RE: CLASSPATH

[Colin Williams <colin.williams@xxxxxxxxxxxx>]

Joe,

Actually writing your own code to add classes/jars from specified
directories is not that bad, Ive done similar myself.

A lot of open source java projects require a lot of jar files added to the
classpath which is a pain, so I created a custom classloader so the I could
read a list of directories from a properties file, and load all the jars in
those directories


public class Runner extends URLClassLoader{
        
...     
    public static void main(String[] args) throws Throwable {
        if (args.length >= 1) {
            
                // get paths to be used for loading
            ClassLoader base = ClassLoader.getSystemClassLoader();
            URL[] urls;
            if (base instanceof URLClassLoader) {
                urls = ((URLClassLoader)base).getURLs();
            } else {
                urls = new URL[] { new File(".").toURI().toURL() };
            }
            
            // list the paths actually being used
            System.out.println("Loading from paths:");
            for (int i = 0; i < urls.length; i++) {
                System.out.println(" " + urls[i]);
            }
            
            // load target class using custom class loader
            Runner loader = new Runner(urls, base.getParent());
            loader.log(args[0]);
            loader.setEnv(args[0]);
            Class clas = loader.loadClass(loader.getClass(args[0]));
                
            // invoke "main" method of target class
            Class[] ptypes = new Class[] { args.getClass() };
            Method main = clas.getDeclaredMethod("main", ptypes);
            String[] pargs = new String[args.length-1];
//            System.arraycopy(args, 1, pargs, 0, pargs.length);
            Thread.currentThread().setContextClassLoader(loader);
            main.invoke(null, new Object[] { args });
                }
    }


        public void setEnv(String dir, String propertiesFile) throws
Throwable {

                if (env == null)
                {
                        env = dir;
                        addLib(dir);
                }
                
                // Load the classpath from the specified properties file
                addJarLib(getClasspath(propertiesFile));
                
        }
        
    public void addJarLib(String liblist) throws Throwable {
        
        // Create filter if necessary
        if (jf == null)
                jf = new JarFilter();
        
        String lib = null;
        
        StringTokenizer st = new StringTokenizer(liblist,":");
        while (st.hasMoreTokens()) {
            lib = st.nextToken();
                    
                // Get a list of jars in the directory 
                File dir = new File(lib);
                
                // Exit if directory not found
                if (!dir.exists())
                {
                        throw new Exception(dir.getAbsolutePath() + " not
found in addJarLib");
                }
        
                File[] files = dir.listFiles(jf);
                if (files.length == 0) 
                {
                    addURL(dir.toURL());
                }
                else
                {
                        for (int i = 0; i < files.length; i++) {
                    addURL(files[i].toURL());
                        }
                }
        }
        
    }
        
    public void addLib(String lib) throws Throwable {
        
        // Refer to directory 
        File dir = new File(lib);
        
        // Exit if directory not found
        if (!dir.exists())
        {
                throw new Exception(dir.getAbsolutePath() + " not found in
addLib");
        }

            addURL(dir.toURL());
        
    }

cheers
Colin.W

http://as400blog.blogspot.com
 
Extension   5800
Direct dial   0870 429 5800


-----Original Message-----
From: Joe Sam Shirah [mailto:jshirah@xxxxxxxxxxxxx] 
Sent: 09 March 2005 05:41
To: Java Programming on and around the iSeries / AS400
Subject: Re: CLASSPATH



    Hi Jon,

    Short of writing your own class loader, there is no way to have all jars
in a directory searched via a simple directory entry in the classpath.  As
David mentions, you have to explicitly list jars on the classpath for the
standard case.

    An alternative is to use the extension mechanism.  You can just dump the
jars in the ext directory.  One issue is that IBM ( and lately Sun ) also
use this directory.  Also, depending on what you use, there may be issues
with new JDK releases.

    You can use the system property "java.ext.dirs" to denote your own
extension directory.  The issue here is that the value *replaces* the
standard java.ext.dirs, so if you just use your own, classes in the standard
one will not be found.  Therefore, you would always want to concatenate the
standard ext dirs along with your own.  Also, you can effectively only set
java.ext.dirs with an arg to the java command; setting the property inside
an application doesn't work to change the VM's notion of the ext dirs.

    Personally, I'd like to see a property like "user.ext.dirs" or allow
java.ext.dirs to be changed ( and noticed by the VM ) internally in an app
with a replace or add option.

    For V5R3 ( we have JDK 1.3 and 1.4 installed ), the java.ext.dirs
property returns:

/QIBM/ProdData/OS400/Java400/jdk/lib/ext:
/QIBM/UserData/Java400/ext:
/QIBM/ProdData/Java400/jdk14/lib/ext:

There is also an

/QIBM/ProdData/OS400/Java400/ext:

directory, but since it is not part of the java.ext.dirs property I don't
know if it is used or not.  Notice this structure is different from the Sun
standard, which is jre/lib/ext.  HTH or at least clarifies things.


                                                         Joe Sam

Joe Sam Shirah -        http://www.conceptgo.com
conceptGO       -        Consulting/Development/Outsourcing
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----- Original Message ----- 
From: "David Gibbs" <david@xxxxxxxxxxxx>
To: "Java Programming on and around the iSeries / AS400"
<java400-l@xxxxxxxxxxxx>
Sent: Tuesday, March 08, 2005 10:22 PM
Subject: Re: CLASSPATH


> Jon Paris wrote:
> > Can someone point me to the docs that define what can be specified 
> > in
the
> > CLASSPATH.  I know I can specify multiple jar files by separating
entries by
> > a colon.  But how do I set it up so that (for example) all jars in a 
> > specified directory will be searched.  I can't find this info in the 
> > IBM docs.
>
> I don't think there's a way to specify that the classpath will consist 
> of all files in a specific directory.
>
> I've always had to write a script that cycles through all the 
> candidate files and adds them, one by one, to the classpath.
>
> david
> --

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