Auto detect Java major version

The commit adds the ability to turn on Java version detection. This
will scan the application to detect the major version of Java that
should be used for the application and then refer to the config file
for the exact version to use.

[#71382852]

Author: Christopher Frost

.idea/dictionaries/cgfrost.xml

@@ -14,16 +14,21 @@
 # limitations under the License.
 
 # Configuration for JRE repositories keyed by vendor
-# To go back to Java 7, permgen should be used instead of metaspace.  Please see the documentation for more detail.
+# Pre Java 1.8, permgen was used instead of metaspace, the buildpack will consume the configuration as appropriate.
+# Please see the documentation for more detail.
 ---
 repository_root: "{default.repository.root}/openjdk/{platform}/{architecture}"
-version: 1.8.0_+
+version:
+  detect_compiled: enabled
+  8: 1.8.0_+
+  7: 1.7.0_+
+  6: 1.6.0_+
 memory_sizes:
   metaspace: 64m..
-  # permgen: 64m..
+  permgen: 64m..
 memory_heuristics:
   heap: 75
   metaspace: 10
-  # permgen: 10
+  permgen: 10
   stack: 5
   native: 10

config/open_jdk_jre.yml

@@ -14,19 +14,24 @@
 # limitations under the License.
 
 # Configuration for JRE repositories keyed by vendor
-# Pre Java 1.8, permgen was used instead of metaspace.  Please see the documentation for more detail.
+# Pre Java 1.8, permgen was used instead of metaspace, the buildpack will consume the configuration as appropriate.
+# Please see the documentation for more detail.
 ---
 # You must specify a the repository root of an Oracle JRE repository. Please see the documentation for more detail.
 # e.g.  repository_root: "http://example.com/oracle-jre/{platform}/{architecture}"
 
 repository_root: ""
-version: 1.8.0_+
+version:
+  detect_compiled: enabled
+  8: 1.8.0_+
+  7: 1.7.0_+
+  6: 1.6.0_+
 memory_sizes:
   metaspace: 64m..
-#  permgen: 64m..
+  permgen: 64m..
 memory_heuristics:
   heap: 75
   metaspace: 10
-#  permgen: 10
+  permgen: 10
   stack: 5
   native: 10

config/oracle_jre.yml

@@ -271,7 +271,7 @@
     <orderEntry type="library" scope="PROVIDED" name="addressable (v2.3.6, rbenv: 1.9.3-p551) [gem]" level="application" />
     <orderEntry type="library" scope="PROVIDED" name="ast (v2.0.0, rbenv: 1.9.3-p551) [gem]" level="application" />
     <orderEntry type="library" scope="PROVIDED" name="astrolabe (v1.3.0, rbenv: 1.9.3-p551) [gem]" level="application" />
-    <orderEntry type="library" scope="PROVIDED" name="bundler (v1.7.8, rbenv: 1.9.3-p551) [gem]" level="application" />
+    <orderEntry type="library" scope="PROVIDED" name="bundler (v1.7.11, rbenv: 1.9.3-p551) [gem]" level="application" />
     <orderEntry type="library" scope="PROVIDED" name="codeclimate-test-reporter (v0.4.3, rbenv: 1.9.3-p551) [gem]" level="application" />
     <orderEntry type="library" scope="PROVIDED" name="crack (v0.4.2, rbenv: 1.9.3-p551) [gem]" level="application" />
     <orderEntry type="library" scope="PROVIDED" name="diff-lcs (v1.2.5, rbenv: 1.9.3-p551) [gem]" level="application" />
@@ -281,13 +281,13 @@
     <orderEntry type="library" scope="PROVIDED" name="powerpack (v0.0.9, rbenv: 1.9.3-p551) [gem]" level="application" />
     <orderEntry type="library" scope="PROVIDED" name="rainbow (v2.0.0, rbenv: 1.9.3-p551) [gem]" level="application" />
     <orderEntry type="library" scope="PROVIDED" name="rake (v10.4.2, rbenv: 1.9.3-p551) [gem]" level="application" />
-    <orderEntry type="library" scope="PROVIDED" name="redcarpet (v3.2.1, rbenv: 1.9.3-p551) [gem]" level="application" />
+    <orderEntry type="library" scope="PROVIDED" name="redcarpet (v3.2.2, rbenv: 1.9.3-p551) [gem]" level="application" />
     <orderEntry type="library" scope="PROVIDED" name="rspec (v3.1.0, rbenv: 1.9.3-p551) [gem]" level="application" />
     <orderEntry type="library" scope="PROVIDED" name="rspec-core (v3.1.7, rbenv: 1.9.3-p551) [gem]" level="application" />
     <orderEntry type="library" scope="PROVIDED" name="rspec-expectations (v3.1.2, rbenv: 1.9.3-p551) [gem]" level="application" />
     <orderEntry type="library" scope="PROVIDED" name="rspec-mocks (v3.1.3, rbenv: 1.9.3-p551) [gem]" level="application" />
     <orderEntry type="library" scope="PROVIDED" name="rspec-support (v3.1.2, rbenv: 1.9.3-p551) [gem]" level="application" />
-    <orderEntry type="library" scope="PROVIDED" name="rubocop (v0.27.1, rbenv: 1.9.3-p551) [gem]" level="application" />
+    <orderEntry type="library" scope="PROVIDED" name="rubocop (v0.28.0, rbenv: 1.9.3-p551) [gem]" level="application" />
     <orderEntry type="library" scope="PROVIDED" name="rubocop-rspec (v1.2.1, rbenv: 1.9.3-p551) [gem]" level="application" />
     <orderEntry type="library" scope="PROVIDED" name="ruby-progressbar (v1.7.0, rbenv: 1.9.3-p551) [gem]" level="application" />
     <orderEntry type="library" scope="PROVIDED" name="rubyzip (v1.1.6, rbenv: 1.9.3-p551) [gem]" level="application" />

java-buildpack.iml

@@ -15,6 +15,7 @@
 # limitations under the License.
 
 require 'fileutils'
+require 'find'
 require 'java_buildpack/component/versioned_dependency_component'
 require 'java_buildpack/jre'
 require 'java_buildpack/jre/memory/openjdk_memory_heuristic_factory'
@@ -24,6 +25,7 @@ module Jre
 
     # Encapsulates the detect, compile, and release functionality for selecting an OpenJDK-like JRE.
     class OpenJDKLike < JavaBuildpack::Component::VersionedDependencyComponent
+      include Find
 
       # Creates an instance
       #
@@ -33,15 +35,20 @@ def initialize(context)
         @component_name = self.class.to_s.space_case
         @configuration  = context[:configuration]
         @droplet        = context[:droplet]
+        @logger         = JavaBuildpack::Logging::LoggerFactory.instance.get_logger OpenJDKLike
 
         @droplet.java_home.root = @droplet.sandbox
       end
 
       # (see JavaBuildpack::Component::BaseComponent#detect)
       def detect
-        @version, @uri             = JavaBuildpack::Repository::ConfiguredItem.find_item(@component_name,
-                                                                                         @configuration)
+        version       = detect_compiled?(@configuration[KEY_VERSION]) ? compiled_version(@application.root) : VERSION_8
+        configuration = { KEY_REPOSITORY_ROOT => @configuration[KEY_REPOSITORY_ROOT],
+                          KEY_VERSION         => @configuration[KEY_VERSION][version] }
+
+        @version, @uri             = JavaBuildpack::Repository::ConfiguredItem.find_item(@component_name, configuration)
         @droplet.java_home.version = @version
+
         super
       end
 
@@ -53,30 +60,96 @@ def compile
 
       # (see JavaBuildpack::Component::BaseComponent#release)
       def release
+        version = detect_compiled?(@configuration[KEY_VERSION]) ? compiled_version(@application.root) : VERSION_8
+
         @droplet.java_opts
           .add_system_property('java.io.tmpdir', '$TMPDIR')
           .add_option('-XX:OnOutOfMemoryError', killjava)
-          .concat memory
+          .concat memory(version)
       end
 
       private
 
+      CAFEBABE = 'cafebabe'.freeze
+
+      KEY_DETECT_COMPILED_VERSION = 'detect_compiled'.freeze
+
       KEY_MEMORY_HEURISTICS = 'memory_heuristics'.freeze
 
       KEY_MEMORY_SIZES = 'memory_sizes'.freeze
 
-      private_constant :KEY_MEMORY_HEURISTICS, :KEY_MEMORY_SIZES
+      KEY_REPOSITORY_ROOT = 'repository_root'.freeze
+
+      KEY_VERSION = 'version'.freeze
+
+      VERSION_6 = 6.freeze
+
+      VERSION_7 = 7.freeze
+
+      VERSION_8 = 8.freeze
+
+      private_constant :CAFEBABE, :KEY_DETECT_COMPILED_VERSION, :KEY_MEMORY_HEURISTICS, :KEY_MEMORY_SIZES,
+                       :KEY_REPOSITORY_ROOT, :KEY_VERSION, :VERSION_6, :VERSION_7, :VERSION_8
+
+      def class?(path)
+        File.extname(path) == '.class'
+      end
+
+      def class_file_format(path)
+        bits = File.open(path).read.unpack('H*')[0]
+        @logger.debug { "Scanning #{path}:  #{bits[0, 8]}/#{bits[14, 2]}" }
+
+        Integer(bits[14, 2]) if magic_number?(bits)
+      end
+
+      def compiled_version(root)
+        @logger.debug { 'Detecting compiled version' }
+
+        versions = find(root.to_path).map do |child|
+          next if File.directory?(child) || !class?(child)
+          class_file_format child
+        end
+
+        version versions.max_by(&:to_i)
+      end
+
+      def detect_compiled?(configuration)
+        configuration[KEY_DETECT_COMPILED_VERSION] == 'enabled'
+      end
 
       def killjava
         @droplet.sandbox + 'bin/killjava.sh'
       end
 
-      def memory
-        sizes      = @configuration[KEY_MEMORY_SIZES] || {}
-        heuristics = @configuration[KEY_MEMORY_HEURISTICS] || {}
+      def magic_number?(bits)
+        bits[0, 8] == CAFEBABE
+      end
+
+      def memory(version)
+        sizes      = @configuration[KEY_MEMORY_SIZES] ? @configuration[KEY_MEMORY_SIZES].clone : {}
+        heuristics = @configuration[KEY_MEMORY_HEURISTICS] ? @configuration[KEY_MEMORY_HEURISTICS].clone : {}
+
+        if version < VERSION_8
+          heuristics.delete 'metaspace'
+          sizes.delete 'metaspace'
+        else
+          heuristics.delete 'permgen'
+          sizes.delete 'permgen'
+        end
+
         OpenJDKMemoryHeuristicFactory.create_memory_heuristic(sizes, heuristics, @version).resolve
       end
 
+      def version(format)
+        if format == 32
+          VERSION_6
+        elsif format == 33
+          VERSION_7
+        else
+          VERSION_8
+        end
+      end
+
     end
 
   end

lib/java_buildpack/jre/open_jdk_like.rb

@@ -0,0 +1,2 @@
+Manifest-Version: 1.0
+

spec/fixtures/jre_java6_application/META-INF/MANIFEST.MF

@@ -0,0 +1,2 @@
+Manifest-Version: 1.0
+