download_tar improvements

A previous change to the download_tar method introduced a bug where
the wrong decompression flag was applied to the tar command.  This
change fixes that bug, applying the appropriate gzip decompression
flag.  This change also adds support for bzip2 compressed tar files.

[resolves #195]

Author: Claude Devarenne

lib/java_buildpack/component/base_component.rb

@@ -122,7 +122,7 @@ def download_tar(version, uri, target_directory = @droplet.sandbox, name = @comp
         download(version, uri, name) do |file|
           with_timing "Expanding #{name} to #{target_directory.relative_path_from(@droplet.root)}" do
             FileUtils.mkdir_p target_directory
-            shell "tar x#{gzipped?(file) ? 'x' : ''}f #{file.path} -C #{target_directory} --strip 1 2>&1"
+            shell "tar x#{compression_flag(file)}f #{file.path} -C #{target_directory} --strip 1 2>&1"
           end
         end
       end
@@ -172,6 +172,20 @@ def gzipped?(file)
         file.path.end_with? '.gz'
       end
 
+      def bzipped?(file)
+        file.path.end_with? '.bz2'
+      end
+
+      def compression_flag(file)
+        if gzipped?(file)
+          'z'
+        elsif bzipped?(file)
+          'j'
+        else
+          ''
+        end
+      end
+
     end
 
   end