用java轻松实现图片缩放

package com.test;

import java.awt.Dimension;
import java.awt.Image;
import java.awt.image.BufferedImage;
import java.awt.image.PixelGrabber;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Iterator;
import java.util.Locale;

import javax.imageio.IIOImage;
import javax.imageio.ImageIO;
import javax.imageio.ImageWriteParam;
import javax.imageio.ImageWriter;
import javax.imageio.plugins.jpeg.JPEGImageWriteParam;
import javax.imageio.stream.ImageOutputStream;

public class ImageUtils {
	public static final int IMAGE_UNKNOWN = -1;

	public static final int IMAGE_JPEG = 0;

	public static final int IMAGE_PNG = 1;

	public static final int IMAGE_GIF = 2;

	public static BufferedImage resizeImage(String imgName, int type,
			int maxWidth, int maxHeight) {
		try {
			return resizeImage(ImageIO.read(new File(imgName)), type, maxWidth,
					maxHeight);
		} catch (IOException e) {
			e.printStackTrace();
			return null;
		}
	}

	public static BufferedImage resizeImage(BufferedImage image, int type,
			int maxWidth, int maxHeight) {
		Dimension largestDimension = new Dimension(maxWidth, maxHeight);
		// Original size
		int imageWidth = image.getWidth(null);
		int imageHeight = image.getHeight(null);
		float aspectRatio = (float) imageWidth / imageHeight;
		if (imageWidth > maxWidth || imageHeight > maxHeight) {
			if ((float) largestDimension.width / largestDimension.height > aspectRatio) {
				largestDimension.width = (int) Math
						.ceil(largestDimension.height * aspectRatio);
			} else {
				largestDimension.height = (int) Math
						.ceil(largestDimension.width / aspectRatio);
			}
			imageWidth = largestDimension.width;
			imageHeight = largestDimension.height;
		}
		return createHeadlessSmoothBufferedImage(image, type, imageWidth,
				imageHeight);
	}

	public static boolean saveImage(BufferedImage image, String toFileName,
			int type) {
		try {
			return ImageIO.write(image, type == IMAGE_JPEG ? "jpg" : "png",
					new File(toFileName));
		} catch (IOException e) {
			e.printStackTrace();
			return false;
		}
	}

	public static void saveCompressedImage(BufferedImage image,
			String toFileName, int type) {
		try {
			if (type == IMAGE_PNG) {
				throw new UnsupportedOperationException(
						"PNG compression not implemented");
			}
			Iterator iter = ImageIO.getImageWritersByFormatName("jpg");
			ImageWriter writer;
			writer = (ImageWriter) iter.next();
			ImageOutputStream ios = ImageIO.createImageOutputStream(new File(
					toFileName));
			writer.setOutput(ios);
			ImageWriteParam iwparam = new JPEGImageWriteParam(Locale
					.getDefault());
			iwparam.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
			iwparam.setCompressionQuality(0.7F);
			writer.write(null, new IIOImage(image, null, null), iwparam);
			ios.flush();
			writer.dispose();
			ios.close();
		} catch (IOException e) {
			e.printStackTrace();
		}
	}

	public static BufferedImage createHeadlessBufferedImage(
			BufferedImage image, int type, int width, int height) {
		if (type == ImageUtils.IMAGE_PNG && hasAlpha(image)) {
			type = BufferedImage.TYPE_INT_ARGB;
		} else {
			type = BufferedImage.TYPE_INT_RGB;
		}
		BufferedImage bi = new BufferedImage(width, height, type);
		for (int y = 0; y < height; y++) {
			for (int x = 0; x < width; x++) {
				bi.setRGB(x, y, image.getRGB(x * image.getWidth() / width, y
						* image.getHeight() / height));
			}
		}
		return bi;
	}

	public static BufferedImage createHeadlessSmoothBufferedImage(
			BufferedImage source, int type, int width, int height) {
		if (type == ImageUtils.IMAGE_PNG && hasAlpha(source)) {
			type = BufferedImage.TYPE_INT_ARGB;
		} else {
			type = BufferedImage.TYPE_INT_RGB;
		}
		BufferedImage dest = new BufferedImage(width, height, type);
		int sourcex;
		int sourcey;
		double scalex = (double) width / source.getWidth();
		double scaley = (double) height / source.getHeight();
		int x1;
		int y1;
		double xdiff;
		double ydiff;
		int rgb;
		int rgb1;
		int rgb2;
		for (int y = 0; y < height; y++) {
			sourcey = y * source.getHeight() / dest.getHeight();
			ydiff = scale(y, scaley) - sourcey;
			for (int x = 0; x < width; x++) {
				sourcex = x * source.getWidth() / dest.getWidth();
				xdiff = scale(x, scalex) - sourcex;
				x1 = Math.min(source.getWidth() - 1, sourcex + 1);
				y1 = Math.min(source.getHeight() - 1, sourcey + 1);
				rgb1 = getRGBInterpolation(source.getRGB(sourcex, sourcey),
						source.getRGB(x1, sourcey), xdiff);
				rgb2 = getRGBInterpolation(source.getRGB(sourcex, y1), source
						.getRGB(x1, y1), xdiff);
				rgb = getRGBInterpolation(rgb1, rgb2, ydiff);
				dest.setRGB(x, y, rgb);
			}
		}
		return dest;
	}

	private static double scale(int point, double scale) {
		return point / scale;
	}

	private static int getRGBInterpolation(int value1, int value2,
			double distance) {
		int alpha1 = (value1 & 0xFF000000) >>> 24;
		int red1 = (value1 & 0x00FF0000) >> 16;
		int green1 = (value1 & 0x0000FF00) >> 8;
		int blue1 = (value1 & 0x000000FF);
		int alpha2 = (value2 & 0xFF000000) >>> 24;
		int red2 = (value2 & 0x00FF0000) >> 16;
		int green2 = (value2 & 0x0000FF00) >> 8;
		int blue2 = (value2 & 0x000000FF);
		int rgb = ((int) (alpha1 * (1.0 - distance) + alpha2 * distance) << 24)
				| ((int) (red1 * (1.0 - distance) + red2 * distance) << 16)
				| ((int) (green1 * (1.0 - distance) + green2 * distance) << 8)
				| (int) (blue1 * (1.0 - distance) + blue2 * distance);
		return rgb;
	}

	public static boolean hasAlpha(Image image) {
		try {
			PixelGrabber pg = new PixelGrabber(image, 0, 0, 1, 1, false);
			pg.grabPixels();
			return pg.getColorModel().hasAlpha();
		} catch (InterruptedException e) {
			return false;
		}
	}
	public static void main(String[] args) {
		try {
			ImageIO.write(ImageUtils.resizeImage("d:/world.jpg", ImageUtils.IMAGE_JPEG, 300, 200),   

					"JPEG", new FileOutputStream("d:/test.jpg"));
		} catch (FileNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}   
	}
}