Java BeanUtils 类作用、语法与示例详解

// 添加依赖
// <dependency>
//     <groupId>commons-beanutils</groupId>
//     <artifactId>commons-beanutils</artifactId>
//     <version>1.9.4</version>
// </dependency>
import org.apache.commons.beanutils.BeanUtils;
public class CommonsExample {
    public static void main(String[] args) throws Exception {
        // 1. 创建源对象
        User source = new User("Alice", 25, new Address("New York"));
        // 2. 创建目标对象
        UserDTO target = new UserDTO();
        // 3. 属性拷贝（同名属性自动复制）
        BeanUtils.copyProperties(target, source);
        System.out.println(target); 
        // 输出: UserDTO{name='Alice', age=25, city='New York'}
        // 4. 动态获取属性
        String city = BeanUtils.getProperty(source, "address.city");
        System.out.println(city); // 输出: New York
        // 5. 动态设置属性
        BeanUtils.setProperty(target, "age", "30"); // 字符串自动转int
        // 6. 对象转Map
        Map<String, String> map = BeanUtils.describe(source);
        System.out.println(map); 
        // {name=Alice, age=25, address=Address[city=New York]}
        // 7. Map转对象
        Map<String, Object> data = new HashMap<>();
        data.put("name", "Bob");
        data.put("age", "35"); // 字符串自动转换
        data.put("address.city", "London"); // 嵌套属性
        User newUser = new User();
        BeanUtils.populate(newUser, data);
        System.out.println(newUser.getAddress().getCity()); // 输出: London
    }
}
// JavaBean 类
class User {
    private String name;
    private int age;
    private Address address;
    // 无参构造器、getter/setter 省略
}
class UserDTO {
    private String name;
    private int age;
    private String city; // 对应 address.city
    // 无参构造器、getter/setter 省略
}
class Address {
    private String city;
    // 构造器、getter/setter 省略
}

// 添加依赖
// <dependency>
//     <groupId>org.springframework</groupId>
//     <artifactId>spring-beans</artifactId>
//     <version>5.3.20</version>
// </dependency>
import org.springframework.beans.BeanUtils;
public class SpringExample {
    public static void main(String[] args) {
        User source = new User("Alice", 25, new Address("New York"));
        UserDTO target = new UserDTO();
        // 1. 基础属性复制
        BeanUtils.copyProperties(source, target);
        System.out.println(target.getCity()); // 输出: null (不自动处理嵌套)
        // 2. 带忽略属性的复制
        BeanUtils.copyProperties(source, target, "age"); // 忽略age属性
        System.out.println(target.getAge()); // 输出: 0 (默认值)
        // 3. 自定义属性处理器
        class CustomConverter implements Converter {
            public Object convert(Class type, Object value) {
                if(value instanceof User) {
                    return ((User) value).getAddress().getCity();
                }
                return null;
            }
        }
        // 4. 处理嵌套属性（需自定义）
        String city = (String) new CustomConverter().convert(String.class, source);
        target.setCity(city);
        System.out.println(target.getCity()); // 输出: New York
    }
}

// Apache 解决方案
BeanUtils.setProperty(target, "address.city", "Paris");
// Spring 解决方案（需自定义）
class AddressMapper {
    public static void map(User source, UserDTO target) {
        target.setCity(source.getAddress().getCity());
    }
}

// 注册自定义转换器
ConvertUtils.register(new Converter() {
    public Object convert(Class type, Object value) {
        return LocalDate.parse(value.toString());
    }
}, LocalDate.class);
// 现在可以处理字符串转LocalDate
BeanUtils.setProperty(target, "birthDate", "2023-01-01");

// Spring 方式
BeanUtils.copyProperties(source, target, "password", "sensitiveData");
// Apache 方式（需额外处理）
Map<String, String> map = BeanUtils.describe(source);
map.remove("password");
BeanUtils.populate(target, map);

// Controller层
public UserDTO getUser(Long id) {
    User user = userService.findById(id);
    UserDTO dto = new UserDTO();
    BeanUtils.copyProperties(user, dto);
    return dto;
}

// 接收表单提交
public String createUser(@ModelAttribute UserForm form) {
    User user = new User();
    BeanUtils.copyProperties(form, user);
    userService.save(user);
    return "redirect:/users";
}

// 从配置文件中读取设置
@Value("${app.settings}")
private Map<String, String> settings;
public void applySettings() {
    AppConfig config = new AppConfig();
    BeanUtils.populate(config, settings);
}

public User mergeUserChanges(User original, User changes) {
    User merged = new User();
    BeanUtils.copyProperties(original, merged); // 复制原始数据
    BeanUtils.copyProperties(changes, merged);  // 覆盖变更数据
    return merged;
}