MD5：字符串和文件

import java.io.FileInputStream;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class Md5Utils {

    //十六进制
    private static final char HEX_DIGITS[] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' };

    /**
     * byte数组转换为转换为16进制
     * @param b 数据
     * @return 返回字符串
     */
    private static String toHexString(byte[] b) {
        StringBuilder sb = new StringBuilder(b.length * 2);
        for (int i = 0; i < b.length; i++) {
            sb.append(HEX_DIGITS[(b[i] & 0xf0) >>> 4]);
            sb.append(HEX_DIGITS[b[i] & 0x0f]);
        }
        return sb.toString();
    }


    /**
     * MD5对字符串校验
     * @param string
     * @return
     */
    public static String md5(String string) {
        byte[] bytes;
        try {
            bytes = MessageDigest.getInstance("MD5").digest(string.getBytes("UTF-8"));
        } catch (NoSuchAlgorithmException e) {
            throw new RuntimeException("MD5 should be supported?", e);
        } catch (UnsupportedEncodingException e) {
            throw new RuntimeException("UTF-8 should be supported?", e);
        }

        return toHexString(bytes);
    }

    /**
     * 取文件MD5值
     * @param filename 文件路径
     * @return MD5值
     */
    public static String fileMD5(String filename) {
        InputStream fis;
        byte[] buffer = new byte[1024];
        int numRead = 0;
        MessageDigest md5;
        try {
            fis = new FileInputStream(filename);
            md5 = MessageDigest.getInstance("MD5");
            while ((numRead = fis.read(buffer)) > 0) {
                md5.update(buffer, 0, numRead);
            }
            fis.close();
            return toHexString(md5.digest());
        } catch (Exception e) {
            System.out.println("error");
            return null;
        }
    }
}
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