复制代码 代码如下:
public class MD5Check {
/**
* 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 char hexDigits[] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' };
protected MessageDigest messagedigest = null;

{
try {
messagedigest = MessageDigest.getInstance("MD5");
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
}
}

public 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 String getFileMD5String(InputStream in) throws IOException {
byte[] buffer = new byte[1024];
int numRead = 0;
while ((numRead = in.read(buffer)) > 0) {
messagedigest.update(buffer, 0, numRead);
}
in.close();
return bufferToHex(messagedigest.digest());
}

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

private 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 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);
}

}