Added the option to get and set a guilds system channel (#431)

src/main/java/net/dv8tion/jda/core/audit/ActionType.java

@@ -37,6 +37,7 @@ public enum ActionType
      *     <li>{@link net.dv8tion.jda.core.audit.AuditLogKey#GUILD_OWNER GUILD_OWNER}</li>
      *     <li>{@link net.dv8tion.jda.core.audit.AuditLogKey#GUILD_REGION GUILD_REGION}</li>
      *     <li>{@link net.dv8tion.jda.core.audit.AuditLogKey#GUILD_SPLASH GUILD_SPLASH}</li>
+     *     <li>{@link net.dv8tion.jda.core.audit.AuditLogKey#GUILD_SYSTEM_CHANNEL GUILD_SYSTEM_CHANNEL}</li>
      * </ul>
      */
     GUILD_UPDATE(1, TargetType.GUILD),

src/main/java/net/dv8tion/jda/core/audit/AuditLogKey.java

@@ -68,13 +68,20 @@ public enum AuditLogKey
 
     /**
      * Change of the {@link net.dv8tion.jda.core.entities.Guild#getAfkChannel() Guild.getAfkChannel()} value represented by a VoiceChannel ID.
-     * <br>Use with {@link net.dv8tion.jda.core.entities.Guild#getVoiceChannelById(String)
-     * Guild.getVoiceChannelById(String)}
+     * <br>Use with {@link net.dv8tion.jda.core.entities.Guild#getVoiceChannelById(String) Guild.getVoiceChannelById(String)}
      *
      * <p>Expected type: <b>String</b>
      */
     GUILD_AFK_CHANNEL("afk_channel_id"),
 
+    /**
+     * Change of the {@link net.dv8tion.jda.core.entities.Guild#getSystemChannel() Guild.getSystemChannel()} value represented by a TextChannel ID.
+     * <br>Use with {@link net.dv8tion.jda.core.entities.Guild#getTextChannelById(String) Guild.getTextChannelById(String)}
+     *
+     * <p>Expected type: <b>String</b>
+     */
+    GUILD_SYSTEM_CHANNEL("system_channel_id"),
+
     /**
      * Change of the {@link net.dv8tion.jda.core.entities.Guild#getExplicitContentLevel() Guild.getExplicitContentLevel()} of a Guild.
      * <br>Use with {@link net.dv8tion.jda.core.entities.Guild.ExplicitContentLevel#fromKey(int) Guild.ExplicitContentLevel.fromKey(int)}

src/main/java/net/dv8tion/jda/core/entities/EntityBuilder.java

@@ -215,16 +215,19 @@ public void createGuildFirstPass(JSONObject guild, Consumer<Guild> secondPassCal
                 }
                 else if (type == ChannelType.VOICE)
                 {
-                    VoiceChannel newChannel = createVoiceChannel(channel, guildObj.getIdLong(), false);
-                    if (!guild.isNull("afk_channel_id")
-                            && newChannel.getId().equals(guild.getString("afk_channel_id")))
-                        guildObj.setAfkChannel(newChannel);
+                    createVoiceChannel(channel, guildObj.getIdLong(), false);
                 }
                 else
                     WebSocketClient.LOG.fatal("Received a channel for a guild that isn't a text or voice channel. JSON: " + channel);
             }
         }
 
+        if (!guild.isNull("system_channel_id"))
+            guildObj.setSystemChannel(guildObj.getTextChannelsMap().get(guild.getLong("system_channel_id")));
+
+        if (!guild.isNull("afk_channel_id"))
+            guildObj.setAfkChannel(guildObj.getVoiceChannelMap().get(guild.getLong("afk_channel_id")));
+
         //If the members that we were provided with (and loaded above) were not all of the
         //  the members in this guild, then we need to request more users from Discord using
         //  op 9 (GUILD_MEMBERS_CHUNK). To do so, we will cache the guild's JSON so we can properly

src/main/java/net/dv8tion/jda/core/entities/Guild.java

@@ -106,6 +106,18 @@ public interface Guild extends ISnowflake
      */
     VoiceChannel getAfkChannel();
 
+    /**
+     * Provides the {@link net.dv8tion.jda.core.entities.TextChannel TextChannel} that has been set as the channel
+     * which newly joined {@link net.dv8tion.jda.core.entities.Member Members} will be announced in.
+     * <br>If no channel has been set as the system channel, this returns {@code null}.
+     * <p>
+     * This value can be modified using {@link net.dv8tion.jda.core.managers.GuildManager#setSystemChannel(TextChannel)}
+     * or {@link net.dv8tion.jda.core.managers.GuildManagerUpdatable#getSystemChannelField()}.
+     *
+     * @return Possibly-null {@link net.dv8tion.jda.core.entities.TextChannel TextChannel} that is the system Channel.
+     */
+    TextChannel getSystemChannel();
+
     /**
      * The {@link net.dv8tion.jda.core.entities.Member Member} object of the owner of this {@link net.dv8tion.jda.core.entities.Guild Guild}.
      * <p>

src/main/java/net/dv8tion/jda/core/entities/impl/GuildImpl.java

@@ -72,6 +72,7 @@ public class GuildImpl implements Guild
     private Region region;
     private TextChannel publicChannel;
     private VoiceChannel afkChannel;
+    private TextChannel systemChannel;
     private Role publicRole;
     private VerificationLevel verificationLevel;
     private NotificationLevel defaultNotificationLevel;
@@ -123,6 +124,12 @@ public VoiceChannel getAfkChannel()
         return afkChannel;
     }
 
+    @Override
+    public TextChannel getSystemChannel()
+    {
+        return systemChannel;
+    }
+
     @Override
     public RestAction<List<Webhook>> getWebhooks()
     {
@@ -739,6 +746,12 @@ public GuildImpl setAfkChannel(VoiceChannel afkChannel)
         return this;
     }
 
+    public GuildImpl setSystemChannel(TextChannel systemChannel)
+    {
+        this.systemChannel = systemChannel;
+        return this;
+    }
+
     public GuildImpl setPublicRole(Role publicRole)
     {
         this.publicRole = publicRole;

src/main/java/net/dv8tion/jda/core/events/guild/update/GuildUpdateSystemChannelEvent.java

@@ -0,0 +1,48 @@
+/*
+ *     Copyright 2015-2017 Austin Keener & Michael Ritter & Florian Spieß
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package net.dv8tion.jda.core.events.guild.update;
+
+import net.dv8tion.jda.core.JDA;
+import net.dv8tion.jda.core.entities.Guild;
+import net.dv8tion.jda.core.entities.TextChannel;
+
+/**
+ * <b><u>GuildUpdateSystemChannelEvent</u></b><br>
+ * Fired if the {@link net.dv8tion.jda.core.entities.Guild#getSystemChannel() system channel} of a {@link net.dv8tion.jda.core.entities.Guild Guild} has been changed.<br>
+ * <br>
+ * Use: Retrieve the {@link #getOldSystemChannel() previous system channel} after a change.<p>
+ */
+public class GuildUpdateSystemChannelEvent extends GenericGuildUpdateEvent
+{
+    private final TextChannel oldSystemChannel;
+
+    public GuildUpdateSystemChannelEvent(JDA api, long responseNumber, Guild guild, TextChannel oldSystemChannel)
+    {
+        super(api, responseNumber, guild);
+        this.oldSystemChannel = oldSystemChannel;
+    }
+
+    /**
+     * Returns the previous system channel.
+     * 
+     * @return The previous system channel
+     */
+    public TextChannel getOldSystemChannel()
+    {
+        return oldSystemChannel;
+    }
+}

src/main/java/net/dv8tion/jda/core/handle/GuildUpdateHandler.java

@@ -18,6 +18,7 @@
 import net.dv8tion.jda.core.Region;
 import net.dv8tion.jda.core.entities.Guild;
 import net.dv8tion.jda.core.entities.Member;
+import net.dv8tion.jda.core.entities.TextChannel;
 import net.dv8tion.jda.core.entities.VoiceChannel;
 import net.dv8tion.jda.core.entities.impl.GuildImpl;
 import net.dv8tion.jda.core.entities.impl.JDAImpl;
@@ -55,6 +56,9 @@ protected Long handleInternally(JSONObject content)
         VoiceChannel afkChannel = !content.isNull("afk_channel_id")
                 ? guild.getVoiceChannelMap().get(content.getLong("afk_channel_id"))
                 : null;
+        TextChannel systemChannel = !content.isNull("system_channel_id")
+                ? guild.getTextChannelsMap().get(content.getLong("system_channel_id"))
+                : null;
 
         if (!Objects.equals(owner, guild.getOwner()))
         {
@@ -155,6 +159,15 @@ protected Long handleInternally(JSONObject content)
                             api, responseNumber,
                             guild, oldAfkChannel));
         }
+        if (!Objects.equals(systemChannel, guild.getSystemChannel()))
+        {
+            TextChannel oldSystemChannel = guild.getSystemChannel();
+            guild.setSystemChannel(systemChannel);
+            api.getEventManager().handle(
+                    new GuildUpdateSystemChannelEvent(
+                            api, responseNumber,
+                            guild, oldSystemChannel));
+        }
         return null;
     }
 }

src/main/java/net/dv8tion/jda/core/hooks/ListenerAdapter.java

@@ -193,6 +193,7 @@ public void onGuildUnban(GuildUnbanEvent event) {}
 
     //Guild Update Events
     public void onGuildUpdateAfkChannel(GuildUpdateAfkChannelEvent event) {}
+    public void onGuildUpdateSystemChannel(GuildUpdateSystemChannelEvent event) {}
     public void onGuildUpdateAfkTimeout(GuildUpdateAfkTimeoutEvent event) {}
     public void onGuildUpdateIcon(GuildUpdateIconEvent event) {}
     public void onGuildUpdateMFALevel(GuildUpdateMFALevelEvent event) {}
@@ -483,6 +484,8 @@ else if (event instanceof GuildUnbanEvent)
         //Guild Update Events
         else if (event instanceof GuildUpdateAfkChannelEvent)
             onGuildUpdateAfkChannel((GuildUpdateAfkChannelEvent) event);
+        else if (event instanceof GuildUpdateSystemChannelEvent)
+            onGuildUpdateSystemChannel((GuildUpdateSystemChannelEvent) event);
         else if (event instanceof GuildUpdateAfkTimeoutEvent)
             onGuildUpdateAfkTimeout((GuildUpdateAfkTimeoutEvent) event);
         else if (event instanceof GuildUpdateIconEvent)

src/main/java/net/dv8tion/jda/core/managers/GuildManager.java

@@ -20,6 +20,7 @@
 import net.dv8tion.jda.core.Region;
 import net.dv8tion.jda.core.entities.Guild;
 import net.dv8tion.jda.core.entities.Icon;
+import net.dv8tion.jda.core.entities.TextChannel;
 import net.dv8tion.jda.core.entities.VoiceChannel;
 import net.dv8tion.jda.core.requests.restaction.AuditableRestAction;
 
@@ -171,6 +172,28 @@ public AuditableRestAction<Void> setAfkChannel(VoiceChannel afkChannel)
         return updatable.getAfkChannelField().setValue(afkChannel).update();
     }
 
+    /**
+     * Sets the system {@link net.dv8tion.jda.core.entities.TextChannel TextChannel} of this {@link net.dv8tion.jda.core.entities.Guild Guild}.
+     * More information can be found {@link GuildManagerUpdatable#getSystemChannelField() here}!
+     *
+     * <p>For information on possible {@link net.dv8tion.jda.core.requests.ErrorResponse ErrorResponses}
+     * by the returned {@link net.dv8tion.jda.core.requests.RestAction RestAction} see {@link GuildManagerUpdatable#update() #update()}
+     *
+     * @param  systemChannel
+     *         The new system channel for this {@link net.dv8tion.jda.core.entities.Guild Guild}
+     *
+     * @return {@link net.dv8tion.jda.core.requests.restaction.AuditableRestAction AuditableRestAction}
+     *         <br>Update RestAction from {@link GuildManagerUpdatable#update() #update()}
+     *
+     * @see    net.dv8tion.jda.core.managers.GuildManagerUpdatable#getSystemChannelField()
+     * @see    net.dv8tion.jda.core.managers.GuildManagerUpdatable#update()
+     */
+    @CheckReturnValue
+    public AuditableRestAction<Void> setSystemChannel(TextChannel systemChannel)
+    {
+        return updatable.getSystemChannelField().setValue(systemChannel).update();
+    }
+
     /**
      * Sets the afk {@link net.dv8tion.jda.core.entities.Guild.Timeout Timeout} of this {@link net.dv8tion.jda.core.entities.Guild Guild}.
      * More information can be found {@link GuildManagerUpdatable#getAfkTimeoutField() here}!

src/main/java/net/dv8tion/jda/core/managers/GuildManagerUpdatable.java

@@ -21,6 +21,7 @@
 import net.dv8tion.jda.core.Region;
 import net.dv8tion.jda.core.entities.Guild;
 import net.dv8tion.jda.core.entities.Icon;
+import net.dv8tion.jda.core.entities.TextChannel;
 import net.dv8tion.jda.core.entities.VoiceChannel;
 import net.dv8tion.jda.core.exceptions.GuildUnavailableException;
 import net.dv8tion.jda.core.exceptions.InsufficientPermissionException;
@@ -59,6 +60,7 @@ public class GuildManagerUpdatable
     protected GuildField<Icon> splash;
     protected GuildField<Region> region;
     protected GuildField<VoiceChannel> afkChannel;
+    protected GuildField<TextChannel> systemChannel;
     protected GuildField<Guild.VerificationLevel> verificationLevel;
     protected GuildField<Guild.NotificationLevel> defaultNotificationLevel;
     protected GuildField<Guild.MFALevel> mfaLevel;
@@ -208,6 +210,30 @@ public GuildField<VoiceChannel> getAfkChannelField()
         return afkChannel;
     }
 
+    /**
+     * An {@link net.dv8tion.jda.core.managers.fields.GuildField GuildField}
+     * for the <b><u>system {@link net.dv8tion.jda.core.entities.TextChannel TextChannel}</u></b> of the selected {@link net.dv8tion.jda.core.entities.Guild Guild}.
+     * <br>To reset the channel of a Guild provide {@code null} to {@link net.dv8tion.jda.core.managers.fields.Field#setValue(Object) setValue(VoiceChannel)}.
+     *
+     * <p>To set the value use {@link net.dv8tion.jda.core.managers.fields.Field#setValue(Object) setValue(TextChannel)}
+     * on the returned {@link net.dv8tion.jda.core.managers.fields.GuildField GuildField} instance.
+     *
+     * <p>A guild system channel <b>must</b> be from this Guild!
+     * <br>Otherwise {@link net.dv8tion.jda.core.managers.fields.Field#setValue(Object) Field.setValue(...)} will
+     * throw an {@link IllegalArgumentException IllegalArgumentException}.
+     *
+     * @throws net.dv8tion.jda.core.exceptions.GuildUnavailableException
+     *         If the Guild is temporarily not {@link net.dv8tion.jda.core.entities.Guild#isAvailable() available}
+     *
+     * @return {@link net.dv8tion.jda.core.managers.fields.GuildField GuildField} - Type: {@link net.dv8tion.jda.core.entities.TextChannel TextChannel}
+     */
+    public GuildField<TextChannel> getSystemChannelField()
+    {
+        checkAvailable();
+
+        return systemChannel;
+    }
+
     /**
      * An {@link net.dv8tion.jda.core.managers.fields.GuildField GuildField}
      * for the <b><u>AFK {@link net.dv8tion.jda.core.entities.Guild.Timeout Timeout}</u></b> of the selected {@link net.dv8tion.jda.core.entities.Guild Guild}.
@@ -338,6 +364,7 @@ public void reset()
         this.icon.reset();
         this.splash.reset();
         this.afkChannel.reset();
+        this.systemChannel.reset();
         this.verificationLevel.reset();
         this.defaultNotificationLevel.reset();
         this.mfaLevel.reset();
@@ -393,6 +420,8 @@ public AuditableRestAction<Void> update()
             body.put("splash", splash.getValue() == null ? JSONObject.NULL : splash.getValue().getEncoding());
         if (afkChannel.shouldUpdate())
             body.put("afk_channel_id", afkChannel.getValue() == null ? JSONObject.NULL : afkChannel.getValue().getId());
+        if (systemChannel.shouldUpdate())
+            body.put("system_channel_id", systemChannel.getValue() == null ? JSONObject.NULL : systemChannel.getValue().getId());
         if (verificationLevel.shouldUpdate())
             body.put("verification_level", verificationLevel.getValue().getKey());
         if (defaultNotificationLevel.shouldUpdate())
@@ -425,6 +454,7 @@ protected boolean needToUpdate()
                 || icon.shouldUpdate()
                 || splash.shouldUpdate()
                 || afkChannel.shouldUpdate()
+                || systemChannel.shouldUpdate()
                 || verificationLevel.shouldUpdate()
                 || defaultNotificationLevel.shouldUpdate()
                 || mfaLevel.shouldUpdate()
@@ -522,6 +552,16 @@ public void checkValue(VoiceChannel value)
             }
         };
 
+        this.systemChannel = new GuildField<TextChannel>(this, guild::getSystemChannel)
+        {
+            @Override
+            public void checkValue(TextChannel value)
+            {
+                if (value != null && !guild.equals(value.getGuild()))
+                    throw new IllegalArgumentException("Provided system channel is not from this Guild!");
+            }
+        };
+
         this.verificationLevel = new GuildField<Guild.VerificationLevel>(this, guild::getVerificationLevel)
         {
             @Override