How to convert a string to a HashMap?

Question

I have a Java Property file and there is a KEY as ORDER. So I retrieve the VALUE of that KEY using the getProperty() method after loading the property file like below.:

String s = prop.getProperty("ORDER");

then

s ="SALES:0,SALE_PRODUCTS:1,EXPENSES:2,EXPENSES_ITEMS:3";

I need to create a HashMap from above string. SALES,SALE_PRODUCTS,EXPENSES,EXPENSES_ITEMS should be KEY of HashMap and 0,1,2,3, should be VALUEs of KEYs.

If it's hard corded, it seems like below:

Map<String, Integer> myMap  = new HashMap<String, Integer>();
myMap.put("SALES", 0);
myMap.put("SALE_PRODUCTS", 1);
myMap.put("EXPENSES", 2);
myMap.put("EXPENSES_ITEMS", 3);

Solution 1

Use the String.split() method with the , separator to get the list of pairs. Iterate the pairs and use split() again with the : separator to get the key and value for each pair.

Map<String, Integer> myMap = new HashMap<String, Integer>();
String s = "SALES:0,SALE_PRODUCTS:1,EXPENSES:2,EXPENSES_ITEMS:3";
String[] pairs = s.split(",");
for (int i=0;i<pairs.length;i++) {
    String pair = pairs[i];
    String[] keyValue = pair.split(":");
    myMap.put(keyValue[0], Integer.valueOf(keyValue[1]));
}

Solution 2

You can do that with Guava's Splitter.MapSplitter:

Map<String, String> properties = Splitter.on(",")
    .withKeyValueSeparator(":")
    .split(inputString);

Solution 3

In one line :

HashMap<String, Integer> map = (HashMap<String, Integer>) Arrays.asList(str.split(",")).stream().map(s -> s.split(":")).collect(Collectors.toMap(e -> e[0], e -> Integer.parseInt(e[1])));

Details:

1) Split entry pairs and convert string array to List<String> in order to use java.lang.Collection.Stream API from Java 1.8

Arrays.asList(str.split(","))

2) Map the resulting string list "key:value" to a string array with [0] as key and [1] as value

map(s -> s.split(":"))

3) Use collect terminal method from stream API to mutate

collect(Collector<? super String, Object, Map<Object, Object>> collector)

4) Use the Collectors.toMap() static method which take two Function to perform mutation from input type to key and value type.

toMap(Function<? super T,? extends K> keyMapper, Function<? super T,? extends U> valueMapper)

where T is the input type, K the key type and U the value type.

5) Following lambda mutate String to String key and String to Integer value

toMap(e -> e[0], e -> Integer.parseInt(e[1]))

Enjoy the stream and lambda style with Java 8. No more loops !

Solution 4

I recommend using com.fasterxml.jackson.databind.ObjectMapper (Maven repo link: https://mvnrepository.com/artifact/com.fasterxml.jackson.core) like

final ObjectMapper mapper = new ObjectMapper();
Map<String, Object> mapFromString = new HashMap<>();
try {
    mapFromString = mapper.readValue(theStringToParse, new TypeReference<Map<String, Object>>() {
        });
} catch (IOException e) {
    LOG.error("Exception launched while trying to parse String to Map.", e);
}

Solution 5

Assuming no key contains either ',' or ':':

Map<String, Integer> map = new HashMap<String, Integer>();
for(final String entry : s.split(",")) {
    final String[] parts = entry.split(":");
    assert(parts.length == 2) : "Invalid entry: " + entry;
    map.put(parts[0], new Integer(parts[1]));
}

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