从流程的输出流中读取行时，扫描仪未断开

Question

I am making a program that runs multiple processes, and one of them is a Java program.

Just say I have a java program that looks like this in a file Foo

System.out.println("Hello World!");

And then I have the program

Process p = Runtime.getRuntime().exec("java Foo");
Scanner scan = new Scanner(p.getInputStream());
while(scan.hasNextLine()) System.out.println(scan.nextLine());
System.out.println("done");
scan.close();

When I run it, it just prints done , and not the Hello World! that should be read from the Process. How would I do this?

Answer 1

You need to either also handle the process' error stream, or simply redirect that to the stream you're already reading via the ProcessBuilder API.

ProcessBuilder builder = new ProcessBuilder();
builder.redirectErrorStream(true);
builder.command("java Foo");
Process p = builder.start();