How to convert String into Hashmap in java

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.

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

@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())));
}

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}}}

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]);
  }

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>

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?

Using Java 8 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.