LazyList.java from Texai at Krugle
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/*
* 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.lang.reflect.Field;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;
import org.texai.kb.ejb.session.DomainEntityLoaderLocal;
import org.texai.kb.persistence.DomainProperty;
import org.texai.util.TexaiException;
/**
*
* @author reed
*/
public final class LazyList implements List {
/** the domain entity loader */
private final DomainEntityLoaderLocal domainEntityLoader;
/** the domain instance */
private final Object domainEntity;
/** the domain instance field */
private final Field field;
/** the domain property */
private final DomainProperty domainProperty;
/** the loaded list */
private List loadedList;
/** the indicator that the lazy list is currently being loaded */
private boolean isLoading = false;
/** the indicator that domain entities can be loaded from the cache */
private final boolean isLoadableFromDomainEntityCache;
/** Creates a new instance of LazyList.
*
* @param domainEntityLoader the domain entity loader
* @param domainInstance the domain instance
* @param field the domain instance field
* @param domainProperty the domain property
* @param isLoadableFromDomainEntityCache the indicator that domain entities can be loaded from the cache
*/
public LazyList(
final DomainEntityLoaderLocal domainEntityLoader,
final Object domainInstance,
final Field field,
final DomainProperty domainProperty,
final boolean isLoadableFromDomainEntityCache) {
super();
//Preconditions
assert domainEntityLoader != null : "domainEntityLoader must not be null";
assert domainInstance != null : "domainInstance must not be null";
assert field != null : "field must not be null";
assert domainProperty != null : "domainProperty must not be null";
this.domainEntityLoader = domainEntityLoader;
this.domainEntity = domainInstance;
this.field = field;
this.domainProperty = domainProperty;
this.isLoadableFromDomainEntityCache = isLoadableFromDomainEntityCache;
}
/** Gets the domain entity loader.
*
* @return the domain entity loader
*/
public DomainEntityLoaderLocal getDomainEntityLoader() {
return domainEntityLoader;
}
/** Gets the domain instance.
*
* @return the domain instance
*/
public Object getDomainInstance() {
return domainEntity;
}
/** Gets the domain instance field.
*
* @return the domain instance field
*/
public Field getField() {
return field;
}
/** Gets the domain property.
*
* @return the domain property
*/
public DomainProperty getDomainProperty() {
return domainProperty;
}
/** Lazily loads the list. */
@SuppressWarnings("unchecked")
private void loadTheList() {
if (! isLoading && loadedList == null) {
isLoading = true;
loadedList = (List) domainEntityLoader.loadDomainEntityField(
domainEntity,
field,
domainProperty,
isLoadableFromDomainEntityCache);
assert loadedList != null : "loadedList must not be null";
isLoading = false;
}
}
/** Returns whether this lazy list is in the process of loading.
*
* @return whether this lazy list is in the process of loading
*/
public boolean isLoading() {
return isLoading();
}
/** Returns whether this lazy list is loaded.
*
* @return whether this lazy list is loaded
*/
public boolean isLoaded() {
return !isLoading && loadedList != null;
}
/**
* Returns a string representation of this object.
*
* @return a string representation of this object
*/
@Override
public String toString() {
if (loadedList == null || isLoading) {
return "[LazyList for " + domainProperty + "]";
} else {
return loadedList.toString();
}
}
// 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
*/
public int size() {
if (isLoading) {
return 0;
} else {
loadTheList();
return loadedList.size();
}
}
/**
* Returns <tt>true</tt> if this list contains no elements.
*
* @return <tt>true</tt> if this list contains no elements
*/
public boolean isEmpty() {
if (isLoading) {
return true;
} 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 o element whose presence in this list is to be tested
* @return <tt>true</tt> if this list contains the specified element
* @throws ClassCastException if the type of the specified element
* is incompatible with this list (optional)
* @throws NullPointerException if the specified element is null and this
* list does not permit null elements (optional)
*/
public boolean contains(Object o) {
if (isLoading) {
throw new TexaiException("recursive call while loading lazy list");
} else {
loadTheList();
return loadedList.contains(o);
}
}
/**
* Returns an iterator over the elements in this list in proper sequence.
*
* @return an iterator over the elements in this list in proper sequence
*/
public Iterator iterator() {
if (isLoading) {
return (new ArrayList(0)).iterator();
} else {
loadTheList();
return loadedList.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
* @see Arrays#asList(Object[])
*/
public 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 a 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
* @throws ArrayStoreException if the runtime type of the specified array
* is not a supertype of the runtime type of every element in
* this list
* @throws NullPointerException if the specified array is null
*/
@SuppressWarnings("unchecked")
public Object[] toArray(Object[] a) {
if (isLoading) {
throw new TexaiException("recursive call while loading lazy list");
} else {
loadTheList();
return loadedList.toArray(a);
}
}
// 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 e element to be appended to this list
* @return <tt>true</tt> (as specified by {@link Collection#add})
* @throws UnsupportedOperationException if the <tt>add</tt> operation
* is not supported by this list
* @throws ClassCastException if the class of the specified element
* prevents it from being added to this list
* @throws NullPointerException if the specified element is null and this
* list does not permit null elements
* @throws IllegalArgumentException if some property of this element
* prevents it from being added to this list
*/
@SuppressWarnings("unchecked")
public boolean add(Object e) {
if (isLoading) {
throw new TexaiException("recursive call while loading lazy list");
} else {
loadTheList();
return loadedList.add(e);
}
}
/**
* 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 o element to be removed from this list, if present
* @return <tt>true</tt> if this list contained the specified element
* @throws ClassCastException if the type of the specified element
* is incompatible with this list (optional)
* @throws NullPointerException if the specified element is null and this
* list does not permit null elements (optional)
* @throws UnsupportedOperationException if the <tt>remove</tt> operation
* is not supported by this list
*/
public boolean remove(Object o) {
if (isLoading) {
throw new TexaiException("recursive call while loading lazy list");
} else {
loadTheList();
return loadedList.remove(o);
}
}
// Bulk Modification Operations
/**
* Returns <tt>true</tt> if this list contains all of the elements of the
* specified collection.
*
* @param c 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
* @throws ClassCastException if the types of one or more elements
* in the specified collection are incompatible with this
* list (optional)
* @throws NullPointerException if the specified collection contains one
* or more null elements and this list does not permit null
* elements (optional), or if the specified collection is null
* @see #contains(Object)
*/
@SuppressWarnings("unchecked")
public boolean containsAll(Collection c) {
if (isLoading) {
throw new TexaiException("recursive call while loading lazy list");
} else {
loadTheList();
return loadedList.containsAll(c);
}
}
/**
* 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 c collection containing elements to be added to this list
* @return <tt>true</tt> if this list changed as a result of the call
* @throws UnsupportedOperationException if the <tt>addAll</tt> operation
* is not supported by this list
* @throws ClassCastException if the class of an element of the specified
* collection prevents it from being added to this list
* @throws NullPointerException if the specified collection contains one
* or more null elements and this list does not permit null
* elements, or if the specified collection is null
* @throws IllegalArgumentException if some property of an element of the
* specified collection prevents it from being added to this list
* @see #add(Object)
*/
@SuppressWarnings("unchecked")
public boolean addAll(Collection c) {
if (isLoading) {
throw new TexaiException("recursive call while loading lazy list");
} else {
loadTheList();
return loadedList.addAll(c);
}
}
/**
* 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 c collection containing elements to be added to this list
* @return <tt>true</tt> if this list changed as a result of the call
* @throws UnsupportedOperationException if the <tt>addAll</tt> operation
* is not supported by this list
* @throws ClassCastException if the class of an element of the specified
* collection prevents it from being added to this list
* @throws NullPointerException if the specified collection contains one
* or more null elements and this list does not permit null
* elements, or if the specified collection is null
* @throws IllegalArgumentException if some property of an element of the
* specified collection prevents it from being added to this list
* @throws IndexOutOfBoundsException if the index is out of range
* (<tt>index < 0 || index > size()</tt>)
*/
@SuppressWarnings("unchecked")
public boolean addAll(int index, Collection c) {
if (isLoading) {
throw new TexaiException("recursive call while loading lazy list");
} else {
loadTheList();
return loadedList.addAll(index, c);
}
}
/**
* Removes from this list all of its elements that are contained in the
* specified collection (optional operation).
*
* @param c collection containing elements to be removed from this list
* @return <tt>true</tt> if this list changed as a result of the call
* @throws UnsupportedOperationException if the <tt>removeAll</tt> operation
* is not supported by this list
* @throws ClassCastException if the class of an element of this list
* is incompatible with the specified collection (optional)
* @throws NullPointerException if this list contains a null element and the
* specified collection does not permit null elements (optional),
* or if the specified collection is null
* @see #remove(Object)
* @see #contains(Object)
*/
@SuppressWarnings("unchecked")
public boolean removeAll(Collection c) {
if (isLoading) {
throw new TexaiException("recursive call while loading lazy list");
} else {
loadTheList();
return loadedList.removeAll(c);
}
}
/**
* 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 c collection containing elements to be retained in this list
* @return <tt>true</tt> if this list changed as a result of the call
* @throws UnsupportedOperationException if the <tt>retainAll</tt> operation
* is not supported by this list
* @throws ClassCastException if the class of an element of this list
* is incompatible with the specified collection (optional)
* @throws NullPointerException if this list contains a null element and the
* specified collection does not permit null elements (optional),
* or if the specified collection is null
* @see #remove(Object)
* @see #contains(Object)
*/
@SuppressWarnings("unchecked")
public boolean retainAll(Collection c) {
if (isLoading) {
throw new TexaiException("recursive call while loading lazy list");
} else {
loadTheList();
return loadedList.retainAll(c);
}
}
/**
* Removes all of the elements from this list (optional operation).
* The list will be empty after this call returns.
*
* @throws UnsupportedOperationException if the <tt>clear</tt> operation
* is not supported by this list
*/
public 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 o the object to be compared for equality with this list
* @return <tt>true</tt> if the specified object is equal to this list
*/
@Override
public boolean equals(Object o) {
if (isLoading) {
return this.equals(o);
} else {
loadTheList();
return loadedList.equals(o);
}
}
/**
* 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 int hashCode() {
if (isLoading) {
return this.hashCode();
} 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
* @throws IndexOutOfBoundsException if the index is out of range
* (<tt>index < 0 || index >= size()</tt>)
*/
public Object get(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
* @throws UnsupportedOperationException if the <tt>set</tt> operation
* is not supported by this list
* @throws ClassCastException if the class of the specified element
* prevents it from being added to this list
* @throws NullPointerException if the specified element is null and
* this list does not permit null elements
* @throws IllegalArgumentException if some property of the specified
* element prevents it from being added to this list
* @throws IndexOutOfBoundsException if the index is out of range
* (<tt>index < 0 || index >= size()</tt>)
*/
@SuppressWarnings("unchecked")
public Object set(int index, 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
* @throws UnsupportedOperationException if the <tt>add</tt> operation
* is not supported by this list
* @throws ClassCastException if the class of the specified element
* prevents it from being added to this list
* @throws NullPointerException if the specified element is null and
* this list does not permit null elements
* @throws IllegalArgumentException if some property of the specified
* element prevents it from being added to this list
* @throws IndexOutOfBoundsException if the index is out of range
* (<tt>index < 0 || index > size()</tt>)
*/
@SuppressWarnings("unchecked")
public void add(int index, 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
* @throws UnsupportedOperationException if the <tt>remove</tt> operation
* is not supported by this list
* @throws IndexOutOfBoundsException if the index is out of range
* (<tt>index < 0 || index >= size()</tt>)
*/
public Object remove(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 o 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
* @throws ClassCastException if the type of the specified element
* is incompatible with this list (optional)
* @throws NullPointerException if the specified element is null and this
* list does not permit null elements (optional)
*/
public int indexOf(Object o) {
if (isLoading) {
throw new TexaiException("recursive call while loading lazy list");
} else {
loadTheList();
return loadedList.indexOf(o);
}
}
/**
* 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 o 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
* @throws ClassCastException if the type of the specified element
* is incompatible with this list (optional)
* @throws NullPointerException if the specified element is null and this
* list does not permit null elements (optional)
*/
public int lastIndexOf(Object o) {
if (isLoading) {
throw new TexaiException("recursive call while loading lazy list");
} else {
loadTheList();
return loadedList.lastIndexOf(o);
}
}
// 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)
*/
public ListIterator listIterator() {
if (isLoading) {
return (new ArrayList(0)).listIterator();
} else {
loadTheList();
return loadedList.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
* @throws IndexOutOfBoundsException if the index is out of range
* (<tt>index < 0 || index > size()</tt>)
*/
public ListIterator listIterator(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
* @throws IndexOutOfBoundsException for an illegal endpoint index value
* (<tt>fromIndex < 0 || toIndex > size ||
* fromIndex > toIndex</tt>)
*/
public List subList(int fromIndex, int toIndex) {
if (isLoading) {
throw new TexaiException("recursive call while loading lazy list");
} else {
loadTheList();
return loadedList.subList(fromIndex, toIndex);
}
}
}
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