Understanding @NotNull, @NotBlank, @NotEmpty and the Difference Between @Valid and @Validated in Spring Boot

The article begins by showing how to add the Spring Boot web starter dependency:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <version>2.0.5.RELEASE</version>
</dependency>

The import statement for the validation constraints is also provided:

import javax.validation.constraints.*;

It then describes three common validation annotations:

@NotNull

Applicable to basic data types (Integer, Long, Double, etc.). When used on a String , the value must not be null but may be empty.

Note: Fields annotated with @NotNull can also be constrained with @Size, @Max, @Min, etc.

@NotBlank

Applicable only to String values; the string must be non‑null and, after trim() , have a length greater than zero.

@NotEmpty

Applicable to String , collections, maps, arrays, etc.; the value must be non‑null and have a size greater than zero.

Example entity demonstrating these annotations:

@Data
public class BigPeople {
    @ApiModelProperty(value = "id", required = true)
    @NotNull(message = "id不能为空")
    @Length(message = "id不能超过{max}个长度", max = 10)
    private Integer id;

    @ApiModelProperty(value = "name", required = true)
    @NotBlank(message = "name不能为空")
    @Size(message = "名字最长为{max} 个字", max = 10)
    private String name;

    @ApiModelProperty(value = "age", required = true)
    @NotNull(message = "age不能为空")
    @Range(message = "age的长度范围为{min}岁到{max}岁之间", min = 5, max = 10)
    private Integer age;

    @ApiModelProperty(value = "treeNode", required = true)
    @NotEmpty(message = "treeNode不能为空")
    private List<String> treeNode;
}

The import statements for the validation groups are:

import javax.validation.Valid;

import org.springframework.validation.annotation.Validated;

Two controller methods illustrate the use of @Valid and @Validated respectively:

@ApiOperation(value = "新增或者修改一个人的信息")
@PostMapping("/updateOrInsert")
public Result updateOrInsert(@Valid @RequestBody Person person) {
    Boolean updateOrInsert = personService.updateOrInsert(person);
    if (updateOrInsert) {
        return new Result(ResultCode.SUCCESS, updateOrInsert);
    }
    return new Result(ResultCode.ERROR, "新增或者修改一个人的信息失败");
}

@ApiOperation(value = "新增或者修改一个人的信息")
@PostMapping("/updateOrInsert")
public Result updateOrInsert(@Validated @RequestBody Person person) {
    Boolean updateOrInsert = personService.updateOrInsert(person);
    if (updateOrInsert) {
        return new Result(ResultCode.SUCCESS, updateOrInsert);
    }
    return new Result(ResultCode.ERROR, "新增或者修改一个人的信息失败");
}

Key differences highlighted:

Both @Valid and @Validated trigger validation of fields annotated with constraints such as @NotNull, @NotEmpty, etc.

When using @Valid , a BindingResult must be provided to capture validation errors; if not handled, execution continues.

When using @Validated , validation failures throw a 400 error automatically, stopping method execution; a global exception handler is needed to return custom messages.

Overall, @Validated offers a more concise approach, reducing boilerplate code.

The article concludes with a brief mention of other common validation annotations available in the same package.