Java8_grouping_by_mapping_and_join

gistfile1.txt

        Map<String,String> areaCode2AddrMap = new HashMap<>();
        for(AreaCode areaCode:areaCodeList){
            if(areaCode2AddrMap.get(areaCode.getCode())!=null){
                String value = areaCode2AddrMap.get(areaCode.getCode())+","+areaCode.getAddr();
                areaCode2AddrMap.put(areaCode.getCode(),value);
            }else{
                areaCode2AddrMap.put(areaCode.getCode(),areaCode.getAddr());
            }
        }
        
        Map<String, String> areaCode2AddrMap = areaCodeList.stream().collect(groupingBy(AreaCode::getCode, mapping(AreaCode::getAddr, joining(","))));