java: useful example of a shutdown hook?
- by Jason S
I'm trying to make sure my Java application takes reasonable steps to be robust, and part of that involves shutting down gracefully. I am reading about shutdown hooks and I don't actually get how to make use of them in practice.
Is there a practical example out there?
Let's say I had a really simple application like this one below, which writes numbers to a file, 10 to a line, in batches of 100, and I want to make sure a given batch finishes if the program is interrupted. I get how to register a shutdown hook but I have no idea how to integrate that into my application. Any suggestions?
package com.example.test.concurrency;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.PrintWriter;
public class GracefulShutdownTest1 {
final private int N;
final private File f;
public GracefulShutdownTest1(File f, int N) { this.f=f; this.N = N; }
public void run()
{
PrintWriter pw = null;
try {
FileOutputStream fos = new FileOutputStream(this.f);
pw = new PrintWriter(fos);
for (int i = 0; i < N; ++i)
writeBatch(pw, i);
}
catch (FileNotFoundException e) {
e.printStackTrace();
}
finally
{
pw.close();
}
}
private void writeBatch(PrintWriter pw, int i) {
for (int j = 0; j < 100; ++j)
{
int k = i*100+j;
pw.write(Integer.toString(k));
if ((j+1)%10 == 0)
pw.write('\n');
else
pw.write(' ');
}
}
static public void main(String[] args)
{
if (args.length < 2)
{
System.out.println("args = [file] [N] "
+"where file = output filename, N=batch count");
}
else
{
new GracefulShutdownTest1(
new File(args[0]),
Integer.parseInt(args[1])
).run();
}
}
}
