如何将Java 2D Shape对象序列化为XML？

Shape接口由Java 2D（ Arc2D ， Area ， CubicCurve2D ， Ellipse2D ， GeneralPath等）的对象实现。

一些具体对象标记为Serializable ，可以使用对象序列化进行存储和恢复，但像Area这样的其他对象不实现接口并抛出错误。

但是，由于我们经常被警告说这种天真的序列化在Java实现或版本中不一定是稳定的，我更喜欢使用某种forms的序列化。

这导致我们使用XMLEncoder和XMLDecoder从XML存储/恢复，但是它能够处理更少的Java 2D Shape对象。

两者的一些结果可以在下面看到。 我们从6个形状开始，尝试通过对象序列化和标准XML序列化来存储/恢复它们。

在此处输入图像描述

我们如何通过XML正确存储所有Shape对象？ 

 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 shapes = new ArrayList(); 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 serializeToFromObject(ArrayList shapes) { ArrayList shps = new ArrayList(); 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 serializeToFromXML(ArrayList shapes) { ArrayList shps = new ArrayList(); 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 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 = rx + 5; int y = ry + 16; if (r.width * r.height != 0) { g.drawString(s, x, y); } } g.dispose(); } private void addTitledLabelToPanel(ArrayList 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); } }

不幸的是，使用XMLEncoder / Decoder对Shape进行简单的XMLEncoder / Decoder通常会破坏Shape所有重要信息！

因此，为了做到这一点，仍然使用上面提到的类，我们序列化并恢复正确构造的bean，这些bean表示从PathIterator获得的形状部分。 这些豆是：

  • PathBean ，用于存储形成Java-2D Shape形状的PathSegment对象的集合。
  • PathSegment ，存储路径特定部分的细节（段类型，缠绕规则和坐标）。

SerializeShapes GUI

用于演示存储和恢复形状的GUI。

  • 单击椭圆 （ Ellipse2D ）， 矩形 （ Rectangle2D Ellipse2D ）或面 （ Area ）按钮几次。
  • 退出GUI。 形状将序列化为磁盘。
  • 重启GUI。 上次随机绘制的形状将从磁盘恢复并重新出现在GUI中。

在此处输入图像描述

所选形状将以绿色填充，其他形状将以红色填充。 

 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 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(); JList allShapes = new JList(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 compatibleFontList = new Vector(); 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 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 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 shapes = new ArrayList(); 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 deserializeShapes() throws FileNotFoundException { return ShapeIO.deserializeShapes(this.getClass()); } class ShapeListCellRenderer extends 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; 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

对XML执行I / O操作。 

 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 shapes, Class serializeClass) throws FileNotFoundException { File f = getSerializeFile(serializeClass); XMLEncoder xmle = new XMLEncoder(new FileOutputStream(f)); ArrayList pathSegmentsCollection = new ArrayList<>(); for (Shape shape : shapes) { ArrayList 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 deserializeShapes(Class serializeClass) throws FileNotFoundException { File f = getSerializeFile(serializeClass); XMLDecoder xmld = new XMLDecoder(new FileInputStream(f)); ArrayList pathSegmentsCollection = (ArrayList) xmld.readObject(); ArrayList shapes = new ArrayList(); 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

从Shape获取PathIterator并将其转换为可序列化的bean。 将bean转换回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 getSegmentsFromShape(Shape shape) { ArrayList shapeSegments = new ArrayList(); 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

在可串行化的bean中存储路径段的集合。 

 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 pathSegments; public PathBean() {} public PathBean(ArrayList pathSegments) { this.pathSegments = pathSegments; } public ArrayList getPathSegments() { return pathSegments; } public void setPathSegments(ArrayList 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

存储整个路径的一部分的路径段。 

 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; } }

笔记

这旨在作为概念certificate，而不是抛光方法。

  • XML序列化数据变得非常快，通常会被压缩。 Zip压缩可能会使序列化对象或类文件的字节大小减少30-40％，但XML减少80-95％。 在任何情况下，zip也适用于下一点。
  • 对于我们希望提供序列化和恢复形状的项目类型，我们可能还希望包含更多形状细节（例如填充颜色或纹理以及绘制颜色或笔划等）以及其他数据（如图像）或字体。 这也是Zip派上用场的地方，因为我们可以将它们全部放在同一个档案中，每个档案都有最佳的压缩级别（例如XML标准和图像无标准）。

可以从我的云端硬盘下载此答案中源文件的zip存档 。

自定义PersistenceDelegate可与XMLEncoder一起使用，以将Path2D或GeneralPath序列化为XML。

请考虑以下XML： 

     0   1.0 1.0   2.0 0.0   0.0 3.0

当由XMLEncoder实例读取时，将执行以下命令… 

 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();

…并且XMLDecoder.readObject()将返回一个封闭的三角形对象。

基于此，我们可以得出结论，如果正确编码， XMLDecoder已经可以对Path2D形状进行反序列化。 XMLEncoder现在为我们做了什么？ 

 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); }

这会产生以下XML： 

     0

不是很好，但也不是太糟糕。 我们只是错过了路径数据。 所以我们只需要扩展DefaultPersistenceDelegate就可以将所需的路径命令添加到输出中。 

 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(); } } }

然后，我们只是使用XMLEncoder注册此持久性委托，它将生成此post顶部显示的XML。 

 Path2DPersistenceDelegate path2d_delegate = new Path2DPersistenceDelegate(); try (XMLEncoder xml = new XMLEncoder(System.out)) { xml.setPersistenceDelegate(Path2D.Float.class, path2d_delegate); xml.writeObject(path); }

由于Path2D.Float是GeneralPath的父类，因此GeneralPath也将被正确编码。 如果要正确编码Path2D.Double形状，则需要修改委托以使用double值和Double对象。

更新：

要使用正确的windingRule属性构造Path2D.Float对象而不是之后设置属性，请将以下构造函数添加到Path2DPersistenceDelegate ： 

 public Path2DPersistenceDelegate() { super(new String[] { "windingRule" }); }

然后XML将读取： 

 ...  0  ...

这会在XML中丢失一些人类可读的上下文信息; 人类需要阅读文档以确定使用Path2D.Float(int)构造函数， int参数是windingRule属性。

更新2：

Polygon持久委托非常简单： 

 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 }); } }

由于Area Constructive Area Geometry对象更复杂，因此无法通过moveTo和lineTo类型方法创建，而只能通过添加，减去或排除Shape对象来创建。 但构造函数接受一个Shape对象，并且可以从Area对象构造Path2D.Double ，因此实际上也可以非常简单地编写持久委托： 

 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 }); } }

由于我们在内部使用Path2D.Double ，我们需要将两个持久委托添加到XMLEncoder ： 

 try (XMLEncoder encoder = new XMLEncoder(baos)) { encoder.setPersistenceDelegate(Area.class, new AreaPersistenceDelegate()); encoder.setPersistenceDelegate(Path2D.Double.class, new Path2DPersistenceDelegate.Double()); encoder.writeObject(area); }

更新3：

已在GitHub上创建了一个带有PersistenceDelegate for Area ， Path2D和GeneralPath的项目。

笔记：

  • 删除了Polygon的持久性委托，因为Java 1.7似乎没有必要

更新4：

对于Java 1.7，必须为每个new Statement()分配pnts数组; 它不能被分配一次并重复使用。 因此，必须按如下方式更改Path2D代理： 

  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 ...*/
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