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Introduction

This rather large tutorial aims at getting you started with plugin development in Bukkit. It is in no way a complete tutorial of all possibilities in Bukkit, but rather a general overview of the basics. It starts with making sure you understand Java, sets up your workspace in an IDE, and introduces the essentials of most Bukkit plugins.

Videos

Learning Java

These tutorials require basic knowledge of the Java programming language. If you are just getting started with Java or need a refresher, the following is a non-exhaustive list.

Oracle's Java Tutorials - Official tutorials

Java2s.com - Tutorials

Java 101 - Tutorials

JavaNotes - Free online textbook

TheNewBoston - TheNewBoston's video tutorials

Derek Banas - Faster paced Video tutorials

MOOC.fi - A big course, designed to take about 12 weeks

The Development Environment

Before developing a plugin (or learning Java) you will need to set up a development environment. This includes but is not limited to installing an IDE (Integrated Development Environment). The following tutorial contains instructions for the Eclipse IDE.

For further information, see Setting Up Your Workspace

You MUST download the Eclipse build for Java developers, NOT the one for Java EE developers. The version for Java EE developers does not ship Maven support, which is required for this tutorial.

Starting a Plugin Project

Create a Project

Before starting you'll need to set up your workspace and files in Eclipse. Start Eclipse, then create a new Project by selecting File -> New -> Project:

Now, open up the Maven folder, and select Maven Project. Click next, and then tick the Create a simple project box on the next page, and then click Next: If you can't see Maven folder, then you need to go download the m2eclipse plugin from here

Now, you need to name your group as follows:

If you have a domain name, the package would be the domain name in reverse. Ex: i-am-a-bukkit-developer.com your package would be com.i_am_a_bukkit_developer source Avoid using a domain you do not own.

No domain? Here are some common conventions Create an account on a source control site such as GitHub or sourceforge For GitHub, follow the instructions here and you will have a sub-domain, so your package would be io.github.<username>

Use your email. Ex: <username>@gmail.com would be com.gmail.<username

This is the least preferred method. Simply use any unique group naming, again, use this as your last resort.



There are several things that your group must not begin with and those are:

org.bukkit

net.bukkit

com.bukkit

net.minecraft

Once you have the base group name, you will want to finish it off with the plugin name. Lets use the GitHub Pages example for this. If you are creating a plugin called TestPlugin your full group name would be io.github.<username>, and your artifact name would be TestPlugin. For the version, simply stick with the default for now. It can be changed later.

Finish the wizard:

If this is your first time using Eclipse, close the Welcome tab by clicking the "X" next to the Welcome tab on the tab bar. Now, you should have a window that looks like this:

Click the arrow to the left of your artifact name, and let's get started!

Reference the Bukkit API

Before you begin developing your plugin you will need to add the Bukkit API library to your project as a dependency, you can also add any other API's you may want to use.

Double-click pom.xml, which is at the bottom of your project's folder. Click the pom.xml tab at the bottom, and you should see something like this:

If you wish to use Java 6+ language features, you must specify the Java version that the project should be built on. Copy and paste this (specifies that the project should be built under Java 7) before </project>:

<build> <plugins> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-compiler-plugin</artifactId> <configuration> <source>1.7</source> <target>1.7</target> </configuration> </plugin> </plugins> </build>

You may use other levels, such as 1.8 for Java 8. Please note that according to MCStats, a sizeable number of servers run Java 7 (~2% as of March 2020), so compiling for Java 8 will result in many server owners being unable to run your plugin. If you do use Java 1.8 features, Eclipse will suggest changing the language level when you hover over the code "error". Do so.

Before the </project> at the bottom, copy and paste this block (it tells Eclipse where Bukkit's repository is located):

The spigot repository is the only working repository as the former repository "bukkit-repo" (http://repo.bukkit.org/content/groups/public/) is down.

Next, before the </project> at the bottom, copy and paste this block (it tells Eclipse that we're building against Bukkit):

<dependencies> <dependency> <groupId>org.bukkit</groupId> <artifactId>bukkit</artifactId> <version>1.12.2-R0.1-SNAPSHOT</version><!--change this value depending on the version or use LATEST--> <type>jar</type> <scope>provided</scope> </dependency> </dependencies>

To use spigot features, also include the following dependency (in addition):

<dependencies> <dependency> <groupId>org.spigotmc</groupId> <artifactId>spigot-api</artifactId> <version>1.12.2-R0.1-SNAPSHOT</version><!--change this value depending on the version--> <type>jar</type> <scope>provided</scope> </dependency> </dependencies>

If you wish to, you may change the version of Bukkit you're building against. You can view the available versions here by looking in the maven-metadata.xml file under versions.

When you finish, your pom.xml should look similar to this:

Save your pom.xml using File -> Save or pressing Cmd + S . It will take a few minutes to download the dependencies and build the workspace. Then, right click the projects title and click Maven -> Update Project.

Bukkit Javadocs

If you have some experience with Eclipse and Java you will know that when you hover your mouse over any built in class or method a yellow box will pop up, containing the documentation for that class or method. This is known as a Javadoc and can also be accessed online at the Oracle website. Bukkit also has documentation which often contains useful descriptions of each method and class provided by the API, which is available here (Beta Javadocs can be found here, and development build Javadocs here). In order to have this information available within Eclipse, so that it will pop up whenever you hover over a Bukkit method or class, first right click on the Bukkit jar where it appears under "Maven Dependencies" in the project explorer, and select "Properties". Choose the Javadoc Location item on the left of the window that pops up, and paste the url https://hub.spigotmc.org/javadocs/spigot/ (or that of the beta/development Javadocs linked above) into the textbox under "Javadoc URL". It should look like this (with the new url):

Click "Validate", and then click "OK". Done! Now the Bukkit Javadocs are linked to the Bukkit source, and you can access helpful documentation from within Eclipse.

Creating a package

Now you need to create a 'package' which will store all the Java class files we will be using. Right click on the folder labelled src/main/java and select New > Package:

For your package name, put your group name, then a period, and then your artifact name in lowercase. For example, if your group name is io.github.name and your artifact name is TestPlugin, your package name would be io.github.name.testplugin.

Creating the Plugin's Class

Now that we have our project set up we can start to add class files and begin making our plugin. The plugin's main class is the class that extends JavaPlugin. There should only ever be one class in your plugin that extends JavaPlugin either directly or indirectly. It's always good practice to create your main class first and give it the same name as your plugin. Right click on the package you created before, and select New > Class. You should have a new class similar to the following

package {$ GroupName }.{ $ArtifactName }; import org.bukkit.plugin.java.JavaPlugin ; public final class { $ArtifactName } extends JavaPlugin { }

Warning: Plugins should never invoke their constructors and create new instances

Creating plugin.yml

Now you have setup the project and the main class. To allow Bukkit to load your plugin, you must create the plugin.yml file. This file will contain essential information, and without it your plugin will NOT work. This time we want to right click on src/main/resources (WARNING: Sometimes having your plugin.yml here could cause errors when you try to run your plugin, if this is the case try placing the plugin.yml directly in the project folder and not inside any src or other folders. This depends on your IDE and environment.). Select New > File. (If you don't see File as an option, select Other > General > File.) Name the file "plugin.yml" and click finish. Eclipse will open your currently blank plugin.yml file in the default text editor. A window may open letting you know editors are available on the Marketplace. Installing one is unnecessary, since .yml files are simple text files. (Hint: If you want to keep your workspace organized, close the text editor and drag the plugin.yml file onto the main workspace(To the right) and you will be able to edit the file inside Eclipse.)

There are three essential attributes that must be declared in the plugin.yml.

name: the simple name of your plugin. main: fully qualified name of the plugin's main class. version: the version string of your plugin.

The most simple plugin.yml file would look like this :

name : { $PluginName } main : { $PackageName } .{$MainClass} version : { $VersionNumber }

Note: The package name for plugins often includes the plugin name so don't be surprised to see <pluginname>.<pluginname> at the end of the second line! Note: Your main class may or may not be the name of your plugin depending on what you named it earlier, keep in mind this is case-sensitive.

For more examples, see #Example_Files_and_Templates

At this point your plugin can be loaded by Bukkit, and will be accompanied with log entries indicating this. But, it will do nothing!

onEnable() and onDisable()

These methods are called whenever the plugin is enabled and disabled. By default your plugin will automatically enable itself when loaded so you can register your events and provide some debug output here. onEnable() is invoked when the plugin is enabled, and should contain logic to set up your plugin when it is enabled. onDisable() is invoked when a plugin is disabled, and should contain logic to clean up your plugin and associated state. Additionally plugins can override the onLoad() method to perform additional logic when the plugin loads.

Introduction to onEnable() and onDisable()

Create the methods onEnable() and onDisable() inside the main class created in the previous section. It will look something like the following

package {$ TopLevelDomain }.{ $Domain }.{ $PluginName }; import org.bukkit.plugin.java.JavaPlugin ; public final class { $PluginName } extends JavaPlugin { @Override public void onEnable () { // TODO Insert logic to be performed when the plugin is enabled } @Override public void onDisable () { // TODO Insert logic to be performed when the plugin is disabled } }

The methods now exist, but they don't do anything yet. Note: There is no reason to print a message such as "{$PluginName} has been enabled!" as bukkit will do this automatically. For more information about events, click here.

Logging a message

A plugin can print a message to the console and the server log. It can accomplish this by invoking the correct method from the plugin's logger. First we must invoke the getLogger() method to retrieve the logger associate with this plugin. Then we can start logging.

We will write to the log when onEnable() method is called. We can do that by inserting the following line into the onEnable() method.

getLogger (). info ( "onEnable has been invoked!" );

You can then do the same inside onDisable() , making sure to change the message.

Your main class should now look something like this:

package {$ TopLevelDomain }.{ $Domain }.{ $PluginName }; import org.bukkit.plugin.java.JavaPlugin ; public final class { $PluginName } extends JavaPlugin { @Override public void onEnable () { getLogger (). info ( "onEnable has been invoked!" ); } @Override public void onDisable () { getLogger (). info ( "onDisable has been invoked!" ); } }

Handling Reloads

It is important to remember that this does not only occur on server shutdown and startup, your plugin can also be disabled and enabled by other plugins or through use of the /reload command while the server is running. Assuming that the server has only just been started when the plugin is enabled is therefore a dangerous assumption, as there may well already be players online, additional worlds loaded, additional chunks loaded, and many other unexpected differences.

For example:

You have a plugin that stores information about a player in a HashMap on the PlayerJoinEvent

You rely on having that information available for every player

An operator uses the /reload command

Your plugin is disabled and all data stored is lost

Your plugin is enabled again with several players already online

These players do not have any information stored for them in the HashMap

You try to retrieve information about them but there is none!

For this to work correctly on reload, you would need to find all players currently online during onEnable and store the correct information for that player in the HashMap.

for ( Player player : Bukkit . getServer (). getOnlinePlayers ()) { playerList . put ( player . getName (), playerData ( player )); }

Listeners

Listeners are classes whose methods are invoked in response to an event. All listeners implement org.bukkit.event.Listener. For further details about creating listeners,

Please See: Event API Reference

Commands

The onCommand() Method

So, you now know how to register events and do something when they happen, but what if you only want something to happen when a command is typed? You use onCommand . This code is run whenever a player types a command preceded by the "/" character. E.g. typing "/do something" would call the onCommand method. In this case nothing would happen because no behavior has been programmed.

Avoid using command names that are the same as those that come with Bukkit, and also consider carefully how unique your commands names will be. E.g. the "give" command is already used by several plugins, and if you implement yet another "give" command, your plugin will become incompatible with those other plugins. You must register your commands in the plugin's plugin.yml or they will not trigger this method.

The onCommand method must always return a boolean value - either true or false. If the value returned is true then you won't see any noticeable events. However if it returns false then the plugin will revert to your plugin files' 'usage: property' and display a message to the user showing them how to use the command as specified in the plugin.yml file.

When using onCommand , you should always register 4 parameters.

CommandSender sender - who sent the command

Command cmd - the command that was executed

String commandLabel - the command alias that was used

String[] args - an array of additional arguments, e.g. typing /hello abc def would put abc in args[0], and def in args[1]

Setting up the command

@Override public boolean onCommand ( CommandSender sender , Command cmd , String label , String [] args ) { if ( cmd . getName (). equalsIgnoreCase ( "basic" )) { // If the player typed /basic then do the following, note: If you only registered this executor for one command, you don't need this // doSomething return true ; } //If this has happened the function will return true. // If this hasn't happened the value of false will be returned. return false ; }

When coding the onCommand function it is always good practice to return false at the very end of the function. Returning false will display the usage dialog set in plugin.yml (see below). This way if anything goes wrong the help message will be displayed. When returning a value the function will exit so if you return true any code underneath won't be run, unless a return statement is nested in an if statement or similar.

The .equalsIgnoreCase("basic") just means that it won't distinguish between upper and lower case characters. For example, the string "BAsIc" and "BasiC" would both equal basic and the code would be executed.

Press Cmd-Shift-O (Organize Imports), importing org.bukkit.command.Command , not org.bukkit.material.Command (this is the command block), or add these two lines at the top of your file:

import org.bukkit.command.Command ; import org.bukkit.command.CommandSender ;

Adding your Command to the Plugin.yml

You will also need to add the command to your plugin.yml file. Add the following to the end of plugin.yml:

name : Basic main : <main package>.<main class> version : 1.0 author : <your IGN or name> commands : basic : description : This is a demo command. usage : /<command> [player] permission : <plugin name>.basic permission-message : You don't have <permission>

basic - the name of the command.

description - the description of the command .

usage - the help dialog that users will see when you return false in the onCommand method. Write clearly, so that others can discern what the command is and how to use it.

permission - This is used by some help plugins to work out which commands to show to the user.

permission-message - This is output when the player attempts but does not have permission to use the command.

Note that yml files use 2 spaces for tabs, as the tab character will cause problems.

Console Commands vs. Player Commands

You may have noticed the CommandSender sender parameter above. CommandSender is a Bukkit interface which has two useful (for plugin writers) subclasses: Player and ConsoleCommandSender . (There are also other subclasses that are less common such as BlockCommandSender )

When you're writing your plugin, it's a very good idea to ensure that commands that can be run from the console actually work, and that commands that should only be run as a logged-in player really are only run as a logged-in player. Some plugins simply return if the sender is not a player (i.e. someone tried to use the plugin's commands from the console), even when those commands make perfect sense from the console (e.g. changing the weather on the server).

One way to do this is:

@Override public boolean onCommand ( CommandSender sender , Command cmd , String label , String [] args ) { if ( cmd . getName (). equalsIgnoreCase ( "basic" )) { // If the player typed /basic then do the following... // do something... return true ; } else if ( cmd . getName (). equalsIgnoreCase ( "basic2" )) { if (!( sender instanceof Player )) { sender . sendMessage ( "This command can only be run by a player." ); } else { Player player = ( Player ) sender ; // do something } return true ; } return false ; }

In this example, the command basic can be run by anyone - a logged-in player, or the server operator on the console. But the command basic2 can only be run by logged-in players.

In general, you should allow as many commands as possible to work on both the console and for players. Commands that need a logged-in player can use the mechanism in the example above to check that the CommandSender is actually a player before continuing. Such commands would generally depend on some attribute of the player, e.g. a teleportation command needs a player to teleport, an item giving command needs a player to give the item to...

If you want to get more advanced, you could do some extra checks on your command arguments so that e.g. a teleportation command could be used from the console if and only if a player's name is also supplied.

Using a separate CommandExecutor class

The examples above just put the onCommand() method into the plugin's main class. For small plugins, this is fine, but if you're writing something more extensive, it may make sense to put your onCommand() method into its own class. Fortunately, this isn't too hard:

Create a new class within your plugin's package. Call it something like MyPluginCommandExecutor (although of course replacing MyPlugin with your plugin's actual name). That class must implement the Bukkit CommandExecutor interface.

In your plugin's onEnable() method, you need to create an instance of your new command executor class, and then make a call like getCommand("basic").setExecutor(myExecutor); , where "basic" is the command we want to handle, and myExecutor is the instance we created.

Best explained by example:

MyPlugin.java (the main plugin class):

@Override public void onEnable () { // This will throw a NullPointerException if you don't have the command defined in your plugin.yml file! this . getCommand ( "basic" ). setExecutor ( new MyPluginCommandExecutor ( this )); }

MyPluginCommandExecutor.java:

public class MyPluginCommandExecutor implements CommandExecutor { private final MyPlugin plugin ; public MyPluginCommandExecutor ( MyPlugin plugin ) { this . plugin = plugin ; // Store the plugin in situations where you need it. } @Override public boolean onCommand ( CommandSender sender , Command cmd , String label , String [] args ) { // implementation exactly as before... } }

Notice how we send a reference of the main plugin object to MyPluginCommandExecutor. This allows us easy access to the main plugin objects's methods if we need to.

By doing this, we can better organise our code - if the main onCommand() method is large and complex, it can be split into submethods without cluttering up the plugin's main class.

Note that if your plugin has multiple commands, you will need set the command executor for each command individually.

Writing a safe onCommand

When writing an onCommand, it's important that you don't assume any information, such as the sender being a Player. Things to keep in mind:

Make sure the sender is a Player before casting

Using simple code like this makes it possible:

@Override public boolean onCommand ( CommandSender sender , Command cmd , String label , String [] args ) { if ( sender instanceof Player ) { Player player = ( Player ) sender ; // do something } else { sender . sendMessage ( "You must be a player!" ); return false ; } // do something return false ; }

Check the arguments length

Don't always assume the sender typed the correct amount of arguments.

@Override public boolean onCommand ( CommandSender sender , Command cmd , String label , String [] args ) { if ( args . length > 4 ) { sender . sendMessage ( "Too many arguments!" ); return false ; } if ( args . length < 2 ) { sender . sendMessage ( "Not enough arguments!" ); return false ; } }

Check if a Player is online before getting them

Sometimes you want to get another player by the name entered by the player. Always make sure the player is online!

@Override public boolean onCommand ( CommandSender sender , Command cmd , String label , String [] args ) { Player target = ( Bukkit . getServer (). getPlayer ( args [ 0 ])); if ( target == null ) { sender . sendMessage ( args [ 0 ] + " is not online!" ); return false ; } return false ; }

If you need to modify a Player currently not online, the OfflinePlayer class provides basic manipulation methods.

Plugin Configuration/Settings

The Bukkit API provides a convenient way for plugins to manage user configurable settings. Additionally it also serves as an easy way to store data.

Please see: Configuration API Reference

Permissions

If you are looking for how to Develop a permissions plugin, refer to http://wiki.bukkit.org/Developing_a_permissions_plugin

With the new Bukkit API for permissions, they couldn't be easier. To find out if a player has a particular permission use the following:

if ( player . hasPermission ( "some.pointless.permission" )) { //Do something } else { //Do something else }

You can also find if a permission has been set or not (equivalent to Java's null) with the following function:

boolean isPermissionSet ( String name )

You may be wondering why there aren't any groups. The answer to that is because they aren't really needed. Previously one of the main uses for groups was to format chat messages. That however can be done just as easily with permissions. Inside your chat plugin's config you would define associations between permissions and prefixes. For example the permission "someChat.prefix.admin" would correspond to the prefix [Admin]. Whenever a player speaks with that permission their name will be prefixed with [Admin].

Another common usage might be to send a message to all users within a group. Again however this can be done with permissions with the following:

for ( Player player : Bukkit . getServer (). getOnlinePlayers ()) { if ( player . hasPermission ( "send.receive.message" )) { player . sendMessage ( "You were sent a message" ); } }

Finally you may be asking, well how do I set and organise player's permissions if there are no groups? Although the bukkit API doesn't provide groups itself, you must install a permission provider plugin such as permissionsBukkit to manage the groups for you. This API provides the interface, not the implementation.

Configuring your permissions

If you want more control over your permissions, for example default values or children then you should consider adding them to your plugin.yml. This is completely optional, however it is advised. Below is an example permissions config that would be appended to the end of your existing plugin.yml:

permissions : doorman.* : description : Gives access to all doorman commands children : doorman.kick : true doorman.ban : true doorman.knock : true doorman.denied : false doorman.kick : description : Allows you to kick a user default : op doorman.ban : description : Allows you to ban a user default : op doorman.knock : description : Knocks on the door! default : true doorman.denied : description : Prevents this user from entering the door

Firstly, each permission your plugin uses is defined as a child node of the permissions node. Each permission can then optionally have a description, a default value, and children.

Defaults

By default when a permission isn't defined for a player hasPermission will return false. Inside your plugin.yml you can change this by setting the default node to be one of four values:

true - The permission will be true by default.

- The permission will be true by default. false - The permission will by false by default.

- The permission will by false by default. op - If the player is an op then this will be true.

- If the player is an op then this will be true. not op - If the player is not an op then this will be true.

Children

Before now you will probably be used to the * permission to automatically assign all sub permissions. This has changed with the bukkit API and you can now define the child permissions. This allows for a lot more flexibility. Below is an example of how you do this:

permissions : doorman.* : description : Gives access to all doorman commands children : doorman.kick : true doorman.ban : true doorman.knock : true doorman.denied : false

Here the doorman.* permission has several child permissions assigned to it. The way child permissions work is when doorman.* is set to true, the child permissions are set to their values defined in the plugin.yml. If however doorman.* was set to false then all child permissions would be inverted.

Setting your own permissions

If you wish to know about developing your own permissions plugins (Ones that actually set permissions) then check out the tutorial on Developing a permissions plugin.

Scheduling Tasks and Background Tasks

Currently, Minecraft servers operate nearly all of the game logic in one thread, so each individual task that happens in the game needs to be kept very short. A complicated piece of code in your plugin has the potential to cause huge delays and lag spikes to the game logic, if not handled properly.

Luckily, Bukkit has support for scheduling code in your plugin. You can submit a Runnable task to occur once in the future, or on a recurring basis, or you can spin off a whole new independent thread that can perform lengthy tasks in parallel with the game logic.

There is a separate Scheduler Programming tutorial which introduces the Scheduler, and gives more information on using it to schedule synchronous tasks, and on kicking off asynchronous tasks in Bukkit.

Block Manipulation

The easiest way to create blocks is to get an existing block and modify it. For example, if you want to change the block that is located five blocks above you, you would first have to get your current location, add five to your current y-coordinate, and then change it. For example:

@EventHandler public void onPlayerMove ( PlayerMoveEvent event ) { // Get the player's location. Location loc = event . getPlayer (). getLocation (); // Sets loc to five above where it used to be. Note that this doesn't change the player's position. loc . setY ( loc . getY () + 5 ); // Gets the block at the new location. Block b = loc . getBlock (); // Sets the block to type id 1 (stone). b . setType ( Material . STONE ); }

The above code gets the player's location, gets the block five blocks above the player, and sets it to stone. Note that once you have a Block , there are other things you can do besides set its type. Consult the JavaDocs for more information.

You can use a similar concept to generate buildings and individual blocks programmatically through the use of algorithms. For example, to generate a solid cube, you could use nested for loops to loop over an entire cube and fill it in.

public void generateCube ( Location loc , int length ) { // Set one corner of the cube to the given location. // Uses getBlockN() instead of getN() to avoid casting to an int later. int x1 = loc . getBlockX (); int y1 = loc . getBlockY (); int z1 = loc . getBlockZ (); // Figure out the opposite corner of the cube by taking the corner and adding length to all coordinates. int x2 = x1 + length ; int y2 = y1 + length ; int z2 = z1 + length ; World world = loc . getWorld (); // Loop over the cube in the x dimension. for ( int xPoint = x1 ; xPoint <= x2 ; xPoint ++) { // Loop over the cube in the y dimension. for ( int yPoint = y1 ; yPoint <= y2 ; yPoint ++) { // Loop over the cube in the z dimension. for ( int zPoint = z1 ; zPoint <= z2 ; zPoint ++) { // Get the block that we are currently looping over. Block currentBlock = world . getBlockAt ( xPoint , yPoint , zPoint ); // Set the block to type 57 (Diamond block!) currentBlock . setType ( Material . DIAMOND_BLOCK ); } } } }

This method will construct a 3D cube or cuboid with the given length and starting point. As for deleting blocks simply follow the same method for creating them but set the ID to 0 (air).



(Player) Inventory Manipulation

This section mostly covers player inventory manipulation, but the same applies to chest inventory manipulation as well if you find out how to get a chest's inventory :P. Here is a simple example of inventory manipulation:

@EventHandler public void onPlayerJoin ( PlayerJoinEvent evt ) { Player player = evt . getPlayer (); // The player who joined PlayerInventory inventory = player . getInventory (); // The player's inventory ItemStack itemstack = new ItemStack ( Material . DIAMOND , 64 ); // A stack of diamonds if ( inventory . contains ( itemstack )) { inventory . addItem ( itemstack ); // Adds a stack of diamonds to the player's inventory player . sendMessage ( "Welcome! You seem to be reeeally rich, so we gave you some more diamonds!" ); } }

So inside onPlayerJoin we first make a few variables to make our job easier: player, inventory and itemstack. Inventory is the player's inventory and itemstack is a ItemStack that has 64 diamonds. After that we check if the player's inventory contains a stack of diamonds. If the player has a stack of diamonds, we give him/her another stack with inventory.addItem(itemstack) and send a message. So inventory manipulation isn't actually that hard, if we wanted we could remove the stack of diamonds by simply replacing inventory.addItem(itemstack) with inventory.remove(itemstack) and change the message a little bit. Hopefully this helped!

Item Manipulation

When dealing with items in the code, you use the ItemStack class for looking up and setting all information on that stack.

Enchantments

To enchant an item you must first know the Bukkit enchantments. If you want to enchant items that can't be enchanted inside normal SMP, use addUnsafeEnchantment() instead of addEnchantment()

For example, to give Sharpness 1 to a stone sword:

ItemStack myItem = new ItemStack ( Material . STONE_SWORD ); //new item of item code myItem . addEnchantment ( Enchantment . DAMAGE_ALL , 1 ); //enchant the item

You can set the display name of an item by doing this.

String myDisplayName = "Awesome Sword" ; //use the displayname you want here ItemStack myItem = new ItemStack ( Material . DIAMOND_SWORD ); //your item ItemMeta im = myItem . getItemMeta (); //get the itemmeta of the item im . setDisplayName ( myDisplayName ); //set the displayname myItem . setItemMeta ( im ); //give the item the new itemmeta

You can also set the lores of an item. The lores are the small annotations on an item, like "+5 attack damage" on a stone sword.

List < String > lores = new ArrayList < String >(); lores . add ( "Example lore" ); lores . add ( "this one comes on line 2" ); ItemStack myItem = new ItemStack ( Material . DIAMOND_SWORD ); //your item ItemMeta im = myItem . getItemMeta (); //get the itemmeta of the item again im . setLore ( lores ); //add the lores of course myItem . setItemMeta ( im ); //give the item the new itemmeta

Metadata

Bukkit is trying to make plugin development as easy as possible, so HashMaps with key of type Player, Entity, World or even a Block were replaced by Metadata. Metadata is some kind of alternative to HashMap. It allows you to add custom "fields" to Players, Entities, Worlds and Blocks. These things are all members of Metadatable class(check [1])It works very simply. Everything that is Metadatable holds its own HashMap of Metadata which you have access to. That means, for example, if you're creating an economy plugin, you would need a HashMap of Player and Float or Double. With Metadata, you don't have to! You just attach to player new metadata value, and that's it!



Why to use Metadata

Metadata is all handled by Bukkit, which makes it a very good alternative to HashMaps.

Metadata can be used to share information between plugins.

Why not use Metadata

Slightly more difficult to get the value.

It is not saved on shutdown (but then again, neither are any Maps that you create).

Getting & Setting Metadata

public void setMetadata ( Metadatable object , String key , Object value , Plugin plugin ) { object . setMetadata ( key , new FixedMetadataValue ( plugin , value )); } public Object getMetadata ( Metadatable object , String key , Plugin plugin ) { List < MetadataValue > values = object . getMetadata ( key ); for ( MetadataValue value : values ) { // Plugins are singleton objects, so using == is safe here if ( value . getOwningPlugin () == plugin ) { return value . value (); } } return null ; }

Note: If you're manipulating with numbers, booleans or strings, use convenient method to get the result. For example, you can use asInt(), asString() or asBoolean() instead of value to find out the value.

Databases

Sometimes flat files aren't enough for what your looking to do, this is where databases come in. The most common database engines available on Linux/Mac/Windows machines typically run on some flavor of SQL (Structured Query Language).

Software offering SQL allow you to create databases with columns and header to identify to contents of each cell. Think of it as a spreadsheet on steroids, where every column you set up in your database can enforce rules to ensure integrity. Apart from being more organised than a simple custom data file, SQL provides faster access and better searching than flat files.

The SQL standard helps applications like Bukkit implement database storage for their data in a consistent way. Unfortunately, there's more than one SQL-ready database engine, and each has minor differences in how to configure and use it. Which one you choose may depend on your particular needs. (Some plugins even offer configurable options to connect to multiple database engines!)

SQLite

Alta189 has written a fantastic SQLite tutorial which I suggest you watch if you're interested in using SQL in your plugins, included with the tutorials is a handy library you can download and import to make using SQL easier. Once you have watched these video tutorials I would suggest you go and learn some SQL syntax, it's very straightforward and shouldn't take you long to pick up. SQL Tutorials @W3Schools and @1Keydata.

SQLite is great for very simple databases, because there's no server concerns to set up. Just make a few calls to create a new database and table. It's easy to back up: just copy the whole database file in one go. SQLite is a little bit weaker at data integrity, flexibility in data types, and it may not be something you would want to trust for huge databases of millions of rows. But for a new plugin in development, it's often easiest and fastest to get the SQL basics squared away with SQLite, even if you "graduate" to a more server-class database engine later.

MySQL

Another popular SQL database engine is called MySQL. It is closer to server-grade than SQLite, where many popular companies or websites depend on it for millions of webpage hits every day. With that security comes a little bit steeper learning-curve, because MySQL has more tunable parameters and capabilities.

The coding for plugins accessing MySQL is mostly the same as tiny SQLite or mega-sized Oracle, with only small differences in syntax here or there. But the administration has room to grow. You may want to set up accounts and privileges inside your MySQL setup. You may want to set up SQL scripts that organize your backups and rollback to previous states.

Deploying your Plugin

Once you have written your plugin, how do you get it from a collection of source files into a working jar file that can be installed on a server? First, set up a CraftBukkit server on your local machine. To do this, visit the wiki page on Setting up a server. Next you have to export your plugin to a .jar so that you can run it on your new server. To do this in Eclipse, right-click the project and click Run as > Maven install:

In the future, when you make code changes to your plugin, you want to delete the previous JAR by right-clicking the project and clicking Run as > Maven clean before doing the above. If you're having issues when building your plugin, check if your Java Development Kit (JDK) is properly installed and review Setting Up Your Workspace. You may need to configure your JDK manually if you see a JDK-related error in the console, as Eclipse may not have detected it correctly. Go to Window -> Preferences, and go to Java -> Installed JREs. Add the latest JDK you've installed as a JRE, tick that one, and untick the active one that was giving you issues:

If your project built successfully, the JAR file is now under the target folder in your project's folder under your Eclipse workspace. The JAR file you have exported should now be a working plugin! Assuming of course that there are no errors in your code or your plugin.yml file. You can now drop the jar file you have exported into your Bukkit server's "plugins" folder, reload or relaunch the server, and test away! In order to connect to a server running locally on your computer, simply put "localhost" as the IP address of the server in Minecraft multiplayer. If you run into errors that you can't solve for yourself, try visiting the plugin development forum, asking in the bukkitdev IRC channel, or re-reading this wiki. Once you have a useful working plugin, consider submitting your project to dev.bukkit for consumption by the Bukkit community. From the wizard above, you can see that the JAR file will be by default a compressed archive (JARs are based on the ZIP archive format). As such, it does not make sense to put your JAR into a ZIP archive when uploading to BukkitDev and will only increase the file size. Further, config files can be placed within the JAR and copied into the plugin's data folder if the configuration file does not exist. There is usually no good reason for packaging JAR files into another archive.

Importing other plugins

You may wish to edit another plugin that has the source available. If that plugin has a pom.xml in its folder (most of the popular ones, for example WorldEdit and Essentials, do), you can import it as a project by selecting File -> Import, and then opening the Maven folder and selecting Existing Maven Projects:

Then select the folder that the pom.xml is in, and the project should be on your sidebar. Edit it and compile it like you usually would.

Tips and Tricks

Setting a Player on Fire

The Bukkit API is capable of a lot of cool stuff. Here are some code snippets for some nice effects!

The following code allows a player to set another player on fire. Running a command like /ignite Notch would cause Notch to be set on fire!

@Override public boolean onCommand ( CommandSender sender , Command cmd , String label , String [] args ) { // Uses equalsIgnoreCase() over equals() to accept "ignite" and "IgNiTe." if ( cmd . getName (). equalsIgnoreCase ( "ignite" )) { // Make sure that the player specified exactly one argument (the name of the player to ignite). if ( args . length != 1 ) { // When onCommand() returns false, the help message associated with that command is displayed. return false ; } // Make sure the sender is a player. if (!( sender instanceof Player )) { sender . sendMessage ( "Only players can set other players on fire." ); sender . sendMessage ( "This is an arbitrary requirement for demonstration purposes only." ); return true ; } // Get the player who should be set on fire. Remember that indecies start with 0, not 1. Player target = Bukkit . getServer (). getPlayer ( args [ 0 ]); // Make sure the player is online. if ( target == null ) { sender . sendMessage ( args [ 0 ] + " is not currently online." ); return true ; } // Sets the player on fire for 1,000 ticks (there are ~20 ticks in second, so 50 seconds total). target . setFireTicks ( 1000 ); return true ; } return false ; }

Killing the player

To keep with the theme, here's a way to kill the player.

Use this for your onCommand method:

@Override public boolean onCommand ( CommandSender sender , Command cmd , String label , String [] args ) { if ( cmd . getName (). equalsIgnoreCase ( "KillPlayer" )) { Player target = sender . getServer (). getPlayer ( args [ 0 ]); // Make sure the player is online. if ( target == null ) { sender . sendMessage ( args [ 0 ] + " is not currently online." ); return true ; } target . setHealth ( 0.0D ); } return false ; }

Here is an extension to that, that will kill the player with an explosion:

float explosionPower = 4F ; //This is the explosion power - TNT explosions are 4F by default Player target = sender . getWorld (). getPlayer ( args [ 0 ]); target . getWorld (). createExplosion ( target . getLocation (), explosionPower ); target . setHealth ( 0.0D );

Creating a Fake Explosion

This code produces the TNT/Creeper Visual and Audio effects. However, no explosion damage is dealt to surrounding entities or blocks. This is useful for nerfing explosions while still keeping the aesthetics of them.

@EventHandler public void onExplosionPrime ( ExplosionPrimeEvent event ) { Entity entity = event . getEntity (); // If the event is about primed TNT (TNT that is about to explode), then do something if ( entity instanceof TNTPrimed ) { entity . getWorld (). createExplosion ( entity . getLocation (), 0 ); } }

Hiding a Player From Another Player

This will hide the player who used this command from a specified player. Everyone else will be able to see the player.

@Override public boolean onCommand ( CommandSender sender , Command cmd , String label , String [] args ) { if ( cmd . getName (). equalsIgnoreCase ( "HideMe" ) && args . length == 1 ) { if (!( sender instanceof Player )) { sender . sendMessage ( "Only players can use this command!" ); return true ; } // After checking to make sure that the sender is a Player, we can safely cast it to one. Player s = ( Player ) sender ; // Gets the player who shouldn't see the sender. //Note: getPlayer(string) is now deprecated, use getPlayer(UUID.fromString(string) instead. Player target = Bukkit . getServer (). getPlayer ( UUID . fromString ( args [ 0 ])); if ( target == null ) { sender . sendMessage ( "Player " + args [ 0 ] + " is not online." ); return true ; } // Hides a given Player (s) from someone (target). target . hidePlayer ( s ); return true ; } return false ; }

Spawn Lightning Bolt Where Player is Looking

The code below allows any player with a fishing rod to create a lightning strike by clicking (and aiming somewhere). It's a simple and funny trick.

@EventHandler public void onPlayerInteractBlock ( PlayerInteractEvent event ) { Player player = event . getPlayer (); if ( player . getItemInHand (). getType () == Material . FISHING_ROD ) { // Creates a bolt of lightning at a given location. In this case, that location is where the player is looking. // Can only create lightning up to 200 blocks away. player . getWorld (). strikeLightning ( player . getTargetBlock (( Set < Material >) null , 200 ). getLocation ()); } }

Automatically formatting your code

Eclipse provides functionality to automatically format your code to Oracle conventions, fixing unconventional indentations, spacing, and such. Simply select your project in the sidebar, and then select Source -> Format.

Request Section

http://forums.bukkit.org/forums/plugin-requests.13/

Example Files and Templates



If you have any more questions on this matter, don't hesitate to visit the BukkitDev IRC channel and ask!