我从文件读取中输入了以下内容，
1|VegemiteScroll|VS5|3|6.99
2|VegemiteScroll|VS5|5|8.99
3|BlueberryMuffin|MB11|2|9.95
4|BlueberryMuffin|MB11|5|16.95
5|BlueberryMuffin|MB11|8|24.95
6|Croissant|CF|3|5.95
7|Croissant|CF|5|9.95
我想使用group by将其放在Hashmap中，如下所示，让我们考虑＃1，＃2行。
Map obj = new HashMap();
obj.put(3,6.99);
obj.put(5,8.99);
List<Map> list = new ArrayList<>();
list.add(obj)
Map<String, List<Map>> map = new HashMap();
map.put("VS5", list);
这是针对第一种情况，对于第二和第三种情况（＃3至＃8），
map.put("MB11", list);
该列表包含上面的地图列表。您能不能请我使用java8流解决这个问题。预先感谢！
答案 0 :(得分：1)
下面是用于目的的代码。尚未完全优化。但这是有效的。
import java.io.File;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Scanner;
/**
*
*/
/**
* @author KishorRaskar
*
*/
public class Main {
/**
* @param args
* @throws Exception
*/
public static void main(String[] args) throws Exception {
// pass the path to the file as a parameter
File file =
new File("C:\\Data\\FAB\\WorkSpace\\Test\\MyCode\\test.txt");
Scanner sc = new Scanner(file);
List<HashMap> mapList = new ArrayList<>();
HashMap<String, String> dataMap = null;
HashMap<String, List<HashMap<String, String>>> dataMapList = new HashMap<>();
while (sc.hasNextLine()) {
String line = sc.nextLine();
if(null == line || line.isEmpty()) {
continue;
}
String[] dataArray = line.split("\\|");
//System.out.println(Arrays.toString(dataArray));
String dataMapKey = dataArray[3].trim();
String dataMapValue = dataArray[4].trim();
String dataMapListKey = dataArray[2].trim();
if(!dataMapList.containsKey(dataMapListKey)) {
dataMapList.put(dataMapListKey, new ArrayList<>());
dataMapList.get(dataMapListKey).add(new HashMap<>());
}
dataMapList.get(dataMapListKey).get(0).put(dataMapKey, dataMapValue);
//System.out.println(line);
}
System.out.println("###############################");
System.out.println(dataMapList);
System.out.println("###############################");
}
}
输入：test.txt 1 |素食滚动| VS5 | 3 | 6.99 2 |素食滚动| VS5 | 5 | 8.99
3 |蓝莓松饼| MB11 | 2 | 9.95 4 |蓝莓松饼| MB11 | 5 | 16.95 5 |蓝莓松饼| MB11 | 8 | 24.95
6 |羊角面包| CF | 3 | 5.95 7 |羊角面包| CF | 5 | 9.95 8 |羊角面包| CF | 9 | 16.99
输出：
##############################
{CF = [{3 = 5.95，5 = 9.95，9 = 16.99}]，MB11 = [{2 = 9.95，5 = 16.95，8 = 24.95}]，VS5 = [{3 = 6.99，5 = 8.99}]} ##############################
答案 1 :(得分：1)
这是一个使用Java 8 Streams，groupingBy和其他“奇特的东西”的解决方案。为了简单起见，我假设输入已经作为字符串提供了。
private static final int EXPECTED_LINE_ELEMENTS = 5;
private static final int LINE_KEY_INDEX = 2;
private static final int DATA_KEY_INDEX = 3;
private static final int DATA_VALUE_INDEX = 4;
private static Map<String, List<Map<Integer, Float>>> convert(final String input) {
return Stream.of(input.split("\\n")) // split input by new line character
.filter(line -> !line.trim().isEmpty()) // filter out empty lines
.map(line -> line.split("\\|")) // split each line by '|' character
.filter(line -> line.length == EXPECTED_LINE_ELEMENTS) // filter out potential elements containing undesired number of columns
.collect(Collectors.groupingBy(line -> line[LINE_KEY_INDEX])) // convert to map using 3rd column as a key and a list of corresponding lines as values
.entrySet()
.stream()
.collect(
Collectors.toMap(
Map.Entry::getKey, // keep the same key
stringListEntry -> Collections.singletonList(convertLinesToMap(stringListEntry.getValue())) // convert list of lines to a singleton list containing a map
)
);
}
private static Map<Integer, Float> convertLinesToMap(final List<String[]> lines) {
return lines.stream()
.collect(Collectors.toMap(
line -> Integer.valueOf(line[DATA_KEY_INDEX].trim()), // use 4th column as key of the map (mapped to Integer)
line -> Float.valueOf(line[DATA_VALUE_INDEX].trim())) // use 5th column as key of the map (mapped to Float)
);
}
然后，以下内容：
System.out.println(convert(input));
应打印以下内容：
{ CF =[{3=5.95, 5=9.95, 9=16.99}], VS5 =[{3=6.99, 5=8.99}], MB11 =[{2=9.95, 5=16.95, 8=24.95}]}
PS。如您所写：
Map obj = new HashMap();
obj.put(3,6.99);
obj.put(5,8.99);
我假设您想将Integers作为键，将Floats作为值。如果不是这种情况，则可以只更新convertLinesToMap方法的适当片段。