PC World Komputer 1998 July & August/Pcwk78a98.iso/Internet/Javadraw/DATA.Z/Beans.java

Text File | 1997-08-30 | 15KB | 484 lines

/*
 * @(#)Beans.java    1.24 97/01/06
 *
 * Copyright (c) 1996 Sun Microsystems, Inc. All Rights Reserved.
 *
 * This software is the confidential and proprietary information of Sun
 * Microsystems, Inc. ("Confidential Information").  You shall not
 * disclose such Confidential Information and shall use it only in
 * accordance with the terms of the license agreement you entered into
 * with Sun.
 *
 * SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF THE
 * SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
 * PURPOSE, OR NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR ANY DAMAGES
 * SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR DISTRIBUTING
 * THIS SOFTWARE OR ITS DERIVATIVES.
 *
 * CopyrightVersion bdk_beta
 *
 */

package java.beans;

import java.io.*;
import java.awt.*;
import java.applet.*;
import java.net.URL;
import java.lang.reflect.Array;

/**
 * This class provides some general purpose beans control methods.
 */

public class Beans {

    /**
     * Instantiate a bean.
     * <p>
     * The bean is created based on a name relative to a class-loader.
     * This name should be a dot-separated name such as "a.b.c".
     * <p>
     * In Beans 1.0 the given name can indicate either a serialized object
     * or a class.  Other mechanisms may be added in the future.  In
     * beans 1.0 we first try to treat the beanName as a serialized object
     * name then as a class name.
     * <p>
     * When using the beanName as a serialized object name we convert the
     * given beanName to a resource pathname and add a trailing ".ser" suffix.
     * We then try to load a serialized object from that resource.
     * <p>
     * For example, given a beanName of "x.y", Beans.instantiate would first
     * try to read a serialized object from the resource "x/y.ser" and if
     * that failed it would try to load the class "x.y" and create an
     * instance of that class.
     * <p>
     * If the bean is a subtype of java.applet.Applet, then it is given
     * some special initialization.  First, it is supplied with a default
     * AppletStub and AppletContext.  Second, if it was instantiated from
     * a classname the applet's "init" method is called.  (If the bean was
     * deserialized this step is skipped.)
     * <p>
     * Note that for beans which are applets, it is the caller's responsiblity
     * to call "start" on the applet.  For correct behaviour, this should be done
     * after the applet has been added into a visible AWT container.
     * <p>
     * Note that applets created via beans.instantiate run in a slightly
     * different environment than applets running inside browsers.  In
     * particular, bean applets have no access to "parameters", so they may
     * wish to provide property get/set methods to set parameter values.  We
     * advise bean-applet developers to test their bean-applets against both
     * the JDK appletviewer (for a reference browser environment) and the
     * BDK BeanBox (for a reference bean container).
     *
     * @param     classLoader the class-loader from which we should create
     *                       the bean.  If this is null, then the system
     *                        class-loader is used.
     * @param     beanName    the name of the bean within the class-loader.
     *                     For example "sun.beanbox.foobah"
     * @exception java.lang.ClassNotFoundException if the class of a serialized
     *              object could not be found.
     * @exception java.io.IOException if an I/O error occurs.
     */
    public static Object instantiate(ClassLoader cls, String beanName)
            throws java.io.IOException, ClassNotFoundException {

    java.io.InputStream ins;
    java.io.ObjectInputStream oins = null;
    Object result = null;
    boolean serialized = false;

    // Try to find a serialized object with this name
    String serName = beanName.replace('.','/').concat(".ser");
    if (cls == null) {
        ins = ClassLoader.getSystemResourceAsStream(serName);
    } else {
        ins  = cls.getResourceAsStream(serName);
    }
    if (ins != null) {
        try {
            if (cls == null) {
            oins = new ObjectInputStream(ins);
            } else {
            oins = new ObjectInputStreamWithLoader(ins, cls);
            }
            result = oins.readObject();
        serialized = true;
            oins.close();
        } catch (java.io.IOException ex) {
        ins.close();
        // For now, drop through and try opening the class.
        // throw ex;
        } catch (ClassNotFoundException ex) {
        ins.close();
        throw ex;
        }
    }

    if (result == null) {
        // No serialized object, try just instantiating the class
        Class cl;
        if (cls == null) {
            cl = Class.forName(beanName);
        } else {
            cl = cls.loadClass(beanName);
        }
        try {
            result = cl.newInstance();
        } catch (Exception ex) {
            throw new ClassNotFoundException();
        }
    }
    // Ok, if the result is an applet initialize it.
    if (result != null && result instanceof Applet) {
        Applet applet = (Applet) result;

        // Figure our the codebase and docbase URLs.  We do this
        // by locating the URL for a known resource, and then
        // massaging the URL.

        // First find the "resource name" corresponding to the bean
        // itself.  So a serialzied bean "a.b.c" would imply a resource
        // name of "a/b/c.ser" and a classname of "x.y" would imply
        // a resource name of "x/y.class".

        String resourceName;
        if (serialized) {
        // Serialized bean
        resourceName = beanName.replace('.','/').concat(".ser");
        } else {
        // Regular class
        resourceName = beanName.replace('.','/').concat(".class");
        }
        URL objectUrl = null;
        URL codeBase = null;
        URL docBase = null;

        // Now get the URL correponding to the resource name.
        if (cls == null) {
        objectUrl = ClassLoader.getSystemResource(resourceName);
        } else {
        objectUrl = cls.getResource(resourceName);
        }

        // If we found a URL, we try to locate the docbase by taking
        // of the final path name component, and the code base by taking
           // of the complete resourceName.
        // So if we had a resourceName of "a/b/c.class" and we got an
        // objectURL of "file://bert/classes/a/b/c.class" then we would
        // want to set the codebase to "file://bert/classes/" and the
        // docbase to "file://bert/classes/a/b/"

        if (objectUrl != null) {
        String s = objectUrl.toExternalForm();
        if (s.endsWith(resourceName)) {
              int ix = s.length() - resourceName.length();
            codeBase = new URL(s.substring(0,ix));
            docBase = codeBase;
            ix = s.lastIndexOf('/');
            if (ix >= 0) {
                docBase = new URL(s.substring(0,ix+1));
            }
        }
        }

        // Setup a default context and stub.
        BeansAppletContext context = new BeansAppletContext(applet);
        BeansAppletStub stub = new BeansAppletStub(applet, context, codeBase, docBase);
        applet.setStub(stub);

        // If it was deserialized then it was already init-ed.  Otherwise
        // we need to initialize it.
        if (!serialized) {
        // We need to set a reasonable initial size, as many
        // applets are unhappy if they are started without
        // having been explicitly sized.
        applet.setSize(100,100);
        applet.init();
        }
        stub.active = true;
    }
    return result;
    }


    /**
     * From a given bean, obtain an object representing a specified
     * type view of that source object.
     * <p>
     * The result may be the same object or a different object.  If
     * the requested target view isn't available then the given
     * bean is returned.
     * <p>
     * This method is provided in Beans 1.0 as a hook to allow the
     * addition of more flexible bean behaviour in the future.
     *
     * @param obj  Object from which we want to obtain a view.
     * @param targetType  The type of view we'd like to get.
     *
     */
    public static Object getInstanceOf(Object bean, Class targetType) {
        return bean;
    }

    /**
     * Check if a bean can be viewed as a given target type.
     * The result will be true if the Beans.getInstanceof method
     * can be used on the given bean to obtain an object that
     * represents the specified targetType type view.
     *
     * @param bean  Bean from which we want to obtain a view.
     * @param targetType  The type of view we'd like to get.
     * @return "true" if the given bean supports the given targetType.
     */
    public static boolean isInstanceOf(Object bean, Class targetType) {
    return Introspector.isSubclass(bean.getClass(), targetType);
    }


    /**
     * Test if we are in design-mode.
     *
     * @return  True if we are running in an application construction
     *        environment.
     */
    public static boolean isDesignTime() {
    return designTime;
    }

    /**
     * @return  True if we are running in an environment where beans
     *       can assume that an interactive GUI is available, so they
     *       can pop up dialog boxes, etc.  This will normally return
     *       true in a windowing environment, and will normally return
     *       false in a server environment or if an application is
     *       running as part of a batch job.
     */
    public static boolean isGuiAvailable() {
    return guiAvailable;
    }

    /**
     * Used to indicate whether of not we are running in an application
     * builder environment.  Note that this method is security checked
     * and is not available to (for example) untrusted applets.
     *
     * @param isDesignTime  True if we're in an application builder tool.
     */

    public static void setDesignTime(boolean isDesignTime)
            throws SecurityException {
    designTime = isDesignTime;
    }

    /**
     * Used to indicate whether of not we are running in an environment
     * where GUI interaction is available.  Note that this method is
     * security checked and is not available to (for example) untrusted
     * applets.
     *
     * @param isGuiAvailable  True if GUI interaction is available.
     */

    public static void setGuiAvailable(boolean isGuiAvailable)
            throws SecurityException {
    guiAvailable = isGuiAvailable;
    }


    private static boolean designTime;
    private static boolean guiAvailable = true;
}

/**
 * This subclass of ObjectInputStream delegates loading of classes to
 * an existing ClassLoader.
 */

class ObjectInputStreamWithLoader extends ObjectInputStream
{
    private ClassLoader loader;

    /**
     * Loader must be non-null;
     */

    public ObjectInputStreamWithLoader(InputStream in, ClassLoader loader)
        throws IOException, StreamCorruptedException {

    super(in);
    if (loader == null) {
            throw new IllegalArgumentException("Illegal null argument to ObjectInputStreamWithLoader");
    }
    this.loader = loader;
    }

    /**
     * Make a primitive array class
     */

    private Class primitiveType(char type) {
    switch (type) {
    case 'B': return byte.class;
        case 'C': return char.class;
    case 'D': return double.class;
    case 'F': return float.class;
    case 'I': return int.class;
    case 'J': return long.class;
    case 'S': return short.class;
    case 'Z': return boolean.class;
    default: return null;
    }
    }

    /**
     * Use the given ClassLoader rather than using the system class
     */
    protected Class resolveClass(ObjectStreamClass classDesc)
    throws IOException, ClassNotFoundException {

    String cname = classDesc.getName();
    if (cname.startsWith("[")) {
        // An array
        Class component;        // component class
        int dcount;            // dimension
        for (dcount=1; cname.charAt(dcount)=='['; dcount++) ;
        if (cname.charAt(dcount) == 'L') {
        component = loader.loadClass(cname.substring(dcount+1,
                                 cname.length()-1));
        } else {
        if (cname.length() != dcount+1) {
            throw new ClassNotFoundException(cname);// malformed
        }
        component = primitiveType(cname.charAt(dcount));
        }
        int dim[] = new int[dcount];
        for (int i=0; i<dcount; i++) {
        dim[i]=0;
        }
        return Array.newInstance(component, dim).getClass();
    } else {
        return loader.loadClass(cname);
    }
    }
}

/**
 * Package private support class.  This provides a default AppletContext
 * for beans which are applets.
 */

class BeansAppletContext implements AppletContext {
    Applet target;
    java.util.Hashtable imageCache = new java.util.Hashtable();

    BeansAppletContext(Applet target) {
        this.target = target;
    }

    public AudioClip getAudioClip(URL url) {
    // We don't currently support audio clips in the Beans.instantiate
    // applet context, unless by some luck there exists a URL content
    // class that can generate an AudioClip from the audio URL.
    try {
        return (AudioClip) url.getContent();
      } catch (Exception ex) {
        return null;
    }
    }

    public synchronized Image getImage(URL url) {
    Object o = imageCache.get(url);
    if (o != null) {
        return (Image)o;
    }
    try {
        o = url.getContent();
        if (o == null) {
        return null;
        }
        if (o instanceof Image) {
        imageCache.put(url, o);
        return (Image) o;
        }
        // Otherwise it must be an ImageProducer.
        Image img = target.createImage((java.awt.image.ImageProducer)o);
        imageCache.put(url, img);
        return img;

      } catch (Exception ex) {
        return null;
    }
    }

    public Applet getApplet(String name) {
    return null;
    }

    public java.util.Enumeration getApplets() {
    java.util.Vector applets = new java.util.Vector();
    applets.addElement(target);
    return applets.elements();
    }

    public void showDocument(URL url) {
    // We do nothing.
    }

    public void showDocument(URL url, String target) {
    // We do nothing.
    }

    public void showStatus(String status) {
    // We do nothing.
    }
}

/**
 * Package private support class.  This provides an AppletStub
 * for beans which are applets.
 */
class BeansAppletStub implements AppletStub {
    transient boolean active;
    transient Applet target;
    transient AppletContext context;
    transient URL codeBase;
    transient URL docBase;

    BeansAppletStub(Applet target,
        AppletContext context, URL codeBase,
                URL docBase) {
        this.target = target;
    this.context = context;
    this.codeBase = codeBase;
    this.docBase = docBase;
    }

    public boolean isActive() {
    return active;
    }

    public URL getDocumentBase() {
    // use the root directory of the applet's class-loader
    return docBase;
    }

    public URL getCodeBase() {
    // use the directory where we found the class or serialized object.
    return codeBase;
    }

    public String getParameter(String name) {
    return null;
    }

    public AppletContext getAppletContext() {
    return context;
    }

    public void appletResize(int width, int height) {
    // we do nothing.
    }
}