MD5、SHA1算法为一种不可逆算法,一定程度上保证了数据安全性,但是不一定100%，在实际当中我们都会加上salt，更高安全的可以在加上可变的时间戳，这样就更增加了被攻破的难度。

算法特点：

• 1、压缩性，任意长度的数据MD5后值长度都是固定
• 2、计算速度快，原数据计算出MD5串速度很快
• 3、防篡改，对原数据进行任何改动，所得到的MD5值都不一样
• 4、强抗碰撞，想找到一个具有相同MD5值的数据非常困难

应用场景：

• 1、防篡改，一致性验证
• 2、数字签名
• 3、安全访问认证

public class EncryptUtil {

    //init any you like.
    public static String salt= "%&#95480234-3=-@qweq.djdcn";


    public static String md5(String str){
        return hash(str,"MD5");
    }

    public static String hash1(String str){
        return hash(str,"SHA1");
    }

    public static String md5File(File file){
        return hash(file,"MD5");
    }

    public static String hash1File(File file){
        return hash(file,"SHA1");
    }

    /**
     *  often is MD5 or SHA1
     * @param str
     * @param algorithm
     * @return
     */
    private static String hash(String str,String algorithm){
        if(str==null||"".equals(str)){
            return "";
        }
        str+=salt;
        MessageDigest messageDigest= null;
        try {
            messageDigest= MessageDigest.getInstance(algorithm);
            byte[] bytes= messageDigest.digest(str.getBytes("UTF-8"));
            StringBuilder builder= new StringBuilder();
            for(byte b:bytes){
                String t= Integer.toHexString(b & 0xff);
                if(t.length()==1){
                    builder.append("0").append(t);
                }
                builder.append(t);
            }
            return builder.toString();
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
        return "";
    }

    /**
     *  often is MD5 or SHA1
     * @param file
     * @param algorithm
     * @return
     */
    private static String hash(File file,String algorithm) {
        if(file==null || !file.isFile() || !file.exists()){
            return "";
        }
        MessageDigest messageDigest= null;
        FileInputStream in = null;
        byte buffer[] = new byte[0124];
        int len;
        try {
            messageDigest= MessageDigest.getInstance(algorithm);
            in= new FileInputStream(file);
            while ((len=in.read(buffer))!=-1){
                messageDigest.update(buffer,0,len);
            }
            byte[] bytes= messageDigest.digest();
            StringBuilder builder= new StringBuilder();
            for(byte b:bytes){
                String t= Integer.toHexString(b&0xff);
                if(t.length()==1){
                    builder.append("0").append(t);
                }
                builder.append(t);
            }
            return builder.toString();
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            if(in!=null){
                try {
                    in.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
        return "";
    }

    public static void main(String[] args) {
        System.out.println(md5("hashTest"));
        System.out.println(md5("hashTest3333sdfartsf"));
        System.out.println(hash1("hashTest"));
        System.out.println(md5File(new File("C:\\Users\\lyk\\Downloads\\20171108105405408.doc")));
        System.out.println(hash1File(new File("C:\\Users\\lyk\\Downloads\\1526004415.png")));
    }
}