MessageDigest类的使用

在前面java中的MessageDigest类中简要介绍了它的一些作用和方法，下面给个例子，对文件和字符串MD5分别给了两个例子，代码如下：

package com.home;import java.io.File;import java.io.FileInputStream;import java.io.IOException;import java.nio.MappedByteBuffer;import java.nio.channels.FileChannel;import java.security.DigestInputStream;import java.security.MessageDigest;import java.security.NoSuchAlgorithmException;public class Test {public static void main(String[] args) {String str1 = "I love Java";System.out.println(getMD5Str(str1));try {System.out.println(getFileMD5String("C:/Main.java"));System.out.println(getFileMD5("C:/Main.java"));} catch (IOException e) {e.printStackTrace();}}/** * 对字符串进行MD5加密 *  * @param input * @return */public static String getMD5Str(String input) {try {MessageDigest m = MessageDigest.getInstance("MD5");m.update(input.getBytes());byte[] md5Data = m.digest();return byteArrayToHex(md5Data);// return byteArrayToHex2(md5Data);} catch (NoSuchAlgorithmException e) {e.printStackTrace();}return null;}/** * 将字节数组换成成16进制的字符串 *  * @param byteArray * @return */public static String byteArrayToHex2(byte[] byteArray) {String output = new String();for (int i = 0; i < byteArray.length; i++) {int b = (0xFF & byteArray[i]);if (b <= 0xF) {output += "0";}output += Integer.toHexString(b);}output = output.toUpperCase();return output;}/** * 将字节数组换成成16进制的字符串 *  * @param byteArray * @return */private static String byteArrayToHex(byte[] byteArray) {char[] hexDigits = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9','A', 'B', 'C', 'D', 'E', 'F' };char[] resultCharArray = new char[byteArray.length * 2];int index = 0;for (byte b : byteArray) {resultCharArray[index++] = hexDigits[b >>> 4 & 0xf];resultCharArray[index++] = hexDigits[b & 0xf];}return new String(resultCharArray);}/** * 对文件进行MD5加密 *  * @param inputFile * @return * @throws IOException */public static String getFileMD5(String inputFile) throws IOException {int bufferSize = 256 * 1024;FileInputStream fileInputStream = null;DigestInputStream digestInputStream = null;try {// 拿到一个MD5转换器（同样，这里可以换成SHA1）MessageDigest messageDigest = MessageDigest.getInstance("MD5");// 使用DigestInputStreamfileInputStream = new FileInputStream(inputFile);digestInputStream = new DigestInputStream(fileInputStream,messageDigest);// read的过程中进行MD5处理，直到读完文件byte[] buffer = new byte[bufferSize];while (digestInputStream.read(buffer) > 0);// 获取最终的MessageDigestmessageDigest = digestInputStream.getMessageDigest();// 拿到结果，也是字节数组，包含16个元素byte[] resultByteArray = messageDigest.digest();// 同样，把字节数组转换成字符串return byteArrayToHex(resultByteArray);} catch (NoSuchAlgorithmException e) {e.printStackTrace();return null;} finally {try {if (digestInputStream != null) {digestInputStream.close();}if (fileInputStream != null) {fileInputStream.close();}} catch (Exception e) {e.printStackTrace();}}}/** * 得到文件MD5 *  * @param path * @return * @throws IOException */public static String getFileMD5String(String path) throws IOException {File file = new File(path);try {MessageDigest messageDigest = MessageDigest.getInstance("MD5");FileInputStream in = new FileInputStream(file);FileChannel ch = in.getChannel();MappedByteBuffer byteBuffer = ch.map(FileChannel.MapMode.READ_ONLY,0, file.length());messageDigest.update(byteBuffer);return byteArrayToHex(messageDigest.digest());} catch (NoSuchAlgorithmException e) {e.printStackTrace();}return null;}}