JRL1004
Here is an example of how to make the runnable for anyone who thinks that you can't loop this without events

import org.bukkit.Material;
import org.bukkit.block.Chest;
import org.bukkit.inventory.ItemStack;
import org.bukkit.scheduler.BukkitRunnable;

public class TestChestParticles extends BukkitRunnable {

    private Chest chest;

    public TestChestParticles(Chest chest) {
        this.chest = chest;
    }

    private boolean isValid() {
        if (!chest.getChunk().isLoaded()) return false; // The chunk is not loaded, do not use this
        if (chest.getBlock().getType() != Material.CHEST) return false;// The block changed and is no longer a chest
        for (ItemStack item : chest.getBlockInventory().getContents()) {
            if(item == null || item.getType() == Material.AIR) continue; // We only want to know if there is an item in it and use this check since the itemstack is a solid array of size Inventory#getSize()
            return true; // It has at least one item in it and is a chest, which makes it valid
        }
        return false; // The chest is empty
    }

    @Override
    public void run() {
        if(!isValid()) {
            chest = null;
            cancel();
            return;
            // Stop everything immediately, we have no reason to continue without a chest
        }
        // Play particle effects after the check
    }

}


And then you would just call it with this:

new TestChestParticles(chest).runTaskTimer(plugin, 0, 2);
// Where 'chest' is the chest object, 'plugin' is an instance of your main class, and 2 is the delay between particle effects in ticks