答题系统后端初步构建

1. 创建父工程

点击next

创建完的项目如下图

修改父工程pom文件

由于父工程一般只需要pom文件，可以删除src文件
pom文件的配置可以从网上搜索，不需要硬背，要理解都导入了哪些东西
maven有三种打包方式，分别为jar，war，pom，注意父工程打包方式要设置为pom即 <packaging>pom</packaging>

参考文章 https://blog.csdn.net/qq_35336425/article/details/82897100

<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.exam</groupId>
    <artifactId>exam_parent</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>pom</packaging>

    <name>exam_parent</name>
    <description>在线答题系统</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.1.RELEASE</version>
        <relativePath/>
    </parent>

    <properties>
        <!--构建用到的字符集，和jdk版本。现在maven好像有默认，不用配也可以-->
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <!--springboot 这里面包含了spring mvc的配置-->
            <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>
    </dependencies>

    <repositories>
        <!--spring仓库地址-->
        <repository>
            <id>spring-snapshots</id>
            <name>Spring Snapshots</name>
            <url>https://repo.spring.io/snapshot</url>
            <snapshots>
                <enabled>true</enabled>
            </snapshots>
        </repository>
        <repository>
            <id>spring-milestones</id>
            <name>Spring Milestones</name>
            <url>https://repo.spring.io/milestone</url>
            <snapshots>
                <enabled>false</enabled>
            </snapshots>
        </repository>
    </repositories>

    <pluginRepositories>
        <!--插件-->
        <pluginRepository>
            <id>spring-snapshots</id>
            <name>Spring Snapshots</name>
            <url>https://repo.spring.io/snapshot</url>
            <snapshots>
                <enabled>true</enabled>
            </snapshots>
        </pluginRepository>
        <pluginRepository>
            <id>spring-milestones</id>
            <name>Spring Milestones</name>
            <url>https://repo.spring.io/milestone</url>
            <snapshots>
                <enabled>false</enabled>
            </snapshots>
        </pluginRepository>
    </pluginRepositories>

</project>

2. 创建公共模块common

右键点击父工程 New -- Module

此处要注意修改Content_root路径，保证模块是在父工程下面，项目结构图如下

创建返回结果实体类

新建entity包
创建Request类，本项目使用restful风格，返回类型需要按照规范自己定义
此处要用到 lombok ，因为每个服务都需要用到，所以可以直接在父工程里添加依赖
添加完依赖就可以使用@Data注解自动生成get , set 方法，构造函数等

<!--自动生成get set等类方法-->
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
        </dependency>

返回结果实体类

package entity;

import lombok.Data;

/**
 * @ClassName : Request
 * @Description : 通用返回结果
 * @Author : WHB
 */
@Data
public class Request {

    private boolean flag; // 是否成功
    private Integer code; // 返回码
    private String message; // 返回信息
    private Object data; // 返回数据

}

分页返回结果实体类

package entity;

import lombok.Data;

import java.util.List;

/**
 * @ClassName : PageRequest
 * @Description : 分页返回结果
 * @Author : WHB
 */
@Data
public class PageRequest<T> {

    private Long total; // 总条数
    private List<T> rows; // 当前页数据

}

返回的状态码比较多但是很固定，所以单独建一个状态码实体类来管理

package entity;

/**
 * @ClassName : StatusCode
 * @Description : 状态码
 * @Author : WHB
 */
public class StatusCode {

    public static final int OK=20000;//成功
    public static final int ERROR =20001;//失败
    public static final int LOGINERROR =20002;//用户名或密码错误
    public static final int ACCESSERROR =20003;//权限不足
    public static final int REMOTEERROR =20004;//远程调用失败
    public static final int REPERROR =20005;//重复操作
    
}

分布式唯一ID的解决方案雪花算法

此处只提供代码，引用两篇可以用来学习此算法的文章

雪花算法的原理和实现
https://blog.csdn.net/lq18050010830/article/details/89845790
分布式ID生成之雪花算法https://developer.51cto.com/art/201909/602525.htm

package until;

import java.lang.management.ManagementFactory;
import java.net.InetAddress;
import java.net.NetworkInterface;

/**
 * @ClassName : IdWorker
 * @Description : 雪花算法
 * @Author : WHB
 */
public class IdWorker {

    // 时间起始标记点，作为基准，一般取系统的最近时间（一旦确定不能变动）
    private final static long twepoch = 1288834974657L;
    // 机器标识位数
    private final static long workerIdBits = 5L;
    // 数据中心标识位数
    private final static long datacenterIdBits = 5L;
    // 机器ID最大值
    private final static long maxWorkerId = -1L ^ (-1L << workerIdBits);
    // 数据中心ID最大值
    private final static long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
    // 毫秒内自增位
    private final static long sequenceBits = 12L;
    // 机器ID偏左移12位
    private final static long workerIdShift = sequenceBits;
    // 数据中心ID左移17位
    private final static long datacenterIdShift = sequenceBits + workerIdBits;
    // 时间毫秒左移22位
    private final static long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;

    private final static long sequenceMask = -1L ^ (-1L << sequenceBits);
    /* 上次生产id时间戳 */
    private static long lastTimestamp = -1L;
    // 0，并发控制
    private long sequence = 0L;

    private final long workerId;
    // 数据标识id部分
    private final long datacenterId;

    public IdWorker(){
        this.datacenterId = getDatacenterId(maxDatacenterId);
        this.workerId = getMaxWorkerId(datacenterId, maxWorkerId);
    }
    /**
     * @param workerId
     *            工作机器ID
     * @param datacenterId
     *            序列号
     */
    public IdWorker(long workerId, long datacenterId) {
        if (workerId > maxWorkerId || workerId < 0) {
            throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
        }
        if (datacenterId > maxDatacenterId || datacenterId < 0) {
            throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
        }
        this.workerId = workerId;
        this.datacenterId = datacenterId;
    }
    /**
     * 获取下一个ID
     *
     * @return
     */
    public synchronized long nextId() {
        long timestamp = timeGen();
        if (timestamp < lastTimestamp) {
            throw new RuntimeException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
        }

        if (lastTimestamp == timestamp) {
            // 当前毫秒内，则+1
            sequence = (sequence + 1) & sequenceMask;
            if (sequence == 0) {
                // 当前毫秒内计数满了，则等待下一秒
                timestamp = tilNextMillis(lastTimestamp);
            }
        } else {
            sequence = 0L;
        }
        lastTimestamp = timestamp;
        // ID偏移组合生成最终的ID，并返回ID
        long nextId = ((timestamp - twepoch) << timestampLeftShift)
                | (datacenterId << datacenterIdShift)
                | (workerId << workerIdShift) | sequence;

        return nextId;
    }

    private long tilNextMillis(final long lastTimestamp) {
        long timestamp = this.timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = this.timeGen();
        }
        return timestamp;
    }

    private long timeGen() {
        return System.currentTimeMillis();
    }

    /**
     * <p>
     * 获取 maxWorkerId
     * </p>
     */
    protected static long getMaxWorkerId(long datacenterId, long maxWorkerId) {
        StringBuffer mpid = new StringBuffer();
        mpid.append(datacenterId);
        String name = ManagementFactory.getRuntimeMXBean().getName();
        if (!name.isEmpty()) {
         /*
          * GET jvmPid
          */
            mpid.append(name.split("@")[0]);
        }
      /*
       * MAC + PID 的 hashcode 获取16个低位
       */
        return (mpid.toString().hashCode() & 0xffff) % (maxWorkerId + 1);
    }

    /**
     * <p>
     * 数据标识id部分
     * </p>
     */
    protected static long getDatacenterId(long maxDatacenterId) {
        long id = 0L;
        try {
            InetAddress ip = InetAddress.getLocalHost();
            NetworkInterface network = NetworkInterface.getByInetAddress(ip);
            if (network == null) {
                id = 1L;
            } else {
                byte[] mac = network.getHardwareAddress();
                id = ((0x000000FF & (long) mac[mac.length - 1])
                        | (0x0000FF00 & (((long) mac[mac.length - 2]) << 8))) >> 6;
                id = id % (maxDatacenterId + 1);
            }
        } catch (Exception e) {
            System.out.println(" getDatacenterId: " + e.getMessage());
        }
        return id;
    }
    
}

答题系统后端初步构建

1. 创建父工程

修改父工程pom文件

2. 创建公共模块common

创建返回结果实体类

分布式唯一ID的解决方案 雪花算法

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分布式唯一ID的解决方案雪花算法