如何在具有相同参数名称的Map中放置许多对象

Question

I have this code but it seems to over write one parameter and I only end up with one myImages parameter no matter how many values i have in imagesList

Is there a way to put the put many objects in a Map with the same name?

for(String imagePath: imagesList){
        File imageFile = new File(imagePath);
        params.put("myImages", imageFile);
    }

edit I must use a map since a library that i am using to make multipart POST requests requires that i put the file in a map

Answer 1

You need to use a collection as the Map value.

A Map stores a unique key -> value mapping so putting the same value again simply overwrites it. You can either use a Map<String, Collection<File>> like so:

final Map<String, Collection<File>> myMap = new HashMap<String, Collection<File>>();
//...
Collection<File> files = myMap.get("myImages");
if(files == null) {
    files = new LinkedList<File>();
    myMap.put("myImages", files);
}
for(String imagePath: imagesList){
    File imageFile = new File(imagePath);        
    files.add(imageFile);
}

Or you could consider using a Multimap implementation from the likes of Guava .

Answer 2

As others have mentioned use Guava's Multimap , it allows you to associate many values against a single key, for example:

Multimap<String, String> multimap = ArrayListMultimap.create();
multimap.put("myImages", file1);
multimap.put("myImages", file2);
multimap.put("myImages", file3);

Collection<File> images = multimap.get("myImages");