集合List、Set的常用Stream方法
1.List<INSCFeerule>对象集合转换为不重复的INSCFeerule对象属性rulesetid的set集合
List<INSCFeerule> srcRuleList = inscFeeruleDao.selectByFeecontentId(feecontentId);
Set<String> rulesetidList = srcRuleList.stream().map(INSCFeerule::getRulesetid).collect(Collectors.toSet());
2.list集合去重，得到list集合
providerIds=providerIds.stream().distinct().collect(Collectors.toList());
3.判断是否存在符合条件的元素，只要一个符合立刻返回true
boolean isParent=totalInsbListPro.stream().anyMatch((INSBProvider provider)-> StringUtil.isNotEmpty(provider.getParentcode())&& provider.getParentcode().equals(pro.getPrvcode()));
类似还有
noneMatch：Stream 中没有一个元素符合的才返回 true
list.stream().noneMatch(item->"guizequery".equals(item.getOperator()))
allMatch：Stream 中全部元素符合传入的 predicate，返回 true
4.将集合inscfees先过滤留下只符合Noti="1"条件的元素，然后映射为自定义的格式String类型数据，最后通过<br>拼接元素返回String类型数据
String temp=inscfees.parallelStream().filter((INSCFeecontent fee)->"1".equals(fee.getNoti())).map((INSCFeecontent fee)->"【"+fee.getDeptname()+" - "+fee.getProvider()+" - "+fee.getVersionno()+"】").collect(Collectors.joining("<br>"));
5.集合元素转为以”,”拼接的String
String newTypeCodeValue=lastTypeCodeList.stream().collect(Collectors.joining(","));
6.List<Map<String,Object>>类型的infoMapList获取key是rulesetid的value的不重复String集合
List<String> addRulesetids=infoMapList.stream().map((Map<String,Object> map)->String.valueOf(map.get("rulesetid"))).distinct().collect(Collectors.toList());
7.List<Map<String,Object>>类型的list获取key是flib_id的value，转为数组类型返回
Arrays.asList(list.stream().map(item -> (String) item.get("flib_id")).toArray();
8.返回特定的结果集合：
List<String> limitLists = forEachLists.stream().skip(2).limit(3).collect(Collectors.toList());
注意skip与limit是有顺序关系的，比如先使用skip(2)会扔掉集合的前两个,然后调用limit(3)会返回前3个
9.按照sortLists里元素的大小进行排序
List<Integer> afterSortLists = sortLists.stream().sorted((In1,In2)->
In1-In2).collect(Collectors.toList());
10.得到其中长度最大的元素
int maxLength = maxLists.stream().mapToInt(s->s.length()).max().getAsInt();
或者
Optional<Integer> maxLength = maxLists.stream().reduce(Integer::max);
或者
Optional<Object> minObject =objects.stream().min(comparing(Object::getValue));
11.List和Map通过forEach循环过滤得到符合条件的数据
List<Map<String, Object>> queryList = ... ...;
List<Map<String, Object>> policyList = new ArrayList<>();//保存符合条件的数据
queryList.forEach(map -> {
map.forEach((k, v) -> {
if ("policyno".equals(k) && v != null) {
policyList.add(map);
}
});
});
12.求和
int sum = numbers.stream().reduce(0, (a, b) -> a + b);
或者
int sum = numbers.stream().reduce(0, Integer::sum);
java8日期常用方法
1.获取当天的日期
System.out.println("---"+LocalDate.now());//---2018-01-17
System.out.println("---"+LocalDateTime.now());//---2018-01-17T14:19:24.525 ,给人阅读的时间戳
System.out.println("---"+Instant.now());//---2018-01-17T06:19:24.525Z，给机器阅读的时间戳
2.获取当前的年月日
LocalDate today = LocalDate.now();
int year = today.getYear();
int month = today.getMonthValue();
int day = today.getDayOfMonth();
System.out.printf("Year : %d Month : %d day : %d \t %n", year, month, day); //Year : 2014 Month : 1 day : 14
3.检查两个日期是否相等
LocalDate date1 = LocalDate.of(2014, 01, 14); if(date1.equals(today)){
//today 2014-01-14 and date1 2014-01-14 are same date
System.out.printf("Today %s and date1 %s are same date %n", today, date1);
}
4.获取当前时间,默认的格式是hh:mm:ss:nnn,LocalTime只有时间，没有日期
LocalTime time = LocalTime.now(); System.out.println("local time now : " + time); //local time now : 16:33:33.369
5.判断某个日期是在另一个日期的前面还是后面
LocalDate today = LocalDate.now();
LocalDate tomorrow = LocalDate.of(2018, 1, 15);
if(tommorow.isAfter(today)){
System.out.println("Tomorrow comes after today");
}
6.检查闰年
LocalDate类有一个isLeapYear()的方法能够返回当前LocalDate对应的那年是否是闰年。
7.获取当前时间戳
Instant timestamp = Instant.now();
//What is value of this instant 2018-01-15T10:33:33.379Z
System.out.println("What is value of this instant " + timestamp);
8.使用预定义的格式器来对日期进行解析/格式化,BASICISODATE格式就是yyyy-mm-dd
String str1 = "20180117";
LocalDate formattedstr1 = LocalDate.parse(str1, DateTimeFormatter.BASIC_ISO_DATE);
//Date generated from String 20180117 is 2018-01-17
System.out.printf("Date generated from String %s is %s %n", str1, formattedstr1);
String str2 = "2018-01-17 14:27:30";
LocalDateTime formattedstr2 = LocalDateTime.parse(str2, DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));
//Date generated from String 20180117 is 2018-01-17T14:27:30
System.out.printf("Date generated from String %s is %s %n", str1, formattedstr2);
9.使用自定义的格式器来解析日期,可以转为String类型，DateTimeFormatter是不可变且线程安全的
LocalDateTime arrivalDate = LocalDateTime.now();
try {
DateTimeFormatter format = DateTimeFormatter.ofPattern("MMM dd yyyy hh:mm a");
String landing = arrivalDate.format(format);
System.out.printf("Arriving at : %s %n", landing);
} catch (DateTimeException ex) {
System.out.printf("%s can't be formatted!%n", arrivalDate);
ex.printStackTrace();
}