Convert HashMap into String with keys and values

Question

I want to create util method which converts HashMap into long String with keys and values:

HashMap<String, String> map = new LinkedhashMap<>();

map.put("first_key", "first_value");
map.put("second_key", "second_value");

I need to get this end result:

first_key=first_value&second_key=second_value

you know that if you call the toString() method of the map you allready get ```{first_key=first_value, second_key=second_value} ``` — Java_Waldi, Aug 10 '18 at 09:22
Are you using this for generating a query string? If so, you also need to consider URL-encoding special characters. — Mick Mnemonic, Aug 10 '18 at 09:27

Lino · Accepted Answer · 2018-08-10T09:48:07.020

11

You can use streams:

String result = map.entrySet().stream()
   .map(e -> e.getKey() + "=" + e.getValue())
   .collect(Collectors.joining("&"));

Note: You should probably use an url encoding. First create a helper method like this:

public static String encode(String s){
    try{
        return java.net.URLEncoder.encode(s, "UTF-8");
    } catch(UnsupportedEncodingException e){
        throw new IllegalStateException(e);
    }
}

And then use that inside of your stream to encode the key and value:

String result = map.entrySet().stream()
   .map(e -> encode(e.getKey()) + "=" + encode(e.getValue()))
   .collect(Collectors.joining("&"));

edited Aug 10 '18 at 09:48

answered Aug 10 '18 at 09:21

Lino

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Yes, How I can set them to UTF-8? – Peter Penzov Aug 10 '18 at 09:27
1

I get `Cannot infer type argument(s) for map(Function super T,? extends R>)` here map.entrySet().stream() – Peter Penzov Aug 10 '18 at 09:41
By the way what will happen if there are empty spaces or `-` into the keys or values? – Peter Penzov Aug 10 '18 at 09:59
@PeterPenzov the spaces will be encoded to `%20`, and the minus will stay – Lino Aug 10 '18 at 09:59

score 4 · Answer 2 · answered Aug 10 '18 at 09:22

4

Try this:

StringBuilder sb = new StringBuilder();
for (Map.Entry<String, String> entry : map.entrySet()) {
    sb.append(entry.getKey());
    sb.append('=');
    sb.append(entry.getValue());
    sb.append('&');
}
sb.deleteCharAt(sb.length() - 1);
String result = sb.toString();

answered Aug 10 '18 at 09:22

Óscar López

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1

If there are no entries in the map then this will throw exception. – Tarun Jul 24 '19 at 17:51

score 0 · Answer 3 · answered Aug 10 '18 at 09:24

0

map.toString().replace(",","&")

answered Aug 10 '18 at 09:24

Java_Waldi

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The leading and trailing brackets `{}` need to be removed too, e.g. by substring – Lino Aug 10 '18 at 09:24

score 0 · Answer 4 · answered Aug 10 '18 at 09:32

0

The output Map::toString is not much different from the output you want. Compare:

{first_key=first_value, second_key=second_value}
first_key=first_value&second_key=second_value

Just perform the right character replacement:

map.toString().replaceAll("[{ }]", "").replace(",","&")

"[{ }]" is regex matching all the brackets {} and the space - those to be removed (replaced with "").
, to be replaced with & character.

answered Aug 10 '18 at 09:32

Nikolas Charalambidis

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Could lead to problems when trying to send strings with spaces or brackets, or commas in them – Lino Aug 10 '18 at 09:34
1

@Lino: Possibly. Applicable well to the OP's example as an alternative solution. The character escaping is another issue. – Nikolas Charalambidis Aug 10 '18 at 09:38

Convert HashMap into String with keys and values

4 Answers4