问题
The Shape interface is implemented by objects of Java 2D (Arc2D, Area, CubicCurve2D, Ellipse2D, GeneralPath etc..).
Some of the concrete objects are marked as Serializable and can be stored and restored using object serialization, but others like Area do not implement the interface and throw errors.
But since we are constantly warned that such naive serialization is not necessarily stable across Java implementations or versions, I'd prefer to use some form of serialization that is.
That leads us to storing/restoring from XML using XMLEncoder and XMLDecoder, but that is capable of handling even less of the Java 2D Shape objects.
Some results for both can be seen below. We start with 6 shapes, and attempt to store/restore them via object serialization and standard XML serialization.
How would we store all Shape objects correctly via XML?
import java.awt.*;
import java.awt.geom.*;
import java.awt.image.BufferedImage;
import java.beans.*;
import java.io.*;
import java.util.ArrayList;
import javax.swing.*;
import javax.swing.border.TitledBorder;
public class Serialize2D {
private JPanel ui;
Serialize2D() {
initUI();
}
public void initUI() {
if (ui != null) {
return;
}
ui = new JPanel(new GridLayout(0, 1));
int[] xpoints = {205, 295, 205, 295};
int[] ypoints = {5, 25, 25, 45};
Polygon polygon = new Polygon(xpoints, ypoints, xpoints.length);
ArrayList<Shape> shapes = new ArrayList<Shape>();
int w = 45;
shapes.add(new Rectangle2D.Double(5, 5, 90, 40));
shapes.add(new Ellipse2D.Double(105, 5, 90, 40));
shapes.add(polygon);
shapes.add(new GeneralPath(new Rectangle2D.Double(5, 55, 90, 40)));
shapes.add(new Path2D.Double(new Rectangle2D.Double(105, 55, 90, 40)));
shapes.add(new Area(new Rectangle2D.Double(205, 55, 90, 40)));
addTitledLabelToPanel(shapes, "Original Shapes");
addTitledLabelToPanel(
serializeToFromObject(shapes), "Serialize via Object");
addTitledLabelToPanel(
serializeToFromXML(shapes), "Serialize via XML");
}
public JComponent getUI() {
return ui;
}
public ArrayList<Shape> serializeToFromObject(ArrayList<Shape> shapes) {
ArrayList<Shape> shps = new ArrayList<Shape>();
try {
ObjectOutputStream oos = null;
ByteArrayOutputStream baos = new ByteArrayOutputStream();
oos = new ObjectOutputStream(baos);
for (Shape shape : shapes) {
try {
oos.writeObject(shape);
} catch (Exception ex) {
System.err.println(ex.toString());
}
}
oos.flush();
oos.close();
System.out.println("length Obj: " + baos.toByteArray().length);
ByteArrayInputStream bais = new ByteArrayInputStream(
baos.toByteArray());
ObjectInputStream ois = new ObjectInputStream(bais);
Object o = null;
try {
o = ois.readObject();
} catch (NotSerializableException ex) {
System.err.println(ex.getMessage());
} catch (ClassNotFoundException ex) {
ex.printStackTrace();
}
while (o != null) {
shps.add((Shape) o);
try {
o = ois.readObject();
} catch (NotSerializableException ex) {
System.err.println(ex.getMessage());
} catch (ClassNotFoundException ex) {
ex.printStackTrace();
}
}
return shps;
} catch (IOException ex) {
ex.printStackTrace();
}
return shps;
}
public ArrayList<Shape> serializeToFromXML(ArrayList<Shape> shapes) {
ArrayList<Shape> shps = new ArrayList<Shape>();
try {
ByteArrayOutputStream baos = new ByteArrayOutputStream();
XMLEncoder xmle = new XMLEncoder(baos);
for (Shape shape : shapes) {
xmle.writeObject(shape);
}
xmle.flush();
xmle.close();
System.out.println("length XML: " + baos.toByteArray().length);
ByteArrayInputStream bais
= new ByteArrayInputStream(baos.toByteArray());
XMLDecoder xmld = new XMLDecoder(bais);
Shape shape = (Shape) xmld.readObject();
while (shape != null) {
shps.add(shape);
try {
shape = (Shape) xmld.readObject();
} catch (ArrayIndexOutOfBoundsException aioobe) {
// we've read last object
shape = null;
}
}
xmld.close();
} catch (Exception ex) {
ex.printStackTrace();
}
return shps;
}
private final static String getType(Object o) {
String s = o.getClass().getName();
String[] parts = s.split("\\.");
s = parts[parts.length - 1].split("\\$")[0];
return s;
}
public static void drawShapesToImage(
ArrayList<Shape> shapes, BufferedImage image) {
Graphics2D g = image.createGraphics();
g.setRenderingHint(
RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
g.setColor(Color.WHITE);
g.fillRect(0, 0, image.getWidth(), image.getHeight());
for (Shape shape : shapes) {
String s = getType(shape);
g.setColor(Color.GREEN);
g.fill(shape);
g.setColor(Color.BLACK);
g.draw(shape);
Rectangle r = shape.getBounds();
int x = r.x + 5;
int y = r.y + 16;
if (r.width * r.height != 0) {
g.drawString(s, x, y);
}
}
g.dispose();
}
private void addTitledLabelToPanel(ArrayList<Shape> shapes, String title) {
int w = 300;
int h = 100;
BufferedImage bi = new BufferedImage(w, h, BufferedImage.TYPE_INT_RGB);
drawShapesToImage(shapes, bi);
JLabel l = new JLabel(new ImageIcon(bi));
l.setBorder(new TitledBorder(title));
ui.add(l);
}
public static void main(String[] args) {
Runnable r = new Runnable() {
@Override
public void run() {
Serialize2D ss = new Serialize2D();
JOptionPane.showMessageDialog(null, ss.getUI());
}
};
SwingUtilities.invokeLater(r);
}
}
回答1:
Unfortunately, naive encoding/decoding of a Shape to XML using XMLEncoder/Decoder often destroys all the vital information of the Shape!
So to do this, still using the above mentioned classes, we serialize and restore properly constructed beans that represent the parts of the shape as obtained from a PathIterator. These beans are:
PathBeanwhich stores the collection ofPathSegmentobjects that form the shape of the Java-2DShape.PathSegmentwhich stores the details of a particular part of the path (segment type, winding rule & coords).
SerializeShapes GUI
A GUI to demonstrate storing and restoring shapes.
- Click the Ellipse (
Ellipse2D), Rectangle (Rectangle2D) or Face (Area) buttons a couple of times. - Exit the GUI. The shapes will be serialized to disk.
- Restart the GUI. The randomly drawn shapes from last time will be restored from disk & reappear in the GUI.
The selected shape will be filled in green, other shapes in red.
package serialize2d;
import java.awt.*;
import java.awt.event.*;
import java.awt.font.FontRenderContext;
import java.awt.geom.AffineTransform;
import java.awt.geom.*;
import java.awt.image.BufferedImage;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.Random;
import java.util.Vector;
import javax.swing.*;
import javax.swing.border.EmptyBorder;
import javax.swing.event.*;
/** A GUI to make it easy to add/remove shapes from a canvas.
It should persist the shapes between runs. */
public class SerializeShapes {
JPanel ui;
JPanel shapePanel;
Random rand;
JPanel shapeCanvas;
DefaultListModel<Shape> allShapesModel;
ListSelectionModel shapeSelectionModel;
RenderingHints renderingHints;
SerializeShapes() {
initUI();
}
public void initUI() {
if (ui != null) {
return;
}
renderingHints = new RenderingHints(RenderingHints.KEY_DITHERING,
RenderingHints.VALUE_DITHER_ENABLE);
renderingHints.put(RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
renderingHints.put(RenderingHints.KEY_ALPHA_INTERPOLATION,
RenderingHints.VALUE_ALPHA_INTERPOLATION_QUALITY);
renderingHints.put(RenderingHints.KEY_COLOR_RENDERING,
RenderingHints.VALUE_COLOR_RENDER_QUALITY);
renderingHints.put(RenderingHints.KEY_RENDERING,
RenderingHints.VALUE_RENDER_QUALITY);
renderingHints.put(RenderingHints.KEY_STROKE_CONTROL,
RenderingHints.VALUE_STROKE_NORMALIZE);
ui = new JPanel(new BorderLayout(4, 4));
ui.setBorder(new EmptyBorder(4, 4, 4, 4));
JPanel controls = new JPanel(new FlowLayout(FlowLayout.CENTER, 4, 4));
ui.add(controls, BorderLayout.PAGE_START);
shapeCanvas = new ShapeCanvas();
ui.add(shapeCanvas);
rand = new Random();
allShapesModel = new DefaultListModel<Shape>();
JList<Shape> allShapes = new JList<Shape>(allShapesModel);
allShapes.setCellRenderer(new ShapeListCellRenderer());
shapeSelectionModel = allShapes.getSelectionModel();
shapeSelectionModel.setSelectionMode(
ListSelectionModel.SINGLE_SELECTION);
ListSelectionListener shapesSelectionListener
= new ListSelectionListener() {
@Override
public void valueChanged(ListSelectionEvent e) {
shapeCanvas.repaint();
}
};
allShapes.addListSelectionListener(shapesSelectionListener);
JScrollPane shapesScroll = new JScrollPane(
allShapes,
JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,
JScrollPane.HORIZONTAL_SCROLLBAR_NEVER
);
// TODO fix this hack..
shapesScroll.getViewport().setPreferredSize(new Dimension(60, 200));
ui.add(shapesScroll, BorderLayout.LINE_START);
Action addEllipse = new AbstractAction("Ellipse") {
@Override
public void actionPerformed(ActionEvent e) {
int w = rand.nextInt(100) + 10;
int h = rand.nextInt(100) + 10;
int x = rand.nextInt(shapeCanvas.getWidth() - w);
int y = rand.nextInt(shapeCanvas.getHeight() - h);
Ellipse2D ellipse = new Ellipse2D.Double(x, y, w, h);
addShape(ellipse);
}
};
addEllipse.putValue(Action.MNEMONIC_KEY, KeyEvent.VK_E);
Action addRectangle = new AbstractAction("Rectangle") {
@Override
public void actionPerformed(ActionEvent e) {
int w = rand.nextInt(100) + 10;
int h = rand.nextInt(100) + 10;
int x = rand.nextInt(shapeCanvas.getWidth() - w);
int y = rand.nextInt(shapeCanvas.getHeight() - h);
Rectangle2D rectangle = new Rectangle2D.Double(x, y, w, h);
addShape(rectangle);
}
};
addRectangle.putValue(Action.MNEMONIC_KEY, KeyEvent.VK_R);
final int faceStart = 128513;
final int faceEnd = 128528;
final int diff = faceEnd - faceStart;
StringBuilder sb = new StringBuilder();
for (int count = faceStart; count <= faceEnd; count++) {
sb.append(Character.toChars(count));
}
final String s = sb.toString();
Vector<Font> compatibleFontList = new Vector<Font>();
GraphicsEnvironment ge
= GraphicsEnvironment.getLocalGraphicsEnvironment();
Font[] fonts = ge.getAllFonts();
for (Font font : fonts) {
if (font.canDisplayUpTo(s) < 0) {
compatibleFontList.add(font);
}
}
JComboBox fontChooser = new JComboBox(compatibleFontList);
ListCellRenderer fontRenderer = new DefaultListCellRenderer() {
@Override
public Component getListCellRendererComponent(
JList list, Object value, int index,
boolean isSelected, boolean cellHasFocus) {
Component c = super.getListCellRendererComponent(
list, value, index,
isSelected, cellHasFocus);
JLabel l = (JLabel) c;
Font font = (Font) value;
l.setText(font.getName());
return l;
}
};
fontChooser.setRenderer(fontRenderer);
final ComboBoxModel<Font> fontModel = fontChooser.getModel();
BufferedImage bi = new BufferedImage(1, 1, BufferedImage.TYPE_INT_RGB);
Graphics2D g = bi.createGraphics();
final FontRenderContext fontRenderContext = g.getFontRenderContext();
Action addFace = new AbstractAction("Face") {
@Override
public void actionPerformed(ActionEvent e) {
int codepoint = faceStart + rand.nextInt(diff);
String text = new String(Character.toChars(codepoint));
Font font = (Font) fontModel.getSelectedItem();
Area area = new Area(
font.deriveFont(80f).
createGlyphVector(fontRenderContext, text).
getOutline());
Rectangle bounds = area.getBounds();
float x = rand.nextInt(
shapeCanvas.getWidth() - bounds.width) - bounds.x;
float y = rand.nextInt(
shapeCanvas.getHeight() - bounds.height) - bounds.y;
AffineTransform move = AffineTransform.
getTranslateInstance(x, y);
area.transform(move);
addShape(area);
}
};
addFace.putValue(Action.MNEMONIC_KEY, KeyEvent.VK_F);
Action delete = new AbstractAction("Delete") {
@Override
public void actionPerformed(ActionEvent e) {
int idx = shapeSelectionModel.getMinSelectionIndex();
if (idx < 0) {
JOptionPane.showMessageDialog(
ui,
"Select a shape to delete",
"Select a Shape",
JOptionPane.ERROR_MESSAGE);
} else {
allShapesModel.removeElementAt(idx);
shapeCanvas.repaint();
}
}
};
delete.putValue(Action.MNEMONIC_KEY, KeyEvent.VK_D);
controls.add(new JButton(addEllipse));
controls.add(new JButton(addRectangle));
controls.add(new JButton(addFace));
controls.add(fontChooser);
controls.add(new JButton(delete));
try {
ArrayList<Shape> shapes = deserializeShapes();
for (Shape shape : shapes) {
allShapesModel.addElement(shape);
}
} catch (Exception ex) {
System.err.println("If first launch, this is as expected!");
ex.printStackTrace();
}
}
private void addShape(Shape shape) {
allShapesModel.addElement(shape);
int size = allShapesModel.getSize() - 1;
shapeSelectionModel.addSelectionInterval(size, size);
}
class ShapeCanvas extends JPanel {
ShapeCanvas() {
setBackground(Color.WHITE);
}
@Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
g2.setRenderingHints(renderingHints);
Stroke stroke = new BasicStroke(1.5f);
g2.setStroke(stroke);
int idx = shapeSelectionModel.getMinSelectionIndex();
Shape selectedShape = null;
if (idx > -1) {
selectedShape = allShapesModel.get(idx);
}
Enumeration en = allShapesModel.elements();
while (en.hasMoreElements()) {
Shape shape = (Shape) en.nextElement();
if (shape.equals(selectedShape)) {
g2.setColor(new Color(0, 255, 0, 191));
} else {
g2.setColor(new Color(255, 0, 0, 191));
}
g2.fill(shape);
g2.setColor(new Color(0, 0, 0, 224));
g2.draw(shape);
}
}
@Override
public Dimension getPreferredSize() {
return new Dimension(500, 300);
}
}
public JComponent getUI() {
return ui;
}
public static void main(String[] args) {
Runnable r = new Runnable() {
@Override
public void run() {
SerializeShapes se = new SerializeShapes();
JFrame f = new JFrame("Serialize Shapes");
f.addWindowListener(new SerializeWindowListener(se));
f.setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE);
f.setContentPane(se.getUI());
f.setResizable(false);
f.pack();
f.setLocationByPlatform(true);
f.setVisible(true);
}
};
SwingUtilities.invokeLater(r);
}
public void serializeShapes() throws FileNotFoundException {
ArrayList<Shape> shapes
= new ArrayList<Shape>();
Enumeration en = allShapesModel.elements();
while (en.hasMoreElements()) {
Shape shape = (Shape) en.nextElement();
shapes.add(shape);
}
ShapeIO.serializeShapes(shapes, this.getClass());
try {
Desktop.getDesktop().open(
ShapeIO.getSerializeFile(this.getClass()));
} catch (Exception e) {
e.printStackTrace();
}
}
public ArrayList<Shape> deserializeShapes() throws FileNotFoundException {
return ShapeIO.deserializeShapes(this.getClass());
}
class ShapeListCellRenderer extends DefaultListCellRenderer {
@Override
public Component getListCellRendererComponent(
JList<? extends Object> list, Object value,
int index, boolean isSelected, boolean cellHasFocus) {
Component c = super.getListCellRendererComponent(list, value, index,
isSelected, cellHasFocus);
JLabel l = (JLabel) c;
Shape shape = (Shape) value;
ShapeIcon icon = new ShapeIcon(shape, 40);
l.setIcon(icon);
l.setText("");
return l;
}
}
class ShapeIcon implements Icon {
Shape shape;
int size;
ShapeIcon(Shape shape, int size) {
this.shape = shape;
this.size = size;
}
@Override
public void paintIcon(Component c, Graphics g, int x, int y) {
Graphics2D g2 = (Graphics2D) g;
g2.setRenderingHints(renderingHints);
Rectangle bounds = shape.getBounds();
int xOff = -bounds.x;
int yOff = -bounds.y;
double xRatio = (double) bounds.width / (double) size;
double yRatio = (double) bounds.height / (double) size;
double ratio = xRatio > yRatio ? xRatio : yRatio;
AffineTransform scale = AffineTransform.getScaleInstance(1 / ratio, 1 / ratio);
AffineTransform shift = AffineTransform.getTranslateInstance(xOff, yOff);
AffineTransform totalTransform = new AffineTransform();
totalTransform.concatenate(scale);
totalTransform.concatenate(shift);
Area b = new Area(shape).createTransformedArea(totalTransform);
bounds = b.getBounds();
g2.setColor(Color.BLACK);
g2.fill(b);
}
@Override
public int getIconWidth() {
return size;
}
@Override
public int getIconHeight() {
return size;
}
}
}
class SerializeWindowListener extends WindowAdapter {
SerializeShapes serializeShapes;
SerializeWindowListener(SerializeShapes serializeShapes) {
this.serializeShapes = serializeShapes;
}
@Override
public void windowClosing(WindowEvent e) {
try {
serializeShapes.serializeShapes();
} catch (FileNotFoundException ex) {
ex.printStackTrace();
System.exit(1);
}
System.exit(0);
}
}
ShapeIO
Performs the I/O to/from XML.
package serialize2d;
import java.awt.Shape;
import java.beans.*;
import java.io.*;
import java.util.ArrayList;
public class ShapeIO {
/** Save the list of shapes to the file system. */
public static void serializeShapes(
ArrayList<Shape> shapes, Class serializeClass)
throws FileNotFoundException {
File f = getSerializeFile(serializeClass);
XMLEncoder xmle = new XMLEncoder(new FileOutputStream(f));
ArrayList<PathBean> pathSegmentsCollection = new ArrayList<>();
for (Shape shape : shapes) {
ArrayList<PathSegment> pathSegments =
BeanConverter.getSegmentsFromShape(shape);
PathBean as = new PathBean(pathSegments);
pathSegmentsCollection.add(as);
}
xmle.writeObject(pathSegmentsCollection);
xmle.flush();
xmle.close();
}
/** Load the list of shapes from the file system. */
public static ArrayList<Shape> deserializeShapes(Class serializeClass)
throws FileNotFoundException {
File f = getSerializeFile(serializeClass);
XMLDecoder xmld = new XMLDecoder(new FileInputStream(f));
ArrayList<PathBean> pathSegmentsCollection
= (ArrayList<PathBean>) xmld.readObject();
ArrayList<Shape> shapes = new ArrayList<Shape>();
for (PathBean pathSegments : pathSegmentsCollection) {
shapes.add(BeanConverter.getShapeFromSegments(pathSegments));
}
return shapes;
}
/** Provide an unique, reproducible & readable/writable path for a class. */
public static File getSerializeFile(Class serializeClass) {
File f = new File(System.getProperty("user.home"));
String[] nameParts = serializeClass.getCanonicalName().split("\\.");
f = new File(f, "java");
for (String namePart : nameParts) {
f = new File(f, namePart);
}
f.mkdirs();
f = new File(f, nameParts[nameParts.length-1] + ".xml");
return f;
}
}
BeanConverter
Obtains a PathIterator from the Shape and converts it to a serializable bean. Converts the bean back into a GeneralPath.
package serialize2d;
import java.awt.Shape;
import java.awt.geom.*;
import java.util.ArrayList;
/** Utility class to convert bean to/from a Shape. */
public class BeanConverter {
/** Convert a shape to a serializable bean. */
public static ArrayList<PathSegment> getSegmentsFromShape(Shape shape) {
ArrayList<PathSegment> shapeSegments = new ArrayList<PathSegment>();
for (
PathIterator pi = shape.getPathIterator(null);
!pi.isDone();
pi.next()) {
double[] coords = new double[6];
int pathSegmentType = pi.currentSegment(coords);
int windingRule = pi.getWindingRule();
PathSegment as = new PathSegment(
pathSegmentType, windingRule, coords);
shapeSegments.add(as);
}
return shapeSegments;
}
/** Convert a serializable bean to a shape. */
public static Shape getShapeFromSegments(PathBean shapeSegments) {
GeneralPath gp = new GeneralPath();
for (PathSegment shapeSegment : shapeSegments.getPathSegments()) {
double[] coords = shapeSegment.getCoords();
int pathSegmentType = shapeSegment.getPathSegmentType();
int windingRule = shapeSegment.getWindingRule();
gp.setWindingRule(windingRule);
if (pathSegmentType == PathIterator.SEG_MOVETO) {
gp.moveTo(coords[0], coords[1]);
} else if (pathSegmentType == PathIterator.SEG_LINETO) {
gp.lineTo(coords[0], coords[1]);
} else if (pathSegmentType == PathIterator.SEG_QUADTO) {
gp.quadTo(coords[0], coords[1], coords[2], coords[3]);
} else if (pathSegmentType == PathIterator.SEG_CUBICTO) {
gp.curveTo(
coords[0], coords[1], coords[2],
coords[3], coords[4], coords[5]);
} else if (pathSegmentType == PathIterator.SEG_CLOSE) {
gp.closePath();
} else {
System.err.println("Unexpected value! " + pathSegmentType);
}
}
return gp;
}
}
PathBean
Stores a collection of path segments in a seriallizable bean.
package serialize2d;
import java.awt.geom.*;
import java.util.ArrayList;
/** PathBean stores the collection of PathSegment objects
that constitute the path of a Shape. */
public class PathBean {
public ArrayList<PathSegment> pathSegments;
public PathBean() {}
public PathBean(ArrayList<PathSegment> pathSegments) {
this.pathSegments = pathSegments;
}
public ArrayList<PathSegment> getPathSegments() {
return pathSegments;
}
public void setPathSegments(ArrayList<PathSegment> pathSegments) {
this.pathSegments = pathSegments;
}
@Override
public String toString() {
StringBuilder sb = new StringBuilder("{");
for (PathSegment pathSegment : pathSegments) {
sb.append(" \n\t");
sb.append(pathSegment.toString());
}
sb.append(" \n");
sb.append("}");
return "PathSegments: " + sb.toString();
}
}
PathSegment
Stores the path segment of one part of the entire path.
package serialize2d;
import java.util.Arrays;
/** PathSegment bean stores the detail on one segment of the path
that constitutes a Shape. */
public class PathSegment {
public int pathSegmentType;
public int windingRule;
public double[] coords;
public PathSegment() {}
public PathSegment(int pathSegmentType, int windingRule, double[] coords) {
this.pathSegmentType = pathSegmentType;
this.windingRule = windingRule;
this.coords = coords;
}
public int getPathSegmentType() {
return pathSegmentType;
}
public void setPathSegmentType(int pathSegmentType) {
this.pathSegmentType = pathSegmentType;
}
public int getWindingRule() {
return windingRule;
}
public void setWindingRule(int windingRule) {
this.windingRule = windingRule;
}
public double[] getCoords() {
return coords;
}
public void setCoords(double[] coords) {
this.coords = coords;
}
@Override
public String toString() {
String sC = (coords != null ? "" : Arrays.toString(coords));
String s = String.format(
"PathSegment: Path Segment Type:- %d \t"
+ "Winding Rule:- %d \tcoords:- %s",
getPathSegmentType(), getWindingRule(), sC);
return s;
}
}
Notes
This is intended as a proof of concept as opposed to a polished approach.
- XML serialized data becomes big real fast, it would normally be zipped. Zip compression might shave 30-40% off the byte size of a serialized object or a class file, but 80-95% off XML. In any case, zip works well for the next point as well.
- For the type of project where we wish to offer to serialize and restore shapes, we'll probably also want to include more details of the shapes (e.g. fill color or texture and draw color or stroke etc.) as well as other data like images or fonts. This is also where Zip comes in handy, since we can put them all in the same archive, each with best levels of compression (e.g. standard for the XML and none for images).
A zip archive of the source files in this answer can be downloaded from my cloud drive.
回答2:
A custom PersistenceDelegate can be used with XMLEncoder to serialize a Path2D or GeneralPath to XML.
Consider the following XML:
<?xml version="1.0" encoding="UTF-8"?>
<java version="1.8.0_60" class="java.beans.XMLDecoder">
<object class="java.awt.geom.Path2D$Float">
<void property="windingRule">
<int>0</int>
</void>
<void method="moveTo">
<float>1.0</float>
<float>1.0</float>
</void>
<void method="lineTo">
<float>2.0</float>
<float>0.0</float>
</void>
<void method="lineTo">
<float>0.0</float>
<float>3.0</float>
</void>
<void method="closePath"/>
</object>
</java>
When read by an XMLEncoder instance, the following commands will be executed ...
Path2D.Float object = new Path2D.Float();
object.setWindingRule(0); // Note: 0 => Path2D.WIND_EVEN_ODD
object.moveTo(1.0, 1.0);
object.lineTo(2.0, 0.0);
object.lineTo(0.0, 3.0);
object.closePath();
... and a closed triangle object will be returned by XMLDecoder.readObject().
Based on this, we can conclude that XMLDecoder can already deserialize a Path2D shape, if it is properly encoded. What does the XMLEncoder do for us now?
Path2D.Float path = new Path2D.Float(GeneralPath.WIND_EVEN_ODD, 10);
path.moveTo(1, 1);
path.lineTo(2, 0);
path.lineTo(0, 3);
path.closePath();
try (XMLEncoder xml = new XMLEncoder(System.out)) {
xml.writeObject(path);
}
This produces the following XML:
<?xml version="1.0" encoding="UTF-8"?>
<java version="1.8.0_60" class="java.beans.XMLDecoder">
<object class="java.awt.geom.Path2D$Float">
<void property="windingRule">
<int>0</int>
</void>
</object>
</java>
Not great, but not too bad. We're just missing the path data. So we just need to extend the DefaultPersistenceDelegate to add the required path commands to the output.
public class Path2DPersistenceDelegate extends DefaultPersistenceDelegate {
@Override
protected void initialize(Class<?> cls, Object oldInstance, Object newInstance, Encoder out) {
super.initialize(cls, oldInstance, newInstance, out);
Shape shape = (Shape) oldInstance;
float coords[] = new float[6];
Float pnt0[] = new Float[0];
Float pnt1[] = new Float[2];
Float pnt2[] = new Float[4];
Float pnt3[] = new Float[6];
Float pnts[];
PathIterator iterator = shape.getPathIterator(null);
while (!iterator.isDone()) {
int type = iterator.currentSegment(coords);
String cmd;
switch (type) {
case PathIterator.SEG_CLOSE:
cmd = "closePath";
pnts = pnt0;
break;
case PathIterator.SEG_MOVETO:
cmd = "moveTo";
pnts = pnt1;
break;
case PathIterator.SEG_LINETO:
cmd = "lineTo";
pnts = pnt1;
break;
case PathIterator.SEG_QUADTO:
cmd = "quadTo";
pnts = pnt2;
break;
case PathIterator.SEG_CUBICTO:
cmd = "curveTo";
pnts = pnt3;
break;
default:
throw new IllegalStateException("Unexpected segment type: " + type);
}
for (int i = 0; i < pnts.length; i++) {
pnts[i] = coords[i];
}
out.writeStatement(new Statement(oldInstance, cmd, pnts));
iterator.next();
}
}
}
Then, we just register this persistence delegate with the XMLEncoder, and it will produce the XML shown at the top of this post.
Path2DPersistenceDelegate path2d_delegate = new Path2DPersistenceDelegate();
try (XMLEncoder xml = new XMLEncoder(System.out)) {
xml.setPersistenceDelegate(Path2D.Float.class, path2d_delegate);
xml.writeObject(path);
}
Since Path2D.Float is the parent class of GeneralPath, a GeneralPath will also be encoded properly. If you want properly encode Path2D.Double shapes, you will need to modify the delegate to use double values and Double objects.
Update:
To construct the Path2D.Float object with the proper windingRule property instead of setting the property afterwards, add the following constructor to the Path2DPersistenceDelegate:
public Path2DPersistenceDelegate() {
super(new String[] { "windingRule" });
}
The XML will then read:
...
<object class="java.awt.geom.Path2D$Float">
<int>0</int>
<void method="moveTo">
...
This loses some human-readable context information in the XML; a human would need to read the documentation to determine that with the Path2D.Float(int) constructor, the int parameter is the windingRule property.
Update 2:
The Polygon persistence delegate is fairly simple:
public class PolygonPersistenceDelegate extends PersistenceDelegate {
@Override
protected Expression instantiate(Object oldInstance, Encoder out) {
Polygon polygon = (Polygon) oldInstance;
return new Expression(oldInstance, oldInstance.getClass(), "new",
new Object[] { polygon.xpoints, polygon.ypoints, polygon.npoints });
}
}
Since Area Constructive Area Geometry object is more complex, it cannot be created by moveTo and lineTo type methods, but rather only by adding, subtracting, or exclusive-or-ing Shape objects. But the constructor takes a Shape object, and a Path2D.Double can be constructed from an Area object, so the persistence delegate actually can be written quite simply as well:
public class AreaPersistenceDelegate extends PersistenceDelegate {
@Override
protected Expression instantiate(Object oldInstance, Encoder out) {
Area area = (Area) oldInstance;
Path2D.Double p2d = new Path2D.Double(area);
return new Expression(oldInstance, oldInstance.getClass(), "new",
new Object[] { p2d });
}
}
Since we are using Path2D.Double internally, we would need to add both persistent delegates to the XMLEncoder:
try (XMLEncoder encoder = new XMLEncoder(baos)) {
encoder.setPersistenceDelegate(Area.class, new AreaPersistenceDelegate());
encoder.setPersistenceDelegate(Path2D.Double.class, new Path2DPersistenceDelegate.Double());
encoder.writeObject(area);
}
Update 3:
A project with the PersistenceDelegate for Area, Path2D and GeneralPath has been created on GitHub.
Notes:
- The persistence delegate for
Polygonwas removed, as it seems to be unnecessary for Java 1.7
Update 4:
For Java 1.7, the pnts array must be allocated for each new Statement(); it cannot be allocated once and reused. Thus, the Path2D delegates must be changed as follows:
float coords[] = new float[6];
/* Removed: Float pnt0[] = new Float[0];
Float pnt1[] = new Float[0];
Float pnt2[] = new Float[4];
Float pnt3[] = new Float[6]; */
Float pnts[];
PathIterator iterator = shape.getPathIterator(null);
while (!iterator.isDone()) {
int type = iterator.currentSegment(coords);
String cmd;
switch (type) {
case PathIterator.SEG_CLOSE:
cmd = "closePath";
pnts = new Float[0]; // Allocate for each segment
break;
case PathIterator.SEG_MOVETO:
cmd = "moveTo";
pnts = new Float[2]; // Allocate for each segment
break;
/* ... etc ...*/
来源：https://stackoverflow.com/questions/26579729/how-to-serialize-java-2d-shape-objects-as-xml