MD5算法 验证字符串（也可验证文件）

不同名文件有可能内容相同，在上传时就需要验证一下，避免重复上传。

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

/**
 *
 * @author zzheng
 */
public class MD5
{

  /**
   * @param args the command line arguments
   */
  public MD5() throws NoSuchAlgorithmException
  {
    md = MessageDigest.getInstance("MD5");
  }
  /*
   * this method will generate MD5 hash code.
   * the code can be used to test Strings, files and so on.
   */

  public String generateMD5(String ss)
  {
    md.update(ss.getBytes());

    //b.size() = 32
    byte[] b = md.digest();
    String hex = "";
    int msb;
    int lsb = 0;

    for (int i = 0; i < b.length; i++)
    {
      msb = ((int) b[i] & 0x000000FF) / 16;
      lsb = ((int) b[i] & 0x000000FF) % 16;
      hex = hex + hexChars[msb] + hexChars[lsb];
    }
    return hex;
  }
  private MessageDigest md = null;
  private static final char[] hexChars =
  {
    '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'
  };
}