举个例子：
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.security.*;
import javax.crypto.*;
import javax.crypto.spec.*;
import javax.swing.*;
/**
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;
FileEncrypter() {
this.setSize(WIDTH, HEIGHT);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.setResizable(false);
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)");
Container c = this.getContentPane();
c.setLayout(new FlowLayout());
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);
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);
}
}
});
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);
}
}
});
}
public static void main(String[] args) {
FileEncrypter fe = new FileEncrypter();
fe.show();
}
/**
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 {
private Component cmpt;
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());
}
}
}
}
/**
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 {
private Component cmpt;
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);
strRet += getHexValue(byt[i] & 15);
}
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;
}
}
}
