How to convert a JSON string to a Map`<String, String>` with Jackson JSON

java

json-parsing

jackson-library

objectmapper

byNikita Barsukov·Oct 1, 2024

To transform JSON to Map<String, String> using Jackson, consider the following code:

ObjectMapper mapper = new ObjectMapper();
Map<String, String> result = mapper.readValue(json, new TypeReference<Map<String, String>>() {});

Here you need to replace json with your own JSON string. This code readily changes the JSON into a Map through readValue() method from Jackson, complemented by TypeReference to designate the Map type.

Compatibility: Working with the right version

Before we start, remember that compatibility is key. If you're wrestling with an outdated version of Jackson, you might need to use alternatives like TypeFactory.mapType(). Also, be sure your JSON is porch-perfect, because if it's not, readValue() method will crash faster than a wifi connection at a tech conference.

try {
    ObjectMapper mapper = new ObjectMapper();
    Map<String, String> result = mapper.readValue(json, new TypeReference<Map<String, String>>() {});
    // I have the power!
} catch (JsonMappingException e) {
    // Map is not territory
} catch (JsonProcessingException e) {
    // The JSON has betrayed us
}

Good old try-catch. Handling exceptions lets your app withstand any curveballs the Jackson library might throw (and trust me, it's got an arm).

Multithreading: Conversion in a busy world

Now, let's talk about ObjectMapper and ObjectReader in Jackson. These mappers are thread-safe. Handy, right? Wherever you are - be it a web service processing concurrent requests or just your usual day, turning JSON into a Map<String, String>, these guys got your back.

ObjectReader reader = new ObjectMapper().readerFor(new TypeReference<Map<String, String>>() {});
Map<String, String> result = reader.readValue(json);

With this pattern, you'll spend less time configuring the mapper for every tombstone, I mean, process.

Typing: Know what you're dealing with

Be sure to explicitly state your key/value pair types when dealing with Map, using TypeFactory.constructMapType(). Suppress any unchecked assignment warnings, but keep an eye out for pitfalls or hidden speedbumps:

ObjectMapper mapper = new ObjectMapper();
TypeReference<?> typeRef = mapper.getTypeFactory().constructMapType(HashMap.class, String.class, String.class);
Map<String, String> result = mapper.readValue(json, typeRef);

Utility class: Because we all love shortcuts

Create a utility method to encapsulate the JSON conversion process. It helps get your beloved "Map" quickly while ensuring unchecked assignments get there alive:

public class JsonUtils {
    private static final ObjectMapper mapper = new ObjectMapper();
    
    @SuppressWarnings("unchecked")
    public static Map<String, String> convertJsonToMap(String json) throws JsonProcessingException {
        // Abracadabra!
        return mapper.readValue(json, Map.class);
    }
}