上传图片的缩放处理 - 非常实用！（感谢loveyourvv兄弟）

import java.io.File;
import java.awt.image.BufferedImage;
import java.awt.Image;
import java.awt.image.AffineTransformOp;
import javax.imageio.ImageIO;
import java.awt.geom.AffineTransform;

public class UploadImg {
    
    String fromdir;            // fromdir 的原始目录
    String todir;            // todir 处理后的存放目录
    String imgfile;            // imgfile 原始
    String sysimgfile;        // sysimgfile 处理后的文件名前缀

    UploadImg( String fromdirNow, String todirNow, String imgfileNow, String sysimgfileNow ){
        fromdir = fromdirNow;
        todir = todirNow;
        imgfile = imgfileNow;
        sysimgfile = sysimgfileNow;
    }

    public boolean CreateThumbnail() throws Exception
        {
        // fileExtNmae是的格式 gif JPG 或png
        // String fileExtNmae="";
        double Ratio = 0.0;
        File F = new File(fromdir,imgfile);
        if ( !F.isFile() )
            throw new Exception(F+" is not image file error in CreateThumbnail!");
        
        //首先判断上传的是gif还是JPG ImageIO只能将gif转换为png
        // if (isJpg(imgfile)){
        //    fileExtNmae="jpg";
        //    }
        //else{
        //    fileExtNmae="png";
        //    }
        File ThF = new File( todir, sysimgfile + ".jpg" );
        
        BufferedImage Bi = ImageIO.read(F);
        //假设宽 高 最大为120 120
        Image Itemp = Bi.getScaledInstance (120,120,Bi.SCALE_SMOOTH);
        
        if ((Bi.getHeight()>120) || (Bi.getWidth()>120)){
            if (Bi.getHeight()>Bi.getWidth())
                Ratio = 120.0/Bi.getHeight();
            else
                Ratio = 120.0/Bi.getWidth();
            }
        
        AffineTransformOp op = new AffineTransformOp(AffineTransform.getScaleInstance(Ratio, Ratio), null);
        Itemp = op.filter(Bi, null);
        try {
            ImageIO.write((BufferedImage)Itemp, "jpg", ThF);
            }
        catch (Exception ex) {
            throw new Exception(" ImageIo.write error in CreatThum.: "+ex.getMessage());
            }
        return (true);
    }

    public static void main(String[] args)
    {
        UploadImg UI;
        boolean ss = false;

        try{
            UI = new UploadImg( "d://javalearn", "d://javalearn", "ps_high.jpg", "ps_low" );
            ss = UI.CreateThumbnail();
            if ( ss ) {
                System.out.println( "Success" );
                }
            else{
                System.out.println( "Error" );
                }
        }
        catch(Exception e){
            System.out.print(e.toString());
        }
    }
} 编辑：xker.com