/home/ythoma/docs/math2mat/svn/wp1/framework/m2mGUI/src/m2m/backend/buildingblocks/BuildingBlockLoader.java

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package m2m.backend.buildingblocks;

import java.util.Hashtable;
import java.io.FileInputStream;

public class BuildingBlockLoader extends ClassLoader {
        
        private static BuildingBlockLoader instance = null;
        
        private Hashtable<String,Class<?>> classes = new Hashtable<String,Class<?>>();
        private String m_dir;
        private String m_packageName;
        
        public static BuildingBlockLoader getInstance() {
                if (instance == null) {
                        instance = new BuildingBlockLoader();
                }
                return instance;
        }
    
        public void setDir(String dir) {
                this.m_dir = dir;
        }
        public void setPackageName(String name) {
                this.m_packageName = name;
        }

        private byte getClassImplFromDataBase(String className)[] {
                //System.out.println(\t>>>>>> Fetching the implementation of "+className);
                byte result[];
                try {
                        FileInputStream fi = 
                                          new FileInputStream(this.m_dir+"/"+className+".class");
                        result = new byte[fi.available()];
                        fi.read(result);
                        return result;
                } catch (Exception e) {
                        /*
                         * If we caught an exception, either the class wasnt found or it
                         * was unreadable by our process.
                         */
                        return null;
                }
        }

        @Override
        public Class<?> loadClass(String className) throws ClassNotFoundException {
                @SuppressWarnings("unchecked")
                Class<?> c=(Class<BuildingBlock>)loadClass(className,true);
                return (c);
        }

        public BuildingBlock newInstance(String className) 
                          throws ClassNotFoundException {
                try { 
                        Object o = (loadClass(className)).newInstance();
                        BuildingBlock b=((BuildingBlock) o); 
                        return b; 
                } catch (Exception e) { 
                        //System.out.println("Caught exception : "+e);
                        return null; 
                } 
        }
        
        public synchronized Class<?> loadClass(String className, boolean resolveIt)
                          throws ClassNotFoundException {
                Class<?> result;
                byte  classData[];

                //System.out.println("\t>>>>>> Load class : "+className);

                try{
                        Class<?> t = Class.forName(className);
                        //System.out.println("The class "+className+" is already loaded!!");
                        //System.out.println("");
                        return t;
                } catch(Exception e) {
                //System.out.println("The class "+className+" is not loaded yet");
                }

                /* Check our local cache of classes */
                result = (Class<?>)this.classes.get(className);
                if (result != null) {
                        //    System.out.println("\t>>>>>> returning cached result.");
                        return result;
                }
                //System.out.println("The class does not exist");
                /* Check with the primordial class loader */
                try {
                        result = super.findSystemClass(className);
                        //System.out.println("\t>>>>>> returning system class (in CLASSPATH).");
                        return result;
                } catch (ClassNotFoundException e) {
                        //System.out.println("\t>>>>>> Not a system class.");
                }

                /* Try to load it from our repository */
                classData = getClassImplFromDataBase(className);
                if (classData == null) {
                        throw new ClassNotFoundException();
                }

                //System.out.println("Class name: " + className);
                /* Define it (parse the class file) */
                /* java 1.6 */
                result = defineClass(this.m_packageName+"."+className,classData, 0, classData.length);
                /* java 1.4 */
                //    result = defineClass(classData, 0, classData.length);
                if (result == null) {
                        throw new ClassFormatError();
                }

                if (resolveIt) {
                        resolveClass(result);
                }
                try{
                        this.classes.put(className, result);
                } catch (NullPointerException e) {
                        //System.out.println("Error with a class get");
                }
                //System.out.println("\t>>>>>> Returning newly loaded class.");
                return result;
        }
}