java实现缩略图,同等大小的图片占用1/7的磁盘空间。

当缩略图的宽和高是原图的一半的时候，占用磁盘减少二十多倍，清晰度还算不错，代码：

 

import java.awt.Image;
import java.awt.image.BufferedImage;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;

import javax.imageio.ImageIO;

import com.sun.image.codec.jpeg.JPEGCodec;
import com.sun.image.codec.jpeg.JPEGImageEncoder;
/**
 * 缩略图
 * @author Administrator
 *
 */
public class ReduceImageUtil {
	public byte[] imageChangeSize(byte[] data,int height,int maxWidth) throws IOException {
		float rate = 1;
		int new_wi = 0;
		int new_he = 0;
		int wi = maxWidth;
		int he = height;
		InputStream is = new ByteArrayInputStream(data);
		BufferedImage bufImg = ImageIO.read(is);
		wi = bufImg.getWidth();
		he = bufImg.getHeight();
		rate = (float) wi / (float) he;
		if (wi > maxWidth && he <= height) {
			new_wi = maxWidth;
			new_he = new Float((float) new_wi / rate).intValue();
		} else if ((he > height && wi <= maxWidth)
				|| (he > height && wi > maxWidth)) {
			new_he = height;
			new_wi = new Float(new_he * rate).intValue();
		} else if (he <= height && wi <= maxWidth) {
			new_wi = wi;
			new_he = he;
		}
		BufferedImage bf = new BufferedImage(new_wi, new_he,
				BufferedImage.TYPE_INT_RGB);
		// bf.getGraphics().drawImage(bufImg,0,0,new_wi,new_he,null);
		bf.getGraphics().drawImage(
				bufImg.getScaledInstance(new_wi, new_he, Image.SCALE_SMOOTH),
				0, 0, new_wi, new_he, null);
		ByteArrayOutputStream out = new ByteArrayOutputStream();
		JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
		encoder.encode(bf); // 近JPEG编码
		byte[] re = out.toByteArray();
		return re;
	}
	/**
	 * 生成缩略图
	 * @param imagePath 原图片路径
	 * @param smallImagePath  缩略图路径
	 * @param height  缩略图高度
	 * @param maxWidth  缩略图最大宽度
	 */
	public void createReduceImage(String imagePath,String smallImagePath,int height,int maxWidth) {
		ImageIO io = null;
		try {
			FileInputStream fis = new FileInputStream(imagePath);
			byte[] buf = new byte[102400];
			int re = 0;
			byte[] dd = new byte[0];
			while ((re = fis.read(buf)) > 0) {
				byte[] d = new byte[dd.length + re];
				System.arraycopy(dd, 0, d, 0, dd.length);
				System.arraycopy(buf, 0, d, dd.length, re);
				dd = d;
			}
			FileOutputStream fos = new FileOutputStream(smallImagePath);
			fos.write(imageChangeSize(dd,height,maxWidth));
			fos.flush();
			fos.close();
			BufferedImage bf2 = io.read(new File(smallImagePath));
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

 调用：

 

String imagePath = "D:\\aa.jpg";
// 缩略图路径
String smallImagePath = "D:\\aasmall.jpg";
ReduceImageUtil testimage = new ReduceImageUtil();
// 生成缩略图
testimage.createReduceImage(imagePath,smallImagePath,768,1024);