Google Guice结合模式

这些绑定方式统称为内置绑定，相相应的还有种及时绑定。假设在解析一个依赖时假设在内置绑定中无法找到。那么Guice将会创建一个及时绑定。

一、链接绑定(LinkdedBindings)

链接绑定即映射一类型到它的实现类，比如映射TransactionLog接口到实现类DatabaseTransactionLog：

public class BillingModule extends AbstractModule {
  @Override 
  protected void configure() {
    bind(TransactionLog.class).to(DatabaseTransactionLog.class);
  }
}

public class BillingModule extends AbstractModule {
  @Override 
  protected void configure() {
    bind(TransactionLog.class).to(DatabaseTransactionLog.class);
    bind(DatabaseTransactionLog.class).to(MySqlDatabaseTransactionLog.class);
  }
}

二、绑定注解
某些情况下你可能想为同一种类型设置多种绑定。这就能够通过绑定注解来实现，该注解与绑定的类型用于唯一结识一个绑定，
合在一起称为Key。演示样例：

package example.pizza;

import com.google.inject.BindingAnnotation;
import java.lang.annotation.Target;
import java.lang.annotation.Retention;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
import static java.lang.annotation.ElementType.PARAMETER;
import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.ElementType.METHOD;

@BindingAnnotation @Target({ FIELD, PARAMETER, METHOD }) @Retention(RUNTIME)
public @interface PayPal {}

public class RealBillingService implements BillingService {

@Inject
	public RealBillingService(@PayPal CreditCardProcessor processor,
		TransactionLog transactionLog) {
		...
	}
}

public class RealBillingService implements BillingService {

  @Inject
  public RealBillingService(@Named("Checkout") CreditCardProcessor processor,
		TransactionLog transactionLog) {
		...
  }
}

bind(CreditCardProcessor.class)
        .annotatedWith(Names.named("Checkout"))
        .to(CheckoutCreditCardProcessor.class);

bind(String.class)
        .annotatedWith(Names.named("JDBC URL"))
        .toInstance("jdbc:mysql://localhost/pizza");
    bind(Integer.class)
        .annotatedWith(Names.named("login timeout seconds"))
        .toInstance(10);

@Inject @Named("JDBC URL")
private String url

public class BillingModule extends AbstractModule {
  @Override
  protected void configure() {
    ...
  }

  @Provides
  TransactionLog provideTransactionLog() {
    DatabaseTransactionLog transactionLog = new DatabaseTransactionLog();
    transactionLog.setJdbcUrl("jdbc:mysql://localhost/pizza");
    transactionLog.setThreadPoolSize(30);
    return transactionLog;
  }
}

@Provides @PayPal
CreditCardProcessor providePayPalCreditCardProcessor(@Named("PayPal API key") String apiKey) {
	PayPalCreditCardProcessor processor = new PayPalCreditCardProcessor();
	processor.setApiKey(apiKey);
	return processor;
}

public interface Provider<T> {
  T get();
}

public class DatabaseTransactionLogProvider implements Provider<TransactionLog> {
  private final Connection connection;

  @Inject
  public DatabaseTransactionLogProvider(Connection connection) {
    this.connection = connection;
  }

  public TransactionLog get() {
    DatabaseTransactionLog transactionLog = new DatabaseTransactionLog();
    transactionLog.setConnection(connection);
    return transactionLog;
  }
}

public class BillingModule extends AbstractModule {
  @Override
  protected void configure() {
    bind(TransactionLog.class)
        .toProvider(DatabaseTransactionLogProvider.class);
  }
}

bind(MyConcreteClass.class)
	.annotatedWith(Names.named("foo"))
    .to(MyConcreteClass.class);
bind(AnotherConcreteClass.class)
	.annotatedWith(Names.named("foo"))
    .to(AnotherConcreteClass.class)
    .in(Singleton.class);

public class BillingModule extends AbstractModule {
  @Override 
  protected void configure() {
    try {
      bind(TransactionLog.class).toConstructor(
          DatabaseTransactionLog.class.getConstructor(DatabaseConnection.class));
    } catch (NoSuchMethodException e) {
      addError(e);
    }
  }
}

public class PayPalCreditCardProcessor implements CreditCardProcessor {
  private final String apiKey;

  @Inject
  public PayPalCreditCardProcessor(@Named("PayPal API key") String apiKey) {
    this.apiKey = apiKey;
  }
}

@ImplementedBy(PayPalCreditCardProcessor.class)
public interface CreditCardProcessor {
  ChargeResult charge(String amount, CreditCard creditCard)
      throws UnreachableException;
}

bind(CreditCardProcessor.class).to(PayPalCreditCardProcessor.class);

@ProvidedBy(DatabaseTransactionLogProvider.class)
public interface TransactionLog {
  void logConnectException(UnreachableException e);
  void logChargeResult(ChargeResult result);
}