领域驱动设计之银行转账：wow框架实战

银行账户转账案例是一个经典的领域驱动设计（ddd）应用场景。接下来我们通过一个简单的银行账户转账案例，来了解如何使用 wow 进行领域驱动设计以及服务开发。

银行转账流程

1. 准备转账（prepare）： 用户发起转账请求，触发 prepare 步骤。这个步骤会向源账户发送准备转账的请求。
2. 校验余额（checkbalance）： 源账户在收到准备转账请求后，会执行校验余额的操作，确保账户有足够的余额进行转账。
3. 锁定金额（lockamount）： 如果余额足够，源账户会锁定转账金额，防止其他操作干扰。
4. 入账（entry）： 接着，转账流程进入到目标账户，执行入账操作。
5. 确认转账（confirm）： 如果入账成功，确认转账；否则，执行解锁金额操作。
   1. 成功路径（success）： 如果一切顺利，完成转账流程。
   2. 失败路径（fail）： 如果入账失败，执行解锁金额操作，并处理失败情况。

运行案例

• 运行 transferexampleserver.java
• 查看 swagger-ui : http://localhost:8080/swagger-ui.html
• 执行 api 测试：transfer.http

自动生成 api 端点

运行之后，访问 swagger-ui : http://localhost:8080/swagger-ui.html 。
该 restful api 端点是由 wow 自动生成的，无需手动编写。

模块划分

领域建模

状态聚合根（accountstate）与命令聚合根（account）分离设计保证了在执行命令过程中，不会修改状态聚合根的状态。

状态聚合根（accountstate）建模

public class accountstate implements identifier {
    private final string id;
    private string name;
    /**
     * 余额
     */
    private long balanceamount = 0l;
    /**
     * 已锁定金额
     */
    private long lockedamount = 0l;
    /**
     * 账号已冻结标记
     */
    private boolean frozen = false;

    @jsoncreator
    public accountstate(@jsonproperty("id") string id) {
        this.id = id;
    }

    @notnull
    @override
    public string getid() {
        return id;
    }

    public string getname() {
        return name;
    }

    public long getbalanceamount() {
        return balanceamount;
    }

    public long getlockedamount() {
        return lockedamount;
    }

    public boolean isfrozen() {
        return frozen;
    }

    void onsourcing(accountcreated accountcreated) {
        this.name = accountcreated.name();
        this.balanceamount = accountcreated.balance();
    }

    void onsourcing(amountlocked amountlocked) {
        balanceamount = balanceamount - amountlocked.amount();
        lockedamount = lockedamount + amountlocked.amount();
    }

    void onsourcing(amountentered amountentered) {
        balanceamount = balanceamount + amountentered.amount();
    }

    void onsourcing(confirmed confirmed) {
        lockedamount = lockedamount - confirmed.amount();
    }

    void onsourcing(amountunlocked amountunlocked) {
        lockedamount = lockedamount - amountunlocked.amount();
        balanceamount = balanceamount + amountunlocked.amount();
    }

    void onsourcing(accountfrozen accountfrozen) {
        this.frozen = true;
    }

}

命令聚合根（account）建模

@statictenantid
@aggregateroot
public class account {
    private final accountstate state;

    public account(accountstate state) {
        this.state = state;
    }

    accountcreated oncommand(createaccount createaccount) {
        return new accountcreated(createaccount.name(), createaccount.balance());
    }

    @oncommand(returns = {amountlocked.class, prepared.class})
    list<?> oncommand(prepare prepare) {
        checkbalance(prepare.amount());
        return list.of(new amountlocked(prepare.amount()), new prepared(prepare.to(), prepare.amount()));
    }

    private void checkbalance(long amount) {
        if (state.isfrozen()) {
            throw new illegalstateexception("账号已冻结无法转账.");
        }
        if (state.getbalanceamount() < amount) {
            throw new illegalstateexception("账号余额不足.");
        }
    }

    object oncommand(entry entry) {
        if (state.isfrozen()) {
            return new entryfailed(entry.sourceid(), entry.amount());
        }
        return new amountentered(entry.sourceid(), entry.amount());
    }

    confirmed oncommand(confirm confirm) {
        return new confirmed(confirm.amount());
    }

    amountunlocked oncommand(unlockamount unlockamount) {
        return new amountunlocked(unlockamount.amount());
    }

    accountfrozen oncommand(freezeaccount freezeaccount) {
        return new accountfrozen(freezeaccount.reason());
    }
}

转账流程管理器（transfersaga）

转账流程管理器（transfersaga）负责协调处理转账的事件，并生成相应的命令。

• onevent(prepared): 订阅转账已准备就绪事件（prepared），并生成入账命令(entry)。
• onevent(amountentered): 订阅转账已入账事件（amountentered），并生成确认转账命令(confirm)。
• onevent(entryfailed): 订阅转账入账失败事件（entryfailed），并生成解锁金额命令(unlockamount)。

@statelesssaga
public class transfersaga {

    entry onevent(prepared prepared, aggregateid aggregateid) {
        return new entry(prepared.to(), aggregateid.getid(), prepared.amount());
    }

    confirm onevent(amountentered amountentered) {
        return new confirm(amountentered.sourceid(), amountentered.amount());
    }

    unlockamount onevent(entryfailed entryfailed) {
        return new unlockamount(entryfailed.sourceid(), entryfailed.amount());
    }
}

单元测试

借助 wow 单元测试套件，可以轻松的编写聚合根和 saga 的单元测试。从而提升代码覆盖率，保证代码质量。

使用 aggregateverifier 进行聚合根单元测试，可以有效的减少单元测试的编写工作量。

account 聚合根单元测试

internal class accountktest {
    @test
    fun createaccount() {
        aggregateverifier<account, accountstate>()
            .given()
            .`when`(createaccount("name", 100))
            .expecteventtype(accountcreated::class.java)
            .expectstate {
                assertthat(it.name, equalto("name"))
                assertthat(it.balanceamount, equalto(100))
            }
            .verify()
    }

    @test
    fun prepare() {
        aggregateverifier<account, accountstate>()
            .given(accountcreated("name", 100))
            .`when`(prepare("name", 100))
            .expecteventtype(amountlocked::class.java, prepared::class.java)
            .expectstate {
                assertthat(it.name, equalto("name"))
                assertthat(it.balanceamount, equalto(0))
            }
            .verify()
    }

    @test
    fun entry() {
        val aggregateid = globalidgenerator.generateasstring()
        aggregateverifier<account, accountstate>(aggregateid)
            .given(accountcreated("name", 100))
            .`when`(entry(aggregateid, "sourceid", 100))
            .expecteventtype(amountentered::class.java)
            .expectstate {
                assertthat(it.name, equalto("name"))
                assertthat(it.balanceamount, equalto(200))
            }
            .verify()
    }

    @test
    fun entrygivenfrozen() {
        val aggregateid = globalidgenerator.generateasstring()
        aggregateverifier<account, accountstate>(aggregateid)
            .given(accountcreated("name", 100), accountfrozen(""))
            .`when`(entry(aggregateid, "sourceid", 100))
            .expecteventtype(entryfailed::class.java)
            .expectstate {
                assertthat(it.name, equalto("name"))
                assertthat(it.balanceamount, equalto(100))
                assertthat(it.isfrozen, equalto(true))
            }
            .verify()
    }

    @test
    fun confirm() {
        val aggregateid = globalidgenerator.generateasstring()
        aggregateverifier<account, accountstate>(aggregateid)
            .given(accountcreated("name", 100), amountlocked(100))
            .`when`(confirm(aggregateid, 100))
            .expecteventtype(confirmed::class.java)
            .expectstate {
                assertthat(it.name, equalto("name"))
                assertthat(it.balanceamount, equalto(0))
                assertthat(it.lockedamount, equalto(0))
                assertthat(it.isfrozen, equalto(false))
            }
            .verify()
    }

    @test
    fun unlockamount() {
        val aggregateid = globalidgenerator.generateasstring()
        aggregateverifier<account, accountstate>(aggregateid)
            .given(accountcreated("name", 100), amountlocked(100))
            .`when`(unlockamount(aggregateid, 100))
            .expecteventtype(amountunlocked::class.java)
            .expectstate {
                assertthat(it.name, equalto("name"))
                assertthat(it.balanceamount, equalto(100))
                assertthat(it.lockedamount, equalto(0))
                assertthat(it.isfrozen, equalto(false))
            }
            .verify()
    }

    @test
    fun freezeaccount() {
        val aggregateid = globalidgenerator.generateasstring()
        aggregateverifier<account, accountstate>(aggregateid)
            .given(accountcreated("name", 100))
            .`when`(freezeaccount(""))
            .expecteventtype(accountfrozen::class.java)
            .expectstate {
                assertthat(it.name, equalto("name"))
                assertthat(it.balanceamount, equalto(100))
                assertthat(it.lockedamount, equalto(0))
                assertthat(it.isfrozen, equalto(true))
            }
            .verify()
    }
}

使用 sagaverifier 进行 saga 单元测试，可以有效的减少单元测试的编写工作量。

transfersaga 单元测试

internal class transfersagatest {

    @test
    fun onprepared() {
        val event = prepared("to", 1)
        sagaverifier<transfersaga>()
            .`when`(event)
            .expectcommandbody<entry> {
                assertthat(it.id, equalto(event.to))
                assertthat(it.amount, equalto(event.amount))
            }
            .verify()
    }

    @test
    fun onamountentered() {
        val event = amountentered("sourceid", 1)
        sagaverifier<transfersaga>()
            .`when`(event)
            .expectcommandbody<confirm> {
                assertthat(it.id, equalto(event.sourceid))
                assertthat(it.amount, equalto(event.amount))
            }
            .verify()
    }

    @test
    fun onentryfailed() {
        val event = entryfailed("sourceid", 1)
        sagaverifier<transfersaga>()
            .`when`(event)
            .expectcommandbody<unlockamount> {
                assertthat(it.id, equalto(event.sourceid))
                assertthat(it.amount, equalto(event.amount))
            }
            .verify()
    }
}