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Ehcache is an open source, standards-based cache used to boost performance,
offload the database and simplify scalability. Ehcache is robust, proven and full-featured and
this has made it the most widely-used Java-based cache.
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package org.jvnet.hk2.component;
import java.io.Serializable;
import java.util.Collection;
import java.util.Collections;
import java.util.LinkedHashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Set;
/**
* Map from a key to multiple values.
* Order is significant among values, and null values are allowed, although null keys are not.
*
* @author Kohsuke Kawaguchi
* @author Jerome Dochez
* @param The key of the multi-map
* @param The types in the multi-map
*/
public class MultiMap implements Serializable, Cloneable {
/**
* For serialization
*/
private static final long serialVersionUID = 893592003056170756L;
private final Map> store = new LinkedHashMap>();
/**
* Creates an empty multi-map with default concurrency controls
*/
public MultiMap() {
}
/**
* Copy constructor.
*
* @param base map to copy
*/
public MultiMap(MultiMap base) {
this();
for (Map.Entry> e : base.entrySet()) {
List value = newList(e.getValue());
if (!value.isEmpty()) {
store.put(e.getKey(), newList(e.getValue()));
}
}
}
/**
* Creates an optionally populated list to be used as an entry in the map.
*
* @param initialVal
* @return
*/
private List newList(Collection initialVals) {
if (null == initialVals) {
return new LinkedList();
}
return new LinkedList(initialVals);
}
/**
* Returns the set of keys associated with this MultiMap
*
* @return The set of keys currently available in this MultiMap. Will not return null,
* but may return a Set of lenght zero
*/
public Set keySet() {
return store.keySet();
}
/**
* Adds one more key-value pair.
*
* @param k key to store the entry under
* @param v value to store in the k's values.
*/
public final void add(K k, V v) {
List l = store.get(k);
if (l == null) {
l = newList(null);
store.put(k, l);
}
l.add(v);
}
/**
* Replaces all the existing values associated with the key
* by the given value. If v is empty the key k will
* be removed from the MultiMap.
*
* @param k key for the values
* @param v Can be null or empty.
*/
public void set(K k, Collection v) {
List addMe = newList(v);
if (addMe.isEmpty()) {
store.remove(k);
}
else {
store.put(k, newList(v));
}
}
/**
* Replaces all the existing values associated with the key
* by the given single value.
*
* @param k key for the values
* @param v singleton value for k key
*
* This is short for set(k,Collections.singleton(v))
*/
public void set(K k, V v) {
List vlist = newList(null);
vlist.add(v);
store.put(k, vlist);
}
/**
* Returns the elements indexed by the provided key
*
* @param k key for the values
* @return Can be empty but never null. Read-only.
*/
public final List get(K k) {
List l = store.get(k);
if (l == null) {
return Collections.emptyList();
}
return Collections.unmodifiableList(l);
}
/**
* This method merges all of the keys and values from another
* MultiMap into this MultiMap. If a key/value pair is
* found in both MultiMaps it is not re-added to this
* MultiMap, but is instead discarded
*
* @param another The MultiMap from which to add values
* to this MultiMap. If null this method does nothing
*/
public void mergeAll(MultiMap another) {
if (another == null) return;
for (Map.Entry> entry : another.entrySet()) {
List ourList = store.get(entry.getKey());
if (null == ourList) {
ourList = newList(entry.getValue());
if (!ourList.isEmpty()) {
store.put(entry.getKey(), ourList);
}
}
else {
for (V v : entry.getValue()) {
if (!ourList.contains(v)) {
ourList.add(v);
}
}
}
}
}
/**
* Package private (for getting the raw map for direct manipulation by the habitat)
*
* @param k the key
* @return
*/
private final List _get(K k) {
List l = store.get(k);
if (l == null) {
return Collections.emptyList();
}
return l;
}
/**
* Checks if the map contains the given key.
*
* @param k key to test
* @return true if the map contains at least one element for this key
*/
public boolean containsKey(K k) {
return !get(k).isEmpty();
}
/**
* Checks if the map contains the given key(s), also extending the search
* to including the sub collection.
*
* @param k1 key from top collection
* @param k2 key (value) from inner collection
* @return true if the map contains at least one element for these keys
*/
public boolean contains(K k1, V k2) {
List list = _get(k1);
return list.contains(k2);
}
/**
* Removes an key value from the map
*
* @param key key to be removed
* @return the value stored under this key or null if there was none
*/
public List remove(K key) {
return store.remove(key);
}
/**
* Removes an key value pair from the map. If the list of
* entries for that key is empty after the remove
* it will be removed from the set of keys
*
* @param key key to be removed
* @param entry the entry to be removed from the key'ed list
* @return true if there was none that was deleted
*/
public boolean remove(K key, V entry) {
List list = store.get(key);
if (list == null) return false;
boolean retVal = list.remove(entry);
if (list.isEmpty()) {
store.remove(key);
}
return retVal;
}
/**
* Gets the first value if any, or null.
*
* This is useful when you know the given key only has one value and you'd like
* to get to that value.
*
* @param k key for the values
* @return null if the key has no values or it has a value but the value is null.
*/
public V getOne(K k) {
return getFirst(k);
}
private V getFirst(K k) {
List lst = store.get(k);
if (null == lst) {
return null;
}
if (lst.isEmpty()) {
return null;
}
return lst.get(0);
}
/**
* Lists up all entries.
*
* @return a {@link java.util.Set} of {@link java.util.Map.Entry} of entries
*/
public Set>> entrySet() {
return store.entrySet();
}
/**
* @return the map as "key=value1,key=value2,...."
*/
public String toCommaSeparatedString() {
StringBuilder buf = new StringBuilder();
for (Map.Entry> e : entrySet()) {
for (V v : e.getValue()) {
if (buf.length() > 0) {
buf.append(',');
}
buf.append(e.getKey()).append('=').append(v);
}
}
return buf.toString();
}
/**
* Creates a copy of the map that contains the exact same key and value set.
* Keys and values won't cloned.
*/
@Override
public MultiMap clone() throws CloneNotSupportedException {
super.clone();
return new MultiMap(this);
}
/**
* Returns the size of the map. This returns the numbers
* of keys in the map, not the number of values
*
* @return integer or 0 if the map is empty
*/
public int size() {
return store.size();
}
@Override
public int hashCode() {
return store.hashCode();
}
@SuppressWarnings("unchecked")
@Override
public boolean equals(Object another) {
if (another == null ||
!(another instanceof MultiMap)) return false;
MultiMap other = (MultiMap) another;
return store.equals(other.store);
}
@Override
public String toString() {
final StringBuilder builder = new StringBuilder();
final String newline = System.getProperty("line.separator");
builder.append("{");
for (final K key : store.keySet()) {
builder.append(key).append(": ");
builder.append(store.get(key));
builder.append(newline);
}
builder.append("}");
return builder.toString();
}
}
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