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Linux: Persistent wake-on-lan

Just a quick reminder for myself: You need to enable wake-on-lan on the nic in most linux distributions via ethtool.

If your nic supports WOL, it probably needs to be enabled in your computers BIOS first.

Most WOL tools use the “MagicPacket(tm)” method, so the right command to enable it on the nic “eth0” would be

ethtool -s eth0 wol g

This is not a persistent setting and it is gone after a reboot. Most tips around recommend creating a runlevel script for executing this command after boot or before shutdown.

I’ve added the command as a hook in my network scripts:

auto eth0
iface eth0 inet dhcp
        pre-down ethtool -s eth0 wol g

You can also use post-up. I like this method because i tend to forget about my runlevel scripts and so i keep the network stuff in one place 😉

If you are a debian user, you maybe need to stop your system from turning off the nic on HALT. To do so, add

NETDOWN=no

to “/etc/default/halt”.

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Oracle: Drop table if exists replacement

Mysql has a nice “if exists” addition to the drop table statement. If the table to be dropped does not exists, it doesn’t raise an exception but only creates a warning.

In Oracle RDMBS you can emulate this behavior like so:

BEGIN EXECUTE immediate 'drop table INSERT_TABLE_NAME_HERE'; EXCEPTION WHEN others THEN IF SQLCODE != -942 THEN RAISE; END IF; END;
/

Ugly, but it works very well.

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An iterable array

Java has the nice Iterable interface (since Java 5, i guess) that allows object oriented loops like

List<String> strings = new ArrayList<String>();
for(String string : strings) 
	System.out.println(string);

but guess what, a simple array is not iterable…

In case you need one, feel free to use this one:

package ac.simons;
 
import java.util.Iterator;
 
public class IterableArray<T> implements Iterable<T> {
	private class ArrayIteratorImpl implements Iterator<T> {
		private int position = 0;
		@Override
		public boolean hasNext() {
			return data != null && this.position < data.length;
		}
 
		@Override
		public T next() {
			return data[position++];
		}
 
		@Override
		public void remove() {
			throw new UnsupportedOperationException();
		}		
	}
 
	private final T[] data;
 
	public IterableArray(T[] data) {
		this.data = data;
	}
 
	@Override
	public Iterator<T> iterator() {
		return new ArrayIteratorImpl();
	}	
}

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Create ZIP Archives containing Unicode filenames with Java

It is harder than i thought to create a simple Zip Archive from within Java that contains entries with unicode names in it.

I’m actually to lazy to read all the specs, but it says something that the entries in a zip archive are encoded using “Cp437”. The buildin Java compressing api has nothing to offer for setting the encoding so i tried Apache Commons Compress.

The manual says the following about interop :

For maximum interop it is probably best to set the encoding to UTF-8, enable the language encoding flag and create Unicode extra fields when writing ZIPs. Such archives should be extracted correctly by java.util.zip, 7Zip, WinZIP, PKWARE tools and most likely InfoZIP tools. They will be unusable with Windows’ “compressed folders” feature and bigger than archives without the Unicode extra fields, though.

That didn’t work for me.

After some cursing, this is my solution:

final ZipArchiveOutputStream zout = new ZipArchiveOutputStream(new BufferedOutputStream(new FileOutputStream(fc.getSelectedFile())));
zout.setEncoding("Cp437");
zout.setFallbackToUTF8(true);
zout.setUseLanguageEncodingFlag(true);								
zout.setCreateUnicodeExtraFields(ZipArchiveOutputStream.UnicodeExtraFieldPolicy.NOT_ENCODEABLE);

I specifying explicitly the encoding but instead of using utf-8, which didn’t work for my utf-8 strings (wtf??), i’m using the Cp437 from the specs and some other magic options and it works for me in 7zip, WinZip and even Windows’ “compressed folders”.

Edit: Unfortunately, in Mac OS X’s Unzip utility, the non Cp437 are broken. If anyone has a good idea, feel free to leave a comment.

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Today: Fun with Unicode, Regex and Java.

Some would say, i have 3 problems 😉

private final static Pattern placeholder = Pattern.compile("#\\{(\\w+?)\\}");

won’t match “Mot#{ö}rhead” for example.

To replace the word character \w you either need the list of possible unicodeblocks like [\p{InLatin}|\p{InEtc}] (you get the codes for the blocks through “Character.UnicodeBlock.forName” or you’re lazy like me and just use the dot:

private final static Pattern placeholder = Pattern.compile("#\\{(.+?)\\}");

Oh what a day… :/

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