Getting a map object in form of Map<String, Map<String, List<SalaryMapper>>> from-CodePudding

There's a JSON array response I am getting as below.

    [{
        contracted: 1
        payrolltype: basicsalary
        otherdata: sampledata
        salary: 1000
    },{
        contracted: 1
        payrolltype: basicsalary
        otherdata: sampledata
        salary: 1001
    },{
        contracted: 2
        payrolltype: basicsalary
        otherdata: sampledata
        salary: 10002
    },
    {
        contracted: 1
        payrolltype: addon
        otherdata: sampledata
        salary: 1004
    }]

I want to structure this data in the form of Map<String, Map<String,List<SalaryMapper>>>

First, I needed to arrange the data by contractId with the List of Object mapped with the objects where contractId field is common.

For this, I have used java stream as given:

List<SalaryMapper> salMap = myArray;
Map<String, List<SalaryMapper>> map = salMap.stream().collect(Collectors.groupingBy(SalaryMapper::getContractId));

Now I am getting the result grouped by contractId. And I am trying to group the map to another level by payrollType: Map<contractId, Map<payrollType, List<SalaryMapper>>>.

For this, I tried to iterate the main map and push it to Map<contractId, Map<payrollType, List<SalaryMapper>>> object, but I am getting lost here.

    Map<String, Map<String,List<SalaryMapper>>> subMap = null;
            
    Map<String,List<SalaryMapper>> newMapForPayrollType = null;
            
    for(Map.Entry<String, List<SalaryMapper>> entry : map.entrySet()) {
                    
    }
            
    return subMap;

CodePudding user response：

You can do nested level groupingBy by passingdownstream Collector to do a secondary groupingBy

Map<Integer, Map<String, List<SalaryMapper>>> map = salMap.stream()
    .collect(Collectors.groupingBy(SalaryMapper::getContractId,
      Collectors.groupingBy(SalaryMapper::getPayrollType)));

As per the data shown in above the contractid is of Integer type and payrolltype is String, more examples can be found here

CodePudding user response：

The naive approach to your question would be as below:

Map<String, Map<String, List<SalaryMapper>>> subMap = new HashMap<>();        

for (SalaryMapper sal: salMap) {
    Map<String, List<SalaryMapper>> payrollTypeMap = new HashMap<>();
    if (subMap.containsKey(sal.getContractId()) {
        payrollTypeMap = subMap.get(sal.getContractId());
        if (payrollTypeMap.containsKey(sal.getPayrollType())) {
            payrollTypeMap.put(sal.getPayrollType(), payrollTypeMap.get(sal.getPayrollType()).add(sal));
        } else {
           payrollTypeMap.put(sal.getPayrollType(), new ArrayList<>(){{add(sal);}};
        }
    } else {
        payrollTypeMap.put(sal.getPayrollType(), new ArrayList<>(){{add(sal);}};
    }
    subMap.put(sal.getContractId(), payrollTypeMap);
}

Above code can be optimized and written with fewer lines of code as below:

Map<Integer, Map<String, List<SalaryMapper>>> subMap = salMap.stream()
       .collect(Collectors.groupingBy(SalaryMapper::getContractId,
         Collectors.groupingBy(SalaryMapper::getPayrollType)));