4 files changed, 103 insertions, 6 deletions
diff --git a/src/main/java/org/spigotmc/builder/Bootstrap.java b/src/main/java/org/spigotmc/builder/Bootstrap.java
index 34cb95e..57a2b78 100644
--- a/src/main/java/org/spigotmc/builder/Bootstrap.java
+++ b/src/main/java/org/spigotmc/builder/Bootstrap.java
@@ -5,24 +5,24 @@ public class Bootstrap
 
     public static void main(String[] args) throws Exception
     {
-        float javaVersion = Float.parseFloat( System.getProperty( "java.class.version" ) );
+        JavaVersion javaVersion = JavaVersion.getCurrentVersion();
 
-        if ( javaVersion < 51.0 )
+        if ( javaVersion.getVersion() < JavaVersion.JAVA_7.getVersion() )
         {
             System.err.println( "Outdated Java detected (" + javaVersion + "). BuildTools requires at least Java 7. Please update Java and try again." );
             System.err.println( "You may use java -version to double check your Java version." );
             return;
         }
 
-        if ( javaVersion < 52.0 )
+        if ( javaVersion.getVersion() < JavaVersion.JAVA_8.getVersion() )
         {
             System.err.println( "*** WARNING *** Outdated Java detected (" + javaVersion + "). Minecraft >= 1.12 requires at least Java 8." );
             System.err.println( "*** WARNING *** You may use java -version to double check your Java version." );
         }
 
-        if ( javaVersion > 55.0 )
+        if ( javaVersion == JavaVersion.UNKNOWN )
         {
-            System.err.println( "*** WARNING *** Unsupported Java detected (" + javaVersion + "). BuildTools has only been tested up to Java 11. Use of development Java version is not supported." );
+            System.err.println( "*** WARNING *** Unsupported Java detected (" + System.getProperty( "java.class.version" ) + "). BuildTools has only been tested up to Java 11. Use of development Java version is not supported." );
             System.err.println( "*** WARNING *** You may use java -version to double check your Java version." );
         }
 
diff --git a/src/main/java/org/spigotmc/builder/BuildInfo.java b/src/main/java/org/spigotmc/builder/BuildInfo.java
index e0500fc..b401e67 100644
--- a/src/main/java/org/spigotmc/builder/BuildInfo.java
+++ b/src/main/java/org/spigotmc/builder/BuildInfo.java
@@ -11,6 +11,7 @@ public class BuildInfo
     private String name;
     private String description;
     private int toolsVersion = -1;
+    private int[] javaVersions;
     private Refs refs;
 
     @Data
diff --git a/src/main/java/org/spigotmc/builder/Builder.java b/src/main/java/org/spigotmc/builder/Builder.java
index 9d96d8b..d864956 100644
--- a/src/main/java/org/spigotmc/builder/Builder.java
+++ b/src/main/java/org/spigotmc/builder/Builder.java
@@ -1,6 +1,7 @@
 package org.spigotmc.builder;
 
 import com.google.common.base.Charsets;
+import com.google.common.base.Preconditions;
 import com.google.common.base.Predicate;
 import com.google.common.base.Throwables;
 import com.google.common.collect.Iterables;
@@ -120,6 +121,7 @@ public class Builder
 
         OptionParser parser = new OptionParser();
         OptionSpec<Void> disableCertFlag = parser.accepts( "disable-certificate-check" );
+        OptionSpec<Void> disableJavaCheck = parser.accepts( "disable-java-check" );
         OptionSpec<Void> dontUpdateFlag = parser.accepts( "dont-update" );
         OptionSpec<Void> skipCompileFlag = parser.accepts( "skip-compile" );
         OptionSpec<Void> generateSourceFlag = parser.accepts( "generate-source" );
@@ -252,7 +254,7 @@ public class Builder
         Git spigotGit = Git.open( spigot );
         Git buildGit = Git.open( buildData );
 
-        BuildInfo buildInfo = new BuildInfo( "Dev Build", "Development", 0, new BuildInfo.Refs( "master", "master", "master", "master" ) );
+        BuildInfo buildInfo = new BuildInfo( "Dev Build", "Development", 0, null, new BuildInfo.Refs( "master", "master", "master", "master" ) );
 
         if ( !dontUpdate )
         {
@@ -281,6 +283,36 @@ public class Builder
                     System.err.println( "**** Your BuildTools is out of date and will not build the requested version. Please grab a new copy from https://www.spigotmc.org/go/buildtools-dl" );
                     System.exit( 1 );
                 }
+
+                if ( !options.has( disableJavaCheck ) )
+                {
+                    if ( buildInfo.getJavaVersions() == null )
+                    {
+                        buildInfo.setJavaVersions( new int[]
+                        {
+                            JavaVersion.JAVA_7.getVersion(), JavaVersion.JAVA_8.getVersion()
+                        } );
+                    }
+
+                    Preconditions.checkArgument( buildInfo.getJavaVersions().length == 2, "Expected only two Java versions, got %s", JavaVersion.printVersions( buildInfo.getJavaVersions() ) );
+
+                    JavaVersion curVersion = JavaVersion.getCurrentVersion();
+                    JavaVersion minVersion = JavaVersion.getByVersion( buildInfo.getJavaVersions()[0] );
+                    JavaVersion maxVersion = JavaVersion.getByVersion( buildInfo.getJavaVersions()[1] );
+
+                    if ( minVersion == JavaVersion.UNKNOWN || maxVersion == JavaVersion.UNKNOWN )
+                    {
+                        System.err.println( "*** This BuildTools doesn't know how to use  Java versions " + JavaVersion.printVersions( buildInfo.getJavaVersions() ) + ", please update" );
+                        System.exit( 1 );
+                    }
+
+                    if ( curVersion.getVersion() < minVersion.getVersion() || curVersion.getVersion() > maxVersion.getVersion() )
+                    {
+                        System.err.println( "*** The version you have requested to build requires Java versions between " + JavaVersion.printVersions( buildInfo.getJavaVersions() ) + ", but you are using " + curVersion );
+                        System.err.println( "*** Please rerun BuildTools using an appropriate Java version. For obvious reasons outdated MC versions do not support Java versions that did not exist at their release." );
+                        System.exit( 1 );
+                    }
+                }
             }
 
             pull( buildGit, buildInfo.getRefs().getBuildData() );
diff --git a/src/main/java/org/spigotmc/builder/JavaVersion.java b/src/main/java/org/spigotmc/builder/JavaVersion.java
new file mode 100644
index 0000000..d86a1ae
--- /dev/null
+++ b/src/main/java/org/spigotmc/builder/JavaVersion.java
@@ -0,0 +1,64 @@
+package org.spigotmc.builder;
+
+import java.util.HashMap;
+import java.util.Map;
+import lombok.Getter;
+
+@Getter
+public enum JavaVersion
+{
+
+    UNKNOWN( -1 ),
+    JAVA_5( 49 ),
+    JAVA_6( 50 ),
+    JAVA_7( 51 ),
+    JAVA_8( 52 ),
+    JAVA_9( 53 ),
+    JAVA_10( 54 ),
+    JAVA_11( 55 );
+
+    private final int version;
+
+    private JavaVersion(int version)
+    {
+        this.version = version;
+    }
+
+    private static final Map<Integer, JavaVersion> byVersion = new HashMap<Integer, JavaVersion>();
+
+    static
+    {
+        for ( JavaVersion version : values() )
+        {
+
+            byVersion.put( version.version, version );
+        }
+    }
+
+    public static JavaVersion getByVersion(int version)
+    {
+        return byVersion.containsKey( version ) ? byVersion.get( version ) : JavaVersion.UNKNOWN;
+    }
+
+    public static JavaVersion getCurrentVersion()
+    {
+        return getByVersion( (int) Float.parseFloat( System.getProperty( "java.class.version" ) ) );
+    }
+
+    public static String printVersions(int[] versions)
+    {
+        StringBuilder sb = new StringBuilder();
+
+        sb.append( '[' );
+        for ( int v : versions )
+        {
+            JavaVersion found = getByVersion( v );
+            sb.append( found == JavaVersion.UNKNOWN ? v : found );
+            sb.append( ", " );
+        }
+        sb.setLength( sb.length() - 2 );
+        sb.append( ']' );
+
+        return sb.toString();
+    }
+}