How to convert String into Hashmap in java

Question

How can I convert a String into a HashMap?

String value = "{first_name = naresh, last_name = kumar, gender = male}"

into

Map<Object, Object> = {
    first_name = naresh,
    last_name = kumar,
    gender = male
}

Where the keys are first_name, last_name and gender and the values are naresh, kumar, male.

Note: Keys can be any thing like city = hyderabad.

I am looking for a generic approach.

Answer 1

This is one solution. If you want to make it more generic, you can use the StringUtils library.

String value = "{first_name = naresh,last_name = kumar,gender = male}";
value = value.substring(1, value.length()-1);           //remove curly brackets
String[] keyValuePairs = value.split(",");              //split the string to creat key-value pairs
Map<String,String> map = new HashMap<>();               

for(String pair : keyValuePairs)                        //iterate over the pairs
{
    String[] entry = pair.split("=");                   //split the pairs to get key and value 
    map.put(entry[0].trim(), entry[1].trim());          //add them to the hashmap and trim whitespaces
}

For example you can switch

 value = value.substring(1, value.length()-1);

to

 value = StringUtils.substringBetween(value, "{", "}");

if you are using StringUtils which is contained in apache.commons.lang package.

Answer 2

In a single line you can convert any type of object to any other type of object.

(Since I use Gson quite liberally, I am sharing a Gson based approach)

Gson gson = new Gson();    
Map<Object,Object> attributes = gson.fromJson(gson.toJson(value),Map.class);

What it does is:

1. gson.toJson(value) will serialize your object into its equivalent Json representation.
2. gson.fromJson will convert the Json string to specified object. (in this example - Map)

There are 2 advantages with this approach:

1. The flexibility to pass any Object instead of String to toJson method.
2. You can use this single line to convert to any object even your own declared objects.

Answer 3

String value = "{first_name = naresh,last_name = kumar,gender = male}"

Let's start

1. Remove { and } from the String>>first_name = naresh,last_name = kumar,gender = male
2. Split the String from ,>> array of 3 element
3. Now you have an array with 3 element
4. Iterate the array and split each element by =
5. Create a Map<String,String> put each part separated by =. first part as Key and second part as Value

Answer 4

@Test
public void testToStringToMap() {
    Map<String,String> expected = new HashMap<>();
    expected.put("first_name", "naresh");
    expected.put("last_name", "kumar");
    expected.put("gender", "male");
    String mapString = expected.toString();
    Map<String, String> actual = Arrays.stream(mapString.replace("{", "").replace("}", "").split(","))
            .map(arrayData-> arrayData.split("="))
            .collect(Collectors.toMap(d-> ((String)d[0]).trim(), d-> (String)d[1]));

    expected.entrySet().stream().forEach(e->assertTrue(actual.get(e.getKey()).equals(e.getValue())));
}

Answer 5

try this out :)

public static HashMap HashMapFrom(String s){
    HashMap base = new HashMap(); //result
    int dismiss = 0; //dismiss tracker
    StringBuilder tmpVal = new StringBuilder(); //each val holder
    StringBuilder tmpKey = new StringBuilder(); //each key holder

    for (String next:s.split("")){ //each of vale
        if(dismiss==0){ //if not writing value
            if (next.equals("=")) //start writing value
                dismiss=1; //update tracker
            else
                tmpKey.append(next); //writing key
        } else {
            if (next.equals("{")) //if it's value so need to dismiss
                dismiss++;
            else if (next.equals("}")) //value closed so need to focus
                dismiss--;
            else if (next.equals(",") //declaration ends
                    && dismiss==1) {
                //by the way you have to create something to correct the type
                Object ObjVal = object.valueOf(tmpVal.toString()); //correct the type of object
                base.put(tmpKey.toString(),ObjVal);//declaring
                tmpKey = new StringBuilder();
                tmpVal = new StringBuilder();
                dismiss--;
                continue; //next :)
            }
            tmpVal.append(next); //writing value
        }
    }
    Object objVal = object.valueOf(tmpVal.toString()); //same as here
    base.put(tmpKey.toString(), objVal); //leftovers
    return base;
}

examples input : "a=0,b={a=1},c={ew={qw=2}},0=a" output : {0=a,a=0,b={a=1},c={ew={qw=2}}}

Answer 6

Should Use this way to convert into map :

    String student[] = students.split("\\{|}");
    String id_name[] = student[1].split(",");

    Map<String,String> studentIdName = new HashMap<>();

    for (String std: id_name) {
        String str[] = std.split("=");
        studentIdName.put(str[0],str[1]);
  }

Answer 7

You can use below library to convert any string to Map object.


<!-- https://mvnrepository.com/artifact/io.github.githubshah/gsonExtension -->
<dependency>
    <groupId>io.github.githubshah</groupId>
    <artifactId>gsonExtension</artifactId>
    <version>4.1.0</version>
</dependency>

Answer 8

Using Java Stream:

Map<String, String> map = Arrays.stream(value.replaceAll("[{}]", " ").split(","))
                .map(s -> s.split("=", 2))
                .collect(Collectors.toMap(s -> s[0].trim(), s -> s[1].trim()));

1. Arrays.stream() to convert string array to stream.
2. replaceAll("[{}]", " "): regex version to replace both braces.
3. split(","): Split the string by , to get individual map entries.
4. s.split("=", 2): Split them by = to get the key and the value and ensure that the array is never larger than two elements.
5. The collect() method in Stream API collects all objects from a stream object and stored in the type of collection.
6. Collectors.toMap(s -> s[0].trim(), s -> s[1].trim()): Accumulates elements into a Map whose keys and values are the result of applying the provided mapping functions to the input elements.

Answer 9

Suprised noone has mentioned just using JSONObject(org.json.JSONObject)

        JSONObject json = new JSONObject(mapStr);
        Map<String,Object> map = json.toMap();

Far better than writing your own parser?