以核心域开始开发——自动售货机模型。首先创建Spring boot项目：

    1. 点击链接Spring Initializer。
    2. 选择Gradle Project->Java->Spring boot版本2.4.4。
    3. group name为com.lugew，artifact name为spring-boot-ddd。
    4. 添加三个依赖JPA、RestRepositories和H2。
    5. 点击生成并导入。

    如图：
    image.png
    之后自动生成。项目结构如图：
    image.png
    生成代码如下：

    1. package com.lugew.springbootddd;
    3. import org.springframework.boot.SpringApplication;
    4. import org.springframework.boot.autoconfigure.SpringBootApplication;
    6. @SpringBootApplication
    7. public class SpringBootDddApplication {
    9.     public static void main(String[] args) {
    10.         SpringApplication.run(SpringBootDddApplication.class, args);
    11.     }
    13. }

    build.gradle

    1. plugins {
    2.     id 'org.springframework.boot' version '2.4.3'
    3.     id 'io.spring.dependency-management' version '1.0.11.RELEASE'
    4. }
    7. ext {
    8.     guavaVersion = "30.0-jre"
    9.     spockVersion = "2.0-M4-groovy-3.0"
    10.     groovyVersion = "3.0.6"
    11.     lombokVersion = "1.18.16"
    12.     openapiVersion = "1.5.2"
    13.     byteBuddyVersion = "1.10.19"
    14.     objenesisVersion = "3.1"
    15. }
    18. apply plugin: 'java'
    19. apply plugin: 'idea'
    20. apply plugin: 'java-library'
    22. group = 'com.lugew'
    23. version = '0.0.1-SNAPSHOT'
    24. sourceCompatibility = '11'
    25. targetCompatibility = '11'
    27. repositories {
    28.     mavenLocal()
    29.     maven {
    30.         name '阿里云'
    31.         url 'https://maven.aliyun.com/repository/public/'
    32.     }
    33.     mavenCentral()
    34.     google()
    35. }
    36. test {
    37.     useJUnitPlatform()
    38. }
    41. apply plugin: 'groovy'
    42. apply plugin: 'org.springframework.boot'
    43. apply plugin: 'io.spring.dependency-management'
    44. apply plugin: 'maven'
    46. dependencies {
    47.     implementation(
    48.             "com.google.guava:guava:${guavaVersion}",
    49.             'org.springframework.boot:spring-boot-starter',
    50.             "org.springframework.boot:spring-boot-starter-web",
    51.             "org.springframework.boot:spring-boot-starter-data-jpa",
    52.     )
    54.     runtimeOnly(
    55.             "com.h2database:h2"
    56.     )
    58.     compileOnly(
    59.             "org.projectlombok:lombok:${lombokVersion}"
    60.     )
    62.     annotationProcessor(
    63.             "org.springframework.boot:spring-boot-configuration-processor",
    64.             "org.projectlombok:lombok:${lombokVersion}"
    65.     )
    67.     testImplementation(
    68.             "org.codehaus.groovy:groovy-all:${groovyVersion}",
    69.             "org.codehaus.groovy:groovy:${groovyVersion}",
    70.             "org.spockframework:spock-core:${spockVersion}",
    71.             "net.bytebuddy:byte-buddy:${byteBuddyVersion}",
    72.             "org.objenesis:objenesis:${objenesisVersion}",
    73.     )
    74. }

    setting.gradle:

    1. rootProject.name = 'spring-boot-ddd'

    随后在springbootdd目录下创建snackmachine目录：
    image.png
    snackmachine下创建SnackMachine类：
    image.png

    1. package com.lugew.springbootddd.snackmachine;
    3. import lombok.Getter;
    4. import lombok.Setter;
    6. @Getter
    7. @Setter
    8. public final class SnackMachine {
    9.     private int oneCentCount;
    10.     private int tenCentCount;
    11.     private int quarterCount;
    12.     private int oneDollarCount;
    13.     private int fiveDollarCount;
    14.     private int twentyDollarCount;
    16.     public void insertMoney(int oneCentCount,
    17.                             int tenCentCount,
    18.                             int quarterCount,
    19.                             int oneDollarCount,
    20.                             int fiveDollarCount,
    21.                             int twentyDollarCount) {
    22.         oneCentCount += oneCentCount;
    23.         tenCentCount += tenCentCount;
    24.         quarterCount += quarterCount;
    25.         oneDollarCount += oneDollarCount;
    26.         fiveDollarCount += fiveDollarCount;
    27.         twentyDollarCount += twentyDollarCount;
    28.     }
    30.     public void returnMoney() {
    31.     }
    32. }

    👆注意，此类使用final修饰符限定。我们使用字段记录当前售货机金额，并且引入insertMoney投币、returnMoney退币、buySnack购买零食功能。对SnackMachine类进一步改造：

    1. package com.lugew.springbootddd.snackmachine;
    3. import lombok.Getter;
    4. import lombok.Setter;
    6. @Getter
    7. @Setter
    8. public final class SnackMachine {
    9.     private int oneCentCount;
    10.     private int tenCentCount;
    11.     private int quarterCount;
    12.     private int oneDollarCount;
    13.     private int fiveDollarCount;
    14.     private int twentyDollarCount;
    17.     private int oneCentCountInTransaction = 0;
    18.     private int tenCentCountInTransaction = 0;
    19.     private int quarterCountInTransaction = 0;
    20.     private int oneDollarCountInTransaction = 0;
    21.     private int fiveDollarCountInTransaction = 0;
    22.     private int twentyDollarCountInTransaction = 0;
    24.     public void insertMoney(int oneCentCount,
    25.                             int tenCentCount,
    26.                             int quarterCount,
    27.                             int oneDollarCount,
    28.                             int fiveDollarCount,
    29.                             int twentyDollarCount) {
    30.         oneCentCountInTransaction += oneCentCount;
    31.         tenCentCountInTransaction += tenCentCount;
    32.         quarterCountInTransaction += quarterCount;
    33.         oneDollarCountInTransaction += oneDollarCount;
    34.         fiveDollarCountInTransaction += fiveDollarCount;
    35.         twentyDollarCountInTransaction += twentyDollarCount;
    37.     }
    39.     public void returnMoney() {
    40.         oneCentCountInTransaction = 0;
    41.         tenCentCountInTransaction = 0;
    42.         quarterCountInTransaction = 0;
    43.         oneDollarCountInTransaction = 0;
    44.         fiveDollarCountInTransaction = 0;
    45.         twentyDollarCountInTransaction = 0;
    46.     }
    48.     public void buySnack() {
    49.         oneCentCount += oneCentCountInTransaction;
    50.         tenCentCount += tenCentCountInTransaction;
    51.         quarterCount += quarterCountInTransaction;
    52.         oneDollarCount += oneDollarCountInTransaction;
    53.         fiveDollarCount += fiveDollarCountInTransaction;
    54.         twentyDollarCount += twentyDollarCountInTransaction;
    55.         oneCentCountInTransaction = 0;
    56.         tenCentCountInTransaction = 0;
    57.         quarterCountInTransaction = 0;
    58.         oneDollarCountInTransaction = 0;
    59.         fiveDollarCountInTransaction = 0;
    60.         twentyDollarCountInTransaction = 0;
    61.     }
    62. }

    InTransaction字段表示用户投币，当用户购买零食时，用户投币将被累加到机器账户，投币也将被清零。零食机的基本功能实现如上，在此基础上我们可以做进一步的改进，比如，我们可以将金额字段抽象于一个类Money中：

    1. package com.lugew.springbootddd.snackmachine;
    3. public class Money {
    4.     private int oneCentCount;
    5.     private int tenCentCount;
    6.     private int quarterCount;
    7.     private int oneDollarCount;
    8.     private int fiveDollarCount;
    9.     private int twentyDollarCount;
    11.     public Money(int oneCentCount, int tenCentCount, int quarterCount, int
    12.             oneDollarCount, int fiveDollarCount, int twentyDollarCount) {
    13.         this.oneCentCount = oneCentCount;
    14.         this.tenCentCount = tenCentCount;
    15.         this.quarterCount = quarterCount;
    16.         this.oneDollarCount = oneDollarCount;
    17.         this.fiveDollarCount = fiveDollarCount;
    18.         this.twentyDollarCount = twentyDollarCount;
    19.     }
    21.     public static Money add(Money money1, Money money2) {
    22.         return new Money(
    23.                 money1.oneCentCount + money2.oneCentCount,
    24.                 money1.tenCentCount + money2.tenCentCount,
    25.                 money1.quarterCount + money2.quarterCount,
    26.                 money1.oneDollarCount + money2.oneDollarCount,
    27.                 money1.fiveDollarCount + money2.fiveDollarCount,
    28.                 money1.twentyDollarCount + money2.twentyDollarCount);
    29.     }
    30. }

    不仅如此，Money类还内聚了add加法功能，从而SnackMachine类可以进一步简化：

    1. package com.lugew.springbootddd.snackmachine;
    3. import lombok.Getter;
    4. import lombok.Setter;
    6. @Getter
    7. @Setter
    8. public final class SnackMachine {
    9.     private Money moneyInside;
    10.     private Money moneyInTransaction;
    12.     public void insertMoney(Money money) {
    13.         moneyInTransaction = Money.add(moneyInTransaction, money);
    15.     }
    17.     public void returnMoney() {
    18.         //moneyInTransaction = 0
    19.     }
    21.     public void buySnack() {
    22.         moneyInside = Money.add(moneyInside, moneyInTransaction);
    23.         //moneyInTransaction = 0
    24.     }
    25. }

    👆可以看到SnackMachine更加精简了。