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POJOS

A POJO is the foundation for making an Entity that is turned into a Database. The Java Persistent API (JPA) allows the database to be queried and updated.

An example of a POJO is Jokes.java which defines the model of the functionality

public class Person {
    // 3 different attributes
    private String firstName;
    private String lastName;
    private int age;

    public Person() { // Constructors
    }

    public Person(String firstName, String lastName, int age) {
        this.firstName = firstName; // initializing variable
        this.lastName = lastName; // referencing current object
        this.age = age; // refers to the age attribute
    }

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}

Example from Jokes.java

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.*;

import java.util.List;
import java.util.Optional;

@RestController // annotation to simplify the creation of RESTful web services
@RequestMapping("/api/jokes")  // all requests in file begin with this URI
public class JokesApiController {

    // Autowired enables Control to connect URI request and POJO Object to easily for Database CRUD operations
    @Autowired
    private JokesJpaRepository repository;

    /* GET List of Jokes
     * @GetMapping annotation is used for mapping HTTP GET requests onto specific handler methods.
     */
    @GetMapping("/")
    public ResponseEntity<List<Jokes>> getJokes() {
        // ResponseEntity returns List of Jokes provide by JPA findAll()
        return new ResponseEntity<>( repository.findAll(), HttpStatus.OK);
    }

    /* Update Like
     * @PutMapping annotation is used for mapping HTTP PUT requests onto specific handler methods.
     */
    @PutMapping("/like/{id}")
    public ResponseEntity<Jokes> setLike(@PathVariable long id) {

        Optional<Jokes> optional = repository.findById(id);
        if (optional.isPresent()) {  // Good ID
            Jokes joke = optional.get();  // value from findByID
            joke.setHaha(joke.getHaha()+1); // increment value
            repository.save(joke);  // save entity
            return new ResponseEntity<>(joke, HttpStatus.OK);  // OK HTTP response: status code, headers, and body
        }
        return new ResponseEntity<>(HttpStatus.BAD_REQUEST);  // Failed HTTP response: status code, headers, and body
    }

    @PutMapping("/jeer/{id}")
    public ResponseEntity<Jokes> setJeer(@PathVariable long id) {
        Optional<Jokes> optional = repository.findById(id);
        if (optional.isPresent()) {  // Good ID
            Jokes joke = optional.get();
            joke.setBoohoo(joke.getBoohoo()+1);
            repository.save(joke);
            return new ResponseEntity<>(joke, HttpStatus.OK);
        }
        return new ResponseEntity<>(HttpStatus.BAD_REQUEST);
    }
}

Changes to a POJO

1. Adding Fields ```java private String email; // New field

// Getter and Setter for the new field public String getEmail() { return email; }

public void setEmail(String email) { this.email = email; }

2. Removing Fields
```java
// Remove the 'age' field

// Remove the getter and setter for 'age'

1. Modify

   private int age;
   

2. Adding Constructor

   public Person(String firstName, String lastName) {
    this.firstName = firstName;
    this.lastName = lastName;
   }
   

3. Update Method

   public void Test() {
   }