java图片等比例缩放

需要引入jar包

package com.gjw.imagetest;

import java.awt.Image;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import javax.imageio.ImageIO;

import com.sun.image.codec.jpeg.JPEGCodec;
import com.sun.image.codec.jpeg.JPEGImageEncoder;

public class ImagePress
{
    public static void main(String[] args)
    {
        try
        {
            File imgageio = new File("C:\\image\\big.jpg");
            File imgageout = new File("C:\\image\\big22.png");
            dosomething(imgageio,imgageout,50,50);
        } catch (FileNotFoundException e)
        {
            e.printStackTrace();
        }catch (IOException e)
        {
            e.printStackTrace();
        }
    }
    public static boolean dosomething(File imagesrc,File imageout,int min_width,int min_height) throws IOException
    {
        if (!imagesrc.exists())
        {
            System.out.println("The original image does not exist!");
            return false;
        }
        Image src = ImageIO.read(imagesrc);
        if (src.getWidth(null)==-1)
        {
            System.out.println("image type problem!");
            return false;
        }else {
            if (src.getWidth(null)>min_width || src.getHeight(null)>min_height)
            {
                double scale = 0.0;
                double w_scale = 0.0;
                double h_scale = 0.0;
                if (src.getWidth(null)>min_width)
                    w_scale = min_width/(double)src.getWidth(null);
                if (src.getHeight(null)>min_height)
                    h_scale = min_height/(double)src.getHeight(null);
                scale=w_scale<h_scale?w_scale:h_scale;
                System.out.println("scaling:="+scale);
                if (scale<1)
                {
                    int width = (int) (src.getWidth(null) * scale);
                    int height = (int) (src.getHeight(null) * scale);
                    System.out.println("w:"+width);
                    System.out.println("h:"+height);
                    /* java提供了4个缩放的微调选项
                     * image.SCALE_SMOOTH //平滑优先
                     * image.SCALE_FAST//速度优先
                     * image.SCALE_AREA_AVERAGING //区域均值
                     * image.SCALE_REPLICATE //像素复制型缩放
                     * image.SCALE_DEFAULT //默认缩放模式
                     * */
                    BufferedImage bufferedImage = new BufferedImage(width, height,BufferedImage.TYPE_INT_BGR);
                    bufferedImage.getGraphics().drawImage(src.getScaledInstance(width, height, Image.SCALE_SMOOTH),0, 0, null);
                    FileOutputStream out = new FileOutputStream(imageout);
                    JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
                    encoder.encode( bufferedImage);
                    out.close();
                    System.out.println("photo compression success!");
                    return true;
                }
            }
            System.out.println("Don't need to compress the images!");
            return true;
        }
    }
}