MD5加密算法，可以对文档整体进行加密

到网上看到一篇不错的数据加密文章，啥也不说了，直接上代码，这里感谢原作者：

package test11;

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.io.*;
import java.security.*;
import javax.crypto.*;
import javax.crypto.spec.*;

/**
 * 文件名：FileEncrypter.java JDK：1.40以上 说明：文件加密 加密方法：三重DES加密
 * 加密过程：对选中的文件加密后在同文件夹下生成一个增加了".tdes" 扩展名的加密文件
 * 
 * 解密过程：对选中的加密文件（必须有".tdes"扩展名）进行解密
 */
public class FileEncrypter extends JFrame {
	public static final int WIDTH = 550;
	public static final int HEIGHT = 200;

	public static void main(String args[]) {
		FileEncrypter fe = new FileEncrypter();
		fe.show();
	}

	FileEncrypter() {
		//设置屏幕窗口大小
		this.setSize(WIDTH, HEIGHT);
		this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		//设置是否可以调节大小
		this.setResizable(false);
		//设置窗口初始出现位置
		Toolkit tk = Toolkit.getDefaultToolkit();
		Dimension screenSize = tk.getScreenSize();
		this.setLocation((screenSize.width - WIDTH) / 2,
				(screenSize.height - HEIGHT) / 2);
		this.setTitle("文件加密器(TriDES)");
		//建立一个容器
		Container c = this.getContentPane();
		//设置布局
		c.setLayout(new FlowLayout());
		//容器中添加内容
		final FilePanel fp = new FilePanel("文件选择：");
		c.add(fp);
		final KeyPanel pp = new KeyPanel("密码：");
		c.add(pp);
		JButton jbE = new JButton("加密");
		c.add(jbE);
		//给加密按钮添加相应事件
		jbE.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent event) {
				File file = new File(fp.getFileName());
				if (file.exists())
					encrypt(file.getAbsoluteFile(), pp.getKey());
				else
					JOptionPane.showMessageDialog(null, "请选择文件！", "提示",JOptionPane.OK_OPTION);
			}
		});
		//添加解密按钮，增加监听事件
		JButton jbD = new JButton("解密");
		c.add(jbD);
		jbD.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent event) {
				File file = new File(fp.getFileName());
				if (file.exists())
					decrypt(file.getAbsoluteFile(), pp.getKey());
				else
					JOptionPane.showMessageDialog(null, "请选择文件！", "提示",JOptionPane.OK_OPTION);
			}
		});
	}

	/**
	 * 加密函数 输入： 要加密的文件，密码（由0-F组成，共48个字符，表示3个8位的密码）如：
	 * AD67EA2F3BE6E5ADD368DFE03120B5DF92A8FD8FEC2F0746 其中： AD67EA2F3BE6E5AD
	 * DES密码一 D368DFE03120B5DF DES密码二 92A8FD8FEC2F0746 DES密码三 输出：
	 * 对输入的文件加密后，保存到同一文件夹下增加了".tdes"扩展名的文件中。
	 */
	private void encrypt(File fileIn, String sKey) {
		try {
			if (sKey.length() == 48) {
				byte[] bytK1 = getKeyByStr(sKey.substring(0, 16));
				byte[] bytK2 = getKeyByStr(sKey.substring(16, 32));
				byte[] bytK3 = getKeyByStr(sKey.substring(32, 48));

				FileInputStream fis = new FileInputStream(fileIn);
				byte[] bytIn = new byte[(int) fileIn.length()];
				for (int i = 0; i < fileIn.length(); i++) {
					bytIn[i] = (byte) fis.read();
				}
				// 加密
				byte[] bytOut = encryptByDES(encryptByDES(encryptByDES(bytIn, bytK1), bytK2), bytK3);
				String fileOut = fileIn.getPath() + ".tdes";
				FileOutputStream fos = new FileOutputStream(fileOut);
				for (int i = 0; i < bytOut.length; i++) {
					fos.write((int) bytOut[i]);
				}
				fos.close();
				JOptionPane.showMessageDialog(this, "加密成功！", "提示",JOptionPane.OK_OPTION);
			} else
				JOptionPane.showMessageDialog(this, "密码长度必须等于48！", "错误信息",JOptionPane.ERROR_MESSAGE);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	/**
	 * 解密函数 输入： 要解密的文件，密码（由0-F组成，共48个字符，表示3个8位的密码）如：
	 * AD67EA2F3BE6E5ADD368DFE03120B5DF92A8FD8FEC2F0746 其中： AD67EA2F3BE6E5AD
	 * DES密码一 D368DFE03120B5DF DES密码二 92A8FD8FEC2F0746 DES密码三 输出：
	 * 对输入的文件解密后，保存到用户指定的文件中。
	 */
	private void decrypt(File fileIn, String sKey) {
		try {
			if (sKey.length() == 48) {
				String strPath = fileIn.getPath();
				if (strPath.substring(strPath.length() - 5).toLowerCase().equals(".tdes"))
					strPath = strPath.substring(0, strPath.length() - 5);
				else {
					JOptionPane.showMessageDialog(this, "不是合法的加密文件！", "提示",JOptionPane.OK_OPTION);
					return;
				}
				JFileChooser chooser = new JFileChooser();
				chooser.setCurrentDirectory(new File("."));
				chooser.setSelectedFile(new File(strPath));
				// 用户指定要保存的文件
				int ret = chooser.showSaveDialog(this);
				if (ret == JFileChooser.APPROVE_OPTION) {

					byte[] bytK1 = getKeyByStr(sKey.substring(0, 16));
					byte[] bytK2 = getKeyByStr(sKey.substring(16, 32));
					byte[] bytK3 = getKeyByStr(sKey.substring(32, 48));

					FileInputStream fis = new FileInputStream(fileIn);
					byte[] bytIn = new byte[(int) fileIn.length()];
					for (int i = 0; i < fileIn.length(); i++) {
						bytIn[i] = (byte) fis.read();
					}
					// 解密
					byte[] bytOut = decryptByDES(decryptByDES(decryptByDES(bytIn, bytK3), bytK2),bytK1);
					File fileOut = chooser.getSelectedFile();
					fileOut.createNewFile();
					FileOutputStream fos = new FileOutputStream(fileOut);
					for (int i = 0; i < bytOut.length; i++) {
						fos.write((int) bytOut[i]);
					}
					fos.close();
					JOptionPane.showMessageDialog(this, "解密成功！", "提示",JOptionPane.OK_OPTION);
				}
			} else
				JOptionPane.showMessageDialog(this, "密码长度必须等于48！", "错误信息",JOptionPane.ERROR_MESSAGE);
		} catch (Exception e) {
			JOptionPane.showMessageDialog(this, "解密失败，请核对密码！", "提示",JOptionPane.OK_OPTION);
		}
	}

	/**
	 * 用DES方法加密输入的字节 bytKey需为8字节长，是加密的密码
	 */
	private byte[] encryptByDES(byte[] bytP, byte[] bytKey) throws Exception {
		DESKeySpec desKS = new DESKeySpec(bytKey);
		SecretKeyFactory skf = SecretKeyFactory.getInstance("DES");
		SecretKey sk = skf.generateSecret(desKS);
		Cipher cip = Cipher.getInstance("DES");
		cip.init(Cipher.ENCRYPT_MODE, sk);
		return cip.doFinal(bytP);
	}

	/**
	 * 用DES方法解密输入的字节 bytKey需为8字节长，是解密的密码
	 */
	private byte[] decryptByDES(byte[] bytE, byte[] bytKey) throws Exception {
		DESKeySpec desKS = new DESKeySpec(bytKey);
		SecretKeyFactory skf = SecretKeyFactory.getInstance("DES");
		SecretKey sk = skf.generateSecret(desKS);
		Cipher cip = Cipher.getInstance("DES");
		cip.init(Cipher.DECRYPT_MODE, sk);
		return cip.doFinal(bytE);
	}

	/**
	 * 输入密码的字符形式，返回字节数组形式。 如输入字符串：AD67EA2F3BE6E5AD 返回字节数组：{
	 * 173,103,234,47,59,230,229,173 }
	 */
	private byte[] getKeyByStr(String str) {
		byte[] bRet = new byte[str.length() / 2];
		for (int i = 0; i < str.length() / 2; i++) {
			Integer itg = new Integer(16 * getChrInt(str.charAt(2 * i))
					+ getChrInt(str.charAt(2 * i + 1)));
			bRet[i] = itg.byteValue();
		}
		return bRet;
	}

	/**
	 * 计算一个16进制字符的10进制值 输入：0-F
	 */
	private int getChrInt(char chr) {
		int iRet = 0;
		if (chr == "0".charAt(0))
			iRet = 0;
		if (chr == "1".charAt(0))
			iRet = 1;
		if (chr == "2".charAt(0))
			iRet = 2;
		if (chr == "3".charAt(0))
			iRet = 3;
		if (chr == "4".charAt(0))
			iRet = 4;
		if (chr == "5".charAt(0))
			iRet = 5;
		if (chr == "6".charAt(0))
			iRet = 6;
		if (chr == "7".charAt(0))
			iRet = 7;
		if (chr == "8".charAt(0))
			iRet = 8;
		if (chr == "9".charAt(0))
			iRet = 9;
		if (chr == "A".charAt(0))
			iRet = 10;
		if (chr == "B".charAt(0))
			iRet = 11;
		if (chr == "C".charAt(0))
			iRet = 12;
		if (chr == "D".charAt(0))
			iRet = 13;
		if (chr == "E".charAt(0))
			iRet = 14;
		if (chr == "F".charAt(0))
			iRet = 15;
		return iRet;
	}
}

/**
 * 文件选择组件。
 */
class FilePanel extends JPanel {
	FilePanel(String str) {
		JLabel label = new JLabel(str);
		JTextField fileText = new JTextField(35);
		JButton chooseButton = new JButton("浏览...");
		this.add(label);
		this.add(fileText);
		this.add(chooseButton);
		clickAction ca = new clickAction(this);
		chooseButton.addActionListener(ca);

	}

	public String getFileName() {
		JTextField jtf = (JTextField) this.getComponent(1);
		return jtf.getText();
	}

	private class clickAction implements ActionListener {
		clickAction(Component c) {
			cmpt = c;
		}

		public void actionPerformed(ActionEvent event) {
			JFileChooser chooser = new JFileChooser();
			chooser.setCurrentDirectory(new File("."));
			int ret = chooser.showOpenDialog(cmpt);
			if (ret == JFileChooser.APPROVE_OPTION) {
				JPanel jp = (JPanel) cmpt;
				JTextField jtf = (JTextField) jp.getComponent(1);
				jtf.setText(chooser.getSelectedFile().getPath());
			}
		}

		private Component cmpt;
	}
}

/**
 * 密码生成组件。
 */
class KeyPanel extends JPanel {
	KeyPanel(String str) {
		JLabel label = new JLabel(str);
		JTextField fileText = new JTextField(35);
		JButton chooseButton = new JButton("随机产生");
		this.add(label);
		this.add(fileText);
		this.add(chooseButton);
		clickAction ca = new clickAction(this);
		chooseButton.addActionListener(ca);

	}

	// 返回生成的密码（48个字符长度）
	public String getKey() {
		JTextField jtf = (JTextField) this.getComponent(1);
		return jtf.getText();
	}

	private class clickAction implements ActionListener {
		clickAction(Component c) {
			cmpt = c;
		}

		public void actionPerformed(ActionEvent event) {
			try {
				KeyGenerator kg = KeyGenerator.getInstance("DES");
				kg.init(56);
				Key ke = kg.generateKey();
				byte[] bytK1 = ke.getEncoded();
				ke = kg.generateKey();
				byte[] bytK2 = ke.getEncoded();
				ke = kg.generateKey();
				byte[] bytK3 = ke.getEncoded();

				JPanel jp = (JPanel) cmpt;
				JTextField jtf = (JTextField) jp.getComponent(1);
				jtf.setText(getByteStr(bytK1) + getByteStr(bytK2)+ getByteStr(bytK3));
			} catch (Exception e) {
				e.printStackTrace();
			}
		}

		private String getByteStr(byte[] byt) {
			String strRet = "";
			for (int i = 0; i < byt.length; i++) {
				 System.out.println(byt[i]);
				strRet += getHexValue((byt[i] & 240) / 16);
				System.out.println(strRet);
				strRet += getHexValue(byt[i] & 15);
				System.out.println(strRet);
			}
			return strRet;
		}

		private String getHexValue(int s) {
			String sRet = null;
			switch (s) {
			case 0:
				sRet = "0";
				break;
			case 1:
				sRet = "1";
				break;
			case 2:
				sRet = "2";
				break;
			case 3:
				sRet = "3";
				break;
			case 4:
				sRet = "4";
				break;
			case 5:
				sRet = "5";
				break;
			case 6:
				sRet = "6";
				break;
			case 7:
				sRet = "7";
				break;
			case 8:
				sRet = "8";
				break;
			case 9:
				sRet = "9";
				break;
			case 10:
				sRet = "A";
				break;
			case 11:
				sRet = "B";
				break;
			case 12:
				sRet = "C";
				break;
			case 13:
				sRet = "D";
				break;
			case 14:
				sRet = "E";
				break;
			case 15:
				sRet = "F";
			}
			return sRet;
		}

		private Component cmpt;
	}
}

下边是一个小的数据加密例子，可以实现简单的文本加密：

package test11;

import java.lang.reflect.Method;

import javax.crypto.Cipher;
import javax.crypto.SecretKey;
import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.DESKeySpec;

public class TestMi {
	//单例模式
	private TestMi nn;
	public TestMi getTestMi(){
		if(nn == null){
			this.nn = new TestMi();
		}
		return nn;
	}
	
	public static void main(String[] args) throws Exception {
		String str = new TestMi().encryption("张三", "12345678", "encryptByDES");
		System.out.println(str);
		String str1 = new TestMi().encryption(str, "12345678", "decryptByDES");
		System.out.println(str1);
		
	}
	
	public String encryption(String str,String psw,String methodName) throws Exception{
		Method m = getTestMi().getClass().getMethod(methodName,new Class[]{String.class,String.class});
		String newStr = null;
		if(m != null){
			newStr =  (String) m.invoke(nn, str,psw);
		}
		return newStr;
	}
	/**
	 * 用DES方法加密输入的字节 bytKey需为8字节长，是加密的密码
	 */
	public String encryptByDES(String str1, String str2) throws Exception {
		byte[] bytP = str1.getBytes("UTF-8");
		byte[] bytKey = str2.getBytes("UTF-8");
		DESKeySpec desKS = new DESKeySpec(bytKey);
		SecretKeyFactory skf = SecretKeyFactory.getInstance("DES");
		SecretKey sk = skf.generateSecret(desKS);
		Cipher cip = Cipher.getInstance("DES");
		cip.init(Cipher.ENCRYPT_MODE, sk);
		return new String(cip.doFinal(bytP),"ISO-8859-1");
	}
	

	/**
	 * 用DES方法解密输入的字节 bytKey需为8字节长，是解密的密码
	 */
	public String decryptByDES(String str1, String str2) throws Exception {
		byte[] bytE = str1.getBytes("ISO-8859-1");
		byte[] bytKey = str2.getBytes("ISO-8859-1");
		DESKeySpec desKS = new DESKeySpec(bytKey);
		SecretKeyFactory skf = SecretKeyFactory.getInstance("DES");
		SecretKey sk = skf.generateSecret(desKS);
		Cipher cip = Cipher.getInstance("DES");
		cip.init(Cipher.DECRYPT_MODE, sk);
		return new String(cip.doFinal(bytE),"UTF-8");
	}
}