Guice 学习入门

Question

这个例子很简单，如果会点 Guice，那么不需要再往下看了。

简单来说，它是 dependeny injection 框架，它与 Spring 相比，作者已经给出了，见 原文。

1.添加依赖

pom.xml 中添加如下依赖

<dependency>
    <groupId>com.google.inject</groupId>
    <artifactId>guice</artifactId>
    <version>4.0</version>
</dependency>

2.定义接口及实现类

2.1 CreditCardProcessor

/**
 * @author dmj1161859184@126.com 2018-09-10 20:00
 * @version 1.0
 * @since 1.0
 */
public interface CreditCardProcessor {
    ChargeResult charge(CreditCard credit, Object amount);
}

/**
 * @author dmj1161859184@126.com 2018-09-10 20:42
 * @version 1.0
 * @since 1.0
 */
public class PaypalCreditCardProcessorImpl implements CreditCardProcessor {
    @Override
    public ChargeResult charge(CreditCard credit, Object amount) {
        LOG.info("charge方法");
        return null;
    }
}

2.2 TransactionLog

/**
 * @author dmj1161859184@126.com 2018-09-10 20:00
 * @version 1.0
 * @since 1.0
 */
public interface TransactionLog {
    void logChargeResult(ChargeResult result);

    void logConnectException(Exception e);
}

/**
 * @author dmj1161859184@126.com 2018-09-10 20:07
 * @version 1.0
 * @since 1.0
 */
public class DatabaseTransactionLogImpl implements TransactionLog {
    @Override
    public void logChargeResult(ChargeResult result) {
        LOG.info("logChargeResult方法");
    }

    @Override
    public void logConnectException(Exception e) {
        LOG.info("logConnectException方法");
    }
}

2.3 BillingService

/**
 * @author dmj1161859184@126.com 2018-09-10 19:59
 * @version 1.0
 * @since 1.0
 */
public interface BillingService {

    Receipt chargeOrder(PizzaOrder order, CreditCard credit);
}

/**
 * @author dmj1161859184@126.com 2018-09-10 20:00
 * @version 1.0
 * @since 1.0
 */
public class BillingServiceImpl implements BillingService {
    private final CreditCardProcessor processor;
    private final TransactionLog transactionLog;

    @Inject
    public BillingServiceImpl(CreditCardProcessor processor,
                              TransactionLog transactionLog) {
        this.processor = processor;
        this.transactionLog = transactionLog;
    }

    @Override
    public Receipt chargeOrder(PizzaOrder order, CreditCard credit) {
        try {
            ChargeResult result = processor.charge(credit, order.getAmount());
            transactionLog.logChargeResult(result);

            return result.wasSuccessful()
                    ? Receipt.forSuccessfulCharge(order.getAmount())
                    : Receipt.forDeclinedCharge(result.getDeclineMessage());
        } catch (Exception e) {
            transactionLog.logConnectException(e);
            return Receipt.forSystemFailure(e.getMessage());
        }
    }
}

3.测试

public class Main {

    public static void main(String[] args) {
        Injector injector = Guice.createInjector(new BillingModule());
        BillingService billingService = injector.getInstance(BillingService.class);
        billingService.chargeOrder(new PizzaOrder(), new CreditCard());
    }
}

运行结果如下图所示：