/*
* LazyList.java
*
* Created on January 18, 2007, 12:48 PM
*
* Description: Provides a means to lazily load a List field.
*
* Copyright (C) 2007 Stephen L. Reed.
*
* This program is free software; you can redistribute it and/or modify it under the terms
* of the GNU General Public License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
* without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
* See the GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along with this program;
* if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
package org.texai.kb.persistence.lazy;
import java.io.Serializable;
import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;
import java.util.Map;
import net.jcip.annotations.ThreadSafe;
import org.openrdf.model.URI;
import org.openrdf.model.Value;
import org.openrdf.repository.RepositoryConnection;
import org.openrdf.repository.RepositoryException;
import org.texai.kb.persistence.DistributedRepositoryManager;
import org.texai.kb.persistence.RDFEntityLoader;
import org.texai.kb.persistence.RDFPersistent;
import org.texai.kb.persistence.RDFProperty;
import org.texai.util.TexaiException;
/** Provides a facility that lazily loads a List field. The list value is loaded automatically from the RDF store when any of its methods are invoked.
* The method call is delegated to the loaded list. Subsequent references to the list field obtain the loaded list directly. Note that because
* not-yet-loaded lazy lists are not persisted to the RDF store, before they are copied into another persistent field they should first be
* initialized (loaded) by invoking any of their defined methods (e.g. size()).
*
* @author reed
*/
@ThreadSafe
public final class LazyList implements List, Serializable {
/** the serial version UID */
private static final long serialVersionUID = 1L;
/** the repository name */
private final String repositoryName;
/** the RDF instance */
private final RDFPersistent rdfEntity;
/** the RDF instance field */
private transient Field field;
/** the RDF instance field name */
private final String fieldName;
/** the RDF property */
private final RDFProperty rdfProperty;
/** the predicate values dictionary, predicate --> RDF values */
private final Map<URI, List<Value>> predicateValuesDictionary;
/** the loaded list */
private List loadedList;
/** the indicator that the lazy list is currently being loaded */
private boolean isLoading = false;
/*** Creates a new instance of LazyList.
*
* @param repositoryConnection the repository connection
* @param rdfEntity the RDF instance
* @param field the RDF instance field
* @param rdfProperty the RDF property
* @param predicateValuesDictionary the predicate values dictionary, predicate --> RDF values
*/
public LazyList(
final RepositoryConnection repositoryConnection,
final RDFPersistent rdfEntity,
final Field field,
final RDFProperty rdfProperty,
final Map<URI, List<Value>> predicateValuesDictionary) {
super();
//Preconditions
assert repositoryConnection != null : "repositoryConnection must not be null";
assert rdfEntity != null : "rdfEntity must not be null";
assert field != null : "field must not be null";
assert rdfProperty != null : "rdfProperty must not be null";
assert predicateValuesDictionary != null : "predicateValuesDictionary must not be null";
repositoryName = repositoryConnection.getRepository().getDataDir().getName();
this.rdfEntity = rdfEntity;
this.field = field;
this.fieldName = field.getName();
this.rdfProperty = rdfProperty;
this.predicateValuesDictionary = predicateValuesDictionary;
}
/** Gets the loaded list.
*
* @return the loaded list
*/
public synchronized List getLoadedList() {
if (isLoading) {
return null; // NOPMD
} else {
loadTheList();
return loadedList;
}
}
/** Lazily loads the list. */
private synchronized void loadTheList() {
if (!isLoading && loadedList == null) {
isLoading = true;
final RDFEntityLoader rdfEntityLoader = new RDFEntityLoader();
// obtain a new repository connection from the named repository
final RepositoryConnection repositoryConnection =
DistributedRepositoryManager.getInstance().getRepositoryConnectionForRepositoryName(repositoryName);
if (field == null) {
try {
field = rdfEntity.getClass().getField(fieldName);
} catch (NoSuchFieldException | SecurityException ex) {
throw new TexaiException(ex);
}
}
loadedList = (List) rdfEntityLoader.loadLazyRDFEntityField(
repositoryConnection,
rdfEntity,
field,
rdfProperty,
predicateValuesDictionary);
assert loadedList != null : "loadedList must not be null";
try {
repositoryConnection.close();
} catch (final RepositoryException ex) {
throw new TexaiException(ex);
} finally {
isLoading = false;
}
}
}
/**
* Returns a string representation of this object.
*
* @return a string representation of this object
*/
@Override
public String toString() {
String string;
if (loadedList == null || isLoading) {
string = "[LazyList for " + rdfProperty + "]";
} else {
string = loadedList.toString();
}
return string;
}
// the List methods
/**
* Returns the number of elements in this list. If this list contains
* more than <tt>Integer.MAX_VALUE</tt> elements, returns
* <tt>Integer.MAX_VALUE</tt>.
*
* @return the number of elements in this list
*/
@Override
public synchronized int size() {
int size;
if (isLoading) {
size = 0;
} else {
loadTheList();
size = loadedList.size();
}
return size;
}
/**
* Returns <tt>true</tt> if this list contains no elements.
*
* @return <tt>true</tt> if this list contains no elements
*/
@Override
public synchronized boolean isEmpty() {
if (isLoading) {
return true; // NOPMD
} else {
loadTheList();
return loadedList.isEmpty();
}
}
/**
* Returns <tt>true</tt> if this list contains the specified element.
* More formally, returns <tt>true</tt> if and only if this list contains
* at least one element <tt>e</tt> such that
* <tt>(o==null ? e==null : o.equals(e))</tt>.
*
* @param element element whose presence in this list is to be tested
* @return <tt>true</tt> if this list contains the specified element
*/
@Override
public synchronized boolean contains(final Object element) {
if (isLoading) {
throw new TexaiException("recursive call while loading lazy list"); // NOPMD
} else {
loadTheList();
return loadedList.contains(element);
}
}
/**
* Returns an iterator over the elements in this list in proper sequence.
*
* @return an iterator over the elements in this list in proper sequence
*/
@Override
public synchronized Iterator<?> iterator() {
Iterator<?> iterator;
if (isLoading) {
iterator = (new ArrayList(0)).iterator();
} else {
loadTheList();
iterator = loadedList.iterator();
}
return iterator;
}
/**
* Returns an array containing all of the elements in this list in proper
* sequence (from first to last element).
*
* <p>The returned array will be "safe" in that no references to it are
* maintained by this list. (In other words, this method must
* allocate a new array even if this list is backed by an array).
* The caller is thus free to modify the returned array.
*
* <p>This method acts as bridge between array-based and collection-based
* APIs.
*
* @return an array containing all of the elements in this list in proper
* sequence
*/
@Override
public synchronized Object[] toArray() {
if (isLoading) {
throw new TexaiException("recursive call while loading lazy list");
} else {
loadTheList();
return loadedList.toArray();
}
}
/**
* Returns an array containing all of the elements in this list in
* proper sequence (from first to last element); the runtime type of
* the returned array is that of the specified array. If the list fits
* in the specified array, it is returned therein. Otherwise, a new
* array is allocated with the runtime type of the specified array and
* the size of this list.
*
* <p>If the list fits in the specified array with room to spare (i.e.,
* the array has more elements than the list), the element in the array
* immediately following the end of the list is set to <tt>null</tt>.
* (This is useful in determining the length of the list <i>only</i> if
* the caller knows that the list does not contain any null elements.)
*
* <p>Like the {@link #toArray()} method, this method acts as bridge between
* array-based and collection-based APIs. Further, this method allows
* precise control over the runtime type of the output array, and may,
* under certain circumstances, be used to save allocation costs.
*
* <p>Suppose <tt>x</tt> is a list known to contain only strings.
* The following code can be used to dump the list into a newly
* allocated array of <tt>String</tt>:
*
* <pre>
* String[] y = x.toArray(new String[0]);</pre>
*
* Note that <tt>toArray(new Object[0])</tt> is identical in function to
* <tt>toArray()</tt>.
*
* @param array the array into which the elements of this list are to
* be stored, if it is big enough; otherwise, a new array of the
* same runtime type is allocated for this purpose.
* @return an array containing the elements of this list
*/
@Override
@SuppressWarnings("unchecked")
public synchronized Object[] toArray(final Object[] array) {
if (isLoading) {
throw new TexaiException("recursive call while loading lazy list");
} else {
loadTheList();
return loadedList.toArray(array);
}
}
// Modification Operations
/**
* Appends the specified element to the end of this list (optional
* operation).
*
* <p>Lists that support this operation may place limitations on what
* elements may be added to this list. In particular, some
* lists will refuse to add null elements, and others will impose
* restrictions on the type of elements that may be added. List
* classes should clearly specify in their documentation any restrictions
* on what elements may be added.
*
* @param element element to be appended to this list
* @return <tt>true</tt> (as specified by {@link Collection#add})
*/
@Override
@SuppressWarnings("unchecked")
public synchronized boolean add(final Object element) {
if (isLoading) {
throw new TexaiException("recursive call while loading lazy list");
} else {
loadTheList();
return loadedList.add(element);
}
}
/**
* Removes the first occurrence of the specified element from this list,
* if it is present (optional operation). If this list does not contain
* the element, it is unchanged. More formally, removes the element with
* the lowest index <tt>i</tt> such that
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>
* (if such an element exists). Returns <tt>true</tt> if this list
* contained the specified element (or equivalently, if this list changed
* as a result of the call).
*
* @param element element to be removed from this list, if present
* @return <tt>true</tt> if this list contained the specified element
*/
@Override
public synchronized boolean remove(final Object element) {
if (isLoading) {
throw new TexaiException("recursive call while loading lazy list");
} else {
loadTheList();
return loadedList.remove(element);
}
}
// Bulk Modification Operations
/**
* Returns <tt>true</tt> if this list contains all of the elements of the
* specified collection.
*
* @param collection collection to be checked for containment in this list
* @return <tt>true</tt> if this list contains all of the elements of the
* specified collection
* @see #contains(Object)
*/
@SuppressWarnings("unchecked")
public synchronized boolean containsAll(final Collection collection) {
if (isLoading) {
throw new TexaiException("recursive call while loading lazy list");
} else {
loadTheList();
return loadedList.containsAll(collection);
}
}
/**
* Appends all of the elements in the specified collection to the end of
* this list, in the order that they are returned by the specified
* collection's iterator (optional operation). The behavior of this
* operation is undefined if the specified collection is modified while
* the operation is in progress. (Note that this will occur if the
* specified collection is this list, and it's nonempty.)
*
* @param collection collection containing elements to be added to this list
* @return <tt>true</tt> if this list changed as a result of the call
* @see #add(Object)
*/
@SuppressWarnings("unchecked")
@Override
public synchronized boolean addAll(final Collection collection) {
if (isLoading) {
throw new TexaiException("recursive call while loading lazy list");
} else {
loadTheList();
return loadedList.addAll(collection);
}
}
/**
* Inserts all of the elements in the specified collection into this
* list at the specified position (optional operation). Shifts the
* element currently at that position (if any) and any subsequent
* elements to the right (increases their indices). The new elements
* will appear in this list in the order that they are returned by the
* specified collection's iterator. The behavior of this operation is
* undefined if the specified collection is modified while the
* operation is in progress. (Note that this will occur if the specified
* collection is this list, and it's nonempty.)
*
* @param index index at which to insert the first element from the
* specified collection
* @param collection collection containing elements to be added to this list
* @return <tt>true</tt> if this list changed as a result of the call
*/
@SuppressWarnings("unchecked")
public synchronized boolean addAll(final int index, final Collection collection) {
if (isLoading) {
throw new TexaiException("recursive call while loading lazy list");
} else {
loadTheList();
return loadedList.addAll(index, collection);
}
}
/**
* Removes from this list all of its elements that are contained in the
* specified collection (optional operation).
*
* @param collection collection containing elements to be removed from this list
* @return <tt>true</tt> if this list changed as a result of the call
* @see #remove(Object)
* @see #contains(Object)
*/
@SuppressWarnings("unchecked")
@Override
public synchronized boolean removeAll(final Collection collection) {
if (isLoading) {
throw new TexaiException("recursive call while loading lazy list");
} else {
loadTheList();
return loadedList.removeAll(collection);
}
}
/**
* Retains only the elements in this list that are contained in the
* specified collection (optional operation). In other words, removes
* from this list all the elements that are not contained in the specified
* collection.
*
* @param collection collection containing elements to be retained in this list
* @return <tt>true</tt> if this list changed as a result of the call
* @see #remove(Object)
* @see #contains(Object)
*/
@SuppressWarnings("unchecked")
@Override
public synchronized boolean retainAll(final Collection collection) {
if (isLoading) {
throw new TexaiException("recursive call while loading lazy list");
} else {
loadTheList();
return loadedList.retainAll(collection);
}
}
/**
* Removes all of the elements from this list (optional operation).
* The list will be empty after this call returns.
*/
@Override
public synchronized void clear() {
if (isLoading) {
throw new TexaiException("recursive call while loading lazy list");
} else {
loadTheList();
loadedList.clear();
}
}
// Comparison and hashing
/**
* Compares the specified object with this list for equality. Returns
* <tt>true</tt> if and only if the specified object is also a list, both
* lists have the same size, and all corresponding pairs of elements in
* the two lists are <i>equal</i>. (Two elements <tt>e1</tt> and
* <tt>e2</tt> are <i>equal</i> if <tt>(e1==null ? e2==null :
* e1.equals(e2))</tt>.) In other words, two lists are defined to be
* equal if they contain the same elements in the same order. This
* definition ensures that the equals method works properly across
* different implementations of the <tt>List</tt> interface.
*
* @param obj the object to be compared for equality with this list
* @return <tt>true</tt> if the specified object is equal to this list
*/
@Override
@SuppressWarnings("EqualsWhichDoesntCheckParameterClass")
public synchronized boolean equals(final Object obj) {
if (isLoading) {
return super.equals(obj); // NOPMD
} else {
loadTheList();
return loadedList.equals(obj);
}
}
/**
* Returns the hash code value for this list. The hash code of a list
* is defined to be the result of the following calculation:
* <pre>
* int hashCode = 1;
* Iterator<E> i = list.iterator();
* while (i.hasNext()) {
* E obj = i.next();
* hashCode = 31*hashCode + (obj==null ? 0 : obj.hashCode());
* }
* </pre>
* This ensures that <tt>list1.equals(list2)</tt> implies that
* <tt>list1.hashCode()==list2.hashCode()</tt> for any two lists,
* <tt>list1</tt> and <tt>list2</tt>, as required by the general
* contract of {@link Object#hashCode}.
*
* @return the hash code value for this list
* @see Object#equals(Object)
* @see #equals(Object)
*/
@Override
public synchronized int hashCode() {
if (isLoading) {
return super.hashCode(); // NOPMD
} else {
loadTheList();
return loadedList.hashCode();
}
}
// Positional Access Operations
/**
* Returns the element at the specified position in this list.
*
* @param index index of the element to return
* @return the element at the specified position in this list
*/
@Override
public synchronized Object get(final int index) {
if (isLoading) {
throw new TexaiException("recursive call while loading lazy list");
} else {
loadTheList();
return loadedList.get(index);
}
}
/**
* Replaces the element at the specified position in this list with the
* specified element (optional operation).
*
* @param index index of the element to replace
* @param element element to be stored at the specified position
* @return the element previously at the specified position
*/
@SuppressWarnings("unchecked")
@Override
public synchronized Object set(final int index, final Object element) {
if (isLoading) {
throw new TexaiException("recursive call while loading lazy list");
} else {
loadTheList();
return loadedList.set(index, element);
}
}
/**
* Inserts the specified element at the specified position in this list
* (optional operation). Shifts the element currently at that position
* (if any) and any subsequent elements to the right (adds one to their
* indices).
*
* @param index index at which the specified element is to be inserted
* @param element element to be inserted
*/
@SuppressWarnings("unchecked")
@Override
public synchronized void add(final int index, final Object element) {
if (isLoading) {
throw new TexaiException("recursive call while loading lazy list");
} else {
loadTheList();
loadedList.add(index, element);
}
}
/**
* Removes the element at the specified position in this list (optional
* operation). Shifts any subsequent elements to the left (subtracts one
* from their indices). Returns the element that was removed from the
* list.
*
* @param index the index of the element to be removed
* @return the element previously at the specified position
*/
@Override
public synchronized Object remove(final int index) {
if (isLoading) {
throw new TexaiException("recursive call while loading lazy list");
} else {
loadTheList();
return loadedList.remove(index);
}
}
// Search Operations
/**
* Returns the index of the first occurrence of the specified element
* in this list, or -1 if this list does not contain the element.
* More formally, returns the lowest index <tt>i</tt> such that
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
* or -1 if there is no such index.
*
* @param element element to search for
* @return the index of the first occurrence of the specified element in
* this list, or -1 if this list does not contain the element
*/
@Override
public synchronized int indexOf(final Object element) {
if (isLoading) {
throw new TexaiException("recursive call while loading lazy list");
} else {
loadTheList();
return loadedList.indexOf(element);
}
}
/**
* Returns the index of the last occurrence of the specified element
* in this list, or -1 if this list does not contain the element.
* More formally, returns the highest index <tt>i</tt> such that
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
* or -1 if there is no such index.
*
* @param element element to search for
* @return the index of the last occurrence of the specified element in
* this list, or -1 if this list does not contain the element
*/
@Override
public synchronized int lastIndexOf(final Object element) {
if (isLoading) {
throw new TexaiException("recursive call while loading lazy list");
} else {
loadTheList();
return loadedList.lastIndexOf(element);
}
}
// List Iterators
/**
* Returns a list iterator over the elements in this list (in proper
* sequence).
*
* @return a list iterator over the elements in this list (in proper
* sequence)
*/
@Override
public synchronized ListIterator<?> listIterator() {
ListIterator<?> listIterator;
if (isLoading) {
listIterator = (new ArrayList(0)).listIterator();
} else {
loadTheList();
listIterator = loadedList.listIterator();
}
return listIterator;
}
/**
* Returns a list iterator of the elements in this list (in proper
* sequence), starting at the specified position in this list.
* The specified index indicates the first element that would be
* returned by an initial call to {@link ListIterator#next next}.
* An initial call to {@link ListIterator#previous previous} would
* return the element with the specified index minus one.
*
* @param index index of first element to be returned from the
* list iterator (by a call to the <tt>next</tt> method)
* @return a list iterator of the elements in this list (in proper
* sequence), starting at the specified position in this list
final */
@Override
public synchronized ListIterator<?> listIterator(final int index) {
if (isLoading) {
throw new TexaiException("recursive call while loading lazy list");
} else {
loadTheList();
return loadedList.listIterator(index);
}
}
// View
/**
* Returns a view of the portion of this list between the specified
* <tt>fromIndex</tt>, inclusive, and <tt>toIndex</tt>, exclusive. (If
* <tt>fromIndex</tt> and <tt>toIndex</tt> are equal, the returned list is
* empty.) The returned list is backed by this list, so non-structural
* changes in the returned list are reflected in this list, and vice-versa.
* The returned list supports all of the optional list operations supported
* by this list.<p>
*
* This method eliminates the need for explicit range operations (of
* the sort that commonly exist for arrays). Any operation that expects
* a list can be used as a range operation by passing a subList view
* instead of a whole list. For example, the following idiom
* removes a range of elements from a list:
* <pre>
* list.subList(from, to).clear();
* </pre>
* Similar idioms may be constructed for <tt>indexOf</tt> and
* <tt>lastIndexOf</tt>, and all of the algorithms in the
* <tt>Collections</tt> class can be applied to a subList.<p>
*
* The semantics of the list returned by this method become undefined if
* the backing list (i.e., this list) is <i>structurally modified</i> in
* any way other than via the returned list. (Structural modifications are
* those that change the size of this list, or otherwise perturb it in such
* a fashion that iterations in progress may yield incorrect results.)
*
* @param fromIndex low endpoint (inclusive) of the subList
* @param toIndex high endpoint (exclusive) of the subList
* @return a view of the specified range within this list
*/
@Override
public synchronized List subList(final int fromIndex, final int toIndex) {
if (isLoading) {
throw new TexaiException("recursive call while loading lazy list");
} else {
loadTheList();
return loadedList.subList(fromIndex, toIndex);
}
}
}