Parsing a subset of JSON in Java using Jackson

Question

Given a Json, is it possible to use Jackson to only parse out a section of the message? Say that the data I\'m interested in is buried in a deep hierarchy of fields and I simply

Answer 1

To do this efficiently with Jackson, use the Streaming API via the JsonParser class (http://fasterxml.github.io/jackson-core/javadoc/2.5/com/fasterxml/jackson/core/JsonParser.html).

This approach will allocate no additional memory and will not incur the cost of deserializing values for all of the skipped data. Since the code will be much longer and more difficult to read than using Jackson's ObjectMapper, only do this if profiling shows unacceptable GC activity or CPU usage during parsing.

You can skip all of the nodes that you are uninterested in until you hit the "phoneNumbers" key. Then you can call the readValueAs function to deserialize the array of phone number dictionaries like so readValueAs(new TypeReference()).

See also:

• a tutorial on reading and writing with JsonParser: http://www.cowtowncoder.com/blog/archives/2009/01/entry_132.html
• The main documentation: https://github.com/FasterXML/jackson-core