com.netflix.config.DerivedStringProperty Maven / Gradle / Ivy
/**
* Copyright 2014 Netflix, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.netflix.config;
import com.google.common.collect.Lists;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.util.List;
import java.util.concurrent.atomic.AtomicReference;
/**
* Derives a complex value from a {@link DynamicStringProperty}.
*
* @author mhawthorne
*/
public abstract class DerivedStringProperty implements Property {
private static final Logger log = LoggerFactory.getLogger(DerivedStringProperty.class);
private final DynamicStringProperty delegate;
private final List callbackList = Lists.newArrayList();
/**
* Holds derived value, which may be null.
*/
private final AtomicReference derived = new AtomicReference(null);
public DerivedStringProperty(String name, String defaultValue) {
delegate = DynamicPropertyFactory.getInstance().getStringProperty(name, defaultValue);
deriveAndSet();
Runnable callback = new Runnable() {
public void run() {
propertyChangedInternal();
}
};
delegate.addCallback(callback);
callbackList.add(callback);
}
/**
* Fetches derived value.
*/
public D get() {
return derived.get();
}
@Override
public D getValue() {
return get();
}
@Override
public D getDefaultValue() {
return derive(delegate.getDefaultValue());
}
@Override
public String getName() {
return delegate.getName();
}
@Override
public long getChangedTimestamp() {
return delegate.getChangedTimestamp();
}
@Override
public void addCallback(Runnable callback) {
delegate.addCallback(callback);
callbackList.add(callback);
}
/**
* Remove all callbacks registered through this instance of property
*/
@Override
public void removeAllCallbacks() {
for (Runnable callback: callbackList) {
delegate.prop.removeCallback(callback);
}
}
/**
* Invoked when property is updated with a new value. Should return the new derived value, which may be null.
*/
protected abstract D derive(String value);
/**
* {@link com.netflix.config.PropertyWrapper#propertyChanged()}
*/
protected void propertyChanged() {}
void propertyChangedInternal() {
deriveAndSet();
propertyChanged();
}
private void deriveAndSet() {
try {
derived.set(derive(this.delegate.get()));
} catch (Exception e) {
log.error("error when deriving initial value", e);
}
}
}