# 一、JsonView
  JsonView 是 Jackson 提供的注解，用于控制对象序列化/反序列化时包含哪些字段。可以实现： 
- 不同接口返回不同字段
- 敏感字段过滤
- 前后端数据分离

## 1.1 添加依赖
```xml
<dependencies>
    <!-- Spring Boot Web -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
</dependencies>
```

## 1.2 使用
1. 定义视图接口
```java
// JsonView 视图定义
public class Views {
    // 基础视图 - 所有接口都包含的字段
    public interface Basic {}
    
    // 返回给前端时使用
    public interface Response extends Basic {}
    
    // 接收前端数据时使用
    public interface Request extends Basic {}
    
    // 管理视图 - 包含所有字段
    public interface AdminView extends ReadView {}
}
```

2. Dto对象使用JsonView
```java
@Data
public class UserDTO {
    @JsonView(Views.Response.class)
    private Long id;
    
    @JsonView(Views.Request.class)
    @NotBlank(message = "密码不能为空")
    @Size(min = 6, message = "密码至少6位")
    private String password;
    
    @JsonView(Views.Basic.class)
    @NotBlank(message = "用户名不能为空")
    private String username;
    
    @JsonView(Views.Basic.class)
    @Email(message = "邮箱格式不正确")
    private String email;
    
    @JsonView(Views.Basic.class)
    private String nickname;

    @JsonView(AdminView.class)
    private Boolean isActive;
}
```

3. Controller中使用
```java
@RestController
@RequestMapping("/api/users")
public class UserController {
    
    @Autowired
    private UserService userService;
    
    @PostMapping
    @JsonView(UserDTO.Response.class)
    public UserDTO createUser(@RequestBody @JsonView(UserDTO.Request.class) UserDTO userDTO) {
        return userService.createUser(userDTO);
    }
    
    @PutMapping("/{id}")
    @JsonView(UserDTO.Response.class)
    public UserDTO updateUser(@PathVariable Long id,
                              @RequestBody @JsonView(UserDTO.Request.class) UserDTO userDTO) {
        return userService.updateUser(id, userDTO);
    }
    
    @GetMapping("/{id}")
    @JsonView(UserDTO.Response.class)
    public UserDTO getUser(@PathVariable Long id) {
        return userService.getUserById(id);
    }
    
    @GetMapping("/{id}/admin")
    @JsonView(UserDTO.AdminView.class)
    public UserDTO getAdminUser(@PathVariable Long id) {
        return userService.getAdminUserById(id);
    }
}
```

# 二、MapStruct
&emsp;&emsp;MapStruct 是一个 Java 注解处理器，用于生成类型安全的 Bean 映射代码：
- 编译时生成映射代码，无运行时性能损失
- 类型安全
- 支持复杂映射

## 2.1 添加依赖
```xml
<properties>
    <org.mapstruct.version>1.5.5.Final</org.mapstruct.version>
</properties>

<dependencies>
    <dependency>
        <groupId>org.mapstruct</groupId>
        <artifactId>mapstruct</artifactId>
        <version>${org.mapstruct.version}</version>
    </dependency>
</dependencies>

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.11.0</version>
            <configuration>
                <annotationProcessorPaths>
                    <path>
                        <groupId>org.mapstruct</groupId>
                        <artifactId>mapstruct-processor</artifactId>
                        <version>${org.mapstruct.version}</version>
                    </path>
                </annotationProcessorPaths>
            </configuration>
        </plugin>
    </plugins>
</build>
```

## 2.2 使用
```java
import org.mapstruct.*;

import java.util.List;
import java.time.format.DateTimeFormatter;

@Mapper
public interface UserMapper {
    
    @Mapping(target = "name", source = "userName")        // 字段名不同
    @Mapping(target = "phoneNumber", source = "phone")    // 字段名不同
    @Mapping(target = "description", source = "remark")   // 字段名不同
    @Mapping(target = "statusDesc", ignore = true)        // 需要特殊处理
    @Mapping(target = "createTime", ignore = true)        // 需要格式化
    UserDTO toDTO(User user);
    
    @Mapping(target = "userName", source = "name")
    @Mapping(target = "phone", source = "phoneNumber")
    @Mapping(target = "remark", source = "description")
    @Mapping(target = "password", ignore = true)          // 密码不映射
    User toEntity(UserDTO dto);
    
    // 列表映射
    List<UserDTO> toDTOList(List<User> users);
    
    // 带默认值的映射
    @Mapping(target = "name", source = "userName")
    @Mapping(target = "phoneNumber", source = "phone")
    @Mapping(target = "description", source = "remark", defaultValue = "暂无描述")
    @Mapping(target = "statusDesc", expression = "java(convertStatus(user.getStatus()))")
    @Mapping(target = "createTime", expression = "java(formatTime(user.getCreateTime()))")
    UserDTO toDTOWithDefault(User user);
    
    // 自定义转换方法
    default String convertStatus(Integer status) {
        if (status == null) return "未知";
        switch (status) {
            case 0: return "禁用";
            case 1: return "正常";
            case 2: return "锁定";
            default: return "未知";
        }
    }
    
    // 时间格式化方法
    default String formatTime(LocalDateTime time) {
        if (time == null) return "";
        return time.format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));
    }
}
```

&emsp;&emsp;需要执行`mvn compile`后检查`target/generated-sources`文件夹下是否存在生成的转换代码。