package test;

import java.awt.image.BufferedImage;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.math.BigDecimal;

import javax.imageio.ImageIO;

import net.coobird.thumbnailator.Thumbnails;

import org.apache.commons.lang3.StringUtils;

public class PicUtils {

    public static void main(String[] args) {

        PicUtils.commpressPicForScale("D:/Picture/001.jpg",
                "D:/Picture/002.jpg", 1000, 0.8, 750, 1334); // 图片小于1000kb

    }

    /**
     * 根据指定大小和指定精度压缩图片
     * 
     * @param srcPath
     *            源图片地址
     * @param desPath
     *            目标图片地址
     * @param desFileSize
     *            指定图片大小,单位kb
     * @param accuracy
     *            精度,递归压缩的比率,建议小于0.9
     * @param desMaxWidth
     *            目标最大宽度
     * @param desMaxHeight
     *            目标最大高度
     * @return 目标文件路径
     */
    public static String commpressPicForScale(String srcPath, String desPath,
            long desFileSize, double accuracy, int desMaxWidth, int desMaxHeight) {
        if (StringUtils.isEmpty(srcPath) || StringUtils.isEmpty(srcPath)) {
            System.out.println("源图片不存在1");
            return null;
        }
        if (!new File(srcPath).exists()) {
            System.out.println("源图片不存在2");
            return null;
        }
        try {
            File srcFile = new File(srcPath);
            long srcFileSize = srcFile.length();
            System.out.println("源图片:" + srcPath + ",大小:" + srcFileSize / 1024 + "kb");
            // 获取图片信息
            BufferedImage bim = ImageIO.read(srcFile);
            int srcWidth = bim.getWidth();
            int srcHeight = bim.getHeight();

            // 先转换成jpg
            Thumbnails.Builder builder = Thumbnails.of(srcFile).outputFormat("jpg");

            // 指定大小(宽或高超出会才会被缩放)
            if (srcWidth > desMaxWidth || srcHeight > desMaxHeight) {
                builder.size(desMaxWidth, desMaxHeight);
            } else {
                // 宽高均小,指定原大小
                builder.size(srcWidth, srcHeight);
            }

            // 写入到内存
            ByteArrayOutputStream baos = new ByteArrayOutputStream(); // 字节输出流(写入到内存)
            builder.toOutputStream(baos);

            // 递归压缩,直到目标文件大小小于desFileSize
            byte[] bytes = commpressPicCycle(baos.toByteArray(), desFileSize, accuracy);

            // 输出到文件
            File desFile = new File(desPath);
            FileOutputStream fos = new FileOutputStream(desFile);
            fos.write(bytes);
            fos.close();

            System.out.println("目标图片:" + desPath + ",大小" + desFile.length() / 1024 + "kb");
            System.out.println("图片压缩完成!");
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        }
        return desPath;
    }

    private static byte[] commpressPicCycle(byte[] bytes, long desFileSize,
            double accuracy) throws IOException {
        long srcFileSizeJPG = bytes.length;
        // 2、判断大小,如果小于500kb,不压缩;如果大于等于500kb,压缩
        if (srcFileSizeJPG <= desFileSize * 1024) {
            return bytes;
        }
        // 计算宽高
        BufferedImage bim = ImageIO.read(new ByteArrayInputStream(bytes));
        int srcWdith = bim.getWidth();
        int srcHeigth = bim.getHeight();
        int desWidth = new BigDecimal(srcWdith).multiply(new BigDecimal(accuracy)).intValue();
        int desHeight = new BigDecimal(srcHeigth).multiply(new BigDecimal(accuracy)).intValue();
        // 字节输出流(写入到内存)
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        Thumbnails.of(new ByteArrayInputStream(bytes))
                .size(desWidth, desHeight).outputQuality(accuracy)
                .toOutputStream(baos);
        return commpressPicCycle(baos.toByteArray(), desFileSize, accuracy);
    }

}

Q.E.D.

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