Java EE 8 Design Patterns and Best Practices

Implementing the PersistenceManager class

We need to manage all processes of persistence and query data. For this, we need to create a class. 

The PersistenceManager class is responsible for managing all persistence processes and query processes:

import javax.annotation.PostConstruct;import javax.inject.Inject;import java.util.LinkedHashSet;import java.util.Optional;import java.util.Set;import java.util.stream.Collectors;public class PersistenceManager {    private Set<StageManager> stateManagers;    @Inject @Transactional Transaction transaction;    @PostConstruct    public void init(){        stateManagers = new LinkedHashSet<StageManager>();    }    public Optional<Entity> persist ( Entity entity ) {        if ( entity instanceof Employee ){            stateManagers.add( new