和 if else说再见，SpringBoot 这样做参数校验才足够优雅！ 上

@Target({ElementType.TYPE, ElementType.METHOD, ElementType.PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Validated {
 /**
  * Specify one or more validation groups to apply to the validation step
  * kicked off by this annotation.
  * <p>JSR-303 defines validation groups as custom annotations which an application declares
  * for the sole purpose of using them as type-safe group arguments, as implemented in
  * {@link org.springframework.validation.beanvalidation.SpringValidatorAdapter}.
  * <p>Other {@link org.springframework.validation.SmartValidator} implementations may
  * support class arguments in other ways as well.
  */
 Class<?>[] value() default {};
}

// User.java
public class User {
    private String id;
    @Valid
    private UserProfile profile;
}
// UserProfile.java
public class UserProfile {
    @NotBlank
    private String nickname;
}

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.2.4.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.ratel</groupId>
    <artifactId>java-validation</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>java-validation</name>
    <description>java validation action</description>
    <properties>
        <java.version>1.8</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <!--在一些高版本springboot中默认并不会引入这个依赖，需要手动引入-->
<!--        <dependency>
            <groupId>org.hibernate.validator</groupId>
            <artifactId>hibernate-validator</artifactId>
            <scope>compile</scope>
        </dependency>-->
        <!-- 保证 Spring AOP 相关的依赖包 -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-aspects</artifactId>
        </dependency>
        <!--lombok相关 方便开发-->
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <scope>provided</scope>
        </dependency>
        <!--knife4j接口文档 方便待会进行接口测试-->
        <dependency>
            <groupId>com.github.xiaoymin</groupId>
            <artifactId>knife4j-spring-boot-starter</artifactId>
            <version>3.0.3</version>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
</project>

package com.ratel.validation.entity;
import lombok.Data;
import org.hibernate.validator.constraints.Length;
import javax.validation.constraints.NotEmpty;
import javax.validation.constraints.Pattern;
/**
 * @Description
 * @Author ratelfu
 * @Date 2023/04/07
 * @Version 1.0
 */
@Data
public class UserAddDTO {
    /**
     * 账号
     */
    @NotEmpty(message = "登录账号不能为空")
    @Length(min = 5, max = 16, message = "账号长度为 5-16 位")
    @Pattern(regexp = "^[A-Za-z0-9]+$", message = "账号格式为数字以及字母")
    private String username;
    /**
     * 密码
     */
    @NotEmpty(message = "密码不能为空")
    @Length(min = 4, max = 16, message = "密码长度为 4-16 位")
    private String password;
}

package com.ratel.validation.cotroller;
import com.ratel.validation.entity.UserAddDTO;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.validation.annotation.Validated;
import org.springframework.web.bind.annotation.*;
import javax.validation.Valid;
import javax.validation.constraints.Min;
@RestController
@RequestMapping("/users")
@Validated
public class UserController {
    private Logger logger = LoggerFactory.getLogger(getClass());
    @GetMapping("/get")
    public UserAddDTO get(@RequestParam("id") @Min(value = 1L, message = "编号必须大于 0") Integer id) {
        logger.info("[get][id: {}]", id);
        UserAddDTO userAddDTO = new UserAddDTO();
        userAddDTO.setUsername("张三");
        userAddDTO.setPassword("123456");
        return userAddDTO;
    }
    @PostMapping("/add")
    public void add(@Valid @RequestBody UserAddDTO addDTO) {
        logger.info("[add][addDTO: {}]", addDTO);
    }
}