Java Pre assign args before passing from command line

Question

I am developing a very simple Java application, through which to take files from a folder, obtain information from them and save them in the database.

The app is launched from the command line, and I need to pass the following parameters: file_path, db_name, db_user, db_host, db_user_psw.

When I run the check to see if all the parameters have been passed, in case a parameter is missing, I get an index out of bound exception, correctly according to java. My need is to bypass this exception and display a string indicating an error message.

For example, if all parameters except db_user_psw are entered, instead of getting index of bound exception I would like the message "You must enter the password to access the db!".

My idea is to pre-assign the args to null, and once the script is run check if they are null or not. Is it possible to do this in java? I accept any advice or suggestion

My code:

if(args[0] == null ){ System.out.println("Insert a valid Path!"); System.exit(0); }
if(args[1] == null ){ System.out.println("Insert the DB IP!"); System.exit(0);}
if(args[2] == null ){ System.out.println("Insert a DB name!"); System.exit(0);}
if(args[3] == null ){ System.out.println("Insert a DB Username!"); System.exit(0);}
if(args[4] == null ){ System.out.println("Insert User DB Password!"); System.exit(0);}

Is it possible to do this in java? Why don't you try it and check for yourself? Or do you face any issues if you have already tried? — kiner_shah
– kiner_shah, Commented Jan 21, 2022 at 10:35
Also, is maven tag relevant w.r.t. this question? If not, can you please remove it? — kiner_shah
– kiner_shah, Commented Jan 21, 2022 at 10:36
Perhaps you would be better served by using something like JCommander jcommander.org (no affiliation) instead. This would make your program much more robust, enable self-documentation, and not require arguments to be in a specific order. — Thomas Timbul
– Thomas Timbul, Commented Jan 21, 2022 at 10:52

Andy Turner · Accepted Answer · 2022-01-21 10:46:13Z

When I run the check to see if all the parameters have been passed, in case a parameter is missing, I get an index out of bound exception, correctly according to java. My need is to bypass this exception and display a string indicating an error message.

Check the length of args instead:

if(args.length == 0){ System.out.println("Insert a valid Path!"); System.exit(0); }
if(args.length == 1){ System.out.println("Insert the DB IP!"); System.exit(0);}
// ...

(You should exit with a non-zero code, in order to indicate an error)

I think you should really consider using named flags, so your command line isn't just a "meaningless" sequence of arguments that can easily be put in the wrong order. So rather than

java YourMainClass whatever blah etc

you provide something like:

java YourMainClass --file_path=whatever --db_name=blah etc

For your specific question of "Is it possible to do this in java?": You can, by copying the args array:

if (args.length < 5) args = Arrays.copyOf(args, 5);
// or
args = Arrays.copyOf(args, Math.max(5, args.length));

If args has fewer than 5 elements, this will create an array with 5 elements, padding the "missing" elements with null.

But this is an odd and unnecessary thing to do: checking the length is easier.

Michael Rosenfeld · Accepted Answer · 2022-01-21 10:41:00Z

0

I am not entirely sure on this, since I am a beginner myself but did you consider to wrap it into a try - catch block?

try {
  //  Your logic to execute
}
catch(Exception e) {
      System.out.println("Insert User DB Password! " + e);
// or something else
}```

answered Jan 21, 2022 at 10:41

Michael Rosenfeld

11 bronze badge

1 Comment

Andy Turner Over a year ago

Don't use exceptions to handle things you can detect by other means: you can determine that there aren't enough args simply by checking the length of the array. Exceptions are very heavyweight compared to an if statement, and also don't necessarily catch the problem you think you're catching. Additionally, you almost never want to catch Exception, but instead a more specific exception.

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