MD5校验

package com.utils;


import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;


public class TestMD5Two {
/**
* 默认的密码字符串组合，用来将字节转换成 16 进制表示的字符,apache校验下载的文件的正确性用的就是默认的这个组合
*/
protected static char hexDigits[] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e',
'f' };


protected static MessageDigest messagedigest = null;
static {
try {
messagedigest = MessageDigest.getInstance("MD5");
} catch (NoSuchAlgorithmException nsaex) {
System.err.println(TestMD5Two.class.getName() + "初始化失败，MessageDigest不支持MD5Util。");
nsaex.printStackTrace();
}
}


/**
* 生成字符串的md5校验值
* 
* @param s
* @return
*/
public static String getMD5String(String s) {
return getMD5String(s.getBytes());
}


/**
* 判断字符串的md5校验码是否与一个已知的md5码相匹配
* 
* @param password
*            要校验的字符串
* @param md5PwdStr
*            已知的md5校验码
* @return
*/
public static boolean checkPassword(String md5, String md5PwdStr) {
return md5.equals(md5PwdStr);
}


/**
* 生成文件的md5校验值
* 
* @param file
* @return
* @throws IOException
*/
public static String getFileMD5String(File file) throws IOException {
InputStream fis;
fis = new FileInputStream(file);
byte[] buffer = new byte[1024];
int numRead = 0;
while ((numRead = fis.read(buffer)) > 0) {
messagedigest.update(buffer, 0, numRead);
}
fis.close();
return bufferToHex(messagedigest.digest());
}


public static String getMD5String(byte[] bytes) {
messagedigest.update(bytes);
return bufferToHex(messagedigest.digest());
}


private static String bufferToHex(byte bytes[]) {
return bufferToHex(bytes, 0, bytes.length);
}


private static String bufferToHex(byte bytes[], int m, int n) {
StringBuffer stringbuffer = new StringBuffer(2 * n);
int k = m + n;
for (int l = m; l < k; l++) {
appendHexPair(bytes[l], stringbuffer);
}
return stringbuffer.toString();
}


private static void appendHexPair(byte bt, StringBuffer stringbuffer) {
char c0 = hexDigits[(bt & 0xf0) >> 4];// 取字节中高 4 位的数字转换, >>>
// 为逻辑右移，将符号位一起右移,此处未发现两种符号有何不同
char c1 = hexDigits[bt & 0xf];// 取字节中低 4 位的数字转换
stringbuffer.append(c0);
stringbuffer.append(c1);
}


public static void main(String[] args) throws IOException {
long begin = System.currentTimeMillis();


File file = new File("E:/1.txt");
String md5 = getFileMD5String(file);


// 文件名不同，内容相同；
File file2 = new File("E:/2.txt");
String md52 = getFileMD5String(file2);




System.out.println("MD5:" + md5);
System.out.println("MD5:" + md52);
System.out.println("两个文件名不同，内荣相同" + checkPassword(md5, md52));
long end = System.currentTimeMillis();
System.out.println("md5:" + md5 + " time:" + ((end - begin) / 1000) + "s");
}


}