Java怎么实现自动生成缩略图片

一、自动生成缩略图方法：

package writeimg;
 
import java.awt.geom.AffineTransform;
import java.awt.image.AffineTransformOp;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
 
public class JpegTool { 
        private boolean isInitFlag = false; //         对象是否己经初始化 
        private String pic_big_pathfilename = null; //定义源图片所在的带路径目录的文件名
        private String pic_small_pathfilename = null; // 生成小图片的带存放路径目录的文件名 
        private int smallpicwidth = 0; //定义生成小图片的宽度和高度，给其一个就可以了 
        private int smallpicheight = 0; 
        private int pic_big_width=0;
        private int pic_big_height=0;
        private double picscale = 0; //定义小图片的相比原图片的比例 
        /** 
        * 构造函数 
        * @param 没有参数 
        */ 
        public JpegTool(){
                this.isInitFlag = false; 
        } 
        /** 
        * 私有函数，重置所有的参数 
        * @param 没有参数 
        * @return 没有返回参数 
        */ 
        private void resetJpegToolParams(){ 
                this.picscale = 0; 
                this.smallpicwidth = 0; 
                this.smallpicheight = 0; 
                this.isInitFlag = false; 
        } 
        /** 
        * @param scale 设置缩影图像相对于源图像的大小比例如 0.5 
        * @throws JpegToolException 
        */ 
        public void SetScale(double scale) throws JpegToolException
        { 
                if(scale<=0){ 
                                throw new JpegToolException(" 缩放比例不能为 0 和负数！ "); 
                } 
                this.resetJpegToolParams(); 
                this.picscale = scale; 
                this.isInitFlag = true; 
        } 
        /** 
        * @param smallpicwidth 设置缩影图像的宽度 
        * @throws JpegToolException 
        */ 
        public void SetSmallWidth(int smallpicwidth) throws JpegToolException 
        { 
                if(smallpicwidth<=0)
                { 
                        throw new JpegToolException(" 缩影图片的宽度不能为 0 和负数！ "); 
                } 
                this.resetJpegToolParams(); 
                this.smallpicwidth = smallpicwidth; 
                this.isInitFlag = true; 
        } 
 
        /** 
        * @param smallpicheight 设置缩影图像的高度 
        * @throws JpegToolException 
        */ 
 
        public void SetSmallHeight(int smallpicheight) throws JpegToolException { 
                if(smallpicheight<=0)
                { 
                   throw new JpegToolException(" 缩影图片的高度不能为 0 和负数！ "); 
                } 
                this.resetJpegToolParams(); 
                this.smallpicheight = smallpicheight; 
                this.isInitFlag = true; 
        } 
        
        /**
         *返回大图片路径 
         */
        public String getpic_big_pathfilename()
        {
                return this.pic_big_pathfilename;
        }
        /**
         * 返回小图片路径
         */
        public String getpic_small_pathfilename()
        {
                return this.pic_small_pathfilename;
        }
        
        public int getsrcw()
        {
                return this.pic_big_width;
        }
        public int getsrch()
        {
                return this.pic_big_height;
        }
        /** 
        * 生成源图像的缩影图像 
        * @param pic_big_pathfilename 源图像文件名，包含路径（如 windows 下 C:\\pic.jpg ； Linux 下 /home/abner/pic/pic.jpg ） 
        * @param pic_small_pathfilename 生成的缩影图像文件名，包含路径（如 windows 下 C:\\pic_small.jpg ； Linux 下 /home/abner/pic/pic_small.jpg ） 
        * @throws JpegToolException 
        */ 
        public void doFinal(String pic_big_pathfilename,String pic_small_pathfilename) throws JpegToolException { 
                if(!this.isInitFlag){ 
                    throw new JpegToolException(" 对象参数没有初始化！ "); 
                } 
                if(pic_big_pathfilename==null || pic_small_pathfilename==null){ 
                    throw new JpegToolException(" 包含文件名的路径为空！ "); 
                } 
                if((!pic_big_pathfilename.toLowerCase().endsWith("jpg")) && (!pic_big_pathfilename.toLowerCase().endsWith("jpeg"))){ 
                    throw new JpegToolException(" 只能处理 JPG/JPEG 文件！ "); 
                } 
                if((!pic_small_pathfilename.toLowerCase().endsWith("jpg")) && !pic_small_pathfilename.toLowerCase().endsWith("jpeg")){ 
                    throw new JpegToolException(" 只能处理 JPG/JPEG 文件！ "); 
                } 
                this.pic_big_pathfilename=pic_big_pathfilename;
                this.pic_small_pathfilename=pic_small_pathfilename;
                int smallw = 0; 
                int smallh = 0; 
                // 新建源图片和生成的小图片的文件对象 
                File fi = new File(pic_big_pathfilename); 
                File fo = new File(pic_small_pathfilename); 
                //生成图像变换对象 
                AffineTransform transform = new AffineTransform(); 
                //通过缓冲读入源图片文件 
                BufferedImage bsrc = null; 
                try { 
                bsrc = ImageIO.read(fi); 
                }catch (IOException ex) { 
                    throw new JpegToolException(" 读取源图像文件出错！ "); 
                } 
                this.pic_big_width= bsrc.getWidth();// 原图像的长度 
                this.pic_big_height = bsrc.getHeight();// 原图像的宽度 
                double scale = (double)pic_big_width/pic_big_height;// 图像的长宽比例 
                if(this.smallpicwidth!=0)
                {// 根据设定的宽度求出长度 
                        smallw = this.smallpicwidth;// 新生成的缩略图像的长度 
                        smallh = (smallw*pic_big_height)/pic_big_width ;// 新生成的缩略图像的宽度 
                }
                else if(this.smallpicheight!=0)
                {// 根据设定的长度求出宽度 
                        smallh = this.smallpicheight;// 新生成的缩略图像的长度 
                        smallw = (smallh*pic_big_width)/pic_big_height;// 新生成的缩略图像的宽度 
                }
                else if(this.picscale!=0)
                {// 根据设置的缩小比例设置图像的长和宽 
                        smallw = (int)((float)pic_big_width*this.picscale); 
                        smallh = (int)((float)pic_big_height*this.picscale); 
                }
                else
                { 
                    throw new JpegToolException(" 对象参数初始化不正确！ "); 
                }
                double sx = (double)smallw/pic_big_width;//小/大图像的宽度比例 
                double sy = (double)smallh/pic_big_height;//小/大图像的高度比例 
                transform.setToScale(sx,sy);// 设置图像转换的比例 
                //生成图像转换操作对象 
                AffineTransformOp ato = new AffineTransformOp(transform,null); 
                //生成缩小图像的缓冲对象 
                BufferedImage bsmall = new BufferedImage(smallw,smallh,BufferedImage.TYPE_3BYTE_BGR); 
                //生成小图像 
                ato.filter(bsrc,bsmall); 
                //输出小图像 
                try{
                        ImageIO.write(bsmall, "jpeg", fo); 
                }
                catch (IOException ex1) 
                { 
                   throw new JpegToolException(" 写入缩略图像文件出错！ "); 
                } 
        }
}

二、异常处理类：

package jpegtool;
 
    public class JpegToolException extends Exception {
            private String errMsg = ""; 
            public JpegToolException(String errMsg) 
            { 
                    this.errMsg = errMsg; 
            } 
 
            public String getMsg(){ 
                return "JpegToolException:"+this.errMsg; 
            } 
    }

三、调用的例子：

package writeimg;
 
public class T {
 
 
    public static void main(String[] args) {
 
        JpegTool j = new JpegTool();
        try {
            j.SetScale(0.7);
            j.SetSmallHeight(100);
            j.doFinal("D:\\305\\c\\javatest\\src\\11.jpg","D:\\305\\c\\javatest\\src\\22.jpg");
        } catch (JpegToolException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
 
}