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/*
* Copyright (c) 2008-2013, Hazelcast, Inc. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.hazelcast.query;
import com.hazelcast.nio.ObjectDataInput;
import com.hazelcast.nio.ObjectDataOutput;
import com.hazelcast.nio.serialization.DataSerializable;
import com.hazelcast.query.impl.QueryContext;
import com.hazelcast.query.impl.QueryableEntry;
import com.hazelcast.util.IterationType;
import com.hazelcast.util.SortingUtil;
import java.io.IOException;
import java.util.AbstractMap;
import java.util.Collections;
import java.util.Comparator;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.LinkedList;
import java.util.Map;
import java.util.Set;
import java.util.List;
/**
* This class is a special Predicate which helps to get a page-by-page result of a query
* Can be constructed with a page-size, an inner predicate for filtering, A comparator for sorting \
* This class is not thread-safe and stateless. To be able to reuse for another query, one should call
* {@link PagingPredicate#reset()}
*
* Example usage could be seen like below;
*
* Predicate lessEqualThanFour = Predicates.lessEqual("this", 4);
*
* // We are constructing our paging predicate with a predicate and page size. In this case query results fetched two
* by two.
* PagingPredicate predicate = new PagingPredicate(lessEqualThanFour, 2);
*
* // we are initializing our map with integers from 0 to 10 as keys and values.
* IMap map = hazelcastInstance.getMap(...);
* for (int i = 0; i < 10; i++) {
* map.put(i, i);
* }
*
* // invoking the query
* Collection values = map.values(predicate);
* System.out.println("values = " + values) // will print 'values = [0, 1]'
* predicate.nextPage(); // we are setting up paging predicate to fetch next page in the next call.
* values = map.values(predicate);
* System.out.println("values = " + values);// will print 'values = [2, 3]'
* Entry anchor = predicate.getAnchor();
* System.out.println("anchor -> " + anchor); // will print 'anchor -> 1=1', since the anchor is the last entry of
* the previous page.
* predicate.previousPage(); // we are setting up paging predicate to fetch previous page in the next call
* values = map.values(predicate);
* System.out.println("values = " + values) // will print 'values = [0, 1]'
*
*/
public class PagingPredicate implements IndexAwarePredicate, DataSerializable {
private Predicate predicate;
private Comparator comparator;
private int pageSize;
private int page;
private final Map anchorMap = new LinkedHashMap();
private IterationType iterationType;
/**
* Used for serialization internally
*/
public PagingPredicate() {
}
/**
* Construct with a pageSize
* results will not be filtered
* results will be natural ordered
* throws {@link IllegalArgumentException} if pageSize is not greater than 0
*
* @param pageSize
*/
public PagingPredicate(int pageSize) {
if (pageSize <= 0) {
throw new IllegalArgumentException("pageSize should be greater than 0 !!!");
}
this.pageSize = pageSize;
}
/**
* Construct with an inner predicate and pageSize
* results will be filtered via inner predicate
* results will be natural ordered
* throws {@link IllegalArgumentException} if pageSize is not greater than 0
* throws {@link IllegalArgumentException} if inner predicate is also {@link PagingPredicate}
*
* @param predicate
* @param pageSize
*/
public PagingPredicate(Predicate predicate, int pageSize) {
this(pageSize);
setInnerPredicate(predicate);
}
/**
* Construct with a comparator and pageSize
* results will not be filtered
* results will be ordered via comparator
* throws {@link IllegalArgumentException} if pageSize is not greater than 0
*
* @param comparator
* @param pageSize
*/
public PagingPredicate(Comparator comparator, int pageSize) {
this(pageSize);
this.comparator = comparator;
}
/**
* Construct with an inner predicate, comparator and pageSize
* results will be filtered via inner predicate
* results will be ordered via comparator
* throws {@link IllegalArgumentException} if pageSize is not greater than 0
* throws {@link IllegalArgumentException} if inner predicate is also {@link PagingPredicate}
*
* @param predicate
* @param comparator
* @param pageSize
*/
public PagingPredicate(Predicate predicate, Comparator comparator, int pageSize) {
this(pageSize);
setInnerPredicate(predicate);
this.comparator = comparator;
}
private void setInnerPredicate(Predicate predicate) {
if (predicate instanceof PagingPredicate) {
throw new IllegalArgumentException("Nested PagingPredicate is not supported!!!");
}
this.predicate = predicate;
}
/**
* Used if inner predicate is instanceof {@link IndexAwarePredicate} for filtering
*
* @param queryContext
* @return
*/
@Override
public Set filter(QueryContext queryContext) {
if (predicate instanceof IndexAwarePredicate) {
Set set = ((IndexAwarePredicate) predicate).filter(queryContext);
if (set == null) {
return null;
}
List list = new LinkedList();
Map.Entry anchor = getAnchor();
for (QueryableEntry entry : set) {
// For comparison, objects to compare must be Comparable instance
if (SortingUtil.isSuitableForCompare(comparator, iterationType, entry)) {
if (anchor != null
&& SortingUtil.compare(comparator, iterationType, anchor, entry) >= 0) {
continue;
}
list.add(entry);
} else {
throw new IllegalArgumentException(
"If there is no comparator, "
+ "objects to compare (keys or values) must be comparable !");
}
}
if (list.isEmpty()) {
return null;
}
Collections.sort(list, SortingUtil.newComparator(this));
if (list.size() > pageSize) {
list = list.subList(0, pageSize);
}
return new LinkedHashSet(list);
}
return null;
}
/**
* Used if inner predicate is instanceof {@link IndexAwarePredicate} for checking if indexed
*
* @param queryContext
* @return
*/
@Override
public boolean isIndexed(QueryContext queryContext) {
if (predicate instanceof IndexAwarePredicate) {
return ((IndexAwarePredicate) predicate).isIndexed(queryContext);
}
return false;
}
/**
* Used for delegating filtering to inner predicate
*
* @param mapEntry
* @return
*/
@Override
public boolean apply(Map.Entry mapEntry) {
if (predicate != null) {
return predicate.apply(mapEntry);
}
return true;
}
/**
* After each query, an anchor entry is set for that page
* anchor entry is the last entry of the query
*
* @param anchor
*/
void setAnchor(Map.Entry anchor) {
if (anchor == null) {
previousPage();
return;
}
anchorMap.put(page + 1, anchor);
}
/**
* resets for reuse
*/
public void reset() {
iterationType = null;
anchorMap.clear();
page = 0;
}
/**
* setting the page value to next page
*/
public void nextPage() {
page++;
}
/**
* setting the page value to previous page
*/
public void previousPage() {
if (page != 0) {
page--;
}
}
public IterationType getIterationType() {
return iterationType;
}
public void setIterationType(IterationType iterationType) {
this.iterationType = iterationType;
}
public int getPage() {
return page;
}
public int getPageSize() {
return pageSize;
}
public Predicate getPredicate() {
return predicate;
}
public Comparator getComparator() {
return comparator;
}
/**
* Retrieve the anchor object which is the last value object on the previous page.
*
* Note: This method will return `null` on the first page of the query result.
* @return Map.Entry
*/
public Map.Entry getAnchor() {
return anchorMap.get(page);
}
@Override
public void writeData(ObjectDataOutput out) throws IOException {
out.writeObject(predicate);
out.writeObject(comparator);
out.writeInt(page);
out.writeInt(pageSize);
out.writeUTF(iterationType.name());
out.writeInt(anchorMap.size());
for (Map.Entry entry : anchorMap.entrySet()) {
out.writeInt(entry.getKey());
final Map.Entry anchorEntry = entry.getValue();
out.writeObject(anchorEntry.getKey());
out.writeObject(anchorEntry.getValue());
}
}
@Override
public void readData(ObjectDataInput in) throws IOException {
predicate = in.readObject();
comparator = in.readObject();
page = in.readInt();
pageSize = in.readInt();
iterationType = IterationType.valueOf(in.readUTF());
int size = in.readInt();
for (int i = 0; i < size; i++) {
final int key = in.readInt();
final Object anchorKey = in.readObject();
final Object anchorValue = in.readObject();
anchorMap.put(key, new AbstractMap.SimpleImmutableEntry(anchorKey, anchorValue));
}
}
}
