Java Stream list转map，Map<String, List<T>>，单个对象属性为KEY，对象List为VALUE

Java Stream List 转 Map，单个对象属性为KEY，对象List为VALUE   

List<FaAdmin> list = Lists.newArrayList();
list.add(new FaAdmin("a"));
list.add(new FaAdmin("b"));
list.add(new FaAdmin("c"));
list.add(new FaAdmin("a"));

// 以List数组对象某个属性为键，相同的放在一个数组中，转换成一个Map
// 单个对象属性为KEY，对象List为VALUE
Map<String, List<FaAdmin>> usernameListMap = list .stream()
        .collect(Collectors.groupingBy(FaAdmin::getUsername));

System.out.println(usernameListMap);