MD5 加密工具类

下面是一个md5加密工具类，一个字符串加密，一个文件MD5码加密。

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Locale;
import java.util.TimeZone;


public class MD5Util {
      
		
	/**
	 * 对字符串进行 MD5 加密
	 * 
	 * @param str
	 *            待加密字符串
	 * 
	 * @return 加密后字符串
	 */
	public static String md5(String str) {
		char hexDigits[] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
				'a', 'b', 'c', 'd', 'e', 'f' };
		MessageDigest md5 = null;
		try {
			md5 = MessageDigest.getInstance("MD5");
			md5.update(str.getBytes("UTF-8"));
		} catch (NoSuchAlgorithmException e) {
			e.printStackTrace();
			throw new RuntimeException(e.getMessage());
		} catch (UnsupportedEncodingException e) {
			e.printStackTrace();
			throw new RuntimeException(e.getMessage());
		}
		byte[] encodedValue = md5.digest();
		int j = encodedValue.length;
		char finalValue[] = new char[j * 2];
		int k = 0;
		for (int i = 0; i < j; i++) {
			byte encoded = encodedValue[i];
			finalValue[k++] = hexDigits[encoded >> 4 & 0xf];
			finalValue[k++] = hexDigits[encoded & 0xf];
		}

		return new String(finalValue);
	}

	/**
	 * 对文件进行 MD5 加密
	 * 
	 * @param file
	 *            待加密的文件
	 * 
	 * @return 文件加密后的 MD5 值
	 * @throws IOException
	 */
	public static String md5(File file) throws IOException {
		FileInputStream is = new FileInputStream(file);
		char hexDigits[] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
				'a', 'b', 'c', 'd', 'e', 'f' };
		MessageDigest md5 = null;
		try {
			md5 = MessageDigest.getInstance("MD5");
			int n = 0;
			byte[] buffer = new byte[1024];
			do {
				n = is.read(buffer);
				if (n > 0) {
					md5.update(buffer, 0, n);
				}
			} while (n != -1);
			is.skip(0);
		} catch (NoSuchAlgorithmException e) {
			e.printStackTrace();
			throw new RuntimeException(e.getMessage());
		} finally {
			is.close();
		}

		byte[] encodedValue = md5.digest();

		int j = encodedValue.length;
		char finalValue[] = new char[j * 2];
		int k = 0;
		for (int i = 0; i < j; i++) {
			byte encoded = encodedValue[i];
			finalValue[k++] = hexDigits[encoded >> 4 & 0xf];
			finalValue[k++] = hexDigits[encoded & 0xf];
		}

		return new String(finalValue);
	}

	/**
	 * 获取 GMT 格式时间戳
	 * 
	 * @return GMT 格式时间戳
	 */
	public static String getGMTDate() {
		SimpleDateFormat formater = new SimpleDateFormat(
				"EEE, d MMM yyyy HH:mm:ss 'GMT'", Locale.US);
		formater.setTimeZone(TimeZone.getTimeZone("GMT"));
		return formater.format(new Date());
	}
	
	
    public static void main(String[] args) throws IOException {
    <span style="white-space:pre">	</span>// 字符串加密
        System.out.println(MD5("20121221"));
        // 文件MD5码s
        System.out.println(md5(new File("README.md")));
    }
    
}