Java Optional<List<T>> to Map conversion

user_2781389 0
Viewed 171

I have a snippet of code like this:

    public Map<String, Details> getAllDetails(final String name) {
        Optional<List<JobExecution>> allJobExecutionsByName = Optional.ofNullable(jobExecutionDao.getAllJobExecutionsByName(name));

//        return allJobExecutionsByName.map(x -> x.stream()
//                                                    .map(execution -> Pair.of(getJobParam(execution, "id"), getDetailsFromExecution(execution)))
//                                                    .collect(toList()))
//                                         .orElse(emptyList());

    }

Instead of returning List<Pair<String, Details>>, I want to return Map<String, Details>

How can I convert Optional<List<JobExecution>> to a Map with the key being id and value being the Detail object?

java-stream option-type java
4 Answers

You can use Collector.toMap to collect as Map

return allJobExecutionsByName.map(x -> 
          x.stream()
           .collect(Collector.toMap(e -> getJobParam(e, "id"),
                                    e -> getDetailsFromExecution(e))))
       .orElse(Collections.emptyMap());
user_42073060

The existing answer suggests that you can use Collectors.toMap, but additionally based on the tags, you should not use Optional in your current context.

public Map<String, Details> getAllDetails(final String name) {
    List<JobExecution>> allJobExecutionsByName = jobExecutionDao.getAllJobExecutionsByName(name);
    
    // perform below check only if you cannot control the returned value above
    if(allJobExecutionsByName == null) return Collections.emptyMap();
    
    return allJobExecutionsByName.stream()
                .collect(Collector.toMap(e -> getJobParam(e, "id"),
                                     e -> getDetailsFromExecution(e))));
}
user_17461180

If your list is null, just return empty list and proceed streaming an empty list.

allJobExecutionsByName.orElse(Collections.emptyList())
    .stream()
    .collect(Collectors.toMap(
        (e -> getJobParam(e, "id"),
        e -> getDetailsFromExecution(e))
    ));
user_41047600

I went through this problem, so I did something like this:

    public Map<String, Details> getAllDetails(final String name) {
        return Optional.ofNullable(jobExecutionDao.getAllJobExecutionsByName(name))
                .map(x -> x.stream()
                .collect(Collector.toMap(e -> getJobParam(e, "id"), e -> getDetailsFromExecution(e)))
                .orElse(Collections.emptyMap());
    }
user_17010290
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