Convert java Map to custom key=value string

Question

I have TreeMap<String,String> which I need to convert to URI-like string and then back to Map. I need to set custom delimiters.

Is there any tool (Guava, Apache commons?) that can do it for me? I know, I can write simple loops, but I'm looking for one-liner :)

For example

key    value
key1   val1
key2   val2

key1_val1|key2_val2

Answer 1

According to David Tulig you could do it in guava via

 String string = Joiner.on("|").withKeyValueSeparator("_").join(map);

The opposite is also available via

 Map<String, String> map = Splitter.on("|").withKeyValueSeparator("_").split(string);

Answer 2

Using Java8:

private static Map<String, String> prepareMap() {
    Map<String, String> map = new LinkedHashMap<>();
    map.put("key1", "val1");
    map.put("key2", "val2");
    return map;
}

@Test
public void toStr() {
    assertEquals("key1_val1|key2_val2", prepareMap().entrySet().stream()
            .map(e -> e.getKey() + "_" + e.getValue())
            .collect(Collectors.joining("|")));
}

@Test
public void toStrFunction() {
    assertEquals("key1_val1|key2_val2", joiner("|", "_").apply(prepareMap()));
}

private static Function<Map<String, String>, String> joiner(String entrySeparator, String valueSeparator) {
    return m -> m.entrySet().stream()
            .map(e -> e.getKey() + valueSeparator + e.getValue())
            .collect(Collectors.joining(entrySeparator));
}

@Test
public void toMap() {
    assertEquals("{key1=val1, key2=val2}", Stream.of("key1_val1|key2_val2".split("\\|"))
            .map(e -> e.split("_", 2))
            .collect(Collectors.toMap(e -> e[0], e -> e.length > 1 ? e[1] : null)).toString());
}

@Test
public void toMapFunction() {
    assertEquals("{key1=val1, key2=val2}", splitter("\\|", "_").apply("key1_val1|key2_val2").toString());
}

private static Function<String, Map<String, String>> splitter(String entrySeparator, String valueSeparator) {
    return s -> Stream.of(s.split(entrySeparator))
            .map(e -> e.split(valueSeparator, 2))
            .collect(Collectors.toMap(e -> e[0], e -> e.length > 1 ? e[1] : null));
}

Answer 3

its not guava or apache commons, and it is a loop, but aside from instantiating the string builder, it is a one liner:

for (Entry<String,String> entry : myMap.entrySet()) {
    sb.append(entry.getKey() + separator + entry.getValue() + "\n");
}

Answer 4

In java 8 and up there is another way without external dependencies: use StringJoiner:

    List<String> cities = Arrays.asList("Milan", 
                                        "London", 
                                        "New York", 
                                        "San Francisco");

    String citiesCommaSeparated = String.join(",", cities);

    System.out.println(citiesCommaSeparated);


    //Output: Milan,London,New York,San Francisco

Credits and example go to this URL (https://reversecoding.net/java-8-convert-list-string-comma/)