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-title: Java常用代码块
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-date: 2020-10-28
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-tags: Java
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-cover: https://static.jqwei.com/blog/img/IMG_3460.PNG
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-comments: true
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-categories: 编程语言
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----
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-
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-## java常用代码块
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-> 为了减少手写出现的错误，可以直接复制使用,大部分是经常使用的代码，对map操作，list 分组，排序，后续可以放到IDEA做成快捷键
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-| 对象 | 排序 | 分组 |分页|
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-| -------- | -------- | -------- |-------|
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-| list | √ | √ |√|
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-| map | √ | ||
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-| set | | ||
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-#### map 根据Key排序
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-
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-```Java
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-private static Map<String, Object> sortByKey(Map<String, Object> map) {
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- Map<String, Object> result = new LinkedHashMap<>(map.size());
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- map.entrySet().stream()
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- .sorted(Map.Entry.comparingByKey())
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- .forEachOrdered(e -> result.put(e.getKey(), e.getValue()));
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- return result;
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- }
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-```
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-
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-
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-#### map 进行遍历
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-
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-```Java
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- for (Map.Entry<String, Object> m : map.entrySet()) {
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- System.out.println("key:" + m.getKey() + " value:" + m.getValue());
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- }
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-
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-```
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-
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-#### list 对象根据某个字段分组
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-
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-``` Java
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- //1 按照某个字段
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- Map<Object,List<Object>> map = demoList.stream().collect(Collectors.groupingBy(Object::getAttr));
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- //2 按照多个字段
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- Map<String, List<Object>> groupBy = objectList.stream().collect(Collectors
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- .groupingBy(o -> o.getAttr1() + "_" + o.getAttr2()));
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-
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- Set<Long> attrs = list.stream().map(Object::getAttr).collect(Collectors.toSet());
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-
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-```
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-#### list 用stream进行排序 .
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-
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-``` Java
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-
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- //根据单个属性排序
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- List<String> stortList = list.stream().sorted().collect(Collectors.toList());
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- //根据对象某个属性排序
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- List<Object> sortList = objectList.stream().sorted(Comparator.comparing(Object::getAttr)
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- .reversed()).collect(Collectors.toList());
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-
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-
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-```
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-
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-#### list 用Guava进行拆分分页
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-
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-```Java
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- List<List<Long>> splitList = Lists.partition(list, 200);
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-```
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-
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-#### jodaTime 两个日期相差小时，天 ，分钟
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-```Java
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- DateTime dt1 = new DateTime("2020-09-05");
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- dt1 = dt1.plusDays(1).plusMinutes(1).plusHours(1);
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- DateTime dt2 = new DateTime("2020-09-06");
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-
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- System.out.println(dt1);
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- System.out.println(dt2);
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-
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- //时间dt2-时间dt1 的差
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- int hours = Hours.hoursBetween(dt1, dt2).getHours();
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- int days = Days.daysBetween(dt1,dt2).getDays();
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- int minutes = Minutes.minutesBetween(dt1,dt2).getMinutes();
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-
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- System.out.println(hours+" "+days+" "+minutes);
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-```
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-
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-### 两个时间是否有交集
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-
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-```Java
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- Date startTime1 = new DateTime("2021-01-10").toDate();
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- Date endTime1 = new DateTime("2021-02-16").toDate();
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- Date startTime2 = new DateTime("2021-01-09").toDate();
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- Date endTime2 = new DateTime("2021-01-24").toDate();
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-
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- if ((startTime1.getTime() > startTime2.getTime()
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- && startTime1.getTime() < endTime2.getTime())
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- || (endTime1.getTime() > startTime2.getTime()
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- && endTime1.getTime() < endTime2.getTime())
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- || (startTime2.getTime() > startTime1.getTime()
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- && endTime2.getTime() < endTime1.getTime())
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- ) {
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- System.out.println("有交集");
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- }
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- if (((startTime1.getTime() >= startTime2.getTime())
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- || (endTime1.getTime() <= startTime2.getTime()))
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- && ((startTime1.getTime() <= startTime2.getTime())
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- || (startTime1.getTime() >= endTime2.getTime()))) {
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- System.out.println("无交集");
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- }
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-```
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-
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-
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-#### 设置新的版本号
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-mvn versions:set -DnewVersion=1.1.3
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-
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-#### 当新版本号设置不正确时可以撤销新版本号的设置
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-mvn versions:revert
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-
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-#### 确认新版本号无误后提交新版本号的设置
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-mvn versions:commit
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