Code used when you want to process Json with only the standard library in Java (improved version) gson unnecessary

gson is also convenient, but I found it troublesome, such as not being able to trace multiple layers at once, so I am making such a tool. Also, there are many boring reasons that "I really want to use Gson in the XX system, but internal approval is troublesome".

• The JVM that is popular in the desktop version is equipped with "JavaScript Engine" as standard, and it is realized by calling it. There is a high possibility that it is not possible in embedded systems.

You can use it like this.

public static void main(String[] args) {
String json = "{'test':'this is test','test2':{'test3':'value3'},'test4':['a','b','c']}";
	{
		Object value = JsonUtil.get(json, "test"); // <- 
		System.out.println(value); // "this is test"
	}
	{
		Object value = JsonUtil.get(json, "test2.test3"); // <-I want to do this
		System.out.println(value); // "value3"
	}
	{
		Object[] value = JsonUtil.getAsArray(json, "test4");
		System.out.println(Arrays.toString(value)); // ["a","b","c"]
		System.err.println(value.getClass());
		for (int n = 0; n < value.length; n++) {
			System.err.println(value[n]);
		}
	}
}

Below is the source code. Feel free to copy or modify it before use.

package pkg;

import java.util.Arrays;
import java.util.Map;
import java.util.Set;

import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;

public class JsonUtil {

	public static Object[] getAsArray(String json, String code) {
		Object obj = get(json, code);
		if (obj instanceof Object[]) {
			return (Object[]) obj;
		} else {
			return null;
		}
	}
	public static Object get(String json, String code) {
		// Get the JavaScript engine
		ScriptEngineManager manager = new ScriptEngineManager();
		ScriptEngine engine = manager.getEngineByName("JavaScript");

		String script = "var obj = " + json + ";";
		try {
			engine.eval(script);
			{
				Object obj = engine.eval("obj." + code);
				if (obj instanceof Map) {
					java.util.Map map = (java.util.Map) obj;
					Set entrySet = map.entrySet();
					Object[] arr = new Object[entrySet.size()];
					int n = 0;
					for (Object objValue : map.values()) {
						if (objValue instanceof String) {
							String sValue = (String) objValue;
							arr[n] = sValue;
						} else {
							arr[n] = map.get(obj);
						}
						n++;
					}
					return arr;
				}
				return obj;
			}
		} catch (ScriptException e) {
			e.printStackTrace();
			return null;
		}
	}
	public static void main(String[] args) {
		String json = "{'test':'this is test','test2':{'test3':'value3'},'test4':['a','b','c']}";
		{
			Object value = JsonUtil.get(json, "test");
			System.out.println(value); // "this is test"
		}
		{
			Object value = JsonUtil.get(json, "test2.test3");
			System.out.println(value); // "value3"
		}
		{
			Object[] value = JsonUtil.getAsArray(json, "test4");
			System.out.println(Arrays.toString(value)); // ["a","b","c"]
			System.err.println(value.getClass());
			for (int n = 0; n < value.length; n++) {
				System.err.println(value[n]);
			}
		}
	}
}