package date0803;
/**
 * 找出系统支持的消息摘要算法
 */
import java.security.Security;

public class PrintMessageDigestAlgorithmsAvailable {

	public static void main(String[] args) {
		System.out.println("---------系统支持的消息摘要算法有--------");
	    for (String s : Security.getAlgorithms("MessageDigest")) {
	      System.out.println(s);
	    }
	}

}

支持的算法有：

---------系统支持的消息摘要算法有--------
SHA-384
SHA-224
SHA-256
MD2
SHA
SHA-512
MD5

package date0803;
/**
 * 编写一个程序来计算文件的消息摘要
 * 使用线程，便于批量计算文件的消息摘要
 * @author zzw922cn
 */
import java.io.FileInputStream;
import java.io.IOException;
import java.security.DigestInputStream;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

import javax.xml.bind.DatatypeConverter;

public class FileDigestThread extends Thread {

	
	private String filename;

	/**
	 * 
	 * @param filename 文件名
	 */
	public FileDigestThread(String filename) {
		super();
		this.filename = filename;
	}

	/**
	 * 线程的主要方法
	 */
	@Override
	public void run() {
		try {
			//文件输入流
			FileInputStream fileInputStream = new FileInputStream(filename);
			
			//指定算法，创建消息摘要的单例
			MessageDigest instance = MessageDigest.getInstance("SHA");
//			MessageDigest instance = MessageDigest.getInstance("SHA-512");
//			MessageDigest instance = MessageDigest.getInstance("SHA-384");
//			MessageDigest instance = MessageDigest.getInstance("SHA-256");
//			MessageDigest instance = MessageDigest.getInstance("SHA-224");
//			MessageDigest instance = MessageDigest.getInstance("MD5");
//			MessageDigest instance = MessageDigest.getInstance("MD2");
			
			
			//创建摘要输入流，即从特定输入流和消息摘要来创建
			DigestInputStream digestInputStream = new DigestInputStream(fileInputStream, instance);
			
			//读取字节，并且更新摘要，然后关闭流
			while(digestInputStream.read()!=-1)
				;
			digestInputStream.close();
			
			//当所有数据已被更新，调用digest()方法完成哈希计算，返回字节数组
			byte[] digest = instance.digest();
			
			//创建字符串构造器，方便字符串的操作
			StringBuilder stringBuilder = new StringBuilder(filename);
			String algorithm = instance.getAlgorithm();
			stringBuilder.append("(algorithm:"+algorithm+"):");
			//将字节数组转化成字符串
			stringBuilder.append(DatatypeConverter.printHexBinary(digest));
			
			//打印消息摘要结果
			System.out.println(stringBuilder.toString());
		
		}catch(IOException ex) {
			System.err.println(ex);
		} catch (NoSuchAlgorithmException ex) {
			System.err.println(ex);
		}
	}
}

package date0803;

import java.io.File;

public class Test1 {

	public static void main(String[] args) {
		File file = new File("E:\\数据挖掘课程PPT");
		File[] listFiles = file.listFiles();
		
		//对于文件，使用绝对路径，便于查找
		for(File subfile:listFiles) {
			String absolutePath = subfile.getAbsolutePath();
			Thread fileDigestThread = new FileDigestThread(absolutePath);
			fileDigestThread.start();
		}
	}

}