---
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


> **大部分是经常使用的代码，对map操作，list 分组，排序**



| 对象 | 排序 | 分组 |
| -------- | -------- | -------- |
| list     | √     | √     |
| map     | √     |      |


### 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.getApplyId() + "_" + o.getSkuId()));

```

### 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());
    
    
```