Does java have a “LinkedConcurrentHashMap” data structure?

Question

I need a data structure that is a LinkedHashMap and is thread safe.

How can I do that ?

Answer 1

I just tried synchronized bounded LRU Map based on insertion order LinkedConcurrentHashMap; with Read/Write Lock for synchronization. So when you are using iterator; you have to acquire WriteLock to avoid ConcurrentModificationException.
This is better than Collections.synchronizedMap.

public class LinkedConcurrentHashMap {

    private LinkedHashMap linkedHashMap = null;
    private final int cacheSize;  
    private ReadWriteLock readWriteLock = null;

    public LinkedConcurrentHashMap(LinkedHashMap psCacheMap, int size) {
        this.linkedHashMap  = psCacheMap;
        cacheSize = size;
        readWriteLock=new ReentrantReadWriteLock();
    }

    public void put(K key, V value) throws SQLException{
        Lock writeLock=readWriteLock.writeLock();
        try{
            writeLock.lock();
            if(linkedHashMap.size() >= cacheSize && cacheSize > 0){
                K oldAgedKey = linkedHashMap.keySet().iterator().next();
                remove(oldAgedKey);
            }
            linkedHashMap.put(key, value);
        }finally{
            writeLock.unlock();
        }
    }

    public V get(K key){
        Lock readLock=readWriteLock.readLock();
        try{
            readLock.lock();
            return linkedHashMap.get(key);
        }finally{
            readLock.unlock();
        }
    }

    public boolean containsKey(K key){
        Lock readLock=readWriteLock.readLock();
        try{
            readLock.lock();
            return linkedHashMap.containsKey(key);
        }finally{
            readLock.unlock();
        }
    }

    public V remove(K key){
        Lock writeLock=readWriteLock.writeLock();
        try{
            writeLock.lock();
            return linkedHashMap.remove(key);
        }finally{
            writeLock.unlock();
        }
    }

    public ReadWriteLock getLock(){
        return readWriteLock;
    }

    public Set> entrySet(){
        return linkedHashMap.entrySet();
    }
}