开发环境：jdk 1.8

需求一：
1、统计每个小时(升序)不同事件的产品产量
2、统计不同事件（OK 、NG）的总产量

public static void main(String[] args) {//数据源List<Map<String, Object>> list = new ArrayList<Map<String,Object>>();Map<String, Object> map1 = new HashMap<String, Object>();map1.put("hour", "10");//小时map1.put("event", "OK");//事件map1.put("number", 12);//产量list.add(map1);Map<String, Object> map2 = new HashMap<String, Object>();map2.put("hour", "08");map2.put("event", "NG");map2.put("number", 10);list.add(map2);Map<String, Object> map3 = new HashMap<String, Object>();map3.put("hour", "09");map3.put("event", "NG");map3.put("number", 7);list.add(map3);Map<String, Object> map4 = new HashMap<String, Object>();map4.put("hour", "08");map4.put("event", "OK");map4.put("number", 30);list.add(map4);System.out.println(list);System.out.println("--------------------------");// 进行分组和汇总 并 按hour字段的升序排序// 按小时统计每个小时的事件和数量Map<String, Map<String, Integer>> hourEventNumberSum = list.stream().collect(Collectors.groupingBy(item -> (String) item.get("hour"),TreeMap::new, // 使用 TreeMap 以保证 hour 字段升序Collectors.groupingBy(item -> (String) item.get("event"),Collectors.summingInt(item -> (Integer) item.get("number")))));// 打印结果// 这里如果直接定义int变量累加计算总和，会报错：Local variable count defined in an enclosing scope must be final or effectively final，增强for里面用外部变量需要final，但这里在做累加计算，无法使用final修饰，所以改用了List<Integer>计算总和//计算OK总和用的集合List<Integer> listOk = new ArrayList<Integer>();//计算NG总和用的集合List<Integer> listNg = new ArrayList<Integer>();hourEventNumberSum.forEach((hour, eventMap) -> {System.out.println("Hour: " + hour);eventMap.forEach((event, number) -> {System.out.println("  Event: " + event + ", Number: " + number);if ("OK".equals(event.toUpperCase())) {listOk.add(number);}else if ("NG".equals(event.toUpperCase())) {listNg.add(number);}});});System.out.println("--------------------------");//计算OK总和int sumOk = listOk.stream().mapToInt(Integer::intValue) // 转换成 IntStream.sum(); // 计算和System.out.println("OK Sum of elements: " + sumOk);//计算NG总和int sumNg = listNg.stream().mapToInt(Integer::intValue) // 转换成 IntStream.sum(); // 计算和System.out.println("NG Sum of elements: " + sumNg); }

执行结果

需求二：
统计每个小时(倒序)不同事件的产品产量

public static void main29(String[] args) {//数据源List<Map<String, Object>> list = new ArrayList<Map<String,Object>>();Map<String, Object> map1 = new HashMap<String, Object>();map1.put("hour", "10");map1.put("event", "B");map1.put("number", 12);list.add(map1);Map<String, Object> map2 = new HashMap<String, Object>();map2.put("hour", "08");map2.put("event", "A");map2.put("number", 10);list.add(map2);Map<String, Object> map3 = new HashMap<String, Object>();map3.put("hour", "09");map3.put("event", "A");map3.put("number", 7);list.add(map3);Map<String, Object> map4 = new HashMap<String, Object>();map4.put("hour", "08");map4.put("event", "B");map4.put("number", 30);list.add(map4);System.out.println(list);System.out.println("--------------------------");// 进行分组和汇总Map<String, Map<String, Integer>> hourEventNumberSum = list.stream().collect(Collectors.groupingBy(item -> (String) item.get("hour"),TreeMap::new, // 使用 TreeMap 以保证按 hour 字段升序Collectors.groupingBy(item -> (String) item.get("event"),Collectors.summingInt(item -> (Integer) item.get("number")))));// 将 TreeMap 转换为倒序的 LinkedHashMapMap<String, Map<String, Integer>> sortedHourEventNumberSum = hourEventNumberSum.entrySet().stream().sorted(Map.Entry.<String, Map<String, Integer>>comparingByKey(Comparator.reverseOrder())).collect(Collectors.toMap(Map.Entry::getKey,Map.Entry::getValue,(e1, e2) -> e1,LinkedHashMap::new));// 打印结果sortedHourEventNumberSum.forEach((hour, eventMap) -> {System.out.println("Hour: " + hour);eventMap.forEach((event, number) -> {System.out.println("  Event: " + event + ", Number: " + number);});});}