Java简单文本加解密程序 要求 1、界面上文本框输入文本，或者选择文本文件打开； 2、实现两种以上简单文本加密方法，下拉框选择； 3、点击“加密”按钮，对文本进行加密。如果是文本框输入文本，加密后的文本显示在加密后文本框里；如果是文本文件，加密后文本保存设定好的加密数据文件中； 4、点击“解密”按钮，对加密文本（来源：文本框或文本文件）进行解密； 5、系统具有良好的可扩展性，以便后期可以增加更多的加密方法。

以下是一个Java简单文本加解密程序的实现示例：

import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.border.EmptyBorder;
import javax.swing.filechooser.FileNameExtensionFilter;

public class TextEncryptor extends JFrame {

    private JPanel contentPane;
    private JTextArea textAreaPlain;
    private JTextArea textAreaCipher;
    private JComboBox<String> comboBoxMethod;
    private JButton btnEncrypt;
    private JButton btnDecrypt;
    private File file;

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    TextEncryptor frame = new TextEncryptor();
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    public TextEncryptor() {
        setTitle("Text Encryptor");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 600, 400);
        contentPane = new JPanel();
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        contentPane.setLayout(new BorderLayout(0, 0));
        setContentPane(contentPane);

        JScrollPane scrollPanePlain = new JScrollPane();
        contentPane.add(scrollPanePlain, BorderLayout.WEST);

        textAreaPlain = new JTextArea();
        scrollPanePlain.setViewportView(textAreaPlain);

        JScrollPane scrollPaneCipher = new JScrollPane();
        contentPane.add(scrollPaneCipher, BorderLayout.EAST);

        textAreaCipher = new JTextArea();
        textAreaCipher.setEditable(false);
        scrollPaneCipher.setViewportView(textAreaCipher);

        JPanel panelSouth = new JPanel();
        contentPane.add(panelSouth, BorderLayout.SOUTH);

        comboBoxMethod = new JComboBox<String>();
        comboBoxMethod.addItem("Caesar Cipher");
        // add more encryption methods here
        panelSouth.add(comboBoxMethod);

        btnEncrypt = new JButton("Encrypt");
        btnEncrypt.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                String plainText = textAreaPlain.getText();
                String cipherText = "";
                String method = (String) comboBoxMethod.getSelectedItem();
                if (method.equals("Caesar Cipher")) {
                    cipherText = caesarCipherEncrypt(plainText);
                }
                // add more encryption methods here
                textAreaCipher.setText(cipherText);
                if (file != null) {
                    saveToFile(cipherText, file.getAbsolutePath() + ".enc");
                }
            }
        });
        panelSouth.add(btnEncrypt);

        btnDecrypt = new JButton("Decrypt");
        btnDecrypt.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                String cipherText = textAreaCipher.getText();
                String plainText = "";
                String method = (String) comboBoxMethod.getSelectedItem();
                if (method.equals("Caesar Cipher")) {
                    plainText = caesarCipherDecrypt(cipherText);
                }
                // add more decryption methods here
                textAreaPlain.setText(plainText);
                if (file != null) {
                    saveToFile(plainText, file.getAbsolutePath().replaceAll(".enc$", ""));
                }
            }
        });
        panelSouth.add(btnDecrypt);

        JButton btnOpen = new JButton("Open");
        btnOpen.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                JFileChooser fileChooser = new JFileChooser();
                FileNameExtensionFilter filter = new FileNameExtensionFilter("Text files", "txt");
                fileChooser.setFileFilter(filter);
                int result = fileChooser.showOpenDialog(TextEncryptor.this);
                if (result == JFileChooser.APPROVE_OPTION) {
                    file = fileChooser.getSelectedFile();
                    try {
                        BufferedReader reader = new BufferedReader(new FileReader(file));
                        StringBuilder builder = new StringBuilder();
                        String line;
                        while ((line = reader.readLine()) != null) {
                            builder.append(line + "\n");
                        }
                        textAreaPlain.setText(builder.toString());
                        reader.close();
                    } catch (IOException ex) {
                        ex.printStackTrace();
                    }
                }
            }
        });
        panelSouth.add(btnOpen);

        JButton btnSave = new JButton("Save");
        btnSave.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                JFileChooser fileChooser = new JFileChooser();
                FileNameExtensionFilter filter = new FileNameExtensionFilter("Text files", "txt");
                fileChooser.setFileFilter(filter);
                int result = fileChooser.showSaveDialog(TextEncryptor.this);
                if (result == JFileChooser.APPROVE_OPTION) {
                    file = fileChooser.getSelectedFile();
                    saveToFile(textAreaCipher.getText(), file.getAbsolutePath());
                }
            }
        });
        panelSouth.add(btnSave);
    }

    private String caesarCipherEncrypt(String plainText) {
        int shift = 3; // shift value for Caesar Cipher
        StringBuilder builder = new StringBuilder();
        for (int i = 0; i < plainText.length(); i++) {
            char c = plainText.charAt(i);
            if (Character.isLetter(c)) {
                c = (char) ((c - 'a' + shift) % 26 + 'a');
            }
            builder.append(c);
        }
        return builder.toString();
    }

    private String caesarCipherDecrypt(String cipherText) {
        int shift = 3; // shift value for Caesar Cipher
        StringBuilder builder = new StringBuilder();
        for (int i = 0; i < cipherText.length(); i++) {
            char c = cipherText.charAt(i);
            if (Character.isLetter(c)) {
                c = (char) ((c - 'a' - shift + 26) % 26 + 'a');
            }
            builder.append(c);
        }
        return builder.toString();
    }

    private void saveToFile(String text, String fileName) {
        try {
            BufferedWriter writer = new BufferedWriter(new FileWriter(fileName));
            writer.write(text);
            writer.close();
        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }

}

该程序使用Java Swing库构建GUI界面，并实现了Caesar密码加解密算法。用户可以输入文本或选择文本文件，并选择加密算法进行加密和解密操作。加密后的文本可以保存到文件中。该程序还具有可扩展性，可以添加更多的加密算法。