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Can Java 8 streams consume multiple items from the mapping pipeline

I have some data stored in a JPA repository that I am trying to process. I would like to use Java 8 Streams for this but cannot figure out how to get the information I need. This particular "Entity" is actually only for recovery, so it contains items to be processed after something like a power failure / restart.

Using pre-Java 8 for loops would look like this:

    List<MyEntity> deletes = myEntityJpaRepository.findByDeletes();
    for (MyEntity item : deletes) {
        String itemJson = item.getData();
        // use a Jackson 'objectMapper' already setup to de-serialize
        MyEventClass deleteEvent = objectMapper.readValue(itemJson, MyEventClass.class);
        processDelete(deleteEvent, item.getId());                   
    }

The problem comes from the parameters method, which is called at the very end. Using Streams, I believe I would do:

//      deletes.stream()
//             .map(i -> i.getData())
//             .map(event -> objectMapper.readValue(event, MyEventClass.class))
//             .forEach(??? can't get 'id' here to invoke 2 parameter method);

I have a solution (no Streams) that I can live with. However, I think this problem comes up a lot, so my question is: In general, is there a way to use Streams to accomplish what I am trying to do?

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3 answers


Why Pair

not go back to your map

operation:

.map(i -> new Pair<>(i.getData(), i.getId()))
.map(pair -> new Pair<>(objectMapper.readValue(pair.getLeft(), MyEventClass.class), pair.getRight())
.forEach(p -> processDelete(pair.getLeft(), pair.getRight()))


I haven't compiled this, so there may be small things that need to be fixed. But in general you will need Holder

to pass your objects to the next stage in such a case. Either a Pair

, or some type, or even array

.

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Why not just do it like that?



deletes.forEach(item -> 
    processDelete(objectMapper.readValue(item.getData(), MyEventClass.class),
                  item.getId()));
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This is at least a start, I think it depends on why you want to use a stream and how much you want to make it more functional.

List<MyEntity> deletes = myEntityJpaRepository.findByDeletes();
deletes.stream().foreach(item -> { 
    String itemJson = item.getData();
    // use a Jackson 'objectMapper' already setup to de-serialize
    MyEventClass deleteEvent = objectMapper.readValue(itemJson, MyEventClass.class);
    processDelete(deleteEvent, item.getId());                   
});
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