Bukkit server "unsupported major minor version 51.0" errors

Question

I have been testing the new plugins I have added to my bukkit minecraft server, and saw this error message:

C:\Users\XXX\XXXXXXX\XXXXXXXXXXXX>java -Xms1024M -Xmx1024M -jar craftbukkit-1.5.
2-R0.1.jar -o true
229 recipes
27 achievements
14:12:34 [INFO] Starting minecraft server version 1.5.2
14:12:34 [INFO] Loading properties
14:12:34 [INFO] Default game type: SURVIVAL
14:12:34 [INFO] Generating keypair
14:12:34 [INFO] Starting Minecraft server on XX.XX.XXX.XXX:25565
14:12:34 [INFO] This server is running CraftBukkit version git-Bukkit-1.5.2-R0.1
-b2771jnks (MC: 1.5.2) (Implementing API version 1.5.2-R0.1)
14:12:34 [SEVERE] Could not load 'plugins\CustomPlayerJoinMessaging.jar' in fold
er 'plugins'
org.bukkit.plugin.InvalidPluginException: java.lang.UnsupportedClassVersionError
: me/xXTh3B3astXxify/CustomJoin/CJMain : Unsupported major.minor version 51.0
        at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.j
ava:184)
        at org.bukkit.plugin.SimplePluginManager.loadPlugin(SimplePluginManager.
java:305)
        at org.bukkit.plugin.SimplePluginManager.loadPlugins(SimplePluginManager
.java:230)
        at org.bukkit.craftbukkit.v1_5_R3.CraftServer.loadPlugins(CraftServer.ja
va:239)
        at org.bukkit.craftbukkit.v1_5_R3.CraftServer.<init>(CraftServer.java:21
7)
        at net.minecraft.server.v1_5_R3.PlayerList.<init>(PlayerList.java:55)
        at net.minecraft.server.v1_5_R3.DedicatedPlayerList.<init>(SourceFile:11
)
        at net.minecraft.server.v1_5_R3.DedicatedServer.init(DedicatedServer.jav
a:106)
        at net.minecraft.server.v1_5_R3.MinecraftServer.run(MinecraftServer.java
:382)
        at net.minecraft.server.v1_5_R3.ThreadServerApplication.run(SourceFile:5
73)
Caused by: java.lang.UnsupportedClassVersionError: me/xXTh3B3astXxify/CustomJoin
/CJMain : Unsupported major.minor version 51.0
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClassCond(Unknown Source)
        at java.lang.ClassLoader.defineClass(Unknown Source)
        at java.security.SecureClassLoader.defineClass(Unknown Source)
        at java.net.URLClassLoader.defineClass(Unknown Source)
        at java.net.URLClassLoader.access$000(Unknown Source)
        at java.net.URLClassLoader$1.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(Unknown Source)
        at org.bukkit.plugin.java.PluginClassLoader.findClass0(PluginClassLoader
.java:80)
        at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.
java:53)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at java.lang.Class.forName0(Native Method)
        at java.lang.Class.forName(Unknown Source)
        at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.j
ava:173)
        ... 9 more
14:12:34 [SEVERE] Could not load 'plugins\SimpleVIPPerks_3.50.jar' in folder 'pl
ugins'
org.bukkit.plugin.InvalidPluginException: java.lang.UnsupportedClassVersionError
: com/gmail/chalkie19/SimpleVIPPerks : Unsupported major.minor version 51.0
        at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.j
ava:184)
        at org.bukkit.plugin.SimplePluginManager.loadPlugin(SimplePluginManager.
java:305)
        at org.bukkit.plugin.SimplePluginManager.loadPlugins(SimplePluginManager
.java:230)
        at org.bukkit.craftbukkit.v1_5_R3.CraftServer.loadPlugins(CraftServer.ja
va:239)
        at org.bukkit.craftbukkit.v1_5_R3.CraftServer.<init>(CraftServer.java:21
7)
        at net.minecraft.server.v1_5_R3.PlayerList.<init>(PlayerList.java:55)
        at net.minecraft.server.v1_5_R3.DedicatedPlayerList.<init>(SourceFile:11
)
        at net.minecraft.server.v1_5_R3.DedicatedServer.init(DedicatedServer.jav
a:106)
        at net.minecraft.server.v1_5_R3.MinecraftServer.run(MinecraftServer.java
:382)
        at net.minecraft.server.v1_5_R3.ThreadServerApplication.run(SourceFile:5
73)
Caused by: java.lang.UnsupportedClassVersionError: com/gmail/chalkie19/SimpleVIP
Perks : Unsupported major.minor version 51.0
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClassCond(Unknown Source)
        at java.lang.ClassLoader.defineClass(Unknown Source)
        at java.security.SecureClassLoader.defineClass(Unknown Source)
        at java.net.URLClassLoader.defineClass(Unknown Source)
        at java.net.URLClassLoader.access$000(Unknown Source)
        at java.net.URLClassLoader$1.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(Unknown Source)
        at org.bukkit.plugin.java.PluginClassLoader.findClass0(PluginClassLoader
.java:80)
        at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.
java:53)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at java.lang.Class.forName0(Native Method)
        at java.lang.Class.forName(Unknown Source)
        at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.j
ava:173)
        ... 9 more
14:12:34 [SEVERE] Could not load 'plugins\AdminConversations.jar' in folder 'plu
gins'
org.bukkit.plugin.InvalidPluginException: java.lang.UnsupportedClassVersionError
: com/momca96/bukkit/AdminConversations/AdminConversations : Unsupported major.m
inor version 51.0
        at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.j
ava:184)
        at org.bukkit.plugin.SimplePluginManager.loadPlugin(SimplePluginManager.
java:305)
        at org.bukkit.plugin.SimplePluginManager.loadPlugins(SimplePluginManager
.java:230)
        at org.bukkit.craftbukkit.v1_5_R3.CraftServer.loadPlugins(CraftServer.ja
va:239)
        at org.bukkit.craftbukkit.v1_5_R3.CraftServer.<init>(CraftServer.java:21
7)
        at net.minecraft.server.v1_5_R3.PlayerList.<init>(PlayerList.java:55)
        at net.minecraft.server.v1_5_R3.DedicatedPlayerList.<init>(SourceFile:11
)
        at net.minecraft.server.v1_5_R3.DedicatedServer.init(DedicatedServer.jav
a:106)
        at net.minecraft.server.v1_5_R3.MinecraftServer.run(MinecraftServer.java
:382)
        at net.minecraft.server.v1_5_R3.ThreadServerApplication.run(SourceFile:5
73)
Caused by: java.lang.UnsupportedClassVersionError: com/momca96/bukkit/AdminConve
rsations/AdminConversations : Unsupported major.minor version 51.0
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClassCond(Unknown Source)
        at java.lang.ClassLoader.defineClass(Unknown Source)
        at java.security.SecureClassLoader.defineClass(Unknown Source)
        at java.net.URLClassLoader.defineClass(Unknown Source)
        at java.net.URLClassLoader.access$000(Unknown Source)
        at java.net.URLClassLoader$1.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(Unknown Source)
        at org.bukkit.plugin.java.PluginClassLoader.findClass0(PluginClassLoader
.java:80)
        at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.
java:53)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at java.lang.Class.forName0(Native Method)
        at java.lang.Class.forName(Unknown Source)
        at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.j
ava:173)
        ... 9 more

(Copied probably more than just the info that is needed to solve this problem, but I dont know what is the needed info of it).

I tried to find a solution on the internet, but got confused of the solution people suggested. I re-installed java on my computer (to the last update) but nothing has changed.

please explain to me exactly what to do to solve this (if there is anything I can do) because I dont understand the special and/or shortened words that people used in the solutions I saw on the internet(such as JRE, and I dont know how to do the test they asked to do.

thank you so much.

Possible duplicate of http://stackoverflow.com/questions/10382929/unsupported-major-minor-version-51-0 — Pradeep Simha, May 27 '13 at 11:38

Steve Oh · Answer 1 · 2013-05-27T11:49:46.973

3

Unsupported major.minor version 51.0 suggests, that a binary class contained in the jar (aka the byte code) is compiled for a newer JRE version.

JRE version docs points out, that version 51 is JRE 7.

Issue command to check your version.

java -version

JRE 7 may not be shipped with your OS. So you might choose to setup the JRE yourself (in /opt) and use JAVA_HOME environment variable to use it.

edited May 27 '13 at 11:49

answered May 27 '13 at 11:40

Steve Oh

1,149
10
18

"Setup a JRE 7 and re-run." How do I do that? – user2217286 May 27 '13 at 11:43
^^ I thought about it. I am not a Mac OS expert. this one may help http://www.mkyong.com/java/how-to-set-java_home-environment-variable-on-mac-os-x/ – Steve Oh May 27 '13 at 11:47
I will try using that. Thank you! – user2217286 May 27 '13 at 11:51

score 0 · Answer 2 · answered Dec 17 '13 at 02:36

You have compiled against Java 7, while your server is only running Java 6. You can install Java 7, though with Bukkit if you plan on making public plugins that you post online I suggest just building against Java 6 as lots of users use it and the developers of Bukkit even suggest such.

Bukkit server "unsupported major minor version 51.0" errors

2 Answers2