Java Map Values to Comma Separated String

Question

Is there an effective way to convert java map values to comma separated string using guava or StringUtils?

Map<String, String> testMap = new HashMap<>();
testMap.put("key1", "val1");
testMap.put("key2", "val2");

looking for a way to convert testMap to a String -> "val1,val2".

Answer 1

OK, here's my guess in case you want something like this (there's no clarification in your Question). This is done without Guava or StringUtils:

Map<Integer, Integer> map = new HashMap<Integer, Integer>();

map.put(1, 2);
map.put(3, 4);

System.out.println(map.toString());

Output:

{1=2, 3=4}

If you want to display the values as a comma separated list, you could use this:

System.out.println(map.values().toString());

Output:

[2, 4]

PS: Remove the []s with .replaceAll() if you want

Answer 2

You can use StringUtils:

final Map<String, String> testMap = new LinkedHashMap<String, String>();
testMap.put("key1", "val1");
testMap.put("key2", "val2");

String csv = StringUtils.join(testMap.values(), ',')); // "val1,val2"

Note that I changed the HashMap to a LinkedHashMap, in order to keep the insertion order.

Answer 3

Guava: Joiner.on(',').join(map.values()).

Answer 4

You can use makeString() in Eclipse Collections.

MutableMap<String, String> testMap = new UnifiedMap<String, String>();
testMap.put("key1", "val1");
testMap.put("key2", "val2");

String commaAndSpace = testMap.makeString();
Assert.assertTrue(commaAndSpace.equals("val1, val2")
  || commaAndSpace.equals("val2, val1"));

String comma = testMap.makeString(",");
Assert.assertTrue(comma.equals("val1,val2")
  || comma.equals("val2,val1"));

If you cannot convert your Map to an Eclipse Collections type, you can use MapAdapter.

MapAdapter.adapt(testMap).makeString();

Note: I am a committer for Eclipse collections.

Answer 5

Here's how to do it in Java 8+ (doesn't require Guava, StringUtils, or other external libraries):

testMap.values().stream().map(Object::toString).collect(Collectors.joining(","));

Answer 6

If you are using spring MVC then this might work for you.

import org.springframework.util.StringUtils;

Map<String, String> groups = //List of Maps
List<String> targetList = new ArrayList<String>(groups).values());
String csv = StringUtils.arrayToCommaDelimitedString(targetList.toArray());

Output: abc,def,ghi

Answer 7

In Java 1.8, a join() method was added to the String class that can do this.

Also Map has a function values() to get all values. map.values() are string type so just pass to String.join. Example:

Map<String, String> testMap = new HashMap<>();
testMap.put("key1", "val1");
testMap.put("key2", "val2");

String valueString = String.join(",",map.values()); //val1,val2

Answer 8

I think sorting may be important here. Not sure if map.values() returns in deterministic order, so i would prefer this:

Map<String, Object> map = new HashMap<>();
map.put("key1","val1");
map.put("key2","val2");

String formatted = map.keySet().stream().sorted()
                .map(k -> map.getOrDefault(k, "").toString())
                .collect(Collectors.joining(","));

At least this sorts by keys and is a bit more safe?