I have a Map:
Map<String, String> utilMap = new HashMap();
utilMap.put("1","1");
utilMap.put("2","2");
utilMap.put("3","3");
utilMap.put("4","4");
I converted it to a String:
String utilMapString = utilMap
.entrySet()
.stream()
.map(e -> e.toString()).collect(Collectors.joining(","));
Out put: 1=1,2=2,3=3,4=4,5=5
How to convert utilMapString to Map in Java8? Who can help me with?
Split the string by , to get individual map entries. Then split them by = to get the key and the value.
Map<String, String> reconstructedUtilMap = Arrays.stream(utilMapString.split(","))
.map(s -> s.split("="))
.collect(Collectors.toMap(s -> s[0], s -> s[1]));
Note: As pointed out by Andreas@ in the comments, this is not a reliable way to convert between a map and a string
EDIT: Thanks to Holger for this suggestion.
Use s.split("=", 2) to ensure that the array is never larger than two elements. This will be useful to not lose the contents (when the value has =)
Example: when the input string is "a=1,b=2,c=3=44=5555"
you will get {a=1, b=2, c=3=44=5555}
Earlier (just using s.split("=")) will give
{a=1, b=2, c=3}
s.split("=", 2) to ensure that the array is never larger than two elements. While we can’t fix ambiguous = characters, we can prevent losing contents when there are more of them.
a=1,b= the above code will throw NullPointerException how we can address the null pointer issue Collectors.toMap(s -> s[0], s -> s[1])Here is another option which streams a list of 1=1 etc. terms into a map.
String input = "1=1,2=2,3=3,4=4,5=5";
Map<String, String> map = Arrays.asList(input.split(",")).stream().collect(
Collectors.toMap(x -> x.replaceAll("=\\d+$", ""),
x -> x.replaceAll("^\\d+=", "")));
System.out.println(Collections.singletonList(map));
[{1=1, 2=2, 3=3, 4=4, 5=5}]
x.replaceFirst("=.*", "") and x.replaceFirst(".*=", "")? Still heavy compared to x.substring(0, x.indexOf('=')) and x.substring(x.indexOf('=')+1), but not trying to bend replaceAll’s behavior towards replaceFirst behavior via regex.If you want to generate a map from String you can it with below way:
Map<String, String> newMap = Stream.of(utilMapString.split("\\,"))
.collect(Collectors.toMap(t -> t.toString().split("=")[0], t -> t.toString().split("=")[1]));
If the sequence may contain values with the same key - use
Map<String, String> skipDuplicatesMap = Stream.of("1=1,2=2,3=3,4=4,5=5".split(",")).
map(el -> el.split("=")).
collect(toMap(arr -> arr[0], arr -> arr[1], (oldValue, newValue) -> oldValue));
utilMap.put("2","2");withutilMap.put(",=",",=,=");, then you end up with1=1,,==,=,=,3=3,4=4,5=5, and that is irreversible.Map<String, String>