获取文件md5值

import java.security.MessageDigest;
//获取文件md5值
public static String md5HashCode(String filePath) {
    try {
        if (!new File(filePath).isFile()) {
            System.err.println("Error: " + filePath
                    + " is not a valid file.");
            return null;
        }
        InputStream fis = new FileInputStream(filePath);
        byte[] buffer = new byte[1024];
        MessageDigest complete = MessageDigest.getInstance("MD5");
        int numRead = -1;

        while ((numRead = fis.read(buffer)) != -1) {
            complete.update(buffer, 0, numRead);
        }

        byte[] b = complete.digest();
        if (null == b) {
            System.err.println(("Error:create md5 string failure!"));
            return null;
        }
        StringBuilder result = new StringBuilder();

        for (int i = 0; i < b.length; i++) {
            result.append(Integer.toString((b[i] & 0xff) + 0x100, 16)
                    .substring(1));
        }
        return result.toString();
    } catch (Exception e) {
        e.printStackTrace();
        return "";
    }
}