedOutputStream for efficiency).

Client

Client will read file binaries from InputStream(not ObjectInputStream) and finish reading when number of bytes read is length of the corresponding file name. The file length can be derived by passing the fileName to HashMap where file length was stored earlier while populating the JList based on DirInfo object received from server. Once the file content is read it will be then saved in the download directory on client machine.