Java error Cannot resolve method 'map' in 'List'

I'm trying to get working backend in Java for CRUD app. I am using Java 1.8. I used the following implementation of findByName(name) [below]. Intellij says that there is error, because "Cannot resolve method 'map' in 'List'". Does it means that Java does have map method? How can I overcome this. I have been trying to add before something like stream etc. but it does not help. I also would like to have device returned in findByName and with some tried solution the error was moving from map method to return device. I would be grateful for help, it is keeping me awake long in the night because I cannot finish.

return deviceRepository.findByName(name).map(device -> {
        LOG.info("Reading device with name " + name + " from database.");
        return device;
    }).orElseThrow(() -> new DeviceNotFoundException("The device with the name " + name + " couldn't be found in the database."));
}

> Does it means that Java does have map method?

No. It means that the List interface does not a map method. You can check the javadocs for yourself to confirm this.

> How can I overcome this.

So it looks like your code is intended to search the list, then either write a log message and return an element, or throw an exception.

There is a pretty fundamental problem with this. The findByName(name) method can clearly return more than one "device". So your code has to decide what to do in that case.

Here is one possible solution:

List<Device> found = deviceRepository.findByName(name);
if (found.size() == 0) {
    throw new DeviceNotFoundException("The device with the name " + name + 
                                      " couldn't be found in the database.");
} else if (found.size() > 1) {
    throw new DeviceNotFoundException("Multiple devices with name " + name + 
                                      " found in the database.");
} else {
    LOG.info("Reading device with name " + name + " from database.");
    return found.get(0);
}

Other possibilities would be to ignore the case where multiple devices have the same name (and just return the first), or change the findByName API to return only one device.

Java's lists do not have a map method and never did. It's also extremely odd for a list to have a method named orElseThrow - is that supposed to be ifEmptyThrow, perhaps? That doesn't exist either, but at least that makes sense. Or is findByName an operation that may or may not find a result, and map is supposed to be a no-op if there is no result, and orElseThrow is to be invoked if no result is found?

'deviceRepository', nor findByName, is recognizable, which is not helping.

If findByName returns a List<Device>, java doesn't make it simple to try to stream your way into 'if empty'.

If findByName is supposed to return 1 or 0 elements, if it returns an Optional, your code as pasted will work. Which makes me assume it doesn't.

That leaves: Stop treating the back of your shoe as a universal tool. It's a nice shoe and all, and great for walking, but not for nails. This is how to do it. Plain. Simple.

List<Device> devices = deviceRepository.findByName(name);
if (devices.isEmpty()) throw new DeviceNotFoundException("The device with name + " name + " couldn't be found in the database");
LOG.info("Reading device with name {} from the database", name");