當圖片很大的時候，要生成預覽圖來提高網站響應速率，採用java的image相關類來生成縮圖

package com.liuc.core;

import java.awt.Image;
import java.awt.image.BufferedImage;
import java.io.File;

import javax.imageio.ImageIO;

import com.liuc.config.ImageSizeConfig;
import com.liuc.util.UUIDUtil;


/**
 * 
 * @brief ThumbnailUtil.java  生成縮圖
 */
public class ThumbnailUtil {


	/**
	 * 寬度
	 */
    private int width;

    /**
     * 高度
     */
    private int height;

    private int scaleWidth;

    double support = (double) 3.0;

    double PI = (double) 3.14159265358978;

    double[] contrib;

    double[] normContrib;

    double[] tmpContrib;

    int startContrib, stopContrib;

    int nDots;

    int nHalfDots;

    /** *//**
     * Start: Use Lanczos filter to replace the original algorithm for image
     * scaling. Lanczos improves quality of the scaled image modify by :blade
     */

    public static void main(String[] args) {
        ThumbnailUtil is = new ThumbnailUtil();
        try {
            is.compressImageAsJpg(new File("D:/123/1.jpg"), new File("D:/123/1111.jpg"), 765, 129);
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    
    public File compressImgByAssignMinBoundLength(File inFile, ImageSizeConfig pc) throws Exception{
        try {
            Image img = ImageIO.read(inFile);
            int width = img.getWidth(null);
            int height = img.getHeight(null);
            int OutputWidth = pc.getWidth();
            int OutputHeight = pc.getHeight();
            int new_w,new_h;
            if (height <= OutputWidth && width <= OutputHeight) {// 不壓縮
                new_w = width;
                new_h = height;
            } else if (height > width) {// 已寬為準
                new_w = OutputWidth;
                new_h = (int) (new_w / ((double) width / (double) height));
            } else {// 已高為準
                new_h = OutputHeight;
                new_w = (int) ((new_h * (double) width / (double) height));
            }
            
            String fileName = UUIDUtil.getUUID() + pc.getExt();
            File tmpFile = new File("D:/123", fileName);
            compressImageAsJpg(inFile, tmpFile, new_w, new_h);
            return tmpFile;
        } catch (Exception e) {
            throw new Exception("compress img error.", e);
        }
        
    }
    
    /**
     * 壓縮圖片
     * @param fromFileStr
     * @param saveToFileStr
     * @param formatWideth
     * @param formatHeight
     * @throws Exception
     */
    public void compressImageAsJpg(File fromFile, File saveToFile,
            int formatWideth, int formatHeight) throws Exception{
        try {
            saveImageAsJpg(fromFile, saveToFile, formatWideth, formatHeight);
        } catch (Exception e) {
            throw new Exception("compress img error.", e);
        }
    }

    // fromFileStr原圖片地址,saveToFileStr生成縮圖地址,formatWideth生成圖片寬度,formatHeight高度
    public void saveImageAsJpg(File inputFile, File saveToFile,
            int formatWideth, int formatHeight) throws Exception {
        BufferedImage srcImage;
        File saveFile = saveToFile;
        File fromFile = inputFile;
        srcImage = javax.imageio.ImageIO.read(fromFile); // construct image
        int imageWideth = srcImage.getWidth(null);
        int imageHeight = srcImage.getHeight(null);
        int changeToWideth = 0;
        int changeToHeight = 0;
        if (imageWideth > 0 && imageHeight > 0) {
            // flag=true;
            if (imageWideth / imageHeight >= formatWideth / formatHeight) {
                if (imageWideth > formatWideth) {
                    changeToWideth = formatWideth;
                    changeToHeight = (imageHeight * formatWideth) / imageWideth;
                } else {
                    changeToWideth = imageWideth;
                    changeToHeight = imageHeight;
                }
            } else {
                if (imageHeight > formatHeight) {
                    changeToHeight = formatHeight;
                    changeToWideth = (imageWideth * formatHeight) / imageHeight;
                } else {
                    changeToWideth = imageWideth;
                    changeToHeight = imageHeight;
                }
            }
        }

        srcImage = imageZoomOut(srcImage, changeToWideth, changeToHeight);
        ImageIO.write(srcImage, "JPEG", saveFile);
    }

    public BufferedImage imageZoomOut(BufferedImage srcBufferImage, int w, int h) {
        width = srcBufferImage.getWidth();
        height = srcBufferImage.getHeight();
        scaleWidth = w;

        if (DetermineResultSize(w, h) == 1) {
            return srcBufferImage;
        }
        CalContrib();
        BufferedImage pbOut = HorizontalFiltering(srcBufferImage, w);
        BufferedImage pbFinalOut = VerticalFiltering(pbOut, h);
        return pbFinalOut;
    }

    /**
     * 決定影象尺寸
     */
    private int DetermineResultSize(int w, int h) {
        double scaleH, scaleV;
        scaleH = (double) w / (double) width;
        scaleV = (double) h / (double) height;
        // 需要判斷一下scaleH，scaleV，不做放大操作
        if (scaleH >= 1.0 && scaleV >= 1.0) {
            return 1;
        }
        return 0;

    } // end of DetermineResultSize()

    private double Lanczos(int i, int inWidth, int outWidth, double Support) {
        double x;

        x = (double) i * (double) outWidth / (double) inWidth;

        return Math.sin(x * PI) / (x * PI) * Math.sin(x * PI / Support)
                / (x * PI / Support);

    }

    private void CalContrib() {
        nHalfDots = (int) ((double) width * support / (double) scaleWidth);
        nDots = nHalfDots * 2 + 1;
        try {
            contrib = new double[nDots];
            normContrib = new double[nDots];
            tmpContrib = new double[nDots];
        } catch (Exception e) {
            System.out.println("init   contrib,normContrib,tmpContrib" + e);
        }

        int center = nHalfDots;
        contrib[center] = 1.0;

        double weight = 0.0;
        int i = 0;
        for (i = 1; i <= center; i++) {
            contrib[center + i] = Lanczos(i, width, scaleWidth, support);
            weight += contrib[center + i];
        }

        for (i = center - 1; i >= 0; i--) {
            contrib[i] = contrib[center * 2 - i];
        }

        weight = weight * 2 + 1.0;

        for (i = 0; i <= center; i++) {
            normContrib[i] = contrib[i] / weight;
        }

        for (i = center + 1; i < nDots; i++) {
            normContrib[i] = normContrib[center * 2 - i];
        }
    } // end of CalContrib()

    // 處理邊緣
    private void CalTempContrib(int start, int stop) {
        double weight = 0;

        int i = 0;
        for (i = start; i <= stop; i++) {
            weight += contrib[i];
        }

        for (i = start; i <= stop; i++) {
            tmpContrib[i] = contrib[i] / weight;
        }

    } // end of CalTempContrib()

    private int GetRedValue(int rgbValue) {
        int temp = rgbValue & 0x00ff0000;
        return temp >> 16;
    }

    private int GetGreenValue(int rgbValue) {
        int temp = rgbValue & 0x0000ff00;
        return temp >> 8;
    }

    private int GetBlueValue(int rgbValue) {
        return rgbValue & 0x000000ff;
    }

    private int ComRGB(int redValue, int greenValue, int blueValue) {

        return (redValue << 16) + (greenValue << 8) + blueValue;
    }

    // 行水平濾波
    private int HorizontalFilter(BufferedImage bufImg, int startX, int stopX,
            int start, int stop, int y, double[] pContrib) {
        double valueRed = 0.0;
        double valueGreen = 0.0;
        double valueBlue = 0.0;
        int valueRGB = 0;
        int i, j;

        for (i = startX, j = start; i <= stopX; i++, j++) {
            valueRGB = bufImg.getRGB(i, y);

            valueRed += GetRedValue(valueRGB) * pContrib[j];
            valueGreen += GetGreenValue(valueRGB) * pContrib[j];
            valueBlue += GetBlueValue(valueRGB) * pContrib[j];
        }

        valueRGB = ComRGB(Clip((int) valueRed), Clip((int) valueGreen),
                Clip((int) valueBlue));
        return valueRGB;

    } // end of HorizontalFilter()

    // 圖片水平濾波
    private BufferedImage HorizontalFiltering(BufferedImage bufImage, int iOutW) {
        int dwInW = bufImage.getWidth();
        int dwInH = bufImage.getHeight();
        int value = 0;
        BufferedImage pbOut = new BufferedImage(iOutW, dwInH,
                BufferedImage.TYPE_INT_RGB);

        for (int x = 0; x < iOutW; x++) {

            int startX;
            int start;
            int X = (int) (((double) x) * ((double) dwInW) / ((double) iOutW) + 0.5);
            int y = 0;

            startX = X - nHalfDots;
            if (startX < 0) {
                startX = 0;
                start = nHalfDots - X;
            } else {
                start = 0;
            }

            int stop;
            int stopX = X + nHalfDots;
            if (stopX > (dwInW - 1)) {
                stopX = dwInW - 1;
                stop = nHalfDots + (dwInW - 1 - X);
            } else {
                stop = nHalfDots * 2;
            }

            if (start > 0 || stop < nDots - 1) {
                CalTempContrib(start, stop);
                for (y = 0; y < dwInH; y++) {
                    value = HorizontalFilter(bufImage, startX, stopX, start,
                            stop, y, tmpContrib);
                    pbOut.setRGB(x, y, value);
                }
            } else {
                for (y = 0; y < dwInH; y++) {
                    value = HorizontalFilter(bufImage, startX, stopX, start,
                            stop, y, normContrib);
                    pbOut.setRGB(x, y, value);
                }
            }
        }

        return pbOut;

    } // end of HorizontalFiltering()

    private int VerticalFilter(BufferedImage pbInImage, int startY, int stopY,
            int start, int stop, int x, double[] pContrib) {
        double valueRed = 0.0;
        double valueGreen = 0.0;
        double valueBlue = 0.0;
        int valueRGB = 0;
        int i, j;

        for (i = startY, j = start; i <= stopY; i++, j++) {
            valueRGB = pbInImage.getRGB(x, i);

            valueRed += GetRedValue(valueRGB) * pContrib[j];
            valueGreen += GetGreenValue(valueRGB) * pContrib[j];
            valueBlue += GetBlueValue(valueRGB) * pContrib[j];
            // System.out.println(valueRed+"->"+Clip((int)valueRed)+"<-");
            //   
            // System.out.println(valueGreen+"->"+Clip((int)valueGreen)+"<-");
            // System.out.println(valueBlue+"->"+Clip((int)valueBlue)+"<-"+"-->");
        }

        valueRGB = ComRGB(Clip((int) valueRed), Clip((int) valueGreen),
                Clip((int) valueBlue));
        // System.out.println(valueRGB);
        return valueRGB;

    } // end of VerticalFilter()

    private BufferedImage VerticalFiltering(BufferedImage pbImage, int iOutH) {
        int iW = pbImage.getWidth();
        int iH = pbImage.getHeight();
        int value = 0;
        BufferedImage pbOut = new BufferedImage(iW, iOutH,
                BufferedImage.TYPE_INT_RGB);

        for (int y = 0; y < iOutH; y++) {

            int startY;
            int start;
            int Y = (int) (((double) y) * ((double) iH) / ((double) iOutH) + 0.5);

            startY = Y - nHalfDots;
            if (startY < 0) {
                startY = 0;
                start = nHalfDots - Y;
            } else {
                start = 0;
            }

            int stop;
            int stopY = Y + nHalfDots;
            if (stopY > (int) (iH - 1)) {
                stopY = iH - 1;
                stop = nHalfDots + (iH - 1 - Y);
            } else {
                stop = nHalfDots * 2;
            }

            if (start > 0 || stop < nDots - 1) {
                CalTempContrib(start, stop);
                for (int x = 0; x < iW; x++) {
                    value = VerticalFilter(pbImage, startY, stopY, start, stop,
                            x, tmpContrib);
                    pbOut.setRGB(x, y, value);
                }
            } else {
                for (int x = 0; x < iW; x++) {
                    value = VerticalFilter(pbImage, startY, stopY, start, stop,
                            x, normContrib);
                    pbOut.setRGB(x, y, value);
                }
            }

        }

        return pbOut;

    } // end of VerticalFiltering()

    int Clip(int x) {
        if (x < 0)
            return 0;
        if (x > 255)
            return 255;
        return x;
    }

}
 

package com.liuc.util;

import java.util.UUID;

public class UUIDUtil {

	public static String getUUID() {
		UUID uuid = UUID.randomUUID();   
        String str = uuid.toString();   
        // 去掉"-"符號   
        String temp = str.substring(0, 8) + str.substring(9, 13) + str.substring(14, 18) + str.substring(19, 23) + str.substring(24);   
        return str+","+temp;   
	}

}
 

package com.liuc.config;

public class ImageSizeConfig {

	public int getWidth() {
		return 320;
	}

	public int getHeight() {
		return 240;
	}

	public String getExt() {
		return ".jpg";
	}

}