This project demonstrates how to implement a tree structure using a composite pattern in Java, extending an abstract NodeComponent class. Below are the steps to set up the entities, repositories, service layer, and configuration required to manage a category hierarchy.
This project constructs with,
- NodeComponent:
abstract class- is to serve as the base class for implementing a composite pattern, which is a structural design pattern that allows you to treat individual objects (leaves) and compositions of objects (composites) uniformly.
- NestedSetNodeRepository:
interface- is a repository implementation that provides operations for entities.
- TreeBuilder:
class- is designed to provide a structured way to construct and manage tree-like hierarchical structures.
First, create a TestNode entity that extends the NodeComponent abstract class. The following annotations are required: @Id, @NameColumn, @LeftColumn, @RightColumn, and @DepthColumn.
@Entity
@Table(name = "node")
public class TestNode extends NodeComponent {
@Id
private Long id;
@NameColumn
private String name;
@LeftColumn
private Integer lft;
@RightColumn
private Integer rgt;
@DepthColumn
private Integer depth;
}Next, create the necessary repository classes for handling data operations.
@Bean
public NestedSetRepositoryConfiguration<CategoryEntity,Long> categoryRepositoryConfiguration(JpaContext context) {
return new NestedSetRepositoryConfiguration<>(context, CategoryEntity.class);
}
@Bean
public NestedSetNodeRepository<CategoryEntity,Long> categoryNodeRepository(NestedSetRepositoryConfiguration<CategoryEntity,Long> configuration) {
return JpaNestedSetNodeRepositoryFactory.create(configuration, new TreeBuilderImpl<>(new CategoryComponentFactory()));
}Create the CategoryLeaf and CategoryComposite classes, both extending NodeComponent. These classes represent the leaf nodes and composite nodes of the category tree, respectively.
public class CategoryLeaf<T> extends NodeComponent<T> {
private T node;
private NodeComponent<T> parent;
public CategoryLeaf(T node) {
super(node);
}
// getter, setter
}
public class CategoryComposite<T> extends NodeComponent<T> {
private T node;
private NodeComponent<T> parent;
private final Set<NodeComponent<T>> children = new HashSet<>();
public CategoryComposite(T node) {
super(node);
}
// getter, setter
}Implement a factory class to create instances of CategoryLeaf and CategoryComposite.
public class CategoryComponentFactory implements NodeComponentFactory<Entity,Long> {
@Override
public NodeComponent<Entity> createCompositeNodeComponent(Entity entity) {
return new CategoryComposite<>(entity);
}
@Override
public NodeComponent<Entity> createLeafNodeComponent(Entity entity) {
return new CategoryLeaf<>(entity);
}
}By following these steps, you can create a robust category tree structure using the composite pattern in Java. The CategoryService class encapsulates the business logic, making it easier to manage and manipulate hierarchical data.