PageSortUtils.java

/*
 * Copyright 2016 Red Hat, Inc. and/or its affiliates.
 *
 * 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 org.guvnor.ala.registry.local.utils;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class PageSortUtils {

    public static <T> List<T> pageSort( Collection<T> values, Comparator<T> comparator, Integer page, Integer pageSize, String sort, boolean sortOrder ) {
        if ( page < 0 ) {
            throw new IllegalStateException( "Page must be greater or equals than 0" );
        }
        if ( pageSize < 1 ) {
            throw new IllegalStateException( "PageSize must be greater than 0" );
        }
        // If the page is 0 and the amount of values is less than the pageSize, just return the values
        if ( page == 0 && values.size() <= pageSize ) {
            List<T> result = new ArrayList<>( values );
            sort( result, comparator, sort, sortOrder );
            return result;
        }
        // if the values are less than  (pageSize * page) means that in the requested page there is no item
        if ( values.size() <= pageSize * page ) {
            return Collections.emptyList();
        }
        List<T> result = new ArrayList<>( pageSize );
        List<T> allValues = new ArrayList<>( values );
        for ( int i = page * pageSize; i < ( page * pageSize ) + pageSize; i++ ) {
            if ( allValues.size() > i ) {
                result.add( allValues.get( i ) );
            }
        }
        sort( result, comparator, sort, sortOrder );
        return result;
    }

    private static <T> void sort( List<T> list, Comparator<T> comparator, String sort, boolean sortOrder ) {
        if ( sort != null && !sort.equals( "" ) ) {
            list.sort( comparator );
            if ( !sortOrder ) {
                Collections.reverse( list );
            }
        }
    }
}