---
title: Java常用代码块
date: 2020-10-28
tags: Java
comments: false
cover: https://static.jqwei.com/blog/img/IMG_3461.PNG
categories: 运维工具
---

## 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;
    }
```





#### 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()));

```




#### 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);
```