在字节流的byte[]下判断图片文件格式(后缀)与大小

===============================直接截取后缀方式判断文件格式===================================

String originalFileName = MultipartFile.getOriginalFilename();

String substring = originalFileName.substring(originalFileName.lastIndexOf("."));

===============================byte[]方式判断文件格式========================================
import jline.internal.Log;

import javax.imageio.ImageIO;
import javax.imageio.ImageReader;
import javax.imageio.stream.MemoryCacheImageInputStream;
import java.io.*;
import java.util.Iterator;

public class TestImage {

    public static void main(String[] args) throws IOException {
        File sourceImage = new File("d:\\\\test.png");
        byte[]  imageByte = File2byte(sourceImage);
        String strImage = getImageType(imageByte);
        Log.info("strImage:"+strImage);
    }
    /**
     * 判断图片文件格式
     *
     * @param mapObj
     * @return
     * @throws IOException
     */
    public static String getImageType(byte[] mapObj) throws IOException {
    // FileOutputStream fout = new FileOutputStream("d:\\test.jpg");
    // //将字节写入文件
    // fout.write(mapObj);
    // fout.close();
    //支持的文件类型: ["gif", "jpeg", "jpg", "bmp", "png"],
    //        if (Base64.decode(requestDTO.getCreditImg()).length > StringUtil.sizeImge) {
   //大于1M
    //            throw new RestException(ErrorDetailEnum.FILE_SIZE_ERROR, WatchLogType.MERCHANTS_IN_CENTER);//文件过大
     //        }

        String type = "";
        ByteArrayInputStream bais = null;
        MemoryCacheImageInputStream mcis = null;
        try {
            bais = new ByteArrayInputStream(mapObj);
            mcis = new MemoryCacheImageInputStream(bais);
            Iterator itr = ImageIO.getImageReaders(mcis);
            while (itr.hasNext()) {
                ImageReader reader = (ImageReader) itr.next();
                String imageName = reader.getClass().getSimpleName();
                if (imageName != null) {
                    if ("GIFImageReader".equals(imageName)) {
                        type = "gif";
                    } else if ("JPEGImageReader".equals(imageName)) {
                        type = "jpg";
                    } else if ("PNGImageReader".equals(imageName)) {
                        type = "png";
                    } else if ("BMPImageReader".equals(imageName)) {
                        type = "bmp";
                    } else {
                        type = "noPic";
                    }
                }
            }
        } catch (Exception e) {
            type = "noPic";
        } finally {
            if (bais != null) {
                try {
                    bais.close();
                } catch (IOException ioe) {
                    type = "noPic";
                }
            }
            if (mcis != null) {
                try {
                    mcis.close();
                } catch (IOException ioe) {
                    type = "noPic";
                }
            }
        }
        return type;
    }

    /**
     * 将文件转换成byte数组
     * @param filePath
     * @return
     */
    public static byte[] File2byte(File tradeFile) {
        byte[] buffer = null;
        try {
            FileInputStream fis = new FileInputStream(tradeFile);
            ByteArrayOutputStream bos = new ByteArrayOutputStream();
            byte[] b = new byte[1024];
            int n;
            while ((n = fis.read(b)) != -1) {
                bos.write(b, 0, n);
            }
            fis.close();
            bos.close();
            buffer = bos.toByteArray();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return buffer;
    }
}