Spring框架中的设计模式（五）

public class CommandTest {
 
  // This test method is a client
  @Test
  public void test() {
    Administrator admin = new Administrator();
    Server server = new Server();
     
    // start Apache
    admin.setCommand(new StartApache(server));
    admin.typeEnter();
     
    // start Tomcat
    admin.setCommand(new StartTomcat(server));
    admin.typeEnter();
     
    // check executed commands
    int executed = server.getExecutedCommands().size();
    assertTrue("Two commands should be executed but only "+
      executed+ " were", executed == 2);
  }
 
}
 
// commands
abstract class ServerCommand {
         
  protected Server server;
   
  public ServerCommand(Server server) {
    this.server = server;
  }
 
  public abstract void execute();
}
 
class StartTomcat extends ServerCommand {
         
  public StartTomcat(Server server) {
    super(server);
  }
   
  @Override
  public void execute() {
    server.launchCommand("sudo service tomcat7 start");
  }
}
 
class StartApache extends ServerCommand {
         
  public StartApache(Server server) {
    super(server);
  }
 
  @Override
  public void execute() {
    server.launchCommand("sudo service apache2 start");
  }
}
 
// invoker
class Administrator {
         
  private ServerCommand command;
   
  public void setCommand(ServerCommand command) {
    this.command = command;
  }
   
  public void typeEnter() {
    this.command.execute();
  }
         
}
 
// receiver
class Server {
         
  // as in common terminals, we store executed commands in history
  private List<String> executedCommands = new ArrayList<String>();
   
  public void launchCommand(String command) {
    System.out.println("Executing: "+command+" on server");
    this.executedCommands.add(command);
  }
   
  public List<String> getExecutedCommands() {
    return this.executedCommands;
  }
         
}

/**
	 * BeanPostProcessor that logs an info message when a bean is created during
	 * BeanPostProcessor instantiation, i.e. when a bean is not eligible for
	 * getting processed by all BeanPostProcessors.
	 */
	private static class BeanPostProcessorChecker implements BeanPostProcessor {

		private static final Log logger = LogFactory.getLog(BeanPostProcessorChecker.class);

		private final ConfigurableListableBeanFactory beanFactory;

		private final int beanPostProcessorTargetCount;

		public BeanPostProcessorChecker(ConfigurableListableBeanFactory beanFactory, int beanPostProcessorTargetCount) {
			this.beanFactory = beanFactory;
			this.beanPostProcessorTargetCount = beanPostProcessorTargetCount;
		}

		@Override
		public Object postProcessBeforeInitialization(Object bean, String beanName) {
			return bean;
		}

		@Override
		public Object postProcessAfterInitialization(Object bean, String beanName) {
			if (bean != null && !(bean instanceof BeanPostProcessor) && !isInfrastructureBean(beanName) &&
					this.beanFactory.getBeanPostProcessorCount() < this.beanPostProcessorTargetCount) {
				if (logger.isInfoEnabled()) {
					logger.info("Bean '" + beanName + "' of type [" + bean.getClass() +
							"] is not eligible for getting processed by all BeanPostProcessors " +
							"(for example: not eligible for auto-proxying)");
				}
			}
			return bean;
		}

		private boolean isInfrastructureBean(String beanName) {
			if (beanName != null && this.beanFactory.containsBeanDefinition(beanName)) {
				BeanDefinition bd = this.beanFactory.getBeanDefinition(beanName);
				return RootBeanDefinition.ROLE_INFRASTRUCTURE == bd.getRole();
			}
			return false;
		}
	}

public static void registerBeanPostProcessors(
			ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {

		String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);

		// Register BeanPostProcessorChecker that logs an info message when
		// a bean is created during BeanPostProcessor instantiation, i.e. when
		// a bean is not eligible for getting processed by all BeanPostProcessors.
		int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
  //BeanPostProcessorChecker
		beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));

		// Separate between BeanPostProcessors that implement PriorityOrdered,
		// Ordered, and the rest.
		List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
		List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();
		List<String> orderedPostProcessorNames = new ArrayList<>();
		List<String> nonOrderedPostProcessorNames = new ArrayList<>();
		for (String ppName : postProcessorNames) {
			if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
				BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
				priorityOrderedPostProcessors.add(pp);
				if (pp instanceof MergedBeanDefinitionPostProcessor) {
					internalPostProcessors.add(pp);
				}
			}
			else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
				orderedPostProcessorNames.add(ppName);
			}
			else {
				nonOrderedPostProcessorNames.add(ppName);
			}
		}

		// First, register the BeanPostProcessors that implement PriorityOrdered.
		sortPostProcessors(beanFactory, priorityOrderedPostProcessors);
		registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);

		// Next, register the BeanPostProcessors that implement Ordered.
		List<BeanPostProcessor> orderedPostProcessors = new ArrayList<>();
		for (String ppName : orderedPostProcessorNames) {
			BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
			orderedPostProcessors.add(pp);
			if (pp instanceof MergedBeanDefinitionPostProcessor) {
				internalPostProcessors.add(pp);
			}
		}
		sortPostProcessors(beanFactory, orderedPostProcessors);
		registerBeanPostProcessors(beanFactory, orderedPostProcessors);

		// Now, register all regular BeanPostProcessors.
		List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<>();
		for (String ppName : nonOrderedPostProcessorNames) {
			BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
			nonOrderedPostProcessors.add(pp);
			if (pp instanceof MergedBeanDefinitionPostProcessor) {
				internalPostProcessors.add(pp);
			}
		}
		registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);

		// Finally, re-register all internal BeanPostProcessors.
		sortPostProcessors(beanFactory, internalPostProcessors);
		registerBeanPostProcessors(beanFactory, internalPostProcessors);

		// Re-register post-processor for detecting inner beans as ApplicationListeners,
		// moving it to the end of the processor chain (for picking up proxies etc).
		beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
	}

public class VisitorTest {
 
  @Test
  public void test() {
    CarComponent car = new Car();
    Mechanic mechanic = new QualifiedMechanic();
    car.accept(mechanic);
    assertTrue("After qualified mechanics visit, the car should be broken",
      car.isBroken());
    Mechanic nonqualifiedMechanic = new NonQualifiedMechanic();
    car.accept(nonqualifiedMechanic);
    assertFalse("Car shouldn't be broken becase non qualified mechanic " +
      " can't see breakdowns", car.isBroken());
  }
 
}
 
// visitor
interface Mechanic {
  public void visit(CarComponent element);
  public String getName();
}
 
class QualifiedMechanic implements Mechanic {
 
  @Override
  public void visit(CarComponent element) {
    element.setBroken(true);
  }
 
  @Override
  public String getName() {
    return "qualified";
  }
}
 
class NonQualifiedMechanic implements Mechanic {
         
  @Override
  public void visit(CarComponent element) {
    element.setBroken(true);
  }
   
  @Override
  public String getName() {
    return "unqualified";
  }
}
 
// visitable
abstract class CarComponent {
  protected boolean broken;
 
  public abstract void accept(Mechanic mechanic);
   
  public void setBroken(boolean broken) {
    this.broken = broken;
  }
   
  public boolean isBroken() {
    return this.broken;
  }
}
 
class Car extends CarComponent {
 
  private boolean broken = false;
  private CarComponent[] components;
   
  public Car() {
    components = new CarComponent[] {
      new Wheels(), new Engine(), new Brake()
    };
  }
   
  @Override
  public void accept(Mechanic mechanic) {
    this.broken = false;
    if (mechanic.getName().equals("qualified")) {
      int i = 0;
      while (i < components.length && this.broken == false) {
        CarComponent component = components[i];
        mechanic.visit(component);
        this.broken = component.isBroken();
        i++;
      }
    }
    // if mechanic isn't qualified, we suppose that 
    // he isn't able to see breakdowns and so 
    // he considers the car as no broken 
    // (even if the car is broken)
  }
 
  @Override
  public boolean isBroken() {
          return this.broken;
  }
}
 
class Wheels extends CarComponent {
 
  @Override
  public void accept(Mechanic mechanic) {
    mechanic.visit(this);
  }
}
 
class Engine extends CarComponent {
 
  @Override
  public void accept(Mechanic mechanic) {
    mechanic.visit(this);
  }
}
 
class Brake extends CarComponent {
 
  @Override
  public void accept(Mechanic mechanic) {
    mechanic.visit(this);
  }
}

/**
 * Traverse the given BeanDefinition object and the MutablePropertyValues
 * and ConstructorArgumentValues contained in them.
 * @param beanDefinition the BeanDefinition object to traverse
 * @see #resolveStringValue(String)
 */
public void visitBeanDefinition(BeanDefinition beanDefinition) {
  visitParentName(beanDefinition);
  visitBeanClassName(beanDefinition);
  visitFactoryBeanName(beanDefinition);
  visitFactoryMethodName(beanDefinition);
  visitScope(beanDefinition);
  visitPropertyValues(beanDefinition.getPropertyValues());
  ConstructorArgumentValues cas = beanDefinition.
    getConstructorArgumentValues();
  visitIndexedArgumentValues(cas.
    getIndexedArgumentValues());
  visitGenericArgumentValues(cas.
    getGenericArgumentValues());
}
 
protected void visitParentName(BeanDefinition beanDefinition) {
  String parentName = beanDefinition.getParentName();
  if (parentName != null) {
    String resolvedName = resolveStringValue(parentName);
    if (!parentName.equals(resolvedName)) {
      beanDefinition.setParentName(resolvedName);
    }
  }
}