Master Elegant Request Parameter Validation in Spring Boot with JSR‑303

Request parameter validation is a common pitfall for beginners; relying only on front‑end checks leaves security holes, and using tangled if/else logic makes maintenance hard.

Therefore server‑side validation is essential and should be elegant, readable, and maintainable.

JSR‑303

JSR‑303 is the Bean Validation specification; Hibernate Validator is its reference implementation and provides built‑in constraints.

Built‑in constraints

Hibernate Validator additional constraints

Using these annotations you can define validation rules for request parameters.

Hands‑on practice

Prepare a Spring Boot 2.x project (or use the example repository).

Step 1 – Add @NotNull

@Data
@ApiModel(description="User entity")
public class User {
    @ApiModelProperty("User ID")
    private Long id;

    @NotNull
    @ApiModelProperty("User name")
    private String name;

    @NotNull
    @ApiModelProperty("User age")
    private Integer age;
}

Step 2 – Add @Valid on controller method

@PostMapping("/")
@ApiOperation(value="Create user", notes="Create user from User object")
public String postUser(@Valid @RequestBody User user) {
    users.put(user.getId(), user);
    return "success";
}

When you POST an empty JSON to localhost:8080/users/ you receive a 400 response with a structured error payload containing timestamp, status, error, and an errors array with field, rejectedValue, defaultMessage, etc.

More complex validation

@Data
@ApiModel(description="User entity")
public class User {
    @ApiModelProperty("User ID")
    private Long id;

    @NotNull
    @Size(min=2, max=5)
    @ApiModelProperty("User name")
    private String name;

    @NotNull
    @Max(100)
    @Min(10)
    @ApiModelProperty("User age")
    private Integer age;

    @NotNull
    @Email
    @ApiModelProperty("User email")
    private String email;
}

Posting invalid values yields a 400 response with detailed error messages for each violated constraint.

Swagger documentation

Swagger partially supports JSR‑303 annotations; supported ones include @NotNull, @Max, @Min, @Size, and @Pattern. For unsupported constraints you can add descriptions in @ApiModelProperty.

Dependency note

The spring-boot-starter-validation starter pulls in hibernate-validator. In Spring Boot 2.1 it is already included via spring-boot-starter-web, so an extra dependency may not be required.

Full source code

The complete example can be found in the chapter2-3 directory of the repository:

GitHub: https://github.com/dyc87112/SpringBoot-Learning/tree/2.x

Gitee: https://gitee.com/didispace/SpringBoot-Learning/tree/2.x