java-design-patterns/abstract-document/src/main/java/com/iluwatar/abstractdocument/AbstractDocument.java

package com.iluwatar.abstractdocument;

import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.function.Function;
import java.util.stream.Stream;

public abstract class AbstractDocument implements Document {

    private final Map<String, Object> properties;

    protected AbstractDocument(Map<String, Object> properties) {
        Objects.requireNonNull(properties, "properties map is required");
        this.properties = properties;
    }

    @Override
    public Void put(String key, Object value) {
        properties.put(key, value);
        return null;
    }

    @Override
    public Object get(String key) {
        return properties.get(key);
    }

    @Override
    public <T> Stream<T> children(String key, Function<Map<String, Object>, T> constructor) {
        return Stream.of(get(key))
                .filter(el -> el != null)
                .map(el -> (List<Map<String, Object>>) el)
                .findAny().get().stream()
                .map(constructor);
    }

    @Override
    public String toString() {
        final StringBuilder builder = new StringBuilder();
        builder.append(getClass().getName()).append("[");
        properties.entrySet().forEach(e ->
                builder.append("[").append(e.getKey()).append(" : ").append(e.getValue()).append("]")
        );
        builder.append("]");
        return builder.toString();
    }

}