java 计算 文件 md5

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);     } }