Java改变图片的大小

前面在做项目的时候，有一个需求是需要上传图片的，然而该图片只是简单的展示一些信息，不需要很大，所以在上传图片的时候改变图片的大小就显得很有必要了！然后就写了下面这个方法来改变图片的大小!

/**  
 * 改变图片的大小到宽为size，然后高随着宽等比例变化  
 * @param is 上传的图片的输入流  
 * @param os 改变了图片的大小后，把图片的流输出到目标OutputStream  
 * @param size 新图片的宽  
 * @param format 新图片的格式  
 * @throws IOException  
 */  
public static void resizeImage(InputStream is, OutputStream os, int size, String format) throws IOException {   
    BufferedImage prevImage = ImageIO.read(is);   
    double width = prevImage.getWidth();   
    double height = prevImage.getHeight();   
    double percent = size/width;   
    int newWidth = (int)(width * percent);   
    int newHeight = (int)(height * percent);   
    BufferedImage image = new BufferedImage(newWidth, newHeight, BufferedImage.TYPE_INT_BGR);   
    Graphics graphics = image.createGraphics();   
    graphics.drawImage(prevImage, 0, 0, newWidth, newHeight, null);   
    ImageIO.write(image, format, os);   
    os.flush();   
    is.close();   
    os.close();   
}  

下面再提供一种方式:

package graphicsTest;   
  
import java.awt.Image;   
import java.awt.image.BufferedImage;   
import java.io.File;   
import java.io.FileOutputStream;   
  
import javax.imageio.ImageIO;   
  
import com.sun.image.codec.jpeg.JPEGCodec;   
import com.sun.image.codec.jpeg.JPEGImageEncoder;   
  
public class GraphicsTest1 {   
  
    // 图片宽和高的最大尺寸   
    public static final int IMAGEMAXBIG = 2000;   
    // 图片宽和高的最小尺寸   
    public static final int IMAGEMINBIG = 10;   
    // 按原图大小生成新图   
    public static final int CREATENEWIMAGETYPE_0 = 0;   
    // 按指定的大小生成新图   
    public static final int CREATENEWIMAGETYPE_1 = 1;   
    // 按原图宽高比例生成新图-按指定的宽度   
    public static final int CREATENEWIMAGETYPE_2 = 2;   
    // 按原图宽高比例生成新图-按指定的高度   
    public static final int CREATENEWIMAGETYPE_3 = 3;   
    // 按原图宽高比例生成新图-按指定的宽和高中较大的尺寸   
    public static final int CREATENEWIMAGETYPE_4 = 4;   
    // 按原图宽高比例生成新图-按指定的宽和高中较小的尺寸   
    public static final int CREATENEWIMAGETYPE_5 = 5;   
  
    /**  
     *   
     * @param _file  
     *            原图片  
     * @param createType  
     *            处理类型  
     * @param newW  
     *            新宽度  
     * @param newH  
     *            新高度  
     * @return  
     * @throws Exception  
     */  
    public static String createNewImage(File _file, int createType, int newW,   
            int newH) throws Exception {   
        if (_file == null)   
            return null;   
        String fileName = _file.getPath();   
        if (fileName == null || "".equals(fileName)   
                || fileName.lastIndexOf(".") == -1)   
            return null;   
        String newFileName = "_NEW";   
        /*  
         * else newFileName = "_" + newFileName;  
         */  
  
        String outFileName = fileName.substring(0, fileName.lastIndexOf("."))   
                + newFileName   
                + fileName.substring(fileName.lastIndexOf("."), fileName   
                        .length());   
        String fileExtName = fileName.substring(   
                (fileName.lastIndexOf(".") + 1), fileName.length());   
        if (newW < IMAGEMINBIG)   
            newW = IMAGEMINBIG;   
        else if (newW > IMAGEMAXBIG)   
            newW = IMAGEMAXBIG;   
  
        if (newH < IMAGEMINBIG)   
            newH = IMAGEMINBIG;   
        else if (newH > IMAGEMAXBIG)   
            newH = IMAGEMAXBIG;   
  
        // 得到原图信息   
        if (!_file.exists() || !_file.isAbsolute() || !_file.isFile()   
                || !checkImageFile(fileExtName))   
            return null;   
        if ((new File(outFileName)).exists()) {   
            System.out.println("file [" + outFileName + "] already exists");   
            throw new Exception();   
        }   
        Image src = ImageIO.read(_file);   
        int w = src.getWidth(null);   
        int h = src.getHeight(null);   
  
        // 确定目标图片的大小   
        int nw = w;   
        int nh = h;   
        if (createType == CREATENEWIMAGETYPE_0)   
            ;   
        else if (createType == CREATENEWIMAGETYPE_1) {   
            nw = newW;   
            nh = newH;   
        } else if (createType == CREATENEWIMAGETYPE_2) {   
            nw = newW;   
            nh = (int) ((double) h / (double) w * nw);   
        } else if (createType == CREATENEWIMAGETYPE_3) {   
            nh = newH;   
            nw = (int) ((double) w / (double) h * nh);   
        } else if (createType == CREATENEWIMAGETYPE_4) {   
            if ((double) w / (double) h >= (double) newW / (double) newH) {   
                nh = newH;   
                nw = (int) ((double) w / (double) h * nh);   
            } else {   
                nw = newW;   
                nh = (int) ((double) h / (double) w * nw);   
            }   
        } else if (createType == CREATENEWIMAGETYPE_5) {   
            if ((double) w / (double) h <= (double) newW / (double) newH) {   
                nh = newH;   
                nw = (int) ((double) w / (double) h * nh);   
            } else {   
                nw = newW;   
                nh = (int) ((double) h / (double) w * nw);   
            }   
        }   
  
        // 构造目标图片   
        BufferedImage tag = new BufferedImage(nw, nh,   
                BufferedImage.TYPE_INT_RGB);   
  
        // 得到目标图片输出流   
        FileOutputStream out = new FileOutputStream(outFileName);   
  
        // 根据需求画出目标图片 方式1   
        tag.getGraphics().drawImage(src, 0, 0, nw, nh, null);   
  
        // 将画好的目标图输出到输出流 方式1   
        JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);   
        encoder.encode(tag);   
        out.close();   
        return outFileName;   
    }   
  
    public static boolean checkImageFile(String extName) {   
  
        if ("jpg".equalsIgnoreCase(extName))   
            return true;   
        if ("gif".equalsIgnoreCase(extName))   
            return true;   
        if ("bmp".equalsIgnoreCase(extName))   
            return true;   
        if ("jpeg".equalsIgnoreCase(extName))   
            return true;   
        if ("png".equalsIgnoreCase(extName))   
            return true;   
        return false;   
    }   
  
}