On Mon, 2002-08-05 at 09:03, Mike Manchester wrote:
> I know there must be a secret Java Society because there is a lot of
> hidden or missing information about setting up and using Java. I mean
> most distro don't even install it as default and if you elect to install
> it after wards it's not easy to find out how to install it. Install the
> package files don't do much.
[big snip]
Hi Mike,
Java's not really hard, there are just things you must understand about
Java programming before it gets really easy. Kind of like when you try
to compile a C app, and you get an error like "can't find
linux/versions.h" (or whatever) and it bombs out. It's not entirely
clear what the error means, but it's easy enough to fix.
JAVA_HOME just needs to point to the root directory where you installed
the JDK. So if, for example, the JDK got installed in
/opt/j2sdk1.4.0_01, then you would set JAVA_HOME to "/opt/j2sdk1.4.0_01"
like:
bash$ export JAVA_HOME=/opt/j2sdk1.4.0_01
Then you need to make sure the 'java' and 'javac' executables are in
your path. They should be under "JAVA_HOME/bin" so you can try
something like this:
bash$ export PATH="$PATH:$JAVA_HOME/bin"
and then type:
bash$ which java
and hope it comes back with something found.
Really, that's all it takes to get the JDK working. But then if you
need to compile something, it can get harder, particularly stuff from
Apache group, since they tend to have lots of dependencies.
JAR files are just like library files for Java. In C programming, you
have .a or .so files, for anything not in libc, which you need to tell
the linker to also use, by adding something like "-lm" or "-lXlib" onto
the compile command-line. In a similar way, you need to put those
dependency .jar files somewhere the JDK can find them, and also tell it
to include those .jar files when it compiles. You do that with the
CLASSPATH. So if you put everything in /opt/classpath, then you can
set:
bash$ export CLASSPATH=$JAVA_HOME/jre/lib/rt.jar:.:/opt/classpath
and the JDK will first look at its default runtime lib (I think newer
versions of the JDK automatically do this, even if you set the CLASSPATH
var explicitly - older versions would _only_ look at the CLASSPATH var),
then in the current directory, then in /opt/classpath for extra .jar
files.
Download those dependency JAR files, put them in /opt/classpath, then
_hope_ that the build script with your application works correctly. If
the build script isn't using make or ant or something that tries to
handle all the directories and paths, then you're going to have to edit
it manually and there's not much you can do about that.
JAR files are a little odd in that they're really just ZIP files of a
particular directory structure. If you use the 'jar' tool (or the
'unzip' utility) you can see what files are in a jar file. It will look
just like a zip or tar of a bunch of class files. Since you can only
have one Java class with a particular name, projects tend to group them
in heirarchies based on their domain name. So stuff from the Apahche
group will put their class files in directories like
org/apache/projectname/somefunction/classname - so you can always look
in your JAR files to look for those "missing class" classes that might
generate errors. You may just be missing another JAR file.
The good thing about Java though, particularly non-GUI Java apps, is
that they really are mostly compile-once-run-anywhere, so you should be
able to just download a "binary" version of the application you're
trying to run and get it working pretty quickly, following the advice on
getting the JAVA_HOME and CLASSPATH vars set properly, and getting all
the dependency .jar files downloaded and put in the right places.
--
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
#!/usr/bin/perl -w
$_='while(read+STDIN,$_,2048){$a=29;$b=73;$c=142;$t=255;@t=map
{$_%16or$t^=$c^=($m=(11,10,116,100,11,122,20,100)[$_/16%8])&110;
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[$_%8]}(16..271);if((@a=unx"C*",$_)[20]&48){$h=5;$_=unxb24,join
"",@b=map{xB8,unxb8,chr($_^$a[--$h+84])}@ARGV;s/...$/1$&/;$d=
unxV,xb25,$_;$e=256|(ord$b[4])<<9|ord$b[3];$d=$d>>8^($f=$t&($d
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print+x"C*",@a}';s/x/pack+/g;eval
usage: qrpff 153 2 8 105 225 < /mnt/dvd/VOB_FILENAME \
| extract_mpeg2 | mpeg2dec -
http://www.cs.cmu.edu/~dst/DeCSS/Gallery/
http://www.eff.org/ http://www.anti-dmca.org/
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