将逗号分隔的文本文件读入HashMap，其中文件在多行Java中具有相同的键

Question

我试图从逗号分隔文件和MeterID（文件中的第一项）读取日期作为键作为值。但我的问题是，该文件在多行中具有相同的日期，当我尝试将文件读入散列图时，我获得了每个键的额外空值。文件中的数据如下MeterID,ServiceLocationID,ESIID,ReadingDate,ReadingTime,kWh,rxKWh,KVARHImprt,KVARhExprt,kWhImprtRateA,kWhImprtRateB,kWhExprtRateA,kWhExprtRateB,kVARhImprtRateA,kVARhImprtRateB,kVARhExprtRateA,kVARhExprtRateB,kVARhTotalRateA,kVARhTotalRateB,ExprtkVARhTotalRateA,ExprtkVARhTotalRateB 1182798,,,13/04/2018,12:00:00AM,12391.000,0.000,,,6196.991,6194.366,0.074,0.000,1119.000,1132.000,0.000,0.000,,,, 1182799,,,14/04/2018,12:00:00AM,690.000,0.000,,,348.468,342.449,0.074,0.000,95.000,96.000,0.000,0.000,,,, 1182800,,,15/04/2018,12:00:00AM,2863.000,0.000,,,1133.865,1729.365,0.074,0.000,37.000,21.000,156.000,135.000,,,, 1182801,,,16/04/2018,12:00:00AM,1578.000,0.000,,,1065.586,512.603,0.074,0.000,225.000,199.000,27.000,14.000,,,, 1182802,,,17/04/2018,12:00:00AM,2059.000,0.000,,,716.310,1343.338,0.074,0.000,58.000,85.000,63.000,78.000,,,, 1182803,,,18/04/2018,12:00:00AM,1824.000,0.000,,,755.363,1069.038,0.074,0.000,234.000,289.000,65.000,73.000,,,, 1182804,,,18/04/2018,12:00:00AM,1824.000,0.000,,,755.363,1069.038,0.074,0.000,234.000,289.000,65.000,73.000,,,,请参阅下面的代码，将文件中的数据读入hashmapString filePath = "electric-enhanced_0000_201804130555.txt";    String delimiter = ",";    HashMap<String, String> map = new HashMap<>();    try (Stream<String> lines = Files.lines(Paths.get(filePath)).skip(1)) {        lines.filter(line -> line.contains(delimiter)).forEach(line -> map.put(line.split(delimiter)[3],                line.split(delimiter)[0] + "," + map.get(line.split(delimiter)[3])));    }    System.out.println(map);例外结果是{15/04/028 = 1182800,14 / 04/2018 = 1182799,17 / 04/2018 = 1182802,18 / 04/2018 = 1182804,1182803,16 / 04/2018 = 1182801,13 / 04/2018 = 1182798 }实际结果是 - 我想要排除的每个键都会出现null{15/04/028 = 1182800，null，14 / 04/2018 = 1182799，null，17 / 04/2018 = 1182802，null，18/04/2018 = 1182804,1182803，null，16 / 04/2018 = 1182801 ，null，13/04/2018 = 1182798，null}

Answer 1

它应该足够写：

lines.stream().filter(line -> line.contains(delimiter)).forEach(line -> map.put(line.split(delimiter)[3],

                    line.split(delimiter)[0]));

您可能还想替换您HashMap的例如org.apache.commons.collections.map.MultiValueMap，这将允许您在同一个键下存储多个值。

所以：

Map<String, String> map = new MultiValueMap();

我在测试数据中添加了一行，现在日期18/04/2018出现两次，输出为{15/04/2018 = [1182800]，14/04/2018 = [1182799]，18/04/2018 = [1182803,1162804]，16 / 04/2018 = [1182801]，13 / 04/2018 = [1182798]