java 等比例压缩图片（背景不会成黑的）

来源：互联网发布：sql 查询一个字段包含编辑：程序博客网时间：2024/04/29 08:31

-下载所需jar包：http://pan.baidu.com/s/1o8y86MI
-1.新建一个工具类

import java.awt.Color;import java.awt.Graphics2D;import java.awt.Image;import java.awt.image.BufferedImage;import java.io.File;import java.io.FileOutputStream;import java.io.IOException;import javax.imageio.IIOImage;import javax.imageio.ImageIO;import javax.imageio.ImageTypeSpecifier;import javax.imageio.metadata.IIOMetadata;import javax.imageio.plugins.jpeg.JPEGImageWriteParam;import javax.imageio.stream.ImageOutputStream;import org.w3c.dom.Element;import com.sun.imageio.plugins.jpeg.JPEGImageWriter;public class ImagesTool {    public static void img_change(String url,String name)     {             Tosmallerpic(url,new File(url+name),"_small",name,30,40,(float)0.7);     }     /**     *     * @param f 图片所在的文件夹路径     * @param file 图片路径     * @param ext 扩展名     * @param n 图片名     * @param w 目标宽     * @param h 目标高     * @param per 百分比     */     private static void  Tosmallerpic(String f,File file,String ext,String n,int w,int h,float per){             Image src;             try {                 src  =  javax.imageio.ImageIO.read(file); //构造Image对象                String img_midname  =  f+n.substring(0,n.indexOf("."))+ext+n.substring(n.indexOf("."));                int old_w = src.getWidth(null); //得到源图宽                int old_h = src.getHeight(null);                int new_w = 0;                int new_h = 0; //得到源图长                double w2 = (old_w*1.00)/(w*1.00);                double h2 = (old_h*1.00)/(h*1.00);                //图片跟据长宽留白，成一个正方形图。                BufferedImage oldpic;                if(old_w>old_h)                {                    oldpic = new BufferedImage(old_w,old_w,BufferedImage.TYPE_INT_RGB);                }else{if(old_w<old_h){                    oldpic = new BufferedImage(old_h,old_h,BufferedImage.TYPE_INT_RGB);                }else{                     oldpic = new BufferedImage(old_w,old_h,BufferedImage.TYPE_INT_RGB);                }                }                 Graphics2D g  =  oldpic.createGraphics();                 g.setColor(Color.white);                 if(old_w>old_h)                 {                     g.fillRect(0, 0, old_w, old_w);                     g.drawImage(src, 0, (old_w - old_h) / 2, old_w, old_h, Color.white, null);                 }else{                     if(old_w<old_h){                     g.fillRect(0,0,old_h,old_h);                     g.drawImage(src, (old_h - old_w) / 2, 0, old_w, old_h, Color.white, null);                     }else{                         //g.fillRect(0,0,old_h,old_h);                         g.drawImage(src.getScaledInstance(old_w, old_h,  Image.SCALE_SMOOTH), 0,0,null);                     }                 }                              g.dispose();                 src  =  oldpic;                 //图片调整为方形结束                if(old_w>w)                new_w = (int)Math.round(old_w/w2);                else                    new_w = old_w;                if(old_h>h)                new_h = (int)Math.round(old_h/h2);//计算新图长宽                else                    new_h = old_h;                BufferedImage image_to_save  =  new BufferedImage(new_w,new_h,BufferedImage.TYPE_INT_RGB);                       image_to_save.getGraphics().drawImage(src.getScaledInstance(new_w, new_h,  Image.SCALE_SMOOTH), 0,0,null);                FileOutputStream fos = new FileOutputStream(img_midname); //输出到文件流                //旧的使用 jpeg classes进行处理的方法//               JPEGImageEncoder encoder  =  JPEGCodec.createJPEGEncoder(fos); //               JPEGEncodeParam jep = JPEGCodec.getDefaultJPEGEncodeParam(image_to_save);                 /* 压缩质量 */ //               jep.setQuality(per, true); //               encoder.encode(image_to_save, jep);                //新的方法               saveAsJPEG(100, image_to_save, per, fos);               fos.close();                } catch (IOException ex) {                 //Logger.getLogger(Img_Middle.class.getName()).log(Level.SEVERE, null, ex);             }     }     /**     * 以JPEG编码保存图片     * @param dpi  分辨率     * @param image_to_save  要处理的图像图片     * @param JPEGcompression  压缩比     * @param fos 文件输出流     * @throws IOException     */    public static void saveAsJPEG(Integer dpi ,BufferedImage image_to_save, float JPEGcompression, FileOutputStream fos) throws IOException {        JPEGImageWriter imageWriter  =  (JPEGImageWriter) ImageIO.getImageWritersBySuffix("jpg").next();        ImageOutputStream ios  =  ImageIO.createImageOutputStream(fos);        imageWriter.setOutput(ios);        //and metadata        IIOMetadata imageMetaData  =  imageWriter.getDefaultImageMetadata(new ImageTypeSpecifier(image_to_save), null);        if(dpi !=  null && !dpi.equals("")){             //old metadata            //jpegEncodeParam.setDensityUnit(com.sun.image.codec.jpeg.JPEGEncodeParam.DENSITY_UNIT_DOTS_INCH);            //jpegEncodeParam.setXDensity(dpi);            //jpegEncodeParam.setYDensity(dpi);            //new metadata            Element tree  =  (Element) imageMetaData.getAsTree("javax_imageio_jpeg_image_1.0");            Element jfif  =  (Element)tree.getElementsByTagName("app0JFIF").item(0);            jfif.setAttribute("Xdensity", Integer.toString(dpi) );            jfif.setAttribute("Ydensity", Integer.toString(dpi));        }        if(JPEGcompression >= 0 && JPEGcompression <= 1f){            //old compression            //jpegEncodeParam.setQuality(JPEGcompression,false);            // new Compression            JPEGImageWriteParam jpegParams  =  (JPEGImageWriteParam) imageWriter.getDefaultWriteParam();            jpegParams.setCompressionMode(JPEGImageWriteParam.MODE_EXPLICIT);            jpegParams.setCompressionQuality(JPEGcompression);        }        //old write and clean        //jpegEncoder.encode(image_to_save, jpegEncodeParam);        //new Write and clean up        imageWriter.write(imageMetaData, new IIOImage(image_to_save, null, null), null);        ios.close();        imageWriter.dispose();    }}

-调用ImagesTool类中的方法

//保存路径，图片名称ImagesTool.img_change(url1,name);

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