Core Java. Lecture #14

Bean life cycle (reminder)

Disambiguation

NoUniqueBeanDefinitionException: No qualifying bean of
type 'edu.phystech.robotlecturer.Bar' available: expected
single matching bean but found 3: bar1,bar2,bar3

Binding by name (implicit)

@Component
public class Foo {
    //Doesn't work... :-(
    @Autowired
    private Bar bar;

    //It works!! :-)
    @Autowired
    private Bar bar1;
    ...
}

Binding by name (explicit)

@Component
public class Foo {
    @Autowired
    @Qualifier("bar1")
    private Bar bar;
    ...
}

Mark one of the implementations as @Primary

@Component
@Primary
public class Bar1 implements Bar {...}

@Component
public class Foo {
    //Bar1 is injected
    @Autowired
    private Bar bar;
    ...
}

But more often we need everything at once!

@Component
public class Foo {

    @Autowired
    private List<Bar> bar;

    //OR

    @Autowired
    private Map<String,Bar> bar;

You can inject not only beans, but also something simpler

@Configuration
//Path to the customization file
@PropertySource("classpath:config.properties")
public class Config {

}

@Component
public class Foo {
    @Value("${url}")
    String url;

    @Value("${password}")
    String password;

Object Initialization

Object Initialization

Finalization

Finalization

Practical task

Aspect-oriented programming to the rescue

AOP terminology

AOP terminology

How can AOP be implemented?

Proxy Object: Implementation

Using AOP in Spring

@Configuration
@EnableAspectJAutoProxy
public class AppConfig{
  ...

}

Example of an aspect

@Component @Aspect
public class BenchmarkAspect {
  @Around("@annotation(Benchmark)")
    //pointcut expression ^^^
  public Object execEntryPoint(ProceedingJoinPoint joinPoint)
                                    throws Throwable {
    System.out.printf("[[[BENCHMARK method %s%n",
                   joinPoint.getSignature().getName());
    long start = System.nanoTime();
    Object retVal = joinPoint.proceed();
    long end = System.nanoTime();
    System.out.printf("Time: %dns]]]%n", end - start);
    return retVal;
  }
}

Spring AOP checklist

Spring AOP checklist

Example of an aspect

@Component @Aspect
public class BenchmarkAspect {
  @Around("@annotation(Benchmark)")
    //pointcut expression ^^^
  public Object execEntryPoint(ProceedingJoinPoint joinPoint)
                                    throws Throwable {
    System.out.printf("[[[BENCHMARK method %s%n",
                   joinPoint.getSignature().getName());
    long start = System.nanoTime();
    Object retVal = joinPoint.proceed();
    long end = System.nanoTime();
    System.out.printf("Time: %dns]]]%n", end - start);
    return retVal;
  }
}

What kinds of the advices are there

@Before

@Before("@annotation(Benchmark)")
public void beforeFooMethods(JoinPoint jp) {
  String methodName = jp.getSignature().getName();
  System.out.println(methodName);
}

@After

@AfterReturning(pointcut= "execution(* edu.phystech..*.foo())",
                returning = "retVal")
public void afterFoo(Double retVal) {
  System.out.println("AFTER foo()" + retVal);
}

@AfterThrowing(
    pointcut= "execution(* aop.example.application..*.*(..))",
    throwing = "ex")
public void dbException(DatabaseRuntimeException ex){
  System.out.println(ex);
}

BeanPostProcessor interface

public interface BeanPostProcessor {
  //inject values into bean
  default Object postProcessBeforeInitialization(
    Object bean, String beanName) throws BeansException {
                return bean;
  }

  //return the the bean's wrapper
  default Object postProcessAfterInitialization(
    Object bean, String beanName) throws BeansException {
                return bean;
  }
}

BeanPostProcessor

Own BeanPostProcessor

@Component public class InjectRandomIntAnnotationBeanPostProcessor
                                    implements BeanPostProcessor {
  @Override public Object postProcessBeforeInitialization(
             Object bean, String beanName) throws BeansException {
    for (Field f : ReflectionUtils.getAllFields(bean.getClass())) {
      InjectRandomInt ann = f.getAnnotation(InjectRandomInt.class);
      if (ann != null) {
        int value = ThreadLocalRandom.current()
                        .nextInt(ann.min(), ann.max() + 1);
        f.setAccessible(true);
        try { f.set(bean, value); }
        catch (IllegalAccessException e) {
          throw new NotWritablePropertyException(
                                bean.getClass(), f.getName()); }
    } }
    return bean;
} }

Demo

Spring Boot

Spring Boot

Dependency Management

<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <!-- ...to spring-boot-dependencies, 3356 LOC -->
    <version>2.2.1.RELEASE</version>
</parent>

Connect the starters

<!-- «We want a web service»-->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <!-- And why don't we specify the version?-->
</dependency>

Writing Main class

//We do not specify packages for scanning
@SpringBootApplication
public class Main {
    public static void main(String[] args) throws SQLException, IOException {
        /*run method returns ApplicationContext,
        but we don't need it:-)*/
        SpringApplication.run(Main.class, args);
    }
}

Writing a controller

//It's also a @Controller, and hence it's a bean
@RestController
public class HelloController {
    @GetMapping("/hello")
    public String sayHello(@RequestParam("name") String name) {
        return String.format("Hello, %s!", name);
    }
}

Spring-boot-maven-plugin is responsible for building the jar file

<plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
</plugin>

How does Spring Boot Starter finds its beans?

Demo

It’s time to round off :-)

Java syntax is evolving

Everyone is waiting for projects

"Java Universe" is expanding at the speed of light

Conclusions — parting words

Never stop learning new things

The old is also useful to learn

Remember about your professional responsibility

Become a part of the community!

Welcome to the Java universe :-)