图片 常用格式验证

通过文件头部字节判断文件格式

本图片验证工具类摘取自itext5的Image类的public static Image getInstance(final URL url, boolean recoverFromImageError)方法

private boolean verifyImageFormat(InputStream imageIS) throws IOException {
        //获取文件头的前8个字节
        int c1 = imageIS.read();
        int c2 = imageIS.read();
        int c3 = imageIS.read();
        int c4 = imageIS.read();
        // jbig2
        int c5 = imageIS.read();
        int c6 = imageIS.read();
        int c7 = imageIS.read();
        int c8 = imageIS.read();
        imageIS.close();
        imageIS = null; // help GC

        if (c1 == 'G' && c2 == 'I' && c3 == 'F') {
            //gif
            return true;
        }
        if (c1 == 0xFF && c2 == 0xD8) {
            //Jpeg
            return true;
        }
        if (c1 == 0x00 && c2 == 0x00 && c3 == 0x00 && c4 == 0x0c) {
            //Jpeg2000
            return true;
        }
        if (c1 == 0xff && c2 == 0x4f && c3 == 0xff && c4 == 0x51) {
            //Jpeg2000
            return true;
        }
        if (c1 == PngImage.PNGID[0] && c2 == PngImage.PNGID[1]
                && c3 == PngImage.PNGID[2] && c4 == PngImage.PNGID[3]) {
            //PngImage
            return true;
        }
        if (c1 == 0xD7 && c2 == 0xCD) {
            //ImgWMF
            return true;
        }
        if (c1 == 'B' && c2 == 'M') {
            //BmpImage
            return true;
        }

        if (c1 == 'M' && c2 == 'M' && c3 == 0 && c4 == 42
                || c1 == 'I' && c2 == 'I' && c3 == 42 && c4 == 0) {
            //TiffImage
            return true;
        }

        if ( c1 == 0x97 && c2 == 'J' && c3 == 'B' && c4 == '2' &&
                c5 == '\r' && c6 == '\n' && c7 == 0x1a && c8 == '\n' ) {
            //JBIG2Image
            return true;
        }

        return false;
    }