How to Create a Pojo

How to create a POJO?

A POJO is just a plain, old Java Bean with the restrictions removed. Java Beans must meet the following requirements:

1. Default no-arg constructor
2. Follow the Bean convention of getFoo (or isFoo for booleans) and setFoo methods for a mutable attribute named foo; leave off the setFoo if foo is immutable.
3. Must implement java.io.Serializable

POJO does not mandate any of these. It's just what the name says: an object that compiles under JDK can be considered a Plain Old Java Object. No app server, no base classes, no interfaces required to use.

The acronym POJO was a reaction against EJB 2.0, which required several interfaces, extended base classes, and lots of methods just to do simple things. Some people, Rod Johnson and Martin Fowler among them, rebelled against the complexity and sought a way to implement enterprise scale solutions without having to write EJBs.

Martin Fowler coined a new acronym.

Rod Johnson wrote "J2EE Without EJBs", wrote Spring, influenced EJB enough so version 3.1 looks a great deal like Spring and Hibernate, and got a sweet IPO from VMWare out of it.

Here's an example that you can wrap your head around:

public class MyFirstPojo
{
    private String name;

    public static void main(String [] args)
    {
       for (String arg : args)
       {
          MyFirstPojo pojo = new MyFirstPojo(arg);  // Here's how you create a POJO
          System.out.println(pojo); 
       }
    }

    public MyFirstPojo(String name)
    {    
        this.name = name;
    }

    public String getName() { return this.name; } 

    public String toString() { return this.name; } 
}

How would I create a POJO class for such a data structure?

First create a Product pojo :

class Product {
  private String productName;
  … 
  …
  // getters / setters
}

then your ProductList class could have a list of Products instead :

class ProductList {
  private boolean availability;
  private List<Product> our_productList; 
  ...
  //Getters & setters
}

Creating a POJO from JSON and retrieving the properties using the POJO classes

You are mixing GSON annotations @SerializedName and @Expose with Jackson ObjectMapper. You should use @JsonProperty annotation instead as follows:

@Data
public class PickEvent {
    @JsonProperty("pickEventActivities")
    private List<PickEventActivity> mPickEventActivities;
}

You must do the same for all the other classes.

Generic way to create different pojo objects and persist in db

If you have resources which use different repositories maybe you should have different REST endpoints (or whatever you are using) and service classes right.

One simple way to get rid of your if-else blocks would be to use a Map

Map<String, Consumer<?>> map = new HashMap<>();
 map.put("Teacher", (e) -> teacherRepository.save(mapper.readValue(e,Teacher.class))
});

and you can use it like,

map.get("Teacher").accept(jsonString);

---

Related Topics