PluginLoader.java

Go to the documentation of this file.

import java.util.*;
import java.io.*;
import java.net.*;
import java.lang.reflect.*;

public class PluginLoader {
    final static private Hashtable classloaders = new Hashtable();
    final static private ClassLoader parentClassLoader = 
        new PluginLoader().getClass().getClassLoader();
    
    /*
    public static Object load(String classType, URL baseURL, 
                              BufferedReader input)
        throws IOException, FileFormatException {
        try { 
            return load(Class.forName(classType),baseURL,input);
        } catch (ClassNotFoundException e) {
            throw new IllegalArgumentException
                ("classType == "+classType+": "+e);
        }
    }
    */

    public static ClassLoader getClassLoader(URL url) {
        //System.out.println("getClassLoader("+url+")");
        URLClassLoader loader =
            (URLClassLoader)classloaders.get(url);
        if (loader==null) {
            loader = URLClassLoader.newInstance
                (new URL[] {url}, parentClassLoader);
            classloaders.put(url,loader);
        }
        return loader;
    }

    public static Object load(Class classType, URL baseURL, 
                              BufferedReader input)
        throws IOException, FileFormatException {

        // reading config file
        String urlstring = input.readLine();
        String className = input.readLine();
        if (className==null)
            throw new FileFormatException
                ("plugin specification is not at least two lines long");

        // getting absolute URL
        URL classurl;
        try {
            classurl = new URL(baseURL,urlstring);
        } catch (MalformedURLException e) {
            throw new FileFormatException
                ("invalid URL "+urlstring+": "+e.getMessage());
        }
        
        // getting class
        Class theClass;
        try {
            try {
                theClass = getClassLoader(classurl).loadClass(className);
            } catch (ClassNotFoundException ex) {
                // Maybe url is just not accessible
                URL proxy = InputManager.makeProxyURL(baseURL,classurl);
                System.out.println("in plugin loader: possibly "+classurl+
                                   " is not accessible. Trying "+proxy+
                                   " instead.");
                theClass = getClassLoader(proxy).loadClass(className);
            }
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
            throw new FileFormatException
                ("in plugin loader: "+baseURL+
                 " does not contain class "+className+
                 ": "+e);
        } catch (NoClassDefFoundError e) {
            throw new FileFormatException
                ("in plugin loader: error loading class "+
                 className+": "+e);
        } catch (UnsupportedClassVersionError e) {
            throw new FileFormatException
                ("in plugin loader: error loading class "+
                 className+": "+e);
        }

        // checking if class has correct type
        if (!classType.isAssignableFrom(theClass))
            throw new FileFormatException
                ("in plugin loader: class "+className+
                 " is not a subclass of "+classType);

        // getting the constructor
        Constructor constructor;
        try {
            constructor = theClass.getConstructor
                (new Class[] { input.getClass() });
        } catch (NoSuchMethodException e) {
            throw new FileFormatException
                ("in plugin loader: cannot create new "+className+
                 "("+input.getClass().getName()+"): "+e);
        }
        
        // getting the object
        Object obj;
        try {
            obj = constructor.newInstance(new Object[]{input});
        } catch (InstantiationException e) {
            throw new FileFormatException
                ("in plugin loader: cannot create new "+className+
                 "("+input.getClass().getName()+"): "+e);
        } catch (IllegalAccessException e) {
            throw new FileFormatException
                ("in plugin loader: cannot create new "+className+
                 "("+input.getClass().getName()+"): "+e);
        } catch (IllegalArgumentException e) {
            throw new FileFormatException
                ("in plugin loader: cannot create new "+className+
                 "("+input.getClass().getName()+"): "+e);
        } catch (ExceptionInInitializerError e) {
            throw new FileFormatException
                ("in plugin loader: cannot create new "+className+
                 "("+input.getClass().getName()+"): "+e);
        } catch (InvocationTargetException e) {
            e.printStackTrace();
            throw new FileFormatException
                ("in plugin loader: "+className+
                 ".createReplacement("+input.getClass().getName()+
                 ") failed: "+e.getTargetException());
        }
        
        return obj;
    }
}

---