用Java语言，在一个文件选择器上可以自由选择RSA或者AES或者DES加解密，并将密钥和加解密文件保存在本地

你可以使用Java语言来实现一个文件选择器，然后结合RSA、AES和DES算法来进行加解密操作，并将密钥和加解密文件保存在本地。下面是一个简单的示例代码：

import javax.crypto.*;
import javax.crypto.spec.DESKeySpec;
import javax.crypto.spec.SecretKeySpec;
import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.*;
import java.security.*;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;

public class FileEncryptorApp extends JFrame {
    private JButton encryptButton;
    private JButton decryptButton;
    private JTextArea logArea;

    public FileEncryptorApp() {
        setTitle("File Encryptor");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        encryptButton = new JButton("Encrypt");
        encryptButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                JFileChooser fileChooser = new JFileChooser();
                int result = fileChooser.showOpenDialog(FileEncryptorApp.this);
                if (result == JFileChooser.APPROVE_OPTION) {
                    File fileToEncrypt = fileChooser.getSelectedFile();
                    String algorithm = chooseAlgorithm();
                    String key = generateKey(algorithm);
                    try {
                        encryptFile(fileToEncrypt, algorithm, key);
                        log("File encrypted successfully.");
                    } catch (Exception ex) {
                        log("Failed to encrypt file: " + ex.getMessage());
                    }
                }
            }
        });

        decryptButton = new JButton("Decrypt");
        decryptButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                JFileChooser fileChooser = new JFileChooser();
                int result = fileChooser.showOpenDialog(FileEncryptorApp.this);
                if (result == JFileChooser.APPROVE_OPTION) {
                    File fileToDecrypt = fileChooser.getSelectedFile();
                    String algorithm = chooseAlgorithm();
                    String key = readKeyFromFile();
                    try {
                        decryptFile(fileToDecrypt, algorithm, key);
                        log("File decrypted successfully.");
                    } catch (Exception ex) {
                        log("Failed to decrypt file: " + ex.getMessage());
                    }
                }
            }
        });

        logArea = new JTextArea();
        logArea.setEditable(false);
        JScrollPane scrollPane = new JScrollPane(logArea);

        setLayout(new BorderLayout());
        add(encryptButton, BorderLayout.NORTH);
        add(decryptButton, BorderLayout.SOUTH);
        add(scrollPane, BorderLayout.CENTER);
        pack();
    }

    private String chooseAlgorithm() {
        String[] options = {"RSA", "AES", "DES"};
        return (String) JOptionPane.showInputDialog(null, "Choose encryption algorithm:", "Algorithm",
                JOptionPane.PLAIN_MESSAGE, null, options, options[0]);
    }

    private String generateKey(String algorithm) throws NoSuchAlgorithmException {
        KeyGenerator keyGenerator;
        if (algorithm.equals("RSA")) {
            keyGenerator = KeyGenerator.getInstance("RSA");
        } else if (algorithm.equals("AES")) {
            keyGenerator = KeyGenerator.getInstance("AES");
        } else if (algorithm.equals("DES")) {
            keyGenerator = KeyGenerator.getInstance("DES");
        } else {
            throw new IllegalArgumentException("Invalid algorithm: " + algorithm);
        }
        keyGenerator.init(128); // Change the key size as needed
        SecretKey secretKey = keyGenerator.generateKey();
        return Base64.getEncoder().encodeToString(secretKey.getEncoded());
    }

    private void encryptFile(File file, String algorithm, String key) throws Exception {
        Cipher cipher = Cipher.getInstance(algorithm);
        SecretKey secretKey = new SecretKeySpec(Base64.getDecoder().decode(key), algorithm);
        cipher.init(Cipher.ENCRYPT_MODE, secretKey);
        byte[] fileBytes = readFileBytes(file);
        byte[] encryptedBytes = cipher.doFinal(fileBytes);
        FileOutputStream outputStream = new FileOutputStream(file);
        outputStream.write(encryptedBytes);
        outputStream.close();
    }

    private void decryptFile(File file, String algorithm, String key) throws Exception {
        Cipher cipher = Cipher.getInstance(algorithm);
        SecretKey secretKey = new SecretKeySpec(Base64.getDecoder().decode(key), algorithm);
        cipher.init(Cipher.DECRYPT_MODE, secretKey);
        byte[] fileBytes = readFileBytes(file);
        byte[] decryptedBytes = cipher.doFinal(fileBytes);
        FileOutputStream outputStream = new FileOutputStream(file);
        outputStream.write(decryptedBytes);
        outputStream.close();
    }

    private byte[] readFileBytes(File file) throws IOException {
        byte[] fileBytes = new byte[(int) file.length()];
        FileInputStream inputStream = new FileInputStream(file);
        inputStream.read(fileBytes);
        inputStream.close();
        return fileBytes;
    }

    private String readKeyFromFile() {
        // Implement your own logic to read the key from a file
        // and return it as a String
        return null;
    }

    private void log(String message) {
        logArea.append(message + "\n");
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new FileEncryptorApp().setVisible(true);
            }
        });
    }
}

在上述代码中，我们创建了一个简单的GUI应用程序，其中包含了加密和解密按钮，并使用JFileChooser来选择要加密或解密的文件。在加密和解密方法中，我们根据选定的算法和生成的密钥初始化Cipher对象，并使用密钥对文件进行加密或解密操作。你需要实现`readKeyFromFile()`方法来读取密钥文件的逻辑。

请注意，这只是一个简单的示例，你可能需要根据实际需求进行修改和完善。此外，为了实现RSA加密和解密，你还需要生成密钥对并将其保存在本地。我希望这个示例对你有所帮助！