方式一：使用javax.validation和spring validation

javax.validation提供的常用注解
@NotNull: 不为NULL
@NotEmpty: 不为NULL，且不为空
@NotBlank : 不为NULL，且不为空（包括去除首尾空格）
@Max: 必须为数值，且小于等于给定值
@Min: 必须为数值，且大于等于给定值
@Email: 必须为邮箱格式
...

GET请求入参

1. 在对应的参数字段上使用对应的注解（注意：如果是自定义对象接参，则需要在接参对象上使用@Valid或@Validate）

   @Data
   public class StudentPageDTO{
   	@NotNull(message="parameter can not be null --- page")
   	@Min(value=1, message="page must be over 0")
   	private Integer page;
   	
   	@NotNull(message="parameter can not be null --- page")
   	@Min(value=1, message="pageSize must be over 0")
   	private Integer pageSize;
   	
   	private String name;
   	
   	private Integer age;	
   }
   

2. 在controller类上使用@Validated注解

   @Validated
   @RestController
   @RequestMapping("/user")
   public class UserController{
   	/**
   	 * 基本类型
   	 */
   	@GetMapping("/id")
   	public Result getById(@NotNull(message="parameter can not be null:id") Integer id){
   		//to do...
   	}
   	
   	/**
   	 * 自定义类型
   	 */
   	@GetMapping("/page-list")
   	public Result getPageList(StudentPageDTO dto){
   		//to do...
   	}
   }
   

POST请求入参

1. 参数的字段使用对应的注解

   @Data
   public class User{
   	private Long id;
   	
       @NotBlank(message = "parameter can not be null or empty:name")
       private String name;
   
       @NotNull(message = "parameter can not be null:age")
       @Min(value = 18,message = "age must be over 17")
       @Max(value = 60,message = "age can not be over 60")
       private Integer age;
   
       @NotBlank(message = "parameter can not be null or empty:email")
       @Email(message = "incorrect email format")
       private String email;
   }
   

2. 参数使用@Valid或@Validate

   @RestController
   @RequestMapping("/user")
   public class StudentController{
   	@PostMapping("/add")
   	public Result list(@Valid @RequestBody User user){
   		//to do...
   	}
   }
   

3. 对于同一个DTO，但不同请求需要不同校验情况的，则必须使用@Validate的分组功能，且分组依据必须是interface类型；

   @Data
   public class User{
   	/**
   	 * 使用分组功能
   	 */
   	@NotNull(group=({UserEdit.class}), message="parameter can not be null:id")
   	private Long id;
   	
   	@NotBlank(message = "parameter can not be null or empty:name")
       private String name;
   
       @NotNull(message = "parameter can not be null:age")
       @Min(value = 18,message = "age must be over 17")
       @Max(value = 60,message = "age can not be over 60")
       private Integer age;
   
       @NotBlank(message = "parameter can not be null or empty:email")
       @Email(message = "incorrect email format")
       private String email;
   	
   	@NotEmpty(message="parameter can not be null or empty:hobby")
   	private List<@NotBlank(message="parameter can not be null or empty:hobby.str") String> hobby;
   }
   

   /**
    * validated分组接口
    */
   public interface UserEdit{}
   

   @RestController
   @RequestMapping("/user")
   public class UserController{
   
   	/**
   	 * 不会校验id
   	 */
   	@PostMapping("add")
   	public Result<Object> add(@Validated @RequestBody User user){
   		//to do...
   	}
   	
   	/**
   	 * 只校验id
   	 */
   	@PostMapping("edit")
   	public Result<Object> add(@Validated({UserEdit.class}) @RequestBody User user){
   		//to do...
   	}
   }
   

4. 对于自定义参数中还有自定义参数的字段校验，必须在上一层的参数使用@Valid

   @Data
   public class User{
   	private Long id;
   	
   	private String name;
   
   	@Valid
   	@NotNull(message="parameter can not be null:department")
   	private Department department;
   }
   

   @Data
   public class Department{
   	@NotNull(message="parameter can not be null:department.id")
   	private Long id;
   	
   	@NotBlank(message="parameter can not be null or empty:department.name")
   	private String name;
   }
   

   @RestController
   @RequestMapping("/user")
   public class UserController{
   	@PostMapping("/add-department")
   	public Result<Object> addDepartment(@Valid @RequestBody User user){
   		//to do...
   	}
   }
   

方式二：使用Spring Assert

通过import org.springframework.util.Assert实现

Assert.notNull(): 不为NULL
Assert.hasLength(): 不为空字符串
Assert.notEmpty(): 不为空
...

@RestController
@RequestMapping("/user")
public class UserController{
	@GetMapping("/id")
	public Result getById(Integer id){
		Assert.notNull(student.getAge,"parameter can not be null:id");
		//to do...
	}
	
	@PostMapping("/add")
	public Result add(@RequestBody User user){
		Assert.hasLength(user.getName(),"parameter can not be null or empty:name");
		Assert.notNull(user.getAge(),"parameter can not be null:age");
		Assert.notEmpty(user.getHobby(),"parameter can not be null:hobby");
		for(String hobby:user.getHobby()){
			Assert.hasLength(hobby,"parameter can not be null:hobby.str");
		}
	}
}

方式三：使用自定义注解

1. 自定义注解

   @Documented
   @Target({ElementType.METHOD,ElementType.FIELD,ElementType.ANNOTATION_TYPE,ElmentType.CONSTRUCTOR,ElementType.PARAMETER,ElementType.TYPE_USE})
   @Retention(RetentionPolicy.RUNTIME)
   @Constraint(validateBy=ListNotEmptyImpl.class)
   public @interface ListNotEmpty{
   	String message() default "list can not be null or empty!";
   	Class<?>[] groups() default{};
   	Class<? extends Payload>[] payload() default{};
   	
   	@Target({ElementType.METHOD,ElementType.FIELD,ElementType.ANNOATION_TYPE,ElementType.CONSTRUCTOR,ElementType.PARAMETER,ElementType.TYPE_USE})
   	@Retention(RetentionPolicy.RUNTIME)
   	@Documented
   	public @interface List{
   		ListNotEmpty[] value();
   	}
   }
   

2. 注解实现类

   public class ListNotEmptyImpl implements ConstraintValidator<ListNotEmpty,List<?>>{
   	@Override
   	public boolean isValid(List list, ConstraintValidatorContext constraintValidatorContext){
   		boolean flag=false;
   		if(list != null){
   			for(Object obj:list){
   				if(obj == null){
   					flag=true;
   					break;
   				}
   			}
   			return !flag;
   		}
   		return false;
   	}
   }
   

3. 自定义类

   @Data
   public class Student implements Serializable{
   	@ListNotEmpty(message="subject can not be null or empty!")
   	private List<String> subjects;
   }
   

4. 控制类

   @RestController
   @RequestMapping("/student")
   public class StudentController{
   	@PostMapping("/customize")
   	public Result<?> customize(@RequstBody @Vaild Student student){
   		//to do
   	}
   }