CODEWITHSUNDEEP
javajava-stream
membersound
membersound

Reputation: 86847

How to join a MultiValueMap with Stream api?

I have a org.springframework.util.MultiValueMap extends Map<String, List<String>> hierarchy. I want to collect all values just as a concatenated csv string:

        HttpHeaders headers;
        headers.entrySet().stream()
                .map((key, values) -> key + "=" + values) //TODO incompatible parameter types
                .collect(Collectors.joining(", "));

Question: how can I join the (key, values) pair correctly? As I get the error above.

Upvotes: 2

Views: 859

Answers (3)

Ryuzaki L
Ryuzaki L

Reputation: 40078

By using Collectors.joining

List<String> result = headers.entrySet().stream()
            .map(e -> e.getKey() + " = " + e.getValue().stream().collect(Collectors.joining(",")))
            .collect(Collectors.toList());

    System.out.println(result);    //[KEY2 = v1,v2,v3, KEY1 = v1,v2,v3]

As @Eugene suggested you can also use String.join

 List<String> result = headers.entrySet().stream()
            .map(e -> e.getKey() + " = " + String.join(",",e.getValue()))
            .collect(Collectors.toList());

Upvotes: 1

developer_hatch
developer_hatch

Reputation: 16224

What about joining the values with streams?

public static void main(String[] args) {
    Map<String, List<String>> headers = new HashMap<>();
    headers.put("KEY1", Arrays.asList("v1,v2,v3"));
    headers.put("KEY2", Arrays.asList("v1,v2,v3"));
    List<String> res = headers.entrySet().stream().map(stringListEntry ->
            stringListEntry.getKey() + "=" +
                    String.join(", ", stringListEntry.getValue())
                                ).collect(Collectors.toList());

    System.out.println(res);
}

result

[KEY2=v1,v2,v3, KEY1=v1,v2,v3]

Upvotes: 0

Arnaud Claudel
Arnaud Claudel

Reputation: 3138

Do the same thing with the values:

[...]
.map(e -> e.getKey() + "=" + e.getValue().stream().collect(Collectors.joining(", "))
[...]

Edit: as @Eugene said, the parameter is a Map.Entry (e) and not (key,values)

Upvotes: 1

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