Java代码如何获取一个文件的MD5值呢?

文件MD5值计算的实现思路:
    1.将文件读取为一个字节数组
	2.声明MD5对象
	3.计算出字节数组对应的MD5值即可

 /**
 * 计算文件MD5
 * @return 文件MD5
 */
public static String getMd5ByFile(String path) throws FileNotFoundException {  
	File file = new File(path);
	String value = null;  
	FileInputStream in = new FileInputStream(file);  
	try {  
		MappedByteBuffer byteBuffer = 
				in.getChannel().map(FileChannel.MapMode.READ_ONLY, 0, file.length());  
		MessageDigest md5 = MessageDigest.getInstance("MD5");  
		md5.update(byteBuffer);  
		BigInteger bi = new BigInteger(1, md5.digest());  
		value = bi.toString(16);  
	} catch (Exception e) {  
		return null;
	} finally {  
		if (null != in) {  
			try {  
				in.close();  
			} catch (IOException e) {  
				return null;
			}  
		}  
	}  
	return value;  
}