https://www.cnblogs.com/donghb/p/7637990.html

BufferedImage

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BufferedImage image = new BufferedImage(IMG_WIDTH, IMG_HEIGHT, BufferedImage.TYPE_INT_RGB);
image = image.getSubimage(50, 50, 20, 20);

ImageIO

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ImageIO.write(image, "jpg", new File("C:\\Users\\lenovo\\Desktop\\image.jpg"));

Graphics，Graphics2D

Graphics类提供基本绘图方法，Graphics2D类提供更强大的绘图能力。

Graphics类提供基本的几何图形绘制方法，主要有：画线段、画矩形、画圆、画带颜色的图形、画椭圆、画圆弧、画多边形等。

Graphics

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public class TransparentImage {
    private static int IMG_WIDTH = 100;
    private static int IMG_HEIGHT = 100;

    public static void main(String[] args) throws IOException {
        BufferedImage image = new BufferedImage(IMG_WIDTH, IMG_HEIGHT, BufferedImage.TYPE_INT_RGB);
        Graphics g = image.getGraphics();
        g.drawLine(0, 0, 100, 100);
        ImageIO.write(image, "jpg", new File("C:\\Users\\lenovo\\Desktop\\image.jpg"));                        // 向页面输出图像
    }
}
  • 画一条线
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g.drawLine(0, 0, 100, 100);
  • 画矩形
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g.drawRect(0,0,50,50);
g.setColor(Color.lightGray);
g.fillRect(50,50,20,20);
  • 画圆
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g.drawRoundRect(5, 5, 30, 30, 30, 30);
g.setColor(Color.lightGray);
g.fillRoundRect(30, 30, 30, 30, 30, 30);

Graphics2D

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public class RenderingHintCase {
    public static void main(String[] args) throws IOException {
        BufferedImage image = new BufferedImage(260, 80, BufferedImage.TYPE_INT_BGR);
        //获取Graphics2D对象
        Graphics2D graphics = image.createGraphics();
        //开启文字抗锯齿
        graphics.setRenderingHint(RenderingHints.KEY_TEXT_ANTIALIASING, RenderingHints.VALUE_TEXT_ANTIALIAS_ON);
        //设置字体
        Font font = new Font("Algerian", Font.ITALIC, 40);
        graphics.setFont(font);
        //向画板上写字
        graphics.drawString("This is test!", 10, 60);
        graphics.dispose();

        ImageIO.write(image, "jpg", new File("C:\\Users\\lenovo\\Desktop\\demo.jpg"));
    }
}