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

The article begins by showing how to add the Spring Boot starter web dependency in <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> <version>2.0.5.RELEASE</version> </dependency> and notes that the validation annotations reside in import javax.validation.constraints.*; .

It then distinguishes three common constraint annotations:

@NotNull – applicable to primitive wrapper types and also to String ; the field cannot be null but may be empty.

@NotBlank – only for String ; the value must be non‑null and, after trim() , have a length greater than zero.

@NotEmpty – works on String , collections, maps, arrays, etc.; the value cannot be null nor have a size of zero.

Example entity code demonstrates these annotations together with Swagger annotations and length checks:

@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 article also shows where to import the validation trigger annotations:

import javax.validation.Valid;

import org.springframework.validation.annotation.Validated;

Two controller method examples illustrate the difference between using @Valid and @Validated on a request body:

@ApiOperation(value = "新增或者修改一个人的信息")
@PostMapping("/updateOrInsert")
public Result updateOrInsert(@Valid @RequestBody Person person) { ... }

@ApiOperation(value = "新增或者修改一个人的信息")
@PostMapping("/updateOrInsert")
public Result updateOrInsert(@Validated @RequestBody Person person) { ... }

Key points of comparison:

Both annotations activate the constraint annotations on fields.

@Valid requires a BindingResult to capture validation errors; if not handled, execution continues.

@Validated throws a 400 error automatically on failure, stopping method execution; a global exception handler is needed to return custom messages.

Overall, @Validated leads to cleaner controller code.

Finally, the article mentions that the same package contains many other useful validation annotations, encouraging readers to explore them for robust backend data checks.