1.lambda去重
public static <T> Predicate<T> distinctByKey(Function<? super T, Object> keyExtractor) { Map<Object, Boolean> seen = new ConcurrentHashMap<>(); return object -> seen.putIfAbsent(keyExtractor.apply(object), Boolean.TRUE) == null; }
//对工号重复的进行去重 ens=ens.stream().filter(distinctByKey(i->{ return i.get("code"); })).collect(Collectors.toList());
2.lambda对map排序
package com.example; import org.junit.Test; import org.junit.runner.RunWith; import org.springframework.boot.test.context.SpringBootTest; import org.springframework.core.annotation.Order; import org.springframework.test.context.junit4.SpringRunner; import java.util.*; import java.util.stream.Collectors; @RunWith(SpringRunner.class) @SpringBootTest public class UeditorTestApplicationTests { @Test public void contextLoads() { Map<String,Object> map = new HashMap<>(); map.put("1","oo1"); map.put("2","oo1"); map.put("3","oo1"); Map<String,Object> map1 = new HashMap<>(); map1.put("1","oo1"); map1.put("2","oo2"); map1.put("3","oo2"); Map<String,Object> map2 = new HashMap<>(); map2.put("1","oo2"); map2.put("2","oo1"); map2.put("3","oo1"); List<Map> list = new ArrayList<>(); list.add(map); list.add(map1); list.add(map2); // ArrayList<Map> collect = list.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(() -> // new TreeSet<>(Comparator.comparing(o -> (String) o.get("1")))), ArrayList::new)); // // System.out.println(collect); // ArrayList<Map> collect1 = list.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(() -> // new TreeSet<>((o1, o2) -> { // String i = (String) o1.get("2"); // String j = (String) o2.get("2"); // return i.compareTo(j); // })), ArrayList::new)); // // System.out.println(collect1); TreeSet<Map<String,Object>> t = new TreeSet<>((o1, o2) -> { String i = (String) o1.get("2"); String j = (String) o2.get("2"); return i.compareTo(j); }); t.add(map); t.add(map1); t.add(map2); System.out.println(t); } class A { } class B implements Comparable { @Override public int compareTo(Object o) { return 0; } } }
3.lambda对List<Map>排序
list=list.stream().sorted(Comparator.comparing(m -> m.get("排序的字段").toString())).collect(Collectors.toList()); //按日期排序 transferList = transferList.stream().sorted((d1, d2) -> { if(d1.get("inTime")!=null&& d2.get("inTime")!=null){ Date date1 = DateUtils.parse((String) d1.get("inTime"), DateUtils.DATE_FORMAT_YYYY_MM_DD_HH_MM_SS); Date date2 = DateUtils.parse((String) d2.get("inTime"), DateUtils.DATE_FORMAT_YYYY_MM_DD_HH_MM_SS); return date1.compareTo(date2); } return 0; }).collect(Collectors.toList());
4.lambda操作map根据key或者value排序，reversed()是倒序，正序就去掉.reversed()
public static <K extends Comparable<? super K>, V > Map<K, V> sortByKey(Map<K, V> map) { Map<K, V> result = new LinkedHashMap<>(); map.entrySet().stream() .sorted(Map.Entry.<K, V>comparingByKey() .reversed()).forEachOrdered(e -> result.put(e.getKey(), e.getValue())); return result; }
public static <K, V extends Comparable<? super V>> Map<K, V> sortByValue(Map<K, V> map) { Map<K, V> result = new LinkedHashMap<>(); map.entrySet().stream() .sorted(Map.Entry.<K, V>comparingByValue() .reversed()).forEachOrdered(e -> result.put(e.getKey(), e.getValue())); return result; }
5.按半小时统计结果值
public static void main(String[] args)throws Exception { List<Chart> charts=new ArrayList<>(); SimpleDateFormat format=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); charts.add(new Chart(format.parse("2020-01-01 01:10:00"),2d)); charts.add(new Chart(format.parse("2020-01-01 01:20:00"),3d)); charts.add(new Chart(format.parse("2020-01-01 01:40:00"),4d)); charts.add(new Chart(format.parse("2020-02-01 01:50:00"),3d)); charts.add(new Chart(format.parse("2020-01-01 02:20:00"),26d)); Map<Long, Chart> collect = charts.stream().collect(Collectors.toMap(chart -> { System.out.println(chart.date.getTime()/(30*60*1000)); return chart.date.getTime()/(30*60*1000); }, Function.identity(), (k1, k2) -> { return k1.date.getTime() > k2.date.getTime() ? k1 : k2; })); Map<String, Double> map=new HashMap<>(); format = new SimpleDateFormat("yyyy-MM-dd"); SimpleDateFormat finalFormat = format; collect.forEach((k, v)->{ //此处把v.date转换为半小时的标准格式 String format1 = finalFormat.format(v.date); String hours = v.date.getHours()+""; int minutes = v.date.getMinutes(); if (minutes>=0&&minutes<30){ hours=format1+" "+hours+":00"; }else { hours=format1+" "+hours+":30"; } map.put(hours,v.value); }); Map<String, Double> stringDoubleMap = sortByKey(map); System.out.println(stringDoubleMap); } public static <K extends Comparable<? super K>, V > Map<K, V> sortByKey(Map<K, V> map) { Map<K, V> result = new LinkedHashMap<>(); map.entrySet().stream() .sorted(Map.Entry.<K, V>comparingByKey()).forEachOrdered(e -> result.put(e.getKey(), e.getValue())); return result; } static class Chart{ public Date date; public Double value; public Chart(Date date, Double value) { this.date = date; this.value = value; } }
6.lambda去重，支持根据条件有选择进行过滤去重
static class User{ String id; String name; public String getId() { return id; } public void setId(String id) { this.id=id; } public String getName() { return name; } public void setName(String name) { this.name = name; } } public static void main(String[] args) throws Exception { List<User> distinctList = new ArrayList(); User user1 = new User(); user1.setId("1"); user1.setName("11"); distinctList.add(user1); User user2 = new User(); user2.setId("2"); user2.setName("21"); distinctList.add(user2); User user3 = new User(); //user3.setId("3"); user3.setName("31"); distinctList.add(user3); User user4 = new User(); //user4.setId("4"); user4.setName("31"); distinctList.add(user4); //list是需要去重的list，返回值是去重后的list List<User> res = distinctList.stream().collect( Collectors.collectingAndThen(Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(o -> { if (StringUtils.isNotBlank(o.getId())) { return o.getName(); } return o.getName(); }))), ArrayList::new)); //筛选 List<User> users=distinctList.stream().collect(Collectors.toMap(key->key.getName(),value->value,(v1,v2)->{ if(v1.getId()!=null){ return v1; }else if(v2.getId()!=null){ return v2; } return v1; })).values().stream().collect(Collectors.toList()); //res = distinctList.stream().filter(ls->ls.getId().equals("222")).collect(Collectors.toList()); System.out.println(users); }
7.Java一个集合中根据，获取某一个日期对象最大值得对象
Optional<Person> max = personList.stream().max(Comparator.comparing(Person::getCreateDate)); Person person= max.get();
