SpringBoot利用@Validated注解优雅实现参数校验

// 实体类  
public class UserDTO {  
    @NotBlank(message = "用户名不能为空")  
    @Size(min = 3, max = 20, message = "长度需 3-20 位")  
    private String username;  
    
    @Email(message = "邮箱格式错误")  
    private String email;  
}  

// 控制器  
@RestController  
public class UserController {  
    @PostMapping("/register")  
    public String register(@Validated @RequestBody UserDTO user) {  
        return "注册成功！";  // 校验通过后执行  
    }  
}  

public interface ValidationGroups {  
    interface Insert extends Default {}  // 新增分组  
    interface Update extends Default {}  // 更新分组  
}  

public class Project {  
    @NotBlank(groups = Update.class, message = "ID 不能为空")  
    private String id;  
    
    @Min(value = 1000, groups = Insert.class, message = "预算不能低于 1000")  
    private int budget;  
}  

​​​​​​​// 控制器  
@RestController  
public class ProjectController {  
    @PostMapping("/add")  
    public String addProject(  
        @Validated(Insert.class) @RequestBody Project project) {  
        return "新增成功！";  
    }  
    
    @PostMapping("/modify")  
    public String modifyProject(  
        @Validated(Update.class) @RequestBody Project project) {  
        return "修改成功！";  
    }  
}  

public class User {  
    @NotBlank  
    private String name;  
    
    @Valid  
    private Address address;  // 嵌套对象需加 @Valid  
}  

public class Address {  
    @NotBlank  
    private String city;  
}  

​​​​​​​// 控制器  
@PostMapping("/user")  
public String user(@Validated @RequestBody User user) {  
    return "校验通过！";  
}  

// 自定义注解  
@Target({ElementType.FIELD})  
@Retention(RetentionPolicy.RUNTIME)  
@Constraint(validatedBy = UniqueUsernameValidator.class)  
public @interface UniqueUsername {  
    String message() default "用户名已存在";  
}  

​​​​​​​// 校验器  
public class UniqueUsernameValidator implements ConstraintValidator<UniqueUsername, String> {  
    @Override  
    public boolean isValid(String username, ConstraintValidatorContext context) {  
        // 调用数据库或缓存验证唯一性  
        return !"admin".equals(username);  // 示例逻辑  
    }  
}  

public class UserDTO {  
    @UniqueUsername  
    private String username;  
}  

@RestControllerAdvice  
public class GlobalExceptionHandler {  
    @ExceptionHandler(MethodArgumentNotValidException.class)  
    public Map<String, String> handleValidationExceptions(  
        MethodArgumentNotValidException ex) {  
        Map<String, String> errors = new HashMap<>();  
        ex.getBindingResult().getAllErrors().forEach((error) -> {  
            String fieldName = ((FieldError) error).getField();  
            String errorMessage = error.getDefaultMessage();  
            errors.put(fieldName, errorMessage);  
        });  
        return errors;  
    }  
}  

<dependency>  
    <groupId>org.springframework.boot</groupId>  
    <artifactId>spring-boot-starter-validation</artifactId>  
</dependency>