How to Convert a JSON String to a Map using Jackson in Java?

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How to Convert a JSON String to a Map with Jackson JSON

Question:

Attempting to convert a JSON string to a Map using Jackson leads to an "Unchecked assignment Map to Map" error. Seeking the correct approach and exploring alternative methods for JSON conversion in Java, similar to json_decode in PHP.

Answer:

The correct approach using Jackson JSON is to leverage a TypeReference to specify the desired map type as follows:

<code class="java">public void testJackson() throws IOException {  
    ObjectMapper mapper = new ObjectMapper(); 
  
    TypeReference<HashMap<String,Object>> typeRef 
            = new TypeReference<HashMap<String,Object>>() {};

    HashMap<String,Object> o = mapper.readValue(from, typeRef); 
    System.out.println("Got " + o); 
}  </code>

For reading from a string, obtain an InputStream using new ByteArrayInputStream(astring.getBytes("UTF-8")) and pass it to mapper.readValue().

Alternative Native Java JSON Conversion:

Jackson is not the only option for JSON conversion in Java. The Gson library from Google provides a more intuitive approach:

1. Import the Gson class.
2. Create a Gson object.
3. Use Gson.fromJson() to convert a JSON string to the desired object type, in this case, a Map.

Additional Note:

The original answer has been updated to reflect the recommendation for using the Gson library instead of Jackson.

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