I have a problem displaying the data right. I have an sql query that returns the following data:
| count (long) | country (string)| ---------------| ------------------ | 6 | null | | 3 | spain | | 6 | italy |
And I have the following method:
private Map<String, Long> countryCount (List<CountryCount> summary) {
Map<String, Long> result = new HashMap<>();
summary.forEach(sum -> {
var country= sum.getCountry();
if (country == null) {
country= "unknown";
}
var count = result.get(country);
if (count == null) {
count = 0L;
}
result.put(country, count + sum.getCount());
});
return result.entrySet().stream().sorted(Map.Entry.comparingByKey())
.collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, (oldValue, newValue) -> oldValue, LinkedHashMap::new));
}
In my method I want to return an object like {"unknown" : 5, "spain" : 3, "italy" : 6} but instead I get {"unknown" : 15}
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Answer
Perhaps this simpler code.
Map < String, Long > map =
listOfCountryCount
.stream()
.collect(
Collectors.toMap(
countryCount -> Objects.isNull( countryCount.getCountry() ) ? "unknown" : countryCount.getCountry() ,
countryCount -> Objects.isNull( countryCount.getCount() ) ? Long.valueOf( 0 ) : countryCount.getCount()
)
);
If you want a sorted map, pass that map to constructor of a SortedMap or NavigableMap implementation.
NavigableMap< String , Long > mapNav = new TreeMap<>( map ) ;
Full example code.
package work.basil.demo;
import java.util.*;
import java.util.stream.Collectors;
class Ideone
{
public static void main ( String[] args ) throws java.lang.Exception
{
List < CountryCount > listOfCountryCount = List.of(
new CountryCount( "Peru" , 17L ) ,
new CountryCount( "Xanadu" , 128L ) ,
new CountryCount( null , 42L ) ,
new CountryCount( "Andorra" , null )
);
Map < String, Long > map =
listOfCountryCount
.stream()
.collect(
Collectors.toMap(
countryCount -> Objects.isNull( countryCount.getCountry() ) ? "unknown" : countryCount.getCountry() ,
countryCount -> Objects.isNull( countryCount.getCount() ) ? Long.valueOf( 0 ) : countryCount.getCount()
)
);
NavigableMap < String, Long > mapNav = new TreeMap <>( map ); // Keys are maintained in sorted order.
System.out.println( "listOfCountryCount = " + listOfCountryCount );
System.out.println( "map = " + map );
System.out.println( "mapNav = " + mapNav );
}
}
final class CountryCount
{
private final String country;
private final Long count;
CountryCount ( String country , Long count )
{
this.country = country;
this.count = count;
}
public String getCountry ( ) { return country; }
public Long getCount ( ) { return count; }
@Override
public boolean equals ( Object obj )
{
if ( obj == this ) return true;
if ( obj == null || obj.getClass() != this.getClass() ) return false;
var that = ( CountryCount ) obj;
return Objects.equals( this.country , that.country ) &&
Objects.equals( this.count , that.count );
}
@Override
public int hashCode ( )
{
return Objects.hash( country , count );
}
@Override
public String toString ( )
{
return "CountryCount[" +
"country=" + country + ", " +
"count=" + count + ']';
}
}
When run.
listOfCountryCount = [CountryCount[country=Peru, count=17], CountryCount[country=Xanadu, count=128], CountryCount[country=null, count=42], CountryCount[country=Andorra, count=null]]
map = {Andorra=0, Xanadu=128, Peru=17, unknown=42}
mapNav = {Andorra=0, Peru=17, Xanadu=128, unknown=42}
If you are not sure about your data being distinct, let’s add a third argument to that Collectors.toMap call. We pass a lambda function to be called in case of duplicate keys. In our case here, we go with a policy of first occurrence wins.
Map < String, Long > map =
listOfCountryCount
.stream()
.collect(
Collectors.toMap(
countryCount -> Objects.isNull( countryCount.getCountry() ) ? "unknown" : countryCount.getCountry() ,
countryCount -> Objects.isNull( countryCount.getCount() ) ? Long.valueOf( 0 ) : countryCount.getCount() ,
( existing , replacement ) -> existing // In case of duplicate key conflict, first one wins.
)
);
We can shorten this code further. Rather than create a TreeMap separately, we can pass a constructor method reference as a fourth argument to our Collectors.toMap: TreeMap :: new. And we change the declaration of the returned map from Map to NavigableMap.
NavigableMap < String, Long > map =
listOfCountryCount
.stream()
.collect(
Collectors.toMap(
countryCount -> Objects.isNull( countryCount.getCountry() ) ? "unknown" : countryCount.getCountry() ,
countryCount -> Objects.isNull( countryCount.getCount() ) ? Long.valueOf( 0 ) : countryCount.getCount() ,
( existing , replacement ) -> existing , // In case of duplicate key conflict, first one wins.
TreeMap :: new
)
);
See this code run live at IdeOne.com.
listOfCountryCount = [CountryCount[country=Peru, count=17], CountryCount[country=Xanadu, count=128], CountryCount[country=null, count=42], CountryCount[country=Andorra, count=null]]
map = {Andorra=0, Peru=17, Xanadu=128, unknown=42}