Java笔记

移位符

1. “<<” 代表 乘2
2. ” >>" 代表 除以2

		Integer a = 8;
		Integer b = a << 3;  // *2的三次方 = a*8
		Integer c = a >> 3;  // /2的三次方 = a/8
		System.out.println(b); // 64
		System.out.println(c); // 1

操作统一返回类

package com.xxx.common.support.controller;

import com.xxx.common.constant.GlobalConstant;
import com.xxx.common.support.domain.IEntity;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

/**
 * ApiResponse
 * Description: 操作统一返回
 * Author: xxx
 * Date: 2022-01-13
 **/
@NoArgsConstructor
@AllArgsConstructor
@Data
public class ApiResponse implements IEntity {

	/**
	 * @Fields serialVersionUID : 序列化标识
	 */
	private static final long serialVersionUID = GlobalConstant.SERIAL_VERSION_UID;
	/**
	 * 成功码
	 */
	public static final String SUCCESS_CODE = "SUCCESS";
	/**
	 * 成功信息
	 */
	public static final String SUCCESS_MESSAGE = "操作成功";
	/**
	 * 错误码
	 */
	public static final String ERROR_CODE = "FAIL";
	/**
	 * 错误信息
	 */
	public static final String ERROR_MESSAGE = "操作失败";

	/** 状态码 */
    private String retcode;

    /** 返回内容 */
    private String retmsg;

    /** 数据对象 */
    private Object data;

    /**
     * 返回成功消息
     *
     * @return 成功消息
     */
    public static ApiResponse success() {
    	return ApiResponse.successMsg(SUCCESS_MESSAGE);
    }
    /**
     * 返回成功消息
     *
     * @return 成功消息
     */
    public static ApiResponse successMsg(String msg) {
    	return ApiResponse.success(msg, null);
    }
    /**
     * 返回成功数据
     *
     * @return 成功消息
     */
    public static ApiResponse success(Object data) {
    	return ApiResponse.success(SUCCESS_MESSAGE, data);
    }
    /**
     * 返回成功消息
     *
     * @param msg 返回内容
     * @param data 数据对象
     * @return 成功消息
     */
    public static ApiResponse success(String msg, Object data) {
    	return new ApiResponse(SUCCESS_CODE, msg, data);
    }
    /**
     * 返回错误消息
     *
     * @return 错误消息
     */
    public static ApiResponse error() {
    	return ApiResponse.error(ERROR_MESSAGE, null);
    }
    /**
     * 返回错误消息
     *
     * @return 错误消息
     */
    public static ApiResponse errorMsg(String msg) {
    	return ApiResponse.error(msg, null);
    }
    /**
     * 返回错误数据
     *
     * @return 错误消息
     */
    public static ApiResponse error(Object data) {
    	return ApiResponse.error(ERROR_MESSAGE, data);
    }
    /**
     * 返回错误消息
     *
     * @param msg 返回内容
     * @param data 数据对象
     * @return 错误消息
     */
    public static ApiResponse error(String msg, Object data) {
    	return new ApiResponse(ERROR_CODE, msg, data);
    }

    /***
     *
     *  success
     * Description: 返回自定义编码和返回值
     * Author: xxx
     * @Date: 2022-01-13
     **/
    public static ApiResponse success(String code, String msg, Object data) {
    	return new ApiResponse(code, msg, data);
    }

    /***
     *
     * @Title:: error
     * @Description: 返回自定义编码和返回值
     * @Author: xxx
     * @Date: 2022-01-13
     **/
    public static ApiResponse error(String code, String msg, Object data) {
        return new ApiResponse(code, msg, data);
    }
}

spring boot升级到jdk11出现错误

Spring Boot 警告：An illegal reflective access operation has occurred

WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by org.springframework.cglib.core.ReflectUtils (file:/D:/Android/.gradle/caches/modules-2/files-2.1/org.springframework/spring-core/5.2.0.RELEASE/e0e1b3c304f70ed19d7905975f6f990916ada219/spring-core-5.2.0.RELEASE.jar) to method java.lang.ClassLoader.defineClass(java.lang.String,byte[],int,int,java.security.ProtectionDomain)
WARNING: Please consider reporting this to the maintainers of org.springframework.cglib.core.ReflectUtils
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release

解决方式：增加 JVM 启动参数 java --illegal-access=deny（不知道为什么测试时候没生效）

不推荐方式： jdk版本降到1.8

SpringBoot项目使用MySQL数据库，误用数据库关键字

JPA

	//实体类加此注解
	@Column(name = "medicine_name")
	private String medicineName;

Mybatis-plus

	//实体类加此注解
	@TableField(value = "`describe`")
    private String describe;

String类型api接口返回值不加双引号

import javax.servlet.http.HttpServletResponse;
...
public void result(String string, HttpServletResponse response) throws Exception {
        response.getWriter().write(string);
        response.getWriter().flush();
        response.getWriter().close();
    }

Java8 stream流使用

//筛选状态为2和3的数据
List<CardDto> resultCardList = cardDtos.stream().filter(s -> ("2".equals(s.getStatus()) || "3".equals(s.getStatus()))).collect(Collectors.toList());

//筛选状态为1的数据
List<CardDto> pendingCardList = cardDtos.stream().filter(s -> "1".equals(s.getStatus())).collect(Collectors.toList());

//获取list对象中的configId属性集合
List<Long> configIds = pendingCardList.stream().map(CardDto::getConfigId).collect(Collectors.toList());

//合起来写 (筛选状态为1的数据的configId集合)       
List<Long> ids = cardDtos.stream().filter(s -> "1".equals(s.getStatus())).collect(Collectors.toList()).stream().map(CardDto::getConfigId).collect(Collectors.toList());	

//分组 Stream的Collectors.groupingBy支持key为null进行分组
//此时这里会抛出空指针异常
Map<String, List<User>> userMap = userList.stream.collect(Collectors.groupingBy(x -> x.getSex()));
//使用Optional包装一层(解决空指针异常)
	Map<Optional<String>, List<User>> userMap = userList.stream().collect(Collectors.groupingBy(x -> Optional.ofNullable(x.getSex())));
}

mybatis 中xml 里判断list写法

<update id="updateStatus">
        UPDATE xx表
            SET `status` = "3"
        WHERE
            del_flag = "0"
        <if test="ids != null and ids.size()!=0">
            AND id in
            <foreach collection="ids" item="id" separator="," open="(" close=")">
                #{id}
            </foreach>
        </if>
    </update>

springboot项目，@Async异步方法需自己解决循环依赖问题，但是不使用异步方法spring boot会内部解决，不会抛出异常

springboot组件修改Pageable 值

Pageable pageable  = PageRequest.of(0, Integer.parseInt(size), pageable.getSort());
//or
pageable= PageRequest.of(page,pageSize, Sort.by(Sort.Direction.DESC,"time"));

项目部署

springboot 项目打包：
mvn clear package
重启服务：
systemctl restart xxxService
vue 项目：
npm run build:prod (打包好的文件在dist文件夹需替换4个)
(打包后部署到dash…)