我想要一个Map实现,在其中我可以为put()事件添加侦听器。
标准库或任何第三方库中都有类似的内容吗?
我不知道有任何标准或第三方,但这很容易,只需创建一个类来包装另一个Map并实现Map接口:
public class MapListener<K, V> implements Map<K, V> {
private final Map<K, V> delegatee;
public MapListener(Map<K, V> delegatee) {
this.delegatee = delegatee;
}
// implement all Map methods, with callbacks you need.
}
调味。这是有代表性的,而非规范性的。当然,它也有问题。
public class ListenerMap extends HashMap {
public static final String PROP_PUT = "put";
private PropertyChangeSupport propertySupport;
public ListenerMap() {
super();
propertySupport = new PropertyChangeSupport(this);
}
public String getSampleProperty() {
return sampleProperty;
}
@Override
public Object put(Object k, Object v) {
Object old = super.put(k, v);
propertySupport.firePropertyChange(PROP_PUT, old, v);
return old;
}
public void addPropertyChangeListener(PropertyChangeListener listener) {
propertySupport.addPropertyChangeListener(listener);
}
public void removePropertyChangeListener(PropertyChangeListener listener) {
propertySupport.removePropertyChangeListener(listener);
}
}
这里是一个映射的工作示例,它在put和remove时触发属性更改事件。实现分为两类:
侦听器型号
包含与添加和删除更改侦听器相关的方法,以及用于激发属性更改的方法。
ListenerMap
通过委托扩展ListenerModel并实现java.util.Map接口。它只触发put和remove方法中的属性更改。在clear()、putAll()等其他方法上激发属性是有意义的。
ListenerModel
import java.beans.PropertyChangeListener;
import java.beans.PropertyChangeSupport;
public class ListenerModel {
private final PropertyChangeSupport changeSupport = new PropertyChangeSupport(this);
public void addPropertyChangeListener(PropertyChangeListener listener) {
changeSupport.addPropertyChangeListener(listener);
}
public void removePropertyChangeListener(PropertyChangeListener listener) {
changeSupport.removePropertyChangeListener(listener);
}
protected void firePropertyChange(String propertyName, Object oldValue, Object newValue) {
changeSupport.firePropertyChange(propertyName, oldValue, newValue);
}
}
ListenerMap
import java.util.*;
public class ListenerMap<K, V> extends ListenerModel implements Map<K, V> {
public static final String PROP_PUT = "put";
public static final String REMOVE_PUT = "remove";
private Map<K, V> delegate = new LinkedHashMap<>();
@Override
public void clear() {
delegate.clear();
}
@Override
public boolean containsKey(Object key) {
return delegate.containsKey(key);
}
@Override
public boolean containsValue(Object value) {
return delegate.containsValue(value);
}
@Override
public Set<Entry<K, V>> entrySet() {
return delegate.entrySet();
}
@Override
public V get(Object key) {
return delegate.get(key);
}
@Override
public boolean isEmpty() {
return delegate.isEmpty();
}
@Override
public Set<K> keySet() {
return delegate.keySet();
}
@Override
public V put(K key, V value) {
V oldValue = delegate.put(key, value);
firePropertyChange(PROP_PUT, oldValue == null ? null : new AbstractMap.SimpleEntry<>(key, oldValue),
new AbstractMap.SimpleEntry<>(key, value));
return oldValue;
}
@Override
public void putAll(Map<? extends K, ? extends V> m) {
delegate.putAll(m);
}
@Override
public V remove(Object key) {
V oldValue = delegate.remove(key);
firePropertyChange(REMOVE_PUT, oldValue == null ? null : new AbstractMap.SimpleEntry<>(key, oldValue),
null);
return oldValue;
}
@Override
public int size() {
return delegate.size();
}
@Override
public Collection<V> values() {
return delegate.values();
}
}
以下是JUnit 4测试:
import org.junit.Before;
import org.junit.Test;
import java.beans.PropertyChangeListener;
import java.util.Map;
import static org.hamcrest.core.Is.is;
import static org.hamcrest.core.IsNull.nullValue;
import static org.junit.Assert.assertThat;
/**
* Created by Gil on 01/07/2017.
*/
public class ListenerMapTest {
private ListenerMap<String, String> map;
@Before
public void setUp() throws Exception {
map = new ListenerMap<>();
}
@Test
public void whenPut_ShouldFireTrigger() throws Exception {
boolean[] fired = {false};
Map.Entry<String, String>[] listenEntry = new Map.Entry[1];
boolean[] checkNull = {true};
PropertyChangeListener propertyChangeListener = evt -> {
if (ListenerMap.PROP_PUT.equals(evt.getPropertyName())) {
if(checkNull[0]) {
assertThat(evt.getOldValue(), is(nullValue()));
}
else {
Map.Entry<String, String> oldValue = (Map.Entry<String, String>) evt.getOldValue();
assertThat(oldValue.getKey(), is("k1"));
assertThat(oldValue.getValue(), is("v1"));
}
listenEntry[0] = (Map.Entry<String, String>) evt.getNewValue();
fired[0] = true;
}
};
map.addPropertyChangeListener(propertyChangeListener);
map.put("k1", "v1");
assertThat(fired[0], is(true));
assertThat(listenEntry[0].getKey(), is("k1"));
assertThat(listenEntry[0].getValue(), is("v1"));
checkNull[0] = false;
map.put("k1", "v2");
}
@Test
public void whenRemove_ShouldNotFire() throws Exception {
boolean[] fired = {false};
PropertyChangeListener propertyChangeListener = evt -> {
fired[0] = true;
};
map.addPropertyChangeListener(propertyChangeListener);
map.put("k1", "v1");
assertThat(fired[0], is(true));
fired[0] = false;
map.removePropertyChangeListener(propertyChangeListener);
map.put("k2", "v2");
assertThat(fired[0], is(false));
}
}
您真正想要的是一个可以提供事件通知的Cache。有一些产品,比如Infinispan,已经为您提供了这些功能,但在不了解您的用例的情况下,很难推荐。
如果你想要一个简单的ObservableMap,它应该很容易实现。您只需创建一个Observer模式。你可以在这里找到一个例子。
Java在其javafx库中有一个javafx.coollections.ObservableMap接口。
ObservableMap实现可以在javafx.collections.FXCollections类中获得。
- observableHashMap()静态方法创建一个Observable HashMap
- observableMap(Map<K,V>Map)静态方法创建一个由传递到该方法中的映射实例支持的Observable转发映射
调用程序向ObservableMap实例注册MapChangeListener以接收onChanged事件。在onChanged事件处理程序中,可以询问MapChangeListener.Change方法参数以确定是否发生了put。