CustomInventory util

CustomInventory.java

import org.bukkit.Bukkit;
import org.bukkit.Material;
import org.bukkit.entity.Player;
import org.bukkit.inventory.Inventory;
import org.bukkit.inventory.ItemStack;
import org.bukkit.inventory.meta.ItemMeta;

import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;

/**
 * @author FerusGrim
 */
public class CustomInventory {

    private String name;
    private int invSize;
    private final Map<Integer, ItemStack> itemMap;

    public CustomInventory(String name, int invSize, Map<Integer, ItemStack> itemMap) {
        this.name = name;
        this.invSize = invSize;
        this.itemMap = itemMap;
    }

    public CustomInventory(String name, int invSize) {
        this(name, invSize, new HashMap<>());
    }

    public CustomInventory(String name) {
        this(name, 1);
    }

    public String getName() {
        return this.name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getInvSize() {
        return this.invSize;
    }

    public void setInvSize(int invSize) {
        this.invSize = invSize;
    }

    public Map<Integer, ItemStack> getItemMap() {
        return this.itemMap;
    }

    public ItemStack getItem(int slot) {
        return this.itemMap.get(slot);
    }

    public void addItem(int slot, ItemStack item) {
        this.itemMap.put(slot, item);
    }

    public void removeItem(int slot) {
        this.itemMap.remove(slot);
    }

    public Inventory generateInventory() {
        final Inventory inventory = Bukkit.createInventory(null, this.invSize, this.name);

        for (int slot : this.itemMap.keySet()) {
            inventory.setItem(slot, this.itemMap.get(slot));
        }

        return inventory;
    }

    public void openInventory(Player player) {
        player.openInventory(this.generateInventory());
    }
}

ExampleUsage.java

    public void setupInventory(Player player) {
        CustomInventory cInv = new CustomInventory("Custom Inventory", 9);
        
        ItemStack itemStack = new ItemStack(Material.BLAZE_ROD);
        ItemMeta meta = itemStack.getItemMeta();
        
        meta.setDisplayName("Rod of Amazingness");
        meta.setLore(Arrays.asList("Destroy your foes with justice!"));
        
        itemStack.setItemMeta(meta);
        
        cInv.addItem(5, itemStack);
        
        cInv.openInventory(player);
    }