The content repository contains the content-bearing objects and groups. These have master data and schema-less content. There are three types.

1. Media objects - media objects are linked to a media such as a PDF or an image file and contains master data. The media object represents this linked media file. Each media object must be assigned to exactly one group. Additionally, any content information can be stored at the media object.
2. Entity object - A content object can contain any content information in addition to its master data. Each object must be assigned to exactly one group. An optional property of a content object is to provide a file name.
3. Group object - objects are structured in groups. These groups can be structured hierarchically. A group object can include any content information to its master data. An optional property of a group object is to provide a directory name. This is used for the objects within the group. Another optional property of a group object is to provide a file name.

Features of the content repository are:

• To store objects and groups
• To make objects and groups findable and return them.
• To version changes of objects and groups.
• To provide the history of an object.
• To lock objects for exclusive write access for others.
• Deliver different versions of an object.
• To be able to compare contents before saving, in order to be able to announce changes of individual fields
• To be able to revert an object to an older version.
• To be able to restore deleted objects (recycle bin).

When saving an object or a group, the changes are always determined so that other components can react to them.

Rule when saving objects: Only the data specified for saving will be changed. All other data remain unchanged. When saving, all changes are compared with the actual state, so that all changed fields are known.

Contents can be structured in lists and sub-objects. If a list is saved, it is not merged but replaced. This means that if a list with three elements is updated with two elements, only the two elements are kept. If not all fields of the list element are specified, only the specified fields are updated, the others remain unchanged.

List elements can be reordered and then saved. In this case, the fields of the list elements that were not specified will also be reordered when saving.

The content module does not handle media but only uses references to media.

The media itself is managed in a media repository.

The architecture follows the principles of Clean Architecture

Ports are interfaces that the core requires for the execution of the individual usecases. The implementation is provided externally.

Is needed to be able to valid the permissions for individual actions.

Basic CRUD operations for repository entries

Publisher to handle publishing

Manage the references to the media-repository

Manage it exclusive write access.

Provides methods to manage the history of an entry

Creates unique ID's for new entries

Recycle Bin Management

Versioning management to be able to get or restore older versions.

public Optional<Entity> remove(@NonNull Identifier identifier) {

	if (identifier == null) {
		throw new IllegalArgumentException("identifier is null");
	}

	// ...
}

public abstract class ContentRepositoryException extends RuntimeException {
	// ...
}

See How to handle Java exceptions in clean code

public class Settings {

	private final String a;
	private final String b;

	private Settings(Builder builder) {
		this.a = builder.a;
		this.b = builder.b;
	}

	public String getA() {
		return this.a;
	}

	public String getB() {
		return this.b;
	}

	public static Builder builder() {
		return new Builder();
	}

	public Builder toBuilder() {
		return new Builder(this);
	}

	public static class Builder {

		private String a;

		private String b;

		private Builder() {}

		private Builder(Settings settings) {
			this.a = settings.a;
			this.b = settings.b;
		}

		public Builder a(String a) {
			this.a = a;
			return this;
		}

		public Builder b(String b) {
			this.b = b;
			return this;
		}

		public Settings build() {
			return new Settings(this);
		}
	}
}

Inheritance is a bit of a challenge in the Builder pattern. See here for a good explanation and apply the proposed solution. com.sitepark.ies.contentrepository.core.domain.entity.Entity shows this solution.