Java在JPanel中自由繪圖，並將繪圖儲存為jpg檔案
阿新 • • 發佈：2019-02-19
在JPanel中繪圖，並利用ImageIO將JPanel儲存為圖片時，往往只儲存一個空白的JPanel，使用者所繪製的圖形往往不能正確儲存，查了很多資料說是要呼叫paintComponent方法而不是paint方法，但是這裡強調的事自由繪圖，而不是畫好圖然後呈現出來。
下面一小段程式是將一個Jpanel儲存為圖片的正常思路，但在自由繪圖時，這個程式只儲存一個空白的JPanel。
要想將使用者的自由繪圖儲存，換一種思路也許很簡單，抓屏，沒錯，Java的一個類Robot提供了抓屏的功能，使用Robot抓屏時可以抓取指定的矩形區域，也可以抓取一個控制元件，當然是提供控制元件的座標位置和大小。下面是Robot的使用方法，直接返回一個BufferedImage物件。public boolean savePanelAsJpg(File file, DrawPanel panel) { Dimension imageSize = panel.getSize(); BufferedImage image = new BufferedImage(imageSize.width,imageSize.height, BufferedImage.TYPE_INT_ARGB); Graphics2D graphics = image.createGraphics(); panel.paint(graphics); graphics.dispose(); try { ImageIO.write(image, "jpg", file); } catch (IOException e) { e.printStackTrace(); return false; } return true; }
//可以指定要抓取的區域 BufferedImage screencapture = new Robot().createScreenCapture( new Rectangle( 15, 15, 150, 150)); //可以抓取指定控制元件： BufferedImage image = new Robot().createScreenCapture( new Rectangle( jFrame.getX(), jFrame.getY(), jFrame.getWidth(), jFrame.getHeight() ) );
下面是一個使用Jpanel繪圖並儲存為jpg檔案的完整例子。
package cvts; import java.awt.AWTException; import java.awt.BasicStroke; import java.awt.Color; import java.awt.Dimension; import java.awt.FlowLayout; import java.awt.Graphics; import java.awt.Graphics2D; import java.awt.Rectangle; import java.awt.Robot; import java.awt.event.MouseAdapter; import java.awt.event.MouseEvent; import java.awt.image.BufferedImage; import java.io.File; import java.io.IOException; import javax.imageio.ImageIO; import javax.swing.JFrame; import javax.swing.JPanel; public class DrawSave { private JFrame jFrame = null; private JPanel jPanel = null; private String path = System.getProperty("user.dir"); //下側右側面板畫圖時的引數 private int startX,startY,endX,endY; public void showGui(){ jFrame = new JFrame(); jPanel = new JPanel(); //設定jPanel大小 jPanel.setPreferredSize(new Dimension(400,400)); jPanel.setLayout(new FlowLayout(FlowLayout.RIGHT)); jPanel.addMouseListener(new MouseAdapter(){ //滑鼠按下事件，重置startX，startY public void mousePressed(MouseEvent e){ startX = e.getX(); startY = e.getY(); } //雙擊面板是儲存繪圖區 public void mouseClicked(MouseEvent e){ if(e.getClickCount() == 2){ savePic(path+"/pic.jpg"); } } }); //滑鼠拖動事件，自由畫圖 jPanel.addMouseMotionListener(new MouseAdapter(){ public void mouseDragged(MouseEvent e){ Graphics graphics = jPanel.getGraphics(); endX = e.getX(); endY = e.getY(); ((Graphics2D) graphics).setColor(new Color(144,242,41)); ((Graphics2D) graphics).setStroke(new BasicStroke(10)); ((Graphics2D)graphics).drawLine(startX,startY,endX,endY); startX=endX; startY=endY; } }); //設定jFrame的位置 jFrame.setLocation(400, 200); jFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); jFrame.add(jPanel); jFrame.pack(); jFrame.setVisible(true); } public void savePic(String path){ BufferedImage myImage = null; try { myImage = new Robot().createScreenCapture( new Rectangle(jFrame.getX()+8, jFrame.getY()+30, jPanel.getWidth(), jPanel.getHeight())); ImageIO.write(myImage, "jpg", new File(path)); } catch (AWTException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } public static void main(String[] args) { DrawSave drawAndSave = new DrawSave(); drawAndSave.showGui(); } }