Tuesday, October 03, 2017

Parsing an arbitrary JSON string and extracting values

Developers use libraries such as Jackson to convert JSON strings to Java objects and vice-versa.
But what if you need to parse a JSON string and do not know the complete schema of it. Since you do not have the complete schema of the JSON, you cannot create the Java class.

Another situation could be when you don't want to create a Java class and just want to extract a few values from the JSON string. Given below are 2 techniques for achieving this:

Option 1:

Convert the JSON string to a HashMap. All libraries such as Jackson, Gson provide methods to convert the JSON string into a map. Then by using standard map functions, you can extract the values you are interested in. Sample code available here.

Option 2: 

Convert the JSON string into a 'tree model' object. Jackson has a default tree model object called JsonNode. Jackson also supports JSON Pointer Expression, so you can directly access a node value like this:

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