详解Java中使用ImageIO类对图片进行压缩的方法

最近做项目需要图片压缩处理，网上找的方法大都使用了 com.sun.image.codec.jpeg.* 这个包中的JPEGImageEncoder类，引入这个包后一直报错，各种google百度，尝试了各种方法，包括手动引jre中的rt.jar,以及在eclipse中把受访问限制的API提示从ERROR改为WARNING，等等，然而这些都是不好使的，因为后来我发现我的java-7-openjdk-amd64中的rt.jar里边根本就没有com.sun.image.*，貌似这个类在java7中已经被彻底remove了，至少我这个版本是没有了。然后搜了个使用ImageIO类来进行处理的替代方案，代码如下：
可以压缩为任意大小，压缩后高清，不变形（留白），可以改后缀名，可以修改压缩分辨率。
可能有朋友也有这个需要，参考一下吧，有问题还请指证！

package cn.com.images; 
 
import java.awt.Graphics; 
import java.awt.Image; 
import java.awt.image.BufferedImage; 
import java.io.File; 
import java.io.IOException; 
import java.math.BigDecimal; 
import java.math.MathContext; 
import java.util.ArrayList; 
 
import javax.imageio.ImageIO; 
 
 
public class ImageHelper { 
 
  private static ImageHelper imageHelper = null; 
 
  public static ImageHelper getImageHelper() { 
    if (imageHelper == null) { 
      imageHelper = new ImageHelper(); 
    } 
    return imageHelper; 
  } 
 
   
  public static void scaleImage(String sourceImagePath, 
      String destinationPath, double scale,String format) { 
 
    File file = new File(sourceImagePath); 
    BufferedImage bufferedImage; 
    try { 
      bufferedImage = ImageIO.read(file); 
      int width = bufferedImage.getWidth(); 
      int height = bufferedImage.getHeight(); 
 
      width = parseDoubleToInt(width * scale); 
      height = parseDoubleToInt(height * scale); 
 
      Image image = bufferedImage.getScaledInstance(width, height, 
   Image.SCALE_SMOOTH); 
      BufferedImage outputImage = new BufferedImage(width, height, 
   BufferedImage.TYPE_INT_RGB); 
      Graphics graphics = outputImage.getGraphics(); 
      graphics.drawImage(image, 0, 0, null); 
      graphics.dispose(); 
 
      ImageIO.write(outputImage, format, new File(destinationPath)); 
    } catch (IOException e) { 
      System.out.println("scaleImage方法压缩图片时出错了"); 
      e.printStackTrace(); 
    } 
 
  } 
 
   
  public static void scaleImageWithParams(String sourceImagePath, 
      String destinationPath, int width, int height, boolean auto,String format) { 
     
    try { 
    File file = new File(sourceImagePath); 
    BufferedImage bufferedImage = null; 
    bufferedImage = ImageIO.read(file); 
      if (auto) { 
 ArrayList paramsArrayList = getAutoWidthAndHeight(bufferedImage,width,height); 
 width = paramsArrayList.get(0); 
 height = paramsArrayList.get(1); 
 System.out.println("自动调整比例，width="+width+" height="+height); 
      } 
     
    Image image = bufferedImage.getScaledInstance(width, height, 
 Image.SCALE_DEFAULT); 
    BufferedImage outputImage = new BufferedImage(width, height, 
 BufferedImage.TYPE_INT_RGB); 
    Graphics graphics = outputImage.getGraphics(); 
    graphics.drawImage(image, 0, 0, null); 
    graphics.dispose(); 
    ImageIO.write(outputImage, format, new File(destinationPath)); 
    } catch (Exception e) { 
      System.out.println("scaleImageWithParams方法压缩图片时出错了"); 
      e.printStackTrace(); 
    } 
     
     
  } 
 
   
  private static int parseDoubleToInt(double sourceDouble) { 
    int result = 0; 
    result = (int) sourceDouble; 
    return result; 
  } 
   
   
  private static ArrayList getAutoWidthAndHeight(BufferedImage bufferedImage,int width_scale,int height_scale){ 
    ArrayList arrayList = new ArrayList(); 
    int width = bufferedImage.getWidth(); 
    int height = bufferedImage.getHeight(); 
    double scale_w =getDot2Decimal( width_scale,width); 
     
    System.out.println("getAutoWidthAndHeight width="+width + "scale_w="+scale_w); 
    double scale_h = getDot2Decimal(height_scale,height); 
    if (scale_w