Added addon request system to request data from an addon in spigot plugins

src/main/java/world/bentobox/bentobox/api/addons/Addon.java

@@ -3,6 +3,8 @@ package world.bentobox.bentobox.api.addons;
 import java.io.File;
 import java.io.IOException;
 import java.io.InputStream;
+import java.util.HashMap;
+import java.util.Map;
 import java.util.Optional;
 import java.util.jar.JarEntry;
 import java.util.jar.JarFile;
@@ -15,6 +17,7 @@ import org.bukkit.configuration.file.YamlConfiguration;
 import org.bukkit.event.Listener;
 
 import world.bentobox.bentobox.BentoBox;
+import world.bentobox.bentobox.api.addons.request.AddonRequestHandler;
 import world.bentobox.bentobox.managers.IslandsManager;
 import world.bentobox.bentobox.managers.PlayersManager;
 
@@ -32,6 +35,7 @@ public abstract class Addon {
     private FileConfiguration config;
     private File dataFolder;
     private File file;
+    private Map<String, AddonRequestHandler> requestHandlers = new HashMap<>();
 
     public Addon() {
         state = State.DISABLED;
@@ -359,4 +363,28 @@ public abstract class Addon {
     public String getPermissionPrefix() {
         return this.getDescription().getName().toLowerCase() + ".";
     }
+
+    /**
+     * Register request handler to answer requests from plugins.
+     * @param handler
+     */
+    public void registerRequestHandler(AddonRequestHandler handler) {
+        requestHandlers.put(handler.getLabel(), handler);
+    }
+
+    /**
+     * Send request to addon.
+     * @param label
+     * @param metaData
+     * @return request response, null if no response.
+     */
+    public Object request(String label, Map<String, Object> metaData) {
+        label = label.toLowerCase();
+        AddonRequestHandler handler = requestHandlers.get(label);
+        if(handler != null) {
+            return handler.handle(metaData);
+        } else {
+            return null;
+        }
+    }
 }

src/main/java/world/bentobox/bentobox/api/addons/exceptions/AddonRequestException.java

@@ -0,0 +1,14 @@
+package world.bentobox.bentobox.api.addons.exceptions;
+
+import world.bentobox.bentobox.api.addons.request.AddonRequestBuilder;
+
+import java.util.UUID;
+
+public class AddonRequestException extends AddonException
+{
+	private static final long serialVersionUID = -5698456013070166174L;
+
+	public AddonRequestException(String errorMessage) {
+		super(errorMessage);
+	}
+}

src/main/java/world/bentobox/bentobox/api/addons/request/AddonRequestBuilder.java

@@ -0,0 +1,64 @@
+package world.bentobox.bentobox.api.addons.request;
+
+import org.apache.commons.lang.Validate;
+import world.bentobox.bentobox.BentoBox;
+import world.bentobox.bentobox.api.addons.Addon;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Optional;
+
+public class AddonRequestBuilder
+{
+	private String addonName;
+	private String requestLabel;
+	private Map<String, Object> metaData = new HashMap<>();
+
+	/**
+	 * Define the addon you wish to request.
+	 *
+	 * @param addonName
+	 */
+	public AddonRequestBuilder addon(String addonName) {
+		this.addonName = addonName;
+		return this;
+	}
+
+	/**
+	 * Define label for addon request.
+	 *
+	 * @param requestLabel
+	 */
+	public AddonRequestBuilder label(String requestLabel) {
+		this.requestLabel = requestLabel;
+		return this;
+	}
+
+	/**
+	 * Add meta data to addon request.
+	 *
+	 * @param key
+	 * @param value
+	 */
+	public AddonRequestBuilder addMetaData(String key, Object value) {
+		metaData.put(key, value);
+		return this;
+	}
+
+	/**
+	 * Send request to addon.
+	 *
+	 * @return request response, null if no response.
+	 */
+	public Object request() {
+		Validate.notNull(addonName);
+		Validate.notNull(requestLabel);
+
+		Optional<Addon> addonOptional = BentoBox.getInstance().getAddonsManager().getAddonByName(addonName);
+		if(addonOptional.isPresent()) {
+			Addon addon = addonOptional.get();
+			return addon.request(requestLabel, metaData);
+		}
+		return null;
+	}
+}

src/main/java/world/bentobox/bentobox/api/addons/request/AddonRequestHandler.java

@@ -0,0 +1,31 @@
+package world.bentobox.bentobox.api.addons.request;
+
+import java.util.Map;
+
+public abstract class AddonRequestHandler
+{
+	private String label;
+
+	public AddonRequestHandler(String label) {
+		this.label = label.toLowerCase();
+	}
+
+	/**
+	 * Get request handler label.
+	 *
+	 * @return label
+	 */
+	public String getLabel() {
+		return label;
+	}
+
+	/**
+	 * Handle an addon request.
+	 * This is used only for Addons to respond to addon requests from plugins.
+	 * Example: request island level from Levels addon.
+	 *
+	 * @param metaData
+	 * @return request response
+	 */
+	public abstract Object handle(Map<String, Object> metaData);
+}