Not able to merge to Map<String, Long> - collections

Question

I am trying to merge several Map into a single map, for doing this I wrote this piece of code.
public static Map<String, Long> mergeMaps(List<Map<String, Long>> maps){
Map<String, Long> mergedMap = new TreeMap<>();
maps.forEach( map -> {
//Map<String, Long> mx = new TreeMap<>(map);
map.forEach((key, value) -> mergedMap.merge(key, value, Long::sum));
});
logger.info("Merge map successful");
return mergedMap;
}
On doing this the code is throwing an error :
org.springframework.batch.core.step.AbstractStep java.lang.ClassCastException: java.lang.Integer cannot be cast to java.lang.Long
at java.util.LinkedHashMap.forEach(LinkedHashMap.java:684) ~[?:1.8.0_201-1-ojdkbuild]
lambda$mergeMaps$1
I have this pojo
public class MappingDto {
public MappingDto(){
map1 = new LinkedHashMap<>();
map2 = new LinkedHashMap<>();
map3 = new LinkedHashMap<>();
}
private Map<String, Long> map1;
private Map<String, Long> map2;
private Map<String, Long> map3;
getters()/Setters()
toString()
}
I populate this pojo maps with the below codes.
MappingDto.setMap1(Arrays.asList(doc.getDescription().split("\\s+")).stream().collect(Collectors.groupingBy(Function.identity(),LinkedHashMap::new,Collectors.counting())));
after generating this I have to merge this map with the some Stored in File, To read the Map I have the below method.
public static <T> T readJsonFile(String filePath, T t) throws JAXBException, IOException, IllegalAccessException, InstantiationException {
ObjectMapper mapper = new ObjectMapper();
if(!Utils.checkIfFileExists(filePath)){
Utils.createANewFile(filePath);
return t;
}
return mapper.readValue(new File(filePath), new TypeReference<T>(){});
}
After getting this maps I pass it to the
mergeMaps(Arrays.asList(MappingDto.getMap1(),storedData));
and
List<Map<String, Long>> dataList = new LinkedList<>();
dataList.add(MappingDto.getMap1());
dataList.add(MappingDto.getMap2());
dataList.add(MappingDto.getMap3());
mergeMaps(dataList);
I went through this code several time, But not able to figure what exactly is causing this issue.
One is reading the Stored JSON map
public static <T> T readJsonFile(String filePath, Class<T> t) throws JAXBException, IOException, IllegalAccessException, InstantiationException {
ObjectMapper mapper = new ObjectMapper();
if(!Utils.checkIfFileExists(filePath)){
Utils.createANewFile(filePath);
return t.newInstance();
}
return mapper.readValue(new File(filePath), new TypeReference<T>(){});
}
I tried this and several other variations but no results.
public static Map<String, Long> mergeMaps(List<Map<String, Long>> maps){
Map<String, Long> mergedMap = new TreeMap<>();
maps.forEach( map -> {
//Map<String, Long> mx = new TreeMap<>(map);
map.forEach((key, value) -> mergedMap.merge(key, Long.valueOf(value), Long::sum));
});
logger.info("Merge map successful");
return mergedMap;
}
Can you please help me understand what is in Integer and why is being cast to Long
Thanks in advance.