Java后端实现图片压缩而不改变像素

    /** 
     *  缩略图实现，将图片(jpg、bmp、png、gif等等)真实的变成想要的大小 
     */  
    package com.joewalker.test;  
      
    import java.awt.Image;  
    import java.awt.image.BufferedImage;  
    import java.io.File;  
    import java.io.FileOutputStream;  
    import java.io.IOException;  
    import javax.imageio.ImageIO;  
    import com.sun.image.codec.jpeg.JPEGCodec;  
    import com.sun.image.codec.jpeg.JPEGImageEncoder;  
      
    /******************************************************************************* 
     * 缩略图类（通用） 本java类能将jpg、bmp、png、gif图片文件，进行等比或非等比的大小转换。 具体使用方法 
     * compressPic(大图片路径,生成小图片路径,大图片文件名,生成小图片文名,生成小图片宽度,生成小图片高度,是否等比缩放(默认为true)) 
     */  
     public class CompressPicDemo {   
         private File file = null; // 文件对象   
         private String inputDir; // 输入图路径  
         private String outputDir; // 输出图路径  
         private String inputFileName; // 输入图文件名  
         private String outputFileName; // 输出图文件名  
         private int outputWidth = 100; // 默认输出图片宽  
         private int outputHeight = 100; // 默认输出图片高  
         private boolean proportion = true; // 是否等比缩放标记(默认为等比缩放)  
         public CompressPicDemo() { // 初始化变量  
             inputDir = "";   
             outputDir = "";   

             inputFileName = "";   
             outputFileName = "";   
             outputWidth = 100;   
             outputHeight = 100;   
         }   
         public void setInputDir(String inputDir) {   
             this.inputDir = inputDir;   
         }   
         public void setOutputDir(String outputDir) {   
             this.outputDir = outputDir;   
         }   
         public void setInputFileName(String inputFileName) {   
             this.inputFileName = inputFileName;  
         }   
         public void setOutputFileName(String outputFileName) {   
             this.outputFileName = outputFileName;   
         }   
         public void setOutputWidth(int outputWidth) {  
             this.outputWidth = outputWidth;   
         }   
         public void setOutputHeight(int outputHeight) {   
             this.outputHeight = outputHeight;   
         }   
         public void setWidthAndHeight(int width, int height) {   
             this.outputWidth = width;  
             this.outputHeight = height;   
         }   
           
         /*  
          * 获得图片大小