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_posts/常用的代码块.md

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