Using JsonPath in Java for JSON Data Extraction and Validation

The author describes a testing platform similar to Postman and introduces JsonPath as a solution for richer validation and multi‑case chaining in the second phase of development.

Adding the jar

compile group: 'com.jayway.jsonpath', name: 'json-path', version: '2.4.0'

JSON data

JSONObject json = JSON.parseObject("{" +
        "    \"store\": {" +
        "        \"book\": [" +
        "            {\"category\": \"reference\", \"author\": \"Nigel Rees\", \"title\": \"Sayings of the Century\", \"price\": 8.95}," +
        "            {\"category\": \"fiction\", \"author\": \"Evelyn Waugh\", \"title\": \"Sword of Honour\", \"price\": 12.99}," +
        "            {\"category\": \"fiction\", \"author\": \"Herman Melville\", \"title\": \"Moby Dick\", \"isbn\": \"0-553-21311-3\", \"price\": 8.99}," +
        "            {\"category\": \"fiction\", \"author\": \"J. R. R. Tolkien\", \"title\": \"The Lord of the Rings\", \"isbn\": \"0-395-19395-8\", \"price\": 22.99}" +
        "        ]," +
        "        \"bicycle\": {\"color\": \"red\", \"price\": 19.95}" +
        "    }," +
        "    \"expensive\": 10," +
        "    \"ss\": [32,32,4,23]" +
        "}");

JsonPath syntax

JsonPath expressions start with $ for the root object or array. They can use dot notation (e.g., $.store.book[0].title) or bracket notation (e.g., $['store']['book'][0]['title']) to navigate JSON structures, similar to XPath for XML.

API

/**
 * Creates a new JsonPath and applies it to the provided Json object
 * @param json      a json object
 * @param jsonPath  the json path
 * @param filters   filters to be applied to the filter place holders [?] in the path
 * @param <T>       expected return type
 * @return list of objects matched by the given path
 */
@SuppressWarnings({"unchecked"})
public static <T> T read(Object json, String jsonPath, Predicate... filters) {
    return parse(json).read(jsonPath, filters);
}

Getting all book authors

Object read = JsonPath.read(json, "$.store.book[*].author");
output(read);

The same query can return a List directly, yielding the identical author list.

List read = JsonPath.read(json, "$.store.book[*].author");
output(read);

If an incompatible return type is used, a ClassCastException will be thrown.

Getting all authors (recursive)

$...author
$.store..price

These expressions retrieve all author values regardless of depth and all price values under store respectively.

Getting all information under a node

$.store.*
$.ss.*

These queries return the complete objects under store and the array ss.

The article concludes by inviting readers to follow future posts on handling JSON arrays.