How to Build a Groovy‑Based JsonPath Utility Class

Overview

JsonUtil is a Groovy wrapper around the com.jayway.jsonpath.JsonPath library that simplifies extracting values from a JSON document. It is designed for Java/Groovy developers and provides typed getters for common primitive types, lists, and generic objects.

Key Features

Factory method JsonUtil.getInstance(JSONObject json) creates an instance.

Typed getters: getString, getInt, getBoolean, getLong, getDouble, getList, getT (generic).

Verification helper getVerify(String path) returns a Verify object for Groovy operator‑overloading based assertions.

All getters delegate to a private get(String path) method that invokes JsonPath.read.

Null or empty JSON triggers a custom ParamException. JsonPath parsing errors are caught and logged, returning null.

Implementation Details

The class extends SourceCode and holds a com.alibaba.fastjson.JSONObject instance. Logging is performed with SLF4J.

Example of the internal get method:

Object get(String path) {
    logger.debug("Matching object: {}, expression: {}", json.toString(), path);
    if (json == null || json.isEmpty())
        ParamException.fail("json is null or empty");
    try {
        return JsonPath.read(this.json, path);
    } catch (JsonPathException e) {
        logger.warn("jsonpath:{} parsing failed, json value", json.toString(), path, e);
        return null;
    }
}

Typed getters convert the raw value to the requested type using helper methods such as changeStringToInt, changeStringToBoolean, etc. The generic getter getT(String path, Class<T> tClass) attempts a cast and logs a warning on ClassCastException.

Usage Example

import com.alibaba.fastjson.JSONObject;
import com.fun.utils.JsonUtil;

def json = new JSONObject();
json.put("store", [book: [[author: "John"], [author: "Jane"]]]);

def util = JsonUtil.getInstance(json);
String author0 = util.getString('$.store.book[0].author');   // "John"
int count = util.getInt('$.store.book.size()');
List authors = util.getList('$.store.book[*].author');

Dependencies

com.jayway.jsonpath:json-path

– provides the JsonPath evaluation engine. com.alibaba.fastjson:fastjson – JSON object representation.

SLF4J for logging.

Future Work

Unit tests are planned using the Groovy‑based Spock framework to verify each getter and the verification helper.