Section 9 Flashcards

Question 1

Q

Create a example where singleton or prototype is used in a class and compare the differences. Use annotations

Answer

A

//TennisCoach class using prototype scope
@Component
@Scope("prototype")
public class TennisCoach implements Coach {

@Autowired
@Qualifier("gymFortuneService")
private FortuneService fortuneService;

    public TennisCoach() {
    }

@Override
public String getDailyWorkout() {
    return "Daily workout method";
}

@Override
public String getDailyFortune() {
    return fortuneService.getFortune();
}

}

//Main class where the result is displayed
public class Main {

public static void main(String[] args) {

        ClassPathXmlApplicationContext context
                = new ClassPathXmlApplicationContext("file:src/main/java/com/springboot/annotations/applicationContext.xml");

    Coach theCoach = context.getBean("tennisCoach", Coach.class);

    Coach alphaCoach = context.getBean("tennisCoach", Coach.class);

    boolean result = (theCoach == alphaCoach);

    System.out.println(result);

    context.close();
}

}

Question 2

Q

What you know about return values of @PostConstruct and @PreDestroy methods ?

Answer

A

Most commonly used in methods with this 2 annotations is void because you cannot capture the return value

Question 3

Q

Which is the difference between a parameter and an argument? Please explain with an example

Answer

A

//color is a parameter
public void getColor( String color ){
System.out.println("The color is": + color);
}

//Purple is an argument
public static void main(String[] args) {
getColor("Purple");
}

Question 4

Q

Methods marked with @PostConstruct or @PreDestroy annotations can have arguments ?

Answer

A

No! this kind of methods could not accept arguments!

Question 5

Q

When @PostConstruct method will execute ? But @PreDestroy ?

Answer

A

@PostConstruct method will execute imediatelly after default contructor initialization.

@PreDestroy will be the last method executed before program will finish the execution.

Question 6

Q

Using TennisCoach class and needed annotations, create the upcomming output:

TennisCoach default constructor should appear before doMyStartupStaff method
TennisCoach: inside of doMyStartupStuff
Daily workout method
Lucky
TennisCoach: inside of doMyCleanupSuff

Answer

A

//Inside TennisCoach class
@Component
public class TennisCoach implements Coach {

@Autowired
@Qualifier("gymFortuneService")
private FortuneService fortuneService;

    public TennisCoach() {
        System.out.println("TennisCoach constructor should appear before doMyStartupStaff method");
    }

@Override
public String getDailyWorkout() {
    return "Daily workout method";
}

@Override
public String getDailyFortune() {
    return fortuneService.getFortune();
}

    //define my init method
    @PostConstruct
    public void doMyStartupStuff() {
        System.out.println("TennisCoach: inside of doMyStartupStuff");
    }

    //define my destroy method
    @PreDestroy
    public void doMyCleanupSuff() {
        System.out.println("TennisCoach: inside of doMyCleanupSuff");

//Main class
  public static void main(String[] args) {

        ClassPathXmlApplicationContext context
                = new ClassPathXmlApplicationContext("file:src/main/java/com/springboot/annotations/applicationContext.xml");

    Coach theCoach = context.getBean("tennisCoach", Coach.class);

    System.out.println(theCoach.getDailyWorkout());
    System.out.println(theCoach.getDailyFortune());

    context.close();
}

Question 7

Q

When the @PreDestroy method is not executed ?

Answer

A

When using Scope(“prototype”)

Question 8

Q

What can we do so the @PreDestroy method to be executed when using prototype scope ?

Answer

A

//A custom bean processor must be created
@Component
public class MyCustomBeanProcessor implements BeanPostProcessor, BeanFactoryAware, DisposableBean {

private BeanFactory beanFactory;

private final List prototypeBeans = new LinkedList<>();

@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {

		// after start up, keep track of the prototype scoped beans. 
		// we will need to know who they are for later destruction

		if (beanFactory.isPrototype(beanName)) {
			synchronized (prototypeBeans) {
				prototypeBeans.add(bean);
			}
		}

	return bean;
}

@Override
public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
	this.beanFactory = beanFactory;
}

@Override
public void destroy() throws Exception {

	// loop through the prototype beans and call the destroy() method on each one

    synchronized (prototypeBeans) {

    	for (Object bean : prototypeBeans) {

    		if (bean instanceof DisposableBean) {
                DisposableBean disposable = (DisposableBean)bean;
                try {
                    disposable.destroy();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }

    	prototypeBeans.clear();
    }

} }

//TennisCoach must implement DisposasbleBean interface also
@Component
@Scope("prototype")
public class TennisCoach implements Coach, DisposableBean {

@Autowired
@Qualifier("gymFortuneService")
private FortuneService fortuneService;

    public TennisCoach() {
        System.out.println("TennisCoach constructor should appear before doMyStartupStaff method");
    }

@Override
public String getDailyWorkout() {
    return "Daily workout method";
}

@Override
public String getDailyFortune() {
    return fortuneService.getFortune();
}

    //define my init method
    @PostConstruct
    public void doMyStartupStuff() {
        System.out.println("TennisCoach: inside of doMyStartupStuff");
    }

    //define my destroy method
    @PreDestroy
    public void doMyCleanupSuff() {
        System.out.println("TennisCoach: inside of doMyCleanupSuff");

}

@Override
public void destroy() throws Exception {
    System.out.println(">> TennisCoach: inside destroy()");

}

Question 9

Q

Practice Activity #6 - Bean Scopes with Annotations

Modify your file based fortune service to make use of the @PostConstruct annotation
In the @PostConstruct code, read the fortunes from a text file (.txt).
Test your application and verify your @PostConstruct code is being executed. Hint, add some println statements.

Output:

> > FileFortuneService: inside default constructor
Oct 11, 2021 7:02:35 PM org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor lambda$buildAutowiringMetadata$2
INFO: Autowired annotation should only be used on methods with parameters: public void com.mycompany.springdemo.FileFortuneService.loadTheFortunesFile()
FileFortuneService: inside method loadTheFortunesFile
Reading fortunes from file: C:\foodbar\fortune-data.txt
File exists: true
PingPongCoach: inside default constructor
Practice your pingpong drop shot
Never give up.

Answer

A

//PingPongCoach
@Component
public class PingPongCoach implements Coach {

@Autowired
@Qualifier("fileFortuneService")
private FortuneService fortuneService;

    public PingPongCoach() {
        System.out.println(">> PingPongCoach: inside default constructor");
    }

@Override
public String getDailyWorkout() {
    return "Practice your pingpong drop shot";
}

@Override
public String getDailyFortune() {
    return fortuneService.getDailyFortune();
}

}

//FileFortuneService
@Component
public class FileFortuneService implements FortuneService {

String file = "C:\\foodbar\\fortune-data.txt";
ArrayList fileItems;

    public FileFortuneService() {
        System.out.println(">> FileFortuneService: inside default constructor");
    }

@Autowired
public void loadTheFortunesFile() {
    System.out.println(">> FileFortuneService: inside method loadTheFortunesFile");

    System.out.println("Reading fortunes from file: C:\\foodbar\\fortune-data.txt");

    fileItems = new ArrayList<>();

    if (!file.toString().equals("")) {

        System.out.println("File exists: true");

        try (BufferedReader br = new BufferedReader(new FileReader(file))) {

            String line;

            while ((line = br.readLine()) != null) {
                fileItems.add(line);
            }

            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    @Override
    public String getDailyFortune() {
        int randomNum = new Random().nextInt(fileItems.size());

    return fileItems.get(randomNum);
}

}

//Main
public class Main {

public static void main(String[] args) {

    ClassPathXmlApplicationContext container = new ClassPathXmlApplicationContext("file:src/main/java/com/mycompany/springdemo/applicationContext.xml");

    Coach coach = container.getBean("pingPongCoach", Coach.class);

    System.out.println(coach.getDailyWorkout());
    System.out.println(coach.getDailyFortune());

    container.close();

}

}

//applicationContext.xml
context:component-scan base-package="com.mycompany.springdemo"

Section 9 Flashcards

(9 cards)