On Wed, 14 Jun 2000, Jacques Bergeron wrote:
> Hi everyone,
>
> I am trying to run Ant directly from a Java program without having prior
> knowledge of Ant`s directory (cannot intialize classpath on program
> startup).
>
> I would need to dynamically change the CLASSPATH once I know Ant`s directory
> (choosen by the user). Since changing the classpath is not possible (so was
> I told) I would need to make a custom ClassLoader!?
>
> 1- Is it true that the classpath cannot be changed dynamically?
>
> 2- If so do you know any exemple of a custom ClassLoader that I could use (I
> was told that Java`s URLClassLoader did not support the file: protocol). So
> I`m searching for a model.
>
> Any help would be welcome :)
I've been vaguely looking at this recently. I don't know what the Java 2
API is like in this area, but classloaders aren't that hard - you just
need to extend ClassLoader and override findClass( String name ) to find
the class you're after. Something along the lines of:
public class FileClassLoader extends ClassLoader
{
private Vector _classpath = new Vector();
public FileClassLoader( String classpath )
{
StringTokenizer tokens = new StringTokenizer( classpath );
while( tokens.hasMoreTokens() )
{
_classpath.add( tokens.nextToken() );
}
}
public Class findClass( String name )
{
StringBuffer nameBuffer = new StringBuffer();
for( int i = 0; i < name.length(); i++ )
{
if( name.charAt( i ) == '.' )
nameBuffer.append( "/" );
else
nameBuffer.append( name.charAt( i ) );
}
Enumeration classPaths = _classpath.elements();
String testpath = null;
File classFile = new File( );
while( classPaths.hasMoreElements() && !classFile.exists() )
{
testpath = (String)classPaths.nextElement() +
nameBuffer.toString();
classFile = new File( testpath );
if( classFile.exists() )
{
FileInputStream classStream = new
FileInputStream( classFile );
byte[] classBytes =
new byte[classFile.length()];
classStream.read
( classBytes, classFile.length() );
/* Not exactly sure on the args to this */
return defineClass( name, classBytes );
}
}
throw new ClassNotFoundException( name );
}
}
Needs some more error-checking, but that's how it works.
--
Tom Cook - Software Engineer
"The brain is a wonderful organ. It starts functioning the moment you get
up in the morning, and does not stop until you get into the office."
- Robert Frost
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