# Convert JSON String to and from Map using Gson

By Atta Ur Rehman Shah (https://attacomsian.com/about). Published Nov 30, 2019. Topics: Java, JSON.
Canonical URL: https://attacomsian.com/blog/gson-convert-json-string-to-map

> A short tutorial to learn how to convert a JSON string to Java Map and vice versa using Gson.

In this short tutorial, you'll learn how to convert a JSON string to a `Map` in Java and vice versa by using the [Gson](https://attacomsian.com/blog/gson-read-write-json) library. 

## Dependencies

To add Gson to your [Gradle](https://attacomsian.com/blog/install-gradle-on-ubuntu) project, add the following dependency to `build.gradle` file:

```groovy
implementation 'com.google.code.gson:gson:2.8.6'
```

For Maven, include the below dependency to your `pom.xml` file:

```xml
<dependency>
  <groupId>com.google.code.gson</groupId>
  <artifactId>gson</artifactId>
  <version>2.8.6</version>
</dependency>
```

## Convert JSON String to Map

To convert a JSON string to a Java `Map` with the same properties and keys, you can use the `fromJson()` method from `Gson`:

```java
try {
    // JSON string
    String json = "{\"name\":\"John Doe\",\"email\":\"john.doe@example.com\"," +
            "\"roles\":[\"Member\",\"Admin\"],\"admin\":true}";

    // convert JSON string to Java Map
    Map<String, Object> map = new Gson().fromJson(json, Map.class);

    // print map keys and values
    for (Map.Entry<String, Object> entry : map.entrySet()) {
        System.out.println(entry.getKey() + "=" + entry.getValue());
    }

} catch (Exception ex) {
    ex.printStackTrace();
}
```

You should see the following output printed on the console:

```bash
name=John Doe
email=john.doe@example.com
roles=[Member, Admin]
admin=true
```

To convert a JSON string stored in a file into a Java map, you can pass an instance of `Reader` to `fromJson()`, as shown below:

```java
Map<String, Object> map = new Gson().fromJson(
        new FileReader("user.json"), 
        Map.class);
```

## Convert Map to JSON String

To convert a Java `Map` to a JSON string, you can use the `toJson()` method from the `Gson` class:

```java
try {
    // create a map
    Map<String, Object> map = new HashMap<>();
    map.put("name", "John Deo");
    map.put("email", "john.doe@example.com");
    map.put("roles", new String[]{"Member", "Admin"});
    map.put("admin", true);

    // convert map to JSON string
    String json = new Gson().toJson(map);

    // print JSON string
    System.out.println(json);

} catch (Exception ex) {
    ex.printStackTrace();
}
```

The above code will produce the following JSON:

```json
{"roles":["Member","Admin"],"name":"John Deo","admin":true,"email":"john.doe@example.com"}
```

If you want to write the converted Map directly to a JSON file, just pass an instance of `Writer` to the `toJson()` method:

```java
try {
    // create a map
    Map<String, Object> map = new HashMap<>();
    map.put("name", "John Deo");
    map.put("email", "john.doe@example.com");
    map.put("roles", new String[]{"Member", "Admin"});
    map.put("admin", true);

    // create a writer
    Writer writer = new FileWriter("user.json");

    // convert map to JSON File
    new Gson().toJson(map, writer);

    // close the writer
    writer.close();
    
} catch (Exception ex) {
    ex.printStackTrace();
}
```

For more Gson examples, check out the [How to read and write JSON using Gson in Java](https://attacomsian.com/blog/gson-read-write-json) tutorial.