I have the below multilevel map:
Map<String, List<Map<String, Map<String, Map<String, Map<String, String>>>>>> input =
ImmutableMap.of("A",
ImmutableList.of(ImmutableMap.of("2",
ImmutableMap.of("3",
ImmutableMap.of("4",
ImmutableMap.of("5", "a"))))));
In short it'll be like
{
"A":[{"2":{"3":{"4":{"5":"a"}}}}],
"B":[{"2":{"3":{"4":{"5":"b"}}}}]
}
My requirement is to construct a map of the form
{
"A":"a",
"B":"b"
}
I tried the below code but for some reason myMap
is always empty even though I'm populating it. What am I missing?
Map<String, String> myMap = new HashMap<>();
input.entrySet()
.stream()
.map(l -> l.getValue().stream().map(m -> m.get(m.keySet().toArray()[0]))
.map(n -> n.get(n.keySet().toArray()[0]))
.map(o -> o.get(o.keySet().toArray()[0]))
.map(p -> myMap.put(l.getKey(), p.get(p.keySet().toArray()[0])))).collect(Collectors.toList());
System.out.println(myMap);
Here's what I get when I add two peek
calls to your pipeline:
input.entrySet().stream()
.peek(System.out::println) //<- this
.map(l -> ...)
.peek(System.out::println) //<- and this
.collect(Collectors.toList());
output:
A=[{2={3={4={5=a}}}}]
java.util.stream.ReferencePipeline$3@d041cf
If you notice the problem, you're collecting streams, and these streams don't get executed through a call to a terminal operation... When I try adding something like .count()
to the inner stream, your expected output is produced:
...
.map(l -> l.getValue().stream().map(m -> m.get(m.keySet().toArray()[0]))
.map(n -> n.get(n.keySet().toArray()[0]))
.map(o -> o.get(o.keySet().toArray()[0]))
.map(p -> myMap.put(l.getKey(), p.get(p.keySet().toArray()[0])))
.count()) //just an example
...
Now, I suppose you know that a terminal operation needs to be called for the intermediate ones to run.
In a rather desperate attempt to simplify this code, as the stream seems to make it simply hard to read, I thought you might be interested in this, which assumes that no collection is empty in the tree but at least addrsses the record as one object, and not a collection of records (but I'm sure no code will look clean for that deep map of of maps).
String key = input.keySet().iterator().next();
String value = input.entrySet().iterator().next()
.getValue().get(0)
.values().iterator().next()
.values().iterator().next()
.values().iterator().next()
.values().iterator().next();
myMap.put(key, value);