playing around with java 8 and application properties

ApplicationPropertyEntity.java

package us.copperdays.snippets.applicationproperty.demo;

import javax.persistence.*;

@Entity
@Table(name = "APP_PROPS",  schema = "DEMO")
public class ApplicationPropertyEntity {
    @Id
    @Column(name = "KEY")
    private String key;

    @Column(name="VALUE")
    private String value;

    public String getKey() {
        return key;
    }

    public void setKey(String key) {
        this.key = key;
    }

    public String getValue() {
        return value;
    }

    public void setValue(String value) {
        this.value = value;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        TestApplicationProperty that = (TestApplicationProperty) o;

        if (!key.equals(that.key)) return false;
        return !(value != null ? !value.equals(that.value) : that.value != null);

    }

    @Override
    public int hashCode() {
        int result = key.hashCode();
        result = 31 * result + (value != null ? value.hashCode() : 0);
        return result;
    }

    @Override
    public String toString() {
        return "ApplicationProperty{" +
                "key='" + key + '\'' +
                ", value='" + value + '\'' +
                '}';
    }
}

ApplicationPropertyRepository.java

package us.copperdays.snippets.applicationproperty.demo;

import org.springframework.data.jpa.repository.JpaRepository;

public interface TestApplicationPropertyRepository extends JpaRepository<ApplicationProperty,String> {
}

ApplicationPropertySource.java

package us.copperdays.snippets.applicationproperty;

import java.util.function.Consumer;

/**
 * Define the basics of an application property source
 *
 * @param <K> type for keys
 */
public interface ApplicationPropertySource<K> {
    /**
     * Given the key, return the value
     *
     * @param key assocated with value
     * @param <T> type of the value
     * @return value assigned or null if not found
     */
    <T> T get(K key);

    /**
     * Is there a value for this key?

     * @param key is this associated with a value?
     * @return true if there is a value associated with this key
     */
    default boolean hasValue(K key) {
        return get(key)!=null;
    }

    /**
     * Given the key return associated value or fallback if not found
     *
     * @param key associated with value
     * @param fallback will be returned if
     * @param <T> value type
     * @return the value or the fallback if the key is not found
     */
    default <T> T get(K key, T fallback) {
        return hasValue(key) ? get(key) : fallback;
    }

    /**
     * Require a value for this key or throw an exception
     *
     * @param key associated with the value
     * @param <T> type of value
     * @return value for the given key
     * @throws PropertyNotFoundException if key is not found
     */
    default <T> T mustGet(K key) throws PropertyNotFoundException {
        if(!hasValue(key)) { throw new PropertyNotFoundException(key); }
        return get(key);
    }

    /**
     *
     * @param key
     * @param valueConsumer
     * @param <T>
     * @see #get(Object)
     */
    default <T> void visit(K key, Consumer<T> valueConsumer) {
        if(hasValue(key)) { valueConsumer.accept(get(key)); }
    }

    /**
     *
     * @param key
     * @param fallback
     * @param valueConsumer
     * @param <T>
     * @see #get(Object, Object)
     */
    default <T> void visit(K key, T fallback, Consumer<T> valueConsumer) {
        valueConsumer.accept(get(key, fallback));
    }

    /**
     *
     * @param key
     * @param valueConsumer
     * @param <T>
     * @see #mustGet(Object)
     */
    default <T> void mustVisit(K key, Consumer<T> valueConsumer) {
        valueConsumer.accept(mustGet(key));
    }

    /**
     * Check for new values in sources for properties
     */
    default void refresh() {};

    class PropertyNotFoundException extends RuntimeException {
        private Object key;

        public PropertyNotFoundException(Object key) {
            super("Could not find property with key ["+key+"]");
            this.key = key;
        }

        public Object getKey() {
            return key;
        }
    }
}

DemoPropertyKey.java

package us.copperdays.snippets.applicationproperty.demo;

public enum DemoPropertyKey {
    DISPATCHER_SCHEDULE,
    DISPATCHER_ENABLED,
    DISPATCHER_REPEAT_DELAY_MS
}

DemoPropertySourceImpl.java

package us.copperdays.snippets.applicationproperty.demo;

import us.copperdays.snippets.applicationproperty.*;

public class DemoPropertySourceImpl implements ApplicationPropertySource<DemoPropertyKey> {
    private ApplicationPropertyRepository repository;

    public DemoPropertySourceImpl(ApplicationPropertyRepository repository) {
        this.repository = repository;
    }

    @Override
    public <T> T get(MessageListenerPropertyKey key) {
        TestApplicationProperty one = repository.findOne(key.name());
        return one==null?null: (T) one.getValue();
    }
}