Java Properties Files

Yesterday I posted about using JSch to SCP a File in Java, and the code I'd written at the time was pretty simplistic. It only sent a file to a remote server, and it even foolishly had string constants in the code that specified the location of the known_hosts file and the information about the remote server. I closed with a call to action to move that to a config file. Well, I've now done that, using the simple but effective Properties files that comes built in with Java.

I added a properties file to the package, and it opened right up for editing. The basic concept is that you fill it out with name-value pairs. Here's the properties file:

knownHostsFilename=/home/sschulte/.ssh/known_hosts
numServers=1
server0_host=172.16.40.128
server0_username=user
server0_password=user

I designed it with the idea in mind that I could send files and commands to multiple servers at once. I'd just have to increment the numServers field and add a new set of server info fields. Pretty nice.

To load the properties file, I just add these lines:

Properties configFile = new Properties();
configFile.load(this.getClass().getClassLoader().getResourceAsStream("remoteappmain/serverconfig.properties"));

Note that "remoteappmain" is the name of my package, which is why it's in the path to the properties file. To get one of the values, you just call the getProperty() method, passing it the key. They're strings, so in the case of numServers I had to parse it into an integer using Integer.parseInt(). No big deal.

To simplify my classes and to standardize their interfaces, I created a RemoteAuth class that encapsulates the hostname, username, and password values. And there's now an abstract base class called RemoteConnector that the FileSender extends. The constructor takes a RemoteAuth object and a known_hosts filename.

Creating an abstract base class allowed me to quickly create another class with useful functionality. This one is RemoteExecutor, which allows you to execute a command on a remote server. Stuff like "ls -la" or "rm my_file" or anything else you might type into the command line.

RemoteExecutor re = new RemoteExecutor(auth, knownHostsFilename);
re.execute("rm AllPhysics.wmv");
re.execute("ls -la");
System.out.println(re.getResult());

That's what you'd do if you wanted to delete a file, then call ls on the directory, and display it to the screen (which is what the getResult() method does).

I think that pretty much covers what I wanted. The main thing I want to add now is a FileGrabber class so I can download a file from a server as well as upload one. I feel like these classes are going to be pretty useful; I guess I'll know more about what I missed here once I use them in a few projects and decide on what they're lacking.