java生成高质量缩略图的代码实现

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import java.awt.Image;
import java.awt.Toolkit;
import java.awt.image.BufferedImage;
import java.awt.image.MemoryImageSource;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;

import javax.imageio.ImageIO;

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

/** *//**
 * @将文件转化为缩略图
 *
 */
public class jpgThumbnail {

    private static final String BMP = "bmp";
    private static final String PNG = "png";
    private static final String GIF = "gif";
    private static final String JPEG = "jpeg";
    private static final String JPG = "jpg";

    public static void getThumbnail(
            String source,String output,int width,int height) {
        boolean adjustSize=true;
        if (source == null || source.equals("") || width < 1 || height < 1) {
            return;
        }
        if(output==null || output.equals(""))
        {
            return;
        }
        source = source.toLowerCase();
        if (source.endsWith(BMP)) {
            BMPThumbnailHandler(source,output,width,height,adjustSize);
        } else if (source.endsWith(PNG) || source.endsWith(GIF)
                || source.endsWith(JPEG) || source.endsWith(JPG)) {
            thumbnailHandler(source,adjustSize);
        }
    }

    private static void thumbnailHandler(
            String source,int height,boolean adjustSize) {
        try {
            File sourceFile = new File(source);
            if (sourceFile.exists()) {
                Image image = ImageIO.read(sourceFile);
                int theImgWidth = image.getWidth(null);
                int theImgHeight = image.getHeight(null);
                int[] size = { theImgWidth,theImgHeight };
                if (adjustSize) {
                    size = adjustImageSize(theImgWidth,theImgHeight,height);
                }
                StringBuffer thumbnailFile=new StringBuffer();
                //thumbnailFile.append(sourceFile.getParent());
                //thumbnailFile.append(File.separatorChar);
                thumbnailFile.append(output);
                writeFile(image,size[0],size[1],thumbnailFile.toString());
            }
        } catch (Exception e) {
            e.printStackTrace();
            return;
        }
    }

    private static void BMPThumbnailHandler(
            String source,boolean adjustSize) {
        try {
            File sourceFile = new File(source);
            if (sourceFile.exists()) {
                Image image = getBMPImage(source);
                int theImgWidth = image.getWidth(null);
                int theImgHeight = image.getHeight(null);
                int[] size = { theImgWidth,thumbnailFile.toString());
            }
        } catch (Exception e) {
            e.printStackTrace();
            return;
        }
    }

    private static Image getBMPImage(String source) throws Exception {

        FileInputStream fs = null;
        Image image = null;
        try {
            fs = new FileInputStream(source);
            int bfLen = 14;
            byte bf[] = new byte[bfLen];
            fs.read(bf,bfLen); // 读取14字节BMP文件头
            int biLen = 40;
            byte bi[] = new byte[biLen];
            fs.read(bi,biLen); // 读取40字节BMP信息头

            // 源图宽度
            int nWidth = (((int) bi[7] & 0xff) << 24)
                    | (((int) bi[6] & 0xff) << 16)
                    | (((int) bi[5] & 0xff) << 8) | (int) bi[4] & 0xff;

            // 源图高度
            int nHeight = (((int) bi[11] & 0xff) << 24)
                    | (((int) bi[10] & 0xff) << 16)
                    | (((int) bi[9] & 0xff) << 8) | (int) bi[8] & 0xff;

            // 位数
            int nBitCount = (((int) bi[15] & 0xff) << 8) | (int) bi[14] & 0xff;

            // 源图大小
            int nSizeImage = (((int) bi[23] & 0xff) << 24)
                    | (((int) bi[22] & 0xff) << 16)
                    | (((int) bi[21] & 0xff) << 8) | (int) bi[20] & 0xff;

            // 对24位BMP进行解析
            if (nBitCount == 24) {
                int nPad = (nSizeImage / nHeight) - nWidth * 3;
                int nData[] = new int[nHeight * nWidth];
                byte bRGB[] = new byte[(nWidth + nPad) * 3 * nHeight];
                fs.read(bRGB,(nWidth + nPad) * 3 * nHeight);
                int nIndex = 0;
                for (int j = 0; j < nHeight; j++) {
                    for (int i = 0; i < nWidth; i++) {
                        nData[nWidth * (nHeight - j - 1) + i] = (255 & 0xff) << 24
                                | (((int) bRGB[nIndex + 2] & 0xff) << 16)
                                | (((int) bRGB[nIndex + 1] & 0xff) << 8)
                                | (int) bRGB[nIndex] & 0xff;
                        nIndex += 3;
                    }
                    nIndex += nPad;
                }
                Toolkit kit = Toolkit.getDefaultToolkit();
                image = kit.createImage(new MemoryImageSource(nWidth,nHeight,nData,nWidth));
            }
        } catch (Exception e) {
            e.printStackTrace();
            throw new Exception(e);
        } finally {
            if (fs != null) {
                fs.close();
            }
        }
        return image;
    }

    private static void writeFile(
            Image image,String thumbnailFile) throws Exception {

        if (image == null) return;

        BufferedImage tag = new BufferedImage(width,BufferedImage.TYPE_INT_RGB);
        tag.getGraphics().drawImage(image,null);
        FileOutputStream out = null;
        try {
            out = new FileOutputStream(thumbnailFile);
            JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
            encoder.encode(tag);
        } catch (Exception e) {
            e.printStackTrace();
            throw new Exception(e);
        } finally {
            if (out != null) {
                out.close();
            }
        }

    }

    private static int[] adjustImageSize(int theImgWidth,int theImgHeight,int defWidth,int defHeight) {        
        int[] size = { 0,0 };

        float theImgHeightFloat=Float.parseFloat(String.valueOf(theImgHeight));
        float theImgWidthFloat=Float.parseFloat(String.valueOf(theImgWidth));
        if (theImgWidth<theImgHeight){
            float scale=theImgHeightFloat/theImgWidthFloat;
            size[0]=Math.round(defHeight/scale);
            size[1]=defHeight;
        }else{
            float scale=theImgWidthFloat/theImgHeightFloat;
            size[0]=defWidth;
            size[1]=Math.round(defWidth/scale);
        }
        return size;
    }

    public static void main(String[] agrs) {
        //zoomPicture("E:1.jpg","E:test.jpg",60,80);
        getThumbnail("E:1.jpg",80);
    }

}

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