对接JPA的代码生成器，可自定义类名

public class CodeGenerator {

    private static final String TEMPLATE_PATH = "src/main/resources/templates";
    private static final String JAVA_PATH = "src/main/java";
    private static final String PACKAGE_PATH = "/com/example/demo/";

    private static final String ENTITY_TEMPLATE = "entity.java.vm";
    private static final String MAPPER_TEMPLATE = "mapper.java.vm";
    private static final String SERVICE_TEMPLATE = "service.java.vm";
    private static final String CONTROLLER_TEMPLATE = "controller.java.vm";

    // 是否覆盖已有文件
    private static final boolean FILE_OVERRIDE = true;

    // 数据库配置
    private static final String DB_URL = "jdbc:mysql://localhost:3306/mydb?useUnicode=true&characterEncoding=utf-8&useSSL=false";
    private static final String DB_USERNAME = "root";
    private static final String DB_PASSWORD = "root";

    // 包名
    private static final String PACKAGE_NAME = "com.example.demo";

    public static void main(String[] args) {
        generate("my_table", "MyTable");
    }

    public static void generate(String tableName, String className) {
        VelocityEngine velocityEngine = new VelocityEngine();
        Properties properties = new Properties();
        properties.setProperty(Velocity.INPUT_ENCODING, "UTF-8");
        properties.setProperty(Velocity.OUTPUT_ENCODING, "UTF-8");
        properties.setProperty(Velocity.FILE_RESOURCE_LOADER_PATH, TEMPLATE_PATH);
        velocityEngine.init(properties);

        JdbcTemplate jdbcTemplate = new JdbcTemplate();
        jdbcTemplate.setDataSource(dataSource());

        // 获取表元数据
        TableMetaData tableMetaData = getTableMetaData(jdbcTemplate, tableName);

        // 生成Entity类
        generateEntity(velocityEngine, tableMetaData, className);

        // 生成Mapper接口
        generateMapper(velocityEngine, tableMetaData, className);

        // 生成Service接口
        generateService(velocityEngine, tableMetaData, className);

        // 生成Controller类
        generateController(velocityEngine, tableMetaData, className);
    }

    private static void generateEntity(VelocityEngine velocityEngine, TableMetaData tableMetaData, String className) {
        String targetPath = JAVA_PATH + PACKAGE_PATH + "entity/" + className + ".java";
        if (!FILE_OVERRIDE && new File(targetPath).exists()) {
            System.out.println(targetPath + " already exists! Skip generating entity.");
            return;
        }

        Map model = new HashMap<>();
        model.put("package", PACKAGE_NAME);
        model.put("className", className);
        model.put("tableMetaData", tableMetaData);

        Template template = velocityEngine.getTemplate(ENTITY_TEMPLATE, "UTF-8");
        String content = mergeTemplate(model, template);
        writeToFile(targetPath, content);
    }

    private static void generateMapper(VelocityEngine velocityEngine, TableMetaData tableMetaData, String className) {
        String targetPath = JAVA_PATH + PACKAGE_PATH + "mapper/" + className + "Mapper.java";
        if (!FILE_OVERRIDE && new File(targetPath).exists()) {
            System.out.println(targetPath + " already exists! Skip generating mapper.");
            return;
        }

        Map model = new HashMap<>();
        model.put("package", PACKAGE_NAME);
        model.put("className", className);
        model.put("tableMetaData", tableMetaData);

        Template template = velocityEngine.getTemplate(MAPPER_TEMPLATE, "UTF-8");
        String content = mergeTemplate(model, template);
        writeToFile(targetPath, content);
    }

    private static void generateService(VelocityEngine velocityEngine, TableMetaData tableMetaData, String className) {
        String targetPath = JAVA_PATH + PACKAGE_PATH + "service/" + className + "Service.java";
        if (!FILE_OVERRIDE && new File(targetPath).exists()) {
            System.out.println(targetPath + " already exists! Skip generating service.");
            return;
        }

        Map model = new HashMap<>();
        model.put("package", PACKAGE_NAME);
        model.put("className", className);
        model.put("tableMetaData", tableMetaData);

        Template template = velocityEngine.getTemplate(SERVICE_TEMPLATE, "UTF-8");
        String content = mergeTemplate(model, template);
        writeToFile(targetPath, content);
    }

    private static void generateController(VelocityEngine velocityEngine, TableMetaData tableMetaData, String className) {
        String targetPath = JAVA_PATH + PACKAGE_PATH + "controller/" + className + "Controller.java";
        if (!FILE_OVERRIDE && new File(targetPath).exists()) {
            System.out.println(targetPath + " already exists! Skip generating controller.");
            return;
        }

        Map model = new HashMap<>();
        model.put("package", PACKAGE_NAME);
        model.put("className", className);
        model.put("tableMetaData", tableMetaData);

        Template template = velocityEngine.getTemplate(CONTROLLER_TEMPLATE, "UTF-8");
        String content = mergeTemplate(model, template);
        writeToFile(targetPath, content);
    }

    private static TableMetaData getTableMetaData(JdbcTemplate jdbcTemplate, String tableName) {
        String sql = "SELECT COLUMN_NAME, DATA_TYPE, COLUMN_COMMENT FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = ?";
        List> result = jdbcTemplate.queryForList(sql, tableName);

        List columns = result.stream().map(row -> new ColumnMetaData(
                (String) row.get("COLUMN_NAME"), (String) row.get("DATA_TYPE"), (String) row.get("COLUMN_COMMENT")))
                .collect(Collectors.toList());

        return new TableMetaData(tableName, columns);
    }

    private static DataSource dataSource() {
        HikariDataSource dataSource = new HikariDataSource();
        dataSource.setDriverClassName("com.mysql.cj.jdbc.Driver");
        dataSource.setJdbcUrl(DB_URL);
        dataSource.setUsername(DB_USERNAME);
        dataSource.setPassword(DB_PASSWORD);
        return dataSource;
    }

    private static String mergeTemplate(Map model, Template template) {
        StringWriter writer = new StringWriter();
        template.merge(new VelocityContext(model), writer);
        return writer.toString();
    }

    private static void writeToFile(String filePath, String content) {
        try (OutputStream outputStream = new FileOutputStream(new File(filePath))) {
            outputStream.write(content.getBytes());
            System.out.println("Generated file: " + filePath);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

}