Minio

MessageDigest

• 可用于为文件生成sha1 md5 等校验信息，对文件进行文件完整性校验

//获取MessageDigest通过getInstance
MessageDigest messageDigest = MessageDigest.getInstance("SHA1");

File f = new File("c:\\install.log");
           if(!f.isFile()){return;}
           FileInputStream Fis= new FileInputStream(f);
           //此处借助DigestInputStream
           DigestInputStream digestInputStream = new DigestInputStream(Fis,messageDigest);
           //为文件生成加密信息的字节数组
           byte[] res =digestInputStream.getMessageDigest().digest();
           //转换16进制
           System.out.println(byteArrayToHex(res));

public static String byteArrayToHex(byte[] byteArray) {
        // 首先初始化一个字符数组，用来存放每个16进制字符
        char[] hexDigits = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'};
        // new一个字符数组，这个就是用来组成结果字符串的（解释一下：一个byte是八位二进制，也就是2位十六进制字符（2的8次方等于16的2次方））
        char[] resultCharArray = new char[byteArray.length * 2];
        // 遍历字节数组，通过位运算（位运算效率高），转换成字符放到字符数组中去
        int index = 0;
        for (byte b : byteArray) {
            resultCharArray[index++] = hexDigits[b >>> 4 & 0xf];
            resultCharArray[index++] = hexDigits[b & 0xf];
        }
        // 字符数组组合成字符串返回
        return new String(resultCharArray);
    }

DigestInputStream

这里使用的DigestInputStream 通过一个输入流和MessageDigest 获取实例 并通过getMessageDigest 获取具体的MessageDigest 使用MessageDigest 的 digest()得到加密的字节信息

public DigestInputStream(InputStream stream, MessageDigest digest) {
        super(stream);
        setMessageDigest(digest);
    }

public MessageDigest getMessageDigest() {
        return digest;
    }

digest方法

public byte[] digest() {
        /* Resetting is the responsibility of implementors. */
        //调用了抽象类的engineDigest方法
        byte[] result = engineDigest();
        state = INITIAL;
        return result;
    }

抽象类的具体实现则是在Security.getImpl(…)方法获得sun.security.provider.SHA

public static MessageDigest getInstance(String algorithm)
    throws NoSuchAlgorithmException {
        try {
          ...
            Object[] objs = Security.getImpl(algorithm, "MessageDigest",(String)null);
            if (objs[0] instanceof MessageDigest) {
                md = (MessageDigest)objs[0];
            } else {
                md = new Delegate((MessageDigestSpi)objs[0], algorithm);
            }
            ...
    }

engineDigest具体调用为sun.security.provider.SHA 的父类sun.security.provider.DigestBase 中的engineDigest

abstract class DigestBase extends MessageDigestSpi implements Cloneable {
    ...
    protected final byte[] engineDigest() {
            byte[] var1 = new byte[this.digestLength];

            try {
                this.engineDigest(var1, 0, var1.length);
                return var1;
            } catch (DigestException var3) {
                throw (ProviderException)(new ProviderException("Internal error")).initCause(var3);
            }
        }
    ...
}