What is the difference between date and instant?

Instant and LocalDateTime are two entirely different animals: One represents a moment, the other does not. Instant represents a moment, a specific point in the timeline. LocalDateTime represents a date and a time-of-day.

How jwt authentication works?

 

Projection in hibernate

 Projection are used to execute aggregate operations and for single value query .

EX -

public static void main(String[] args) {
    SessionFactory factory = new Configuration().configure().addAnnotatedClass(Student.class).buildSessionFactory();
    Session session = factory.getCurrentSession();
    try {
        session.beginTransaction();
        Criteria c = session.createCriteria(Student.class);
        Projection p = Projections.property("lastName");
        List<String> students = c.setProjection(p).list();
        for(String s:students)
            System.out.println(s);
        session.getTransaction().commit();
        session.close();
    } finally {
        factory.close();
    }
}

It will return values of last name column.

Projections are useful for 

1.Fetching only certain column of the table.

2.To execute aggregate function.

@Mock,@InjectMocks and @RunWith(MockitoJunitRunner.class) in mockito

 In previous example we have created a Mock like below-

DataService dataServiceMock = mock(DataService.class);

but we can create mock using @Mock annotations.

@Mock

DataService dataServiceMock;

when mock is created then we need to inject into beans 

@InjectMocks

SomeBusinessImpl businessImpl;// dataServiceMock will inject into SomeBusinessImpl

Then we no need to inject this dependencies through constructor or setter injection.

MockitoJUnitRunner checks if all settings are ok or any mistakes have take places.

so put it to the top of the test class

@RunWith(MockitoJUnitRunner.class)

Previous example using mockito

 package com.example.mockitoEx.MockitoEx;

import static org.junit.jupiter.api.Assertions.assertEquals;

import static org.mockito.Mockito.mock;

import static org.mockito.Mockito.when;

import org.junit.jupiter.api.Test;

class SomeBusinessTestMock {

@Test

public void findGreatestFromAllData() {

DataService dataServiceMock = mock(DataService.class);

when(dataServiceMock.retrieveAllData()).thenReturn(new int[] { 24, 15, 10 });

SomeBusinessImpl businessImpl = new SomeBusinessImpl(dataServiceMock);

int result = businessImpl.findTheGreatestFromAllData();

assertEquals(24, result);

}

}

Using mock method we can create a mock object of any interface or object.