Java example source code file (ObjectView.java)

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Java - Java tags/keywords

attributeset, awt, bean, beaninfo, class, component, componentview, gui, introspectionexception, javabean, jlabel, method, object, objectview, propertydescriptor, string, text, throwable, util

The ObjectView.java Java example source code

/*
 * Copyright (c) 1998, 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */
package javax.swing.text.html;

import java.util.Enumeration;
import java.awt.*;
import javax.swing.*;
import javax.swing.text.*;
import java.beans.*;
import java.lang.reflect.*;

import sun.reflect.misc.MethodUtil;
import sun.reflect.misc.ReflectUtil;

/**
 * Component decorator that implements the view interface
 * for <object> elements.
 * <p>
 * This view will try to load the class specified by the
 * <code>classid attribute.  If possible, the Classloader
 * used to load the associated Document is used.
 * This would typically be the same as the ClassLoader
 * used to load the EditorKit.  If the document's
 * ClassLoader is null, <code>Class.forName is used.
 * <p>
 * If the class can successfully be loaded, an attempt will
 * be made to create an instance of it by calling
 * <code>Class.newInstance.  An attempt will be made
 * to narrow the instance to type <code>java.awt.Component
 * to display the object.
 * <p>
 * This view can also manage a set of parameters with limitations.
 * The parameters to the <object> element are expected to
 * be present on the associated elements attribute set as simple
 * strings.  Each bean property will be queried as a key on
 * the AttributeSet, with the expectation that a non-null value
 * (of type String) will be present if there was a parameter
 * specification for the property.  Reflection is used to
 * set the parameter.  Currently, this is limited to a very
 * simple single parameter of type String.
 * <p>
 * A simple example HTML invocation is:
 * <pre>
 *      <object classid="javax.swing.JLabel">
 *      <param name="text" value="sample text">
 *      </object>
 * </pre>
 *
 * @author Timothy Prinzing
 */
public class ObjectView extends ComponentView  {

    /**
     * Creates a new ObjectView object.
     *
     * @param elem the element to decorate
     */
    public ObjectView(Element elem) {
        super(elem);
    }

    /**
     * Create the component.  The classid is used
     * as a specification of the classname, which
     * we try to load.
     */
    protected Component createComponent() {
        AttributeSet attr = getElement().getAttributes();
        String classname = (String) attr.getAttribute(HTML.Attribute.CLASSID);
        try {
            ReflectUtil.checkPackageAccess(classname);
            Class c = Class.forName(classname, true,Thread.currentThread().
                                    getContextClassLoader());
            Object o = c.newInstance();
            if (o instanceof Component) {
                Component comp = (Component) o;
                setParameters(comp, attr);
                return comp;
            }
        } catch (Throwable e) {
            // couldn't create a component... fall through to the
            // couldn't load representation.
        }

        return getUnloadableRepresentation();
    }

    /**
     * Fetch a component that can be used to represent the
     * object if it can't be created.
     */
    Component getUnloadableRepresentation() {
        // PENDING(prinz) get some artwork and return something
        // interesting here.
        Component comp = new JLabel("??");
        comp.setForeground(Color.red);
        return comp;
    }

    /**
     * Initialize this component according the KEY/VALUEs passed in
     * via the <param> elements in the corresponding
     * <object> element.
     */
    private void setParameters(Component comp, AttributeSet attr) {
        Class k = comp.getClass();
        BeanInfo bi;
        try {
            bi = Introspector.getBeanInfo(k);
        } catch (IntrospectionException ex) {
            System.err.println("introspector failed, ex: "+ex);
            return;             // quit for now
        }
        PropertyDescriptor props[] = bi.getPropertyDescriptors();
        for (int i=0; i < props.length; i++) {
            //      System.err.println("checking on props[i]: "+props[i].getName());
            Object v = attr.getAttribute(props[i].getName());
            if (v instanceof String) {
                // found a property parameter
                String value = (String) v;
                Method writer = props[i].getWriteMethod();
                if (writer == null) {
                    // read-only property. ignore
                    return;     // for now
                }
                Class[] params = writer.getParameterTypes();
                if (params.length != 1) {
                    // zero or more than one argument, ignore
                    return;     // for now
                }
                Object [] args = { value };
                try {
                    MethodUtil.invoke(writer, comp, args);
                } catch (Exception ex) {
                    System.err.println("Invocation failed");
                    // invocation code
                }
            }
        }
    }

}