java 的 MD5编码处理

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当需要对一个大文件计算MD5校验和时，JDK提供的方法速度是非常快的，甚至比操作系统提供的本地工具还要快。详情可以查看这个链接 http://www.twmacinta.com/myjava/fast_md5.php

 

这里有一个简单的示例，来自 http://www.javalobby.org/java/forums/t84420.html：

public static void main(String[] args) throws NoSuchAlgorithmException, FileNotFoundException {
	MessageDigest digest = MessageDigest.getInstance("MD5");
	File f = new File("c:\\myfile.txt");
	InputStream is = new FileInputStream(f);				
	byte[] buffer = new byte[8192];
	int read = 0;
	try {
		while( (read = is.read(buffer)) > 0) {
			digest.update(buffer, 0, read);
		}		
		byte[] md5sum = digest.digest();
		BigInteger bigInt = new BigInteger(1, md5sum);
		String output = bigInt.toString(16);
		System.out.println("MD5: " + output);
	}
	catch(IOException e) {
		throw new RuntimeException("Unable to process file for MD5", e);
	}
	finally {
		try {
			is.close();
		}
		catch(IOException e) {
			throw new RuntimeException("Unable to close input stream for MD5 calculation", e);
		}
	}		
}

 

如果需要对一个较短字符串进行处理，只要使用String的getBytes方法即可