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Set of Java utility classes, all completely independent, to provide lightweight solutions for common situations
package com.tectonica.gae;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Set;
import java.util.concurrent.locks.Lock;
import com.google.appengine.api.datastore.Blob;
import com.google.appengine.api.datastore.DatastoreService;
import com.google.appengine.api.datastore.DatastoreServiceFactory;
import com.google.appengine.api.datastore.Entity;
import com.google.appengine.api.datastore.EntityNotFoundException;
import com.google.appengine.api.datastore.Key;
import com.google.appengine.api.datastore.KeyFactory;
import com.google.appengine.api.datastore.Query;
import com.google.appengine.api.datastore.Query.Filter;
import com.google.appengine.api.datastore.Query.FilterOperator;
import com.google.appengine.api.datastore.Query.FilterPredicate;
import com.tectonica.collections.KeyValueStore;
import com.tectonica.util.SerializeUtil;
public class GaeKeyValueStore extends KeyValueStore
{
private static DatastoreService ds = DatastoreServiceFactory.getDatastoreService();
private final Class valueClass;
private final String kind;
private final Key ancestor; // dummy parent for all entities to guarantee Datastore consistency
private final List> indexes;
public GaeKeyValueStore(Class valueClass, KeyMapper keyMapper)
{
super(keyMapper);
if (valueClass == null)
throw new NullPointerException();
this.valueClass = valueClass;
this.kind = valueClass.getSimpleName();
this.ancestor = KeyFactory.createKey(kind, BOGUS_ANCESTOR_KEY_NAME);
this.indexes = new ArrayList<>();
}
/***********************************************************************************
*
* GETTERS
*
***********************************************************************************/
@Override
public V get(String key)
{
try
{
return entityToValue(ds.get(KeyFactory.createKey(ancestor, kind, key)));
}
catch (EntityNotFoundException e)
{
return null;
}
}
@Override
public Iterator> iterator()
{
return entryIteratorOfQuery(newQuery()); // query without filters = all
}
@Override
public Iterator keyIterator()
{
return keyIteratorOfQuery(newQuery().setKeysOnly());
}
@Override
public Iterator valueIterator()
{
return valueIteratorOfQuery(newQuery());
}
@Override
public Iterator> iteratorFor(Set keySet)
{
Filter filter = new FilterPredicate(Entity.KEY_RESERVED_PROPERTY, FilterOperator.IN, keySet);
return entryIteratorOfQuery(newQuery().setFilter(filter));
}
/***********************************************************************************
*
* SETTERS (UTILS)
*
***********************************************************************************/
@Override
protected Modifier getModifier(final String key, ModificationType purpose)
{
// insert, replace and update are all treated the same in GAE: all simply do save()
return new Modifier()
{
@Override
public V getModifiableValue()
{
return get(key); // same implementation as read-only get, as in both cases we deserialize a new instance
}
@Override
public void commit(V value)
{
save(key, value);
}
};
}
@Override
public Lock getModificationLock(String key)
{
return GaeMemcacheLock.getLock(kind + ":" + key, true);
}
/***********************************************************************************
*
* SETTERS
*
***********************************************************************************/
@Override
public void insert(String key, V value)
{
save(key, value);
}
/***********************************************************************************
*
* DELETERS
*
***********************************************************************************/
@Override
public void delete(String key)
{
ds.delete(KeyFactory.createKey(ancestor, kind, key));
}
@Override
public void truncate()
{
for (Entity entity : ds.prepare(newQuery().setKeysOnly()).asIterable())
ds.delete(entity.getKey());
}
/***********************************************************************************
*
* INDEXES
*
***********************************************************************************/
@Override
public Index createIndex(String indexName, IndexMapper mapFunc)
{
GaeIndexImpl index = new GaeIndexImpl<>(mapFunc, indexName);
indexes.add(index);
return index;
}
/**
* GAE implementation of an index - simply exposes the Datastore property filters
*
* @author Zach Melamed
*/
public class GaeIndexImpl extends Index
{
public GaeIndexImpl(IndexMapper mapFunc, String name)
{
super(mapFunc, name);
if (name == null || name.isEmpty())
throw new RuntimeException("index name is mandatory in " + GaeIndexImpl.class.getSimpleName());
}
public Iterator keyIteratorOf(F f)
{
return keyIteratorOfQuery(newIndexQuery(f).setKeysOnly());
}
@Override
public Iterator valueIteratorOf(F f)
{
return valueIteratorOfQuery(newIndexQuery(f));
}
private Query newIndexQuery(F f)
{
Filter filter = new FilterPredicate(propertyName(), FilterOperator.EQUAL, f);
return newQuery().setFilter(filter);
}
private String propertyName()
{
return COL_NAME_INDEX_PREFIX + name;
}
private F getIndexedFieldOf(V value)
{
return mapper.getIndexedFieldOf(value);
}
}
/***********************************************************************************
*
* DATASTORE UTILS
*
***********************************************************************************/
private static final String COL_NAME_ENTRY_VALUE = "value";
private static final String COL_NAME_INDEX_PREFIX = "_i_";
private static final String BOGUS_ANCESTOR_KEY_NAME = " ";
private V entityToValue(Entity entity)
{
Blob blob = (Blob) entity.getProperty(COL_NAME_ENTRY_VALUE);
return SerializeUtil.bytesToObj(blob.getBytes(), valueClass);
}
private Entity entryToEntity(String key, V value)
{
Entity entity = new Entity(kind, key, ancestor);
entity.setProperty(COL_NAME_ENTRY_VALUE, new Blob(SerializeUtil.objToBytes(value)));
for (int i = 0; i < indexes.size(); i++)
{
GaeIndexImpl index = indexes.get(i);
Object field = (value == null) ? null : index.getIndexedFieldOf(value);
entity.setProperty(index.propertyName(), field);
}
return entity;
}
private void save(String key, V value)
{
ds.put(entryToEntity(key, value));
}
private Query newQuery()
{
return new Query(kind).setAncestor(ancestor);
}
private Iterator> entryIteratorOfQuery(Query q)
{
final Iterator iter = ds.prepare(q).asIterator();
return new Iterator>()
{
@Override
public boolean hasNext()
{
return iter.hasNext();
}
@Override
public KeyValue next()
{
final Entity entity = iter.next();
return new KeyValue()
{
@Override
public String getKey()
{
return entity.getKey().getName();
}
@Override
public V getValue()
{
return entityToValue(entity);
}
};
}
@Override
public void remove()
{
throw new UnsupportedOperationException();
}
};
}
private Iterator keyIteratorOfQuery(Query q)
{
final Iterator iter = ds.prepare(q).asIterator();
return new Iterator()
{
@Override
public boolean hasNext()
{
return iter.hasNext();
}
@Override
public String next()
{
return iter.next().getKey().getName();
}
@Override
public void remove()
{
throw new UnsupportedOperationException();
}
};
}
private Iterator valueIteratorOfQuery(Query q)
{
final Iterator iter = ds.prepare(q).asIterator();
return new Iterator()
{
@Override
public boolean hasNext()
{
return iter.hasNext();
}
@Override
public V next()
{
return entityToValue(iter.next());
}
@Override
public void remove()
{
throw new UnsupportedOperationException();
}
};
}
}