Here is a simple class I have written to retrieve grand exchange information for specified osrs items, using the json file hosted by rsbuddy at: https://rsbuddy.com/exchange/summary.json
Note the retrieval of this data should only be done once at the start of your script, and you should store the map for use later rather than re-calling the method. You may also get better performance using a JSON library.
RSExchange.java
import java.io.BufferedReader;
import java.io.InputStr