压缩图片至额定大小

import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.image.BufferedImage;
import java.awt.image.ConvolveOp;
import java.awt.image.Kernel;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.net.URLConnection;

import javax.imageio.ImageIO;

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


/**
	 * 根据图片路径压缩图片至额定大小
	 * @param picUrl 需要压缩的图片路径
	 * @param scale 压缩比例 不能大于1,默认0.5
	 * @param quality 压缩品质介于0.1~1.0之间,默认0.75
	 * @param imgSize 图片大小压缩上限
	 * @param img 二次压缩图片对象
	 * @return
	 * @throws IOException
	 */
	public static byte[] imageCompress(String picUrl, float scale, float quality, long imgSize, Image img) throws IOException{
    	Image image = null;
    	if(img == null){//第一次是读取image
//根据图片路径获取图片转为字节输入流
    		URL url = new URL(picUrl);
    		URLConnection uc = url.openConnection();
    		InputStream in = uc.getInputStream();
    		//字节输入流转为要输出流
    		ByteArrayOutputStream swapStream = new ByteArrayOutputStream();
    		byte[] buff = new byte[100];
    		int rc = 0;
    		while ((rc = in.read(buff)) > 0) {
    			swapStream.write(buff, 0, rc);
    		}
    		byte[] imagSize = swapStream.toByteArray();

//    		System.out.println("图片实际大小："+imagSize.length);
//如果图片本身大小已在限额内则直接返回图片字节输出流
    		if(imagSize.length <= imgSize)
    			return imagSize;
    		else
    			image = javax.imageio.ImageIO.read(url);
    	}
    	else{//第二次开始不读图片，直接把第一次的图片压缩
    		image = img;
    	}
//图片本身大小已超过限额，则根据比率从尺寸上降低
		int imageWidth = image.getWidth(null);
        int imageHeight = image.getHeight(null);
        imageWidth = (int)(scale*imageWidth);
        imageHeight = (int)(scale*imageHeight);

        image = image.getScaledInstance(imageWidth, imageHeight, Image.SCALE_AREA_AVERAGING);
        // Make a BufferedImage from the Image.
        BufferedImage mBufferedImage = new BufferedImage(imageWidth, imageHeight,BufferedImage.TYPE_INT_RGB);
        Graphics2D g2 = mBufferedImage.createGraphics();

        g2.drawImage(image, 0, 0,imageWidth, imageHeight, Color.white,null);
        g2.dispose();

        float[] kernelData2 = { 
          -0.125f, -0.125f, -0.125f,
          -0.125f,2, -0.125f,
          -0.125f,-0.125f, -0.125f};
        Kernel kernel = new Kernel(3, 3, kernelData2);
        ConvolveOp cOp = new ConvolveOp(kernel, ConvolveOp.EDGE_NO_OP, null);
        mBufferedImage = cOp.filter(mBufferedImage, null);

        ByteArrayOutputStream out = new ByteArrayOutputStream();
        JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
        JPEGEncodeParam param = encoder.getDefaultJPEGEncodeParam(mBufferedImage);
//        System.out.println(quality);
//降低图像品质（不是降低DPI）
        param.setQuality(quality, true);//
        encoder.setJPEGEncodeParam(param);
        encoder.encode(mBufferedImage);
        byte[] comImage = out.toByteArray();
//        System.out.println(comImage.length);
        if(comImage.length > imgSize){//如果图像压缩后大小还是超过限额则继续降低压缩比率降低品质
        	scale = scale - 0.10f;
        	quality = quality - 0.10f;
        	imageCompress(picUrl, scale, quality, imgSize, image);
        }
        return comImage;
    }

/**
	 * 压缩图片到指定品质和比例
	 * @param picUrl 需要压缩的图片路径
	 * @param fileName 要压缩的图片名称
	 * @param toFileName 压缩后的图片名称
	 * @param scale 压缩比例 不能大于1,默认0.5
	 * @param quality 压缩品质介于0.1~1.0之间 
	 */
	@SuppressWarnings("unused")
	private static void imageCompress(String picUrl, String fileName,String toFileName,
			float scale, float quality){
		try {
            long start = System.currentTimeMillis();
            Image image = javax.imageio.ImageIO.read(new File(picUrl + fileName));
            int imageWidth = image.getWidth(null);
            int imageHeight = image.getHeight(null);
            imageWidth = (int)(scale*imageWidth);
            imageHeight = (int)(scale*imageHeight);

            image = image.getScaledInstance(imageWidth, imageHeight, Image.SCALE_AREA_AVERAGING);
            // Make a BufferedImage from the Image.
            BufferedImage mBufferedImage = new BufferedImage(imageWidth, imageHeight,BufferedImage.TYPE_INT_RGB);
            Graphics2D g2 = mBufferedImage.createGraphics();

            g2.drawImage(image, 0, 0,imageWidth, imageHeight, Color.white,null);
            g2.dispose();

                float[] kernelData2 = { 
                        -0.125f, -0.125f, -0.125f,
              -0.125f,2, -0.125f,
              -0.125f,-0.125f, -0.125f };
            Kernel kernel = new Kernel(3, 3, kernelData2);
            ConvolveOp cOp = new ConvolveOp(kernel, ConvolveOp.EDGE_NO_OP, null);
            mBufferedImage = cOp.filter(mBufferedImage, null);

            FileOutputStream out = new FileOutputStream(picUrl + toFileName);
            JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
            JPEGEncodeParam param = encoder.getDefaultJPEGEncodeParam(mBufferedImage);
            param.setQuality(quality, true);//默认0.75
            encoder.setJPEGEncodeParam(param);
            encoder.encode(mBufferedImage);
            out.close();
            long end = System.currentTimeMillis();
            System.out.println("图片："+fileName+"，压缩时间："+(end - start) + "ms");
        }catch (FileNotFoundException fnfe){
        	fnfe.printStackTrace();
        }catch (IOException ioe){
            ioe.printStackTrace();
        }catch(Exception ex){
            ex.printStackTrace();
        }
	}

调用实例

    public static void main(String[] args){
    	PicUtil.imageCompress("D:\\", "background_new.png", "background_new2.png", 0.9f, 0.9f);
    }