Jackson – Marshall String to JsonNode

1. Overview

This quick tutorial will show how to use Jackson 2 to convert a JSON String to a JsonNode (com.fasterxml.jackson.databind.JsonNode).

If you want to dig deeper and learn other cool things you can do with the Jackson 2 – head on over to the main Jackson tutorial.

2. Quick Parsing

Very simply, to parse the JSON String we only need an ObjectMapper:

@Test
public void whenParsingJsonStringIntoJsonNode_thenCorrect() 
  throws JsonParseException, IOException {
    String jsonString = "{"k1":"v1","k2":"v2"}";

    ObjectMapper mapper = new ObjectMapper();
    JsonNode actualObj = mapper.readTree(jsonString);

    assertNotNull(actualObj);
}

3. Low Level Parsing

If, for some reason, you need to go lower level than that, the following example exposes the JsonParser responsible with the actual parsing of the String:

@Test
public void givenUsingLowLevelApi_whenParsingJsonStringIntoJsonNode_thenCorrect() 
  throws JsonParseException, IOException {
    String jsonString = "{"k1":"v1","k2":"v2"}";

    ObjectMapper mapper = new ObjectMapper();
    JsonFactory factory = mapper.getFactory();
    JsonParser parser = factory.createParser(jsonString);
    JsonNode actualObj = mapper.readTree(parser);

    assertNotNull(actualObj);
}

4. Using the JsonNode

After the JSON is parsed into a JsonNode Object, we can work with the Jackson JSON Tree Model:

@Test
public void givenTheJsonNode_whenRetrievingDataFromId_thenCorrect() 
  throws JsonParseException, IOException {
    String jsonString = "{"k1":"v1","k2":"v2"}";
    ObjectMapper mapper = new ObjectMapper();
    JsonNode actualObj = mapper.readTree(jsonString);

    // When
    JsonNode jsonNode1 = actualObj.get("k1");
    assertThat(jsonNode1.textValue(), equalTo("v1"));
}

5. Conclusion

This article illustrated how to parse JSON Strings into the Jackson JsonNode model to enable a structured processing of the JSON Object.

The implementation of all these examples and code snippets can be found in my github project – this is an Eclipse based project, so it should be easy to import and run as it is.

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