Main.java Source code

Introduction

Here is the source code for Main.java

Source

//package com.java2s;

import java.util.ArrayList;
import java.util.Arrays;

import java.util.Comparator;
import java.util.HashMap;

import java.util.List;
import java.util.Map;
import java.util.Set;

public class Main {
    /**
     * pre: takes a valid resultSet List, a columnName to group by<br>
     * post: separates the list into a List of List with each sub-list having the
     * same columnName value sorted by the natural comparator
     * 
     * @param resultSet
     * @param columnName
     * @return null if resultSet is null
     */
    @SuppressWarnings("rawtypes")
    public static List<List<Map>> splitSqlList(List<Map> resultSet, String columnName) {
        return splitSqlList(resultSet, columnName, null);
    }

    /**
     * 
     * pre: takes a valid resultSet List, a columnName to group by, a valid
     * comparator for the columnName's value<br>
     * post: separates the list into a List of List with each sub-list having the
     * same columnName value sorted by the keyComparator
     * 
     * @param resultSet
     * @param columnName
     * @param keyComparator
     * @return null if resultSet is null
     */
    @SuppressWarnings("rawtypes")
    public static List<List<Map>> splitSqlList(List<Map> resultSet, String columnName, Comparator keyComparator) {

        if (resultSet == null)
            return null;

        Map<Object, List<Map>> map = sqlMapListToMap(resultSet, columnName);
        Set keys = map.keySet();
        Object[] keyArray = keys.toArray();
        if (keyComparator == null) {
            Arrays.sort(keyArray);
        } else {
            Arrays.sort(keyArray, keyComparator);
        }

        List<List<Map>> rs = new ArrayList<List<Map>>(keyArray.length);
        for (Object key : keyArray) {
            rs.add(map.get(key));
        }
        return rs;
    }

    /**
     * 
     * pre : resultSet must be a valid List&lt;Map&gt; <br>
     * post : a Map&lt;columnName, List of same columnName&gt;
     * 
     * @param <K>
     * @param resultSet
     *          result set from sql. no need order by
     * @param columnName
     *          the column name that need to group by
     * @return null if resultSet is null
     */
    @SuppressWarnings("rawtypes")
    public static <K> Map<K, List<Map>> sqlMapListToMap(List<Map> resultSet, String columnName) {

        if (resultSet == null)
            return null;

        Map<K, List<Map>> rs = new HashMap<K, List<Map>>();
        for (Map<?, ?> map : resultSet) {

            K colValue = (K) map.get(columnName);

            List<Map> inMap = rs.get(colValue);
            if (inMap == null)
                inMap = new ArrayList<Map>();
            inMap.add(map);
            rs.put(colValue, inMap);
        }
        return rs;
    }
}