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使用场景：Springboot项目中，作为java后端程序员经常需要对数据进行封装处理，比如常见的分组，去重，合并等。Java8的新特性Stream流处理方式可以提高我们对数据处理的效率。推荐可以多尝试新特性的写法，能一定程度提高代码的可读性与性能
数据处理转换
将 List<Map<String,String>> list 转换成 Map<String,List<String>> res 如下：
Map<String,List<String>> res =
list.stream().collect(Collectors.groupingBy(f->f.get("key"),Collectors.collectingAndThen(Collectors.toList(),m->{
List<String> value = new ArrayList<>(); for(Map<String,String> map : m){
value.add(map.get("value")); } return value; })));
数据样例：
list:[
{"key":"name","value":"zhangsan"},
{"key":"name","value":"lisi"},
{"key":"age","value":"20"},
{"key":"age","value":"22"}
]
按list元素map的key值进行分组Collectors.groupingBy()，并通过Collectors.collectingAndThen()处理合并同组内的vlaue值，转换如下：
res:{
"name":["zhangsan",lisi],
"age":["20","22"]
}
最后总结一下，如果在dao.xml数据映射文件中sql语句能直接处理转换得到最终的数据样式，则尽量避免在java层面通过代码再去处理，sql处理数据会效率高些，java层面代码再进行数据的处理则会影响接口效率性能
