Practical Guide to JsonPath: Filtering JSON Data with Operators and Functions

Continuing from the previous three parts, this post focuses on the JsonPath API for filtering JSON data. JsonPath operators (e.g., == , > , =~ ) follow language conventions, while functions such as in , nin , and anyof provide more expressive queries.

The first part of the article briefly mentions that the operators are straightforward and concentrates on demonstrating the usage of functions.

json data

The sample JSON object is extended with two new fields: page and pages .

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

Field value in a specific array

Using the in function to select books whose page is either 'A' or 'C':

JsonPath expression: $.store.book[?(@.page in ['A','C'])]

Object read = JsonPath.read(json, "$.store.book[?(@.page in ['A','C'])]");
output(JSONArray.parseArray(read.toString()));

The console output shows the matching JSON objects.

Field value not in a specific array

Using the nin (not in) function to select books whose page is not 'A' or 'C':

JsonPath expression: $.store.book[?(@.page nin ['A','C'])]

Object read = JsonPath.read(json, "$.store.book[?(@.page nin ['A','C'])]");
output(JSONArray.parseArray(read.toString()));

Subset check

The subsetof operator verifies that the array field pages is a subset of a given list:

JsonPath expression: $.store.book[?(@.pages subsetof ['A','B','C'])]

Object read = JsonPath.read(json, "$.store.book[?(@.pages subsetof ['A','B','C'])]");
output(JSONArray.parseArray(read.toString()));

Array length and string length validation

The size operator can validate the length of arrays or strings. Examples:

Array length: $.store.book[?(@.pages size 3)]

String length: $.store.book[?(@.author size 16)]

Object read = JsonPath.read(json, "$.store.book[?(@.pages size 3)]");
output(JSONArray.parseArray(read.toString()));

Object read2 = JsonPath.read(json, "$.store.book[?(@.author size 16)]");
output(JSONArray.parseArray(read2.toString()));

Empty check

When checking for empty values, the size 0 expression can be used as a reliable alternative.

Finally, the article includes a brief promotion of the FunTester public account and links to other popular articles.