面试题之-Java中判断200==200为false但127==127为true的疑问

Spring中使用JSR303请求约束判空

1. 适用场景

有时候我们在表单里提交一系列参数, 到后台封装成一个对象, 要对对象的属性做各种字段值的约束; 这时候, 当然可以if-else一个一个的判断, 有更简洁的做法, 就是使用 JSR303+spring的validation:

2. 使用方法步骤(分3步)

• 1. 实体类加字段约束注解
• 2. Controller类中@Valid标注启用(@Validated也兼容@Valid)
• 3. BindingResult获取报错信息

     2.1 实体类加字段约束注解

如我们要收集前端表单的字段数据到Person实体中:

对需要约束的字段进行注解标注;

示例:

2.1.1 Person.java

package com.niewj.demo.model;

import lombok.Data;
import org.hibernate.validator.constraints.Length;
import org.hibernate.validator.constraints.URL;

import javax.validation.constraints.*;
import java.util.List;

@Data
public class Person {
    @Length(min = 4, max = 10)
    @NotNull(message = "name不能为空")
    private String name;

    @Min(0)
    @Max(40)
    @NotNull(message = "age不能为空")
    private Integer age;

    @NotBlank
    @NotBlank
    @URL(message = "logo必须是URL格式")
    private String logo;

    @NotEmpty(message = "hobbies不能为空")
    private List<String> hobbies;

    @Email
    @NotNull(message = "email不能为空!")
    private String mail;
}

@NotNull 约束字段不可为空;

@NotEmpty 约束集合/map等不能为空不能为0元素

@Email 约束是 email格式

@URL 约束必须是url的格式

message属性可以修改默认错误说明

2.2 Controller类中@Valid标注启用(@Validated兼容@Valid)

2.2.1 HelloController.java

package com.niewj.demo.controller;

import com.google.gson.Gson;
import com.niewj.demo.common.Result;
import com.niewj.demo.model.Person;
import com.niewj.demo.service.TestService1;
import org.springframework.stereotype.Controller;
import org.springframework.validation.BindingResult;
import org.springframework.web.bind.annotation.*;

import javax.annotation.Resource;
import javax.validation.Valid;
import java.util.HashMap;
import java.util.Map;

/**
 * test
 *
 * @author niewj
 * @since 2020/11/16 15:22
 */
@Controller
public class HelloController {

    /**
     * @param person
     * @param bindingResult
     * @return
     */
    @PostMapping("/test")
    @ResponseBody
    public Result doSth(@Valid @RequestBody Person person, BindingResult bindingResult) {
        Map<String, String> map = new HashMap<>();
        if (bindingResult.hasErrors()) {
            bindingResult.getFieldErrors().stream().forEach(fe-> map.put(fe.getField(), fe.getDefaultMessage()));
            System.out.println(bindingResult.getFieldError().getDefaultMessage());
            return Result.withErrorParamData(map);
        }

        return Result.withSuccessData(person);
    }
}

@RequestBody可以将body中的请求流信息(Request.getInputStream)通过HttpMessageConverter自动转换为目标java类型:

• 如果前端 Content-Type为application/json, 就使用 JSON消息转换器 帮你转为JSON对象;
• 如果前端 Content-Type为application/xml, 就使用 XML消息转换器 帮你转为xml;
• 如果前端 Content-Type为text/plain, 就是用 String消息转换器 帮你转成 String; (只有类型为String时才可以转换)

2.2.2 Result.java:

package com.niewj.demo.common;

import lombok.Data;

import java.io.Serializable;
import java.util.Map;

/**
 * 返回结果模板封装
 *
 * @author niewj
 * @since 2020/12/17 18:05
 */
@Data
public class Result<T> implements Serializable {
    private int code;
    private String msg;
    private T data;

    public Result(int code, String msg, T data) {
        this(code, msg);
        this.data = data;
    }

    public Result(int code, String msg) {
        this.msg = msg;
        this.code = code;
    }

    public static <T> Result<T> withData(ResponseEnum responseCode, T data) {
        Result<T> re = new Result(responseCode.getCode(), responseCode.getMsg());
        re.data = data;
        return re;
    }

    public static Result<String> withSuccessNoData() {
        Result re = new Result(ResponseEnum.SUCCESS.getCode(), ResponseEnum.SUCCESS.getMsg());
        re.data = "";
        return re;
    }

    public static <T> Result<T> withSuccessData(T data) {
        Result re = new Result(ResponseEnum.SUCCESS.getCode(), ResponseEnum.SUCCESS.getMsg());
        re.data = data;
        return re;
    }

    public static Result<Map<String, String>> withErrorParamData(Map<String, String> data) {
        Result re = new Result(ResponseEnum.BAD_REQUEST.getCode(), ResponseEnum.BAD_REQUEST.getMsg());
        re.data = data;
        return re;
    }
}

2.2.3 ResponseEnum.java

package com.niewj.demo.common;

/**
 * 通用响应码
 */
public enum ResponseEnum {

    SUCCESS(200, "成功"),
    BAD_REQUEST(400, "请求参数不合规");

    /**
     * 错误码
     */
    private Integer code;
    /**
     * 错误信息
     */
    private String msg;

    ResponseEnum(Integer code, String msg) {
        this.code = code;
        this.msg = msg;
    }

    public String getMsg() {
        return msg;
    }

    public Integer getCode() {
        return code;
    }
}

2.3 BindingResult获取报错信息

1. BindingResult用来收集约束字段的错误信息, 可通过 bindingResult.hasErrors()的 true来过滤错误信息;
2. bindingResult.getFieldErrors() 会返回 List<FieldError>;
3. FieldError 得到字段名: getField(); 得到错误信息: getDefaultMessage()

3. 调用测试:

http://localhost:8888/test

3.1 请求用例1: 字段为空

header: Content-Type: application/json

{
    "name": "1"
}

响应:

{
    "code": 400,
    "msg": "请求参数不合规",
    "data": {
        "mail": "email不能为空!",
        "hobbies": "hobbies不能为空",
        "name": "长度需要在4和10之间",
        "logo": "不能为空",
        "age": "age不能为空"
    }
}

3.2 请求用例2: list无元素/email/url格式不对

header: Content-Type: application/json

{
    "name": "1234",
    "hobbies": [],
    "mail": "niewj",
    "logo": "niewj.com"
}

响应:

{
    "code": 400,
    "msg": "请求参数不合规",
    "data": {
        "mail": "不是一个合法的电子邮件地址",
        "hobbies": "hobbies不能为空",
        "logo": "logo必须是URL格式",
        "age": "age不能为空"
    }
}

3.3 请求用例3: 完整字段信息

header: Content-Type: application/json

{
    "name": "1234",
    "hobbies": ["running"],
    "mail": "hi@niewj.com",
    "logo": "http://niewj.com",
    "age": 40
}

响应:

{
    "code": 200,
    "msg": "成功",
    "data": {
        "name": "1234",
        "age": 40,
        "logo": "http://niewj.com",
        "hobbies": [
            "running"
        ],
        "mail": "hi@niewj.com"
    }
}

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