basichtml.java

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/*
 * @(#)BasicHTML.java	1.22 04/07/23
 *
 * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */
package javax.swing.plaf.basic;

import java.io.*;
import java.awt.*;
import java.net.URL;

import javax.swing.*;
import javax.swing.text.*;
import javax.swing.text.html.*;

import com.sun.java.swing.SwingUtilities2;

/**
 * Support for providing html views for the swing components.
 * This translates a simple html string to a javax.swing.text.View
 * implementation that can render the html and provide the necessary
 * layout semantics.
 *
 * @author  Timothy Prinzing
 * @version 1.22 07/23/04
 */
public class BasicHTML {

    /**
     * Create an html renderer for the given component and
     * string of html.
     */
    public static View createHTMLView(JComponent c, String html) {
	BasicEditorKit kit = getFactory();
	Document doc = kit.createDefaultDocument(c.getFont(),
                                                 c.getForeground());
	Object base = c.getClientProperty(documentBaseKey);
	if (base instanceof URL) {
	    ((HTMLDocument)doc).setBase((URL)base);
	}
	Reader r = new StringReader(html);
	try {
	    kit.read(r, doc, 0);
	} catch (Throwable e) {
	}
	ViewFactory f = kit.getViewFactory();
	View hview = f.create(doc.getDefaultRootElement());
	View v = new Renderer(c, f, hview);
	return v;
    }

    /**
     * Check the given string to see if it should trigger the
     * html rendering logic in a non-text component that supports 
     * html rendering.
     */
    public static boolean isHTMLString(String s) {
	if (s != null) {
	    if ((s.length() >= 6) && (s.charAt(0) == '<') && (s.charAt(5) == '>')) {
		String tag = s.substring(1,5);
		return tag.equalsIgnoreCase(propertyKey);
	    }
	}
	return false;
    }

    /**
     * Stash the HTML render for the given text into the client
     * properties of the given JComponent. If the given text is 
     * <em>NOT HTML</em> the property will be cleared of any
     * renderer.
     * <p>
     * This method is useful for ComponentUI implementations
     * that are static (i.e. shared) and get their state
     * entirely from the JComponent.
     */
    public static void updateRenderer(JComponent c, String text) {
	View value = null;
        View oldValue = (View)c.getClientProperty(BasicHTML.propertyKey);
        Boolean htmlDisabled = (Boolean) c.getClientProperty(htmlDisable);
	if (htmlDisabled != Boolean.TRUE && BasicHTML.isHTMLString(text)) {
	    value = BasicHTML.createHTMLView(c, text);
	}
        if (value != oldValue && oldValue != null) {
            for (int i = 0; i < oldValue.getViewCount(); i++) {
                oldValue.getView(i).setParent(null);
            }
        }
	c.putClientProperty(BasicHTML.propertyKey, value);
    }

    /**
     * If this client property of a JComponent is set to Boolean.TRUE
     * the component's 'text' property is never treated as HTML.
     */
    private static final String htmlDisable = "html.disable";

    /**
     * Key to use for the html renderer when stored as a 
     * client property of a JComponent.
     */
    public static final String propertyKey = "html";

    /**
     * Key stored as a client property to indicate the base that relative
     * references are resolved against. For example, lets say you keep
     * your images in the directory resources relative to the code path,
     * you would use the following the set the base:
     * <pre>
     *   jComponent.putClientProperty(documentBaseKey,
     *                                xxx.class.getResource("resources/"));
     * </pre>
     */
    public static final String documentBaseKey = "html.base";

    static BasicEditorKit getFactory() {
	if (basicHTMLFactory == null) {
            basicHTMLViewFactory = new BasicHTMLViewFactory();
	    basicHTMLFactory = new BasicEditorKit();
	}
	return basicHTMLFactory;
    }

    /**
     * The source of the html renderers
     */
    private static BasicEditorKit basicHTMLFactory;

    /**
     * Creates the Views that visually represent the model.
     */
    private static ViewFactory basicHTMLViewFactory;

    /**
     * Overrides to the default stylesheet.  Should consider
     * just creating a completely fresh stylesheet.
     */
    private static final String styleChanges = 
    "p { margin-top: 0; margin-bottom: 0; margin-left: 0; margin-right: 0 }" +
    "body { margin-top: 0; margin-bottom: 0; margin-left: 0; margin-right: 0 }";

    /**
     * The views produced for the ComponentUI implementations aren't
     * going to be edited and don't need full html support.  This kit
     * alters the HTMLEditorKit to try and trim things down a bit.  
     * It does the following:
     * <ul>
     * <li>It doesn't produce Views for things like comments, 
     * head, title, unknown tags, etc.  
     * <li>It installs a different set of css settings from the default
     * provided by HTMLEditorKit.
     * </ul>
     */
    static class BasicEditorKit extends HTMLEditorKit {
	/** Shared base style for all documents created by us use. */
	private static StyleSheet defaultStyles;

	/**
	 * Overriden to return our own slimmed down style sheet.
	 */
	public StyleSheet getStyleSheet() {
	    if (defaultStyles == null) {
		defaultStyles = new StyleSheet();
		StringReader r = new StringReader(styleChanges);
		try {
		    defaultStyles.loadRules(r, null);
		} catch (Throwable e) {
		    // don't want to die in static initialization... 
		    // just display things wrong.
		}
		r.close();
		defaultStyles.addStyleSheet(super.getStyleSheet());
	    }
	    return defaultStyles;
	}

	/**
	 * Sets the async policy to flush everything in one chunk, and
	 * to not display unknown tags.
	 */
        public Document createDefaultDocument(Font defaultFont,
                                              Color foreground) {
	    StyleSheet styles = getStyleSheet();
	    StyleSheet ss = new StyleSheet();
	    ss.addStyleSheet(styles);
	    BasicDocument doc = new BasicDocument(ss, defaultFont, foreground);
	    doc.setAsynchronousLoadPriority(Integer.MAX_VALUE);
	    doc.setPreservesUnknownTags(false);
	    return doc;
	}

        /**
         * Returns the ViewFactory that is used to make sure the Views don't
         * load in the background.
         */
        public ViewFactory getViewFactory() {
            return basicHTMLViewFactory;
        }
    }


    /**
     * BasicHTMLViewFactory extends HTMLFactory to force images to be loaded
     * synchronously.
     */
    static class BasicHTMLViewFactory extends HTMLEditorKit.HTMLFactory {
        public View create(Element elem) {
            View view = super.create(elem);

            if (view instanceof ImageView) {
                ((ImageView)view).setLoadsSynchronously(true);
            }
            return view;
        }
    }


    /**
     * The subclass of HTMLDocument that is used as the model. getForeground
     * is overridden to return the foreground property from the Component this
     * was created for.
     */
    static class BasicDocument extends HTMLDocument {
	/** The host, that is where we are rendering. */
	// private JComponent host;

	BasicDocument(StyleSheet s, Font defaultFont, Color foreground) {
	    super(s);
	    setPreservesUnknownTags(false);
            setFontAndColor(defaultFont, foreground);
	}

        /**
         * Sets the default font and default color. These are set by
         * adding a rule for the body that specifies the font and color.
         * This allows the html to override these should it wish to have
         * a custom font or color.
         */
	private void setFontAndColor(Font font, Color fg) {
            getStyleSheet().addRule(com.sun.java.swing.SwingUtilities2.
                                    displayPropertiesToCSS(font,fg));
	}
    }


    /**
     * Root text view that acts as an HTML renderer.
     */
    static class Renderer extends View {

        Renderer(JComponent c, ViewFactory f, View v) {
            super(null);
	    host = c;
	    factory = f;
	    view = v;
	    view.setParent(this);
	    // initially layout to the preferred size
	    setSize(view.getPreferredSpan(X_AXIS), view.getPreferredSpan(Y_AXIS));
        }