CODEWITHSUNDEEP
javaprocessbuilder
Shiny_and_Chrome
Shiny_and_Chrome

Reputation: 320

Understanding example code for processbuilder in Java

I have some example code where a process builder is used and given two commands to execute, but I can't fully understand what each line of code is doing.

Also the commands don't seem to be actually executing.

Code:

public static void main(String[] args) {

    ArrayList<String> commands = new ArrayList(); // commands in a processbuilder is an Arraylist of of strings
    commands.add("myfile.pdf"); // supposed to open the file?
    commands.add("bash\", \"-c\", \"ls"); // supposed to use ls command in terminal
    execute(commands); // should execute the two commands above
    System.out.println("executed commands"); // only thing that actually happens
}

public static void execute(ArrayList<String> command) {
    try {
        ProcessBuilder builder = new ProcessBuilder(command); // a new builder which takes a command passed into the method
        Map<String, String> environ = builder.environment(); // ???
        Process p = builder.start(); // p is never used?
    } catch (Exception e) {
        e.printStackTrace();
    }
}

I get no errors or warnings.

Tried reading the API on the processbuilder but I didn't really understand it

Upvotes: 0

Views: 752

Answers (1)

SirFartALot
SirFartALot

Reputation: 1225

ProcessBuilder helps to start external processes.

First, the command line parts (executable, parameters) are taken as a list of String, which is very comfortable. ("command" is rather misleading here, since it consists of executable and parameters).

Second, you can edit the environment of the new process (environment variables like "$HOME", "$PATH", etc.).

Your p can be used, for example to check, if the process has finished yet or to retrieve the input/output of the new process. Since you only start the process (fire-and-forget), you don't need it here.

You may also use Runtime.exec(...) to start an external process, which is the historical way to do so, but I think it's more comfortable to use ProcessBuilder.

Upvotes: 2

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