ImageTool

import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

import javax.imageio.ImageIO;

public class ImageTool {
	public static final int WIDTH = 240;
	public static final int HEIGTH = 240;
	public static void getPreviewImage(File source, File destImage, String format){
		try {
			BufferedImage bufferedImage = ImageIO.read(source);
			BufferedImage image = new BufferedImage(WIDTH, HEIGTH, BufferedImage.TYPE_INT_RGB);
			//创建缩放后的画布  TYPE_INT_RGB是具有合成整数像素的 8 位 RGB 颜色分量
			
			
			int x = bufferedImage.getWidth();
			int y = bufferedImage.getHeight();
			int x1 = WIDTH;
			int y1 = HEIGTH;
			
			if(WIDTH*y<HEIGTH*x){  //高度不够
				y1 = WIDTH*y/x;
			}
			if(WIDTH*y<HEIGTH*x){  //宽度不够
				x1 = HEIGTH*x/y;
			}
			
			Graphics2D graphics2d = image.createGraphics();
			graphics2d.setColor(new Color(255,255,255));
			graphics2d.fillRect(0, 0, WIDTH, HEIGTH);
			Image image2 = bufferedImage.getScaledInstance(x1, y1, bufferedImage.SCALE_SMOOTH);
			graphics2d.drawImage(image2, (WIDTH-x1)/2, (HEIGTH-y1)/2, null);
			ImageIO.write(image, format, destImage);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
	
	public static void main(String[] args) {
		getPreviewImage(new File("e:/re.png"),new File("e:/aa.jpg"),"jpg");
	}
}