How to connect MySql 5.x using Hibernate 5

In this post, I'll discuss below points

• How to create 'SessionFactory' and 'Session'
• How to choose  'dialect'

Create 'SessionFactory' and 'Session'

Hibernate 5 comes with major changes and they change the way we can building 'SessionFactory'

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.boot.Metadata;
import org.hibernate.boot.MetadataSources;
import org.hibernate.boot.registry.StandardServiceRegistry;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;

....

StandardServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder().configure("hibernate.cfg.xml").build();
Metadata metadata = new MetadataSources(serviceRegistry).getMetadataBuilder().build();
SessionFactory sf = metadata.getSessionFactoryBuilder().build();
Session session = sf.openSession()

...

Select 'dialect'.

In hibernate 5, we can below below dialects when connecting to the MySQL

org.hibernate.dialect.MySQL5Dialect
org.hibernate.dialect.MySQL55Dialect
org.hibernate.dialect.MySQL57Dialect

Note: org.hibernate.dialect.MySQLDialect is for MySQL 4.x or earlier.

Enjoy...!!

Spring - Execute a init method when initializing bean and destroying bean.

There are couple of ways to achieve this requirement.

First methodology
You can simply implements below interfaces in the bean

• InitializingBean
• DisposableBean

Then you have to override below methods respectively above interfaces. 

• afterPropertiesSet()
• destroy()

Note: You have to use registerShutdownHook (link) to see the effect of the destroy method.

Second methodology
In this scenario, I would like to introduce the way we can execute the custom method when initializing and destroying beans.

Initially, you have to implement custom methods for init and destroy as below

    public void myInit() {

        System.out.println("This is the custom init method");

    }

....

    public void myDestroy() {

        System.out.println("This is the custom destroy method");



    }

In the bean configuration file you have to tell to the Spring what are the init and destroy methods as below.

<beans>

    <bean id="student" class="com.home.model.Student" init-method="myInit" destroy-method="myDestroy">

        .....

    </bean>

 .....

 .....

</beans>

Enjoy...!!!

Spring - How to destroy beans when application shutdown? (registerShutdownHook)

If someone needs to destroy the beans when shutdown then application, what you need to do is:

• Create a 'AbstractApplicationContext'
• call the 'registerShutdownHook'

Find the below code for your reference

AbstractApplicationContext context = new ClassPathXmlApplicationContext("spring.xml");
context.registerShutdownHook();

Once this "registerShutdownHook()" method executes, it destroy the beans when down the application.

Enjoy..!!

Lambda (Java 8) - Transfer one type of object to another type of object

We will assume that we have list of Students to convert into list of Persions.

public class Student {
    private String name;
    private String school;
    private int age;

    public Student(String name, String school, int age) {
        this.name = name;
        this.school = school;
        this.age = age;
    }

    // getters/setters should come here

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", school='" + school + '\'' +
                ", age=" + age +
                '}';
    }
}

public class Person {
    private String fullName;
    private int age;

    public Person(String fullName, int age) {
        this.fullName = fullName;
        this.age = age;
    }

    //getters/setters should come here

    @Override
    public String toString() {
        return "Person{" +
                "fullName='" + fullName + '\'' +
                ", age='" + age + '\'' +
                '}';
    }
}

In this article, I'm going to use functional interface call Funcation to achieve this.

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.function.Function;

public class StudentApplication {
    public static void main(String[] args) {
        Function<Student, Person> functionStuToPer = student -> new Person(student.getName(), student.getAge());

        List<Student> students = Arrays.asList(
                new Student("Tharanga", "UOC", 22),
                new Student("Ruwan", "UOM", 24),
                new Student("Ruvini", "UOK", 20),
                new Student("Randika", "TOUC", 25),
                new Student("Amara", "UOR", 23)
        );

        List<Person> persons = convertStudentListToPerson(students, functionStuToPer);
        persons.forEach(System.out::println);

    }

    private static List<Person> convertStudentListToPerson(List<Student> students, Function<Student, Person> functions) {
        List<Person> persons = new ArrayList<>();
        for (Student student: students) {
            persons.add(functions.apply(student));
        }
        return persons;
    }
}

Enjoy...!!

Lambda (Java 8) - How to sort and filter array

In this article, I'm going to explain about the way we can sort and filter an array using lambda expressions.

TASK 1

We will assume that, we have a list of students as follows:

 List<Student> students = Arrays.asList(
         new Student("Tharanga", "UOC", 22),
         new Student("Ruwan", "UOM", 24),
         new Student("Ruvini", "UOK", 20),
         new Student("Randika", "TOUC", 25),
         new Student("Amara", "UOR", 23)
);

In this scenario, we will assume that we have to sort the students by name:

Initially, how we cater this without lambda expression:

Collections.sort(students, new Comparator<Student>() {
       @Override
       public int compare(Student o1, Student o2) {
           return o1.getName().compareTo(o2.getName());
       }
});

Now will cater this requirement with lambda expressions.

 Collections.sort(students, (o1, o2) -> o1.getName().compareTo(o2.getName()));

Note: Since 'Comparator' interface is a functional interface we can sort the object list as above.

TASK 2

In here, we will assume that we need to filter the students, name starting with 'R'

Without lambda expression we can achieve this as below.

import java.util.Arrays;
import java.util.Collections;
import java.util.List;

public class StudentApplication {
    public static void main(String[] args) {
        List<Student> students = Arrays.asList(
                new Student("Tharanga", "UOC", 22),
                new Student("Ruwan", "UOM", 24),
                new Student("Ruvini", "UOK", 20),
                new Student("Randika", "TOUC", 25),
                new Student("Amara", "UOR", 23)
        );

        Collections.sort(students, (o1, o2) -> o1.getName().compareTo(o2.getName()));

        printConditionally(students, new Condition() {
            @Override
            public boolean test(Student student) {
                return student.getName().startsWith("R");
            }
        });

    }

    private static void printConditionally(List<Student> students, Condition condition) {
        for (Student student: students) {
            if(condition.test(student)) {
                System.out.println(student);
            }
        }
    }
}

interface Condition {
    boolean test(Student student);
} 

How we achieve this using lambda expression.

import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.function.Predicate;

public class StudentApplication {
    public static void main(String[] args) {
        List<Student> students = Arrays.asList(
                new Student("Tharanga", "UOC", 22),
                new Student("Ruwan", "UOM", 24),
                new Student("Ruvini", "UOK", 20),
                new Student("Randika", "TOUC", 25),
                new Student("Amara", "UOR", 23)
        );

        Collections.sort(students, (o1, o2) -> o1.getName().compareTo(o2.getName()));

        printConditionally(students, student -> student.getName().startsWith("R"));

    }

    private static void printConditionally(List<Student> students, Predicate<Student> predicate) {
        for (Student student: students) {
            if(predicate.test(student)) {
                System.out.println(student);
            }
        }
    }
}

Note: Java 8, OFTB support many functional interfaces such as "Predicate". You can find more on here.

Note: Find more information about funcational interfaces here.

Lambda (Java 8) - Functional Interface

To write a lambda expression, the interface should have only one abstract method. If an interface has more than one abstract method, we cannot write lambda expression.

When we work as a team, someone creates an interface to write a lambda expression. Later, another team member can add another abstract method to that interface to fulfill his requirement. But in this scenario, that change will effect to the lambda expression and it will not work.

To avoid above scenarios, we need to tell specifically, this interface should have only one abstract method.

We have a lovely annotation to cater this requirement as @FunctionalInterface. It restricts the adding more than one abstract method to the interface.

Find the below sample:

@FunctionalInterface
public interface Greeting {
    String perform(String s) ;
}

Enjoy...!!

Lambda (Java 8) - How to use Runnable interface

In this article, I'm going to explain the way we can use lambda to implement the Runnable interface.

General scenario is below:

  
   ...
   Thread myThread = new Thread(new Runnable() {
        @Override
        public void run() {
            System.out.println("Printed inside runnable");
            System.out.println(Thread.currentThread().getId());
        }
   });
   myThread.start();
   ...

Below is the code segment, same above implementation with lambda.

   ...
        Thread myLambdaThread = new Thread(() -> {
            System.out.println("printed inside the lambda expression");
            System.out.println("Thread Id: " + Thread.currentThread().getId());
        });

        myLambdaThread.start();
   ...

• Empty parentheses: because run() method doesn't allow any arguments.
• If there is more than one line of the implementation, we need to write the implementation inside the curly brackets.

Note: Runable interface only one method call run(), so we can write lambda expression. If there is more than one method declaration inside a interface, we cannot write lambda expression.

Enjoy..!!