PHP设计模式 PHP 代理模式

目的

为昂贵或者无法复制的资源提供接口。

例子

• Doctrine2 使用代理来实现框架特性（如延迟初始化），同时用户还是使用自己的实体类并且不会使用或者接触到代理

UML 图

代码

BankAccount.php

<?php
declare(strict_types=1);
namespace DesignPatterns\Structural\Proxy;
interface BankAccount
{
    public function deposit(int $amount);
    public function getBalance(): int;
}

HeavyBankAccount.php

<?php
declare(strict_types=1);
namespace DesignPatterns\Structural\Proxy;
class HeavyBankAccount implements BankAccount
{
    /**
     * @var int[]
     */
    private array $transactions = [];
    public function deposit(int $amount)
    {
        $this->transactions[] = $amount;
    }
    public function getBalance(): int
    {
        // this is the heavy part, imagine all the transactions even from
        // years and decades ago must be fetched from a database or web service
        // and the balance must be calculated from it
        return array_sum($this->transactions);
    }
}

BankAccountProxy.php

<?php
declare(strict_types=1);
namespace DesignPatterns\Structural\Proxy;
class BankAccountProxy extends HeavyBankAccount implements BankAccount
{
    private ?int $balance = null;
    public function getBalance(): int
    {
        // because calculating balance is so expensive,
        // the usage of BankAccount::getBalance() is delayed until it really is needed
        // and will not be calculated again for this instance
        if ($this->balance === null) {
            $this->balance = parent::getBalance();
        }
        return $this->balance;
    }
}

测试

ProxyTest.php

<?php
declare(strict_types=1);
namespace DesignPatterns\Structural\Proxy\Tests;
use DesignPatterns\Structural\Proxy\BankAccountProxy;
use PHPUnit\Framework\TestCase;
class ProxyTest extends TestCase
{
    public function testProxyWillOnlyExecuteExpensiveGetBalanceOnce()
    {
        $bankAccount = new BankAccountProxy();
        $bankAccount->deposit(30);
        // this time balance is being calculated
        $this->assertSame(30, $bankAccount->getBalance());
        // inheritance allows for BankAccountProxy to behave to an outsider exactly like ServerBankAccount
        $bankAccount->deposit(50);
        // this time the previously calculated balance is returned again without re-calculating it
        $this->assertSame(30, $bankAccount->getBalance());
    }
}