Use $JAVA_HOME/bin/java for JUnit test

'java' in $PATH was used. Hope it won't break CI env. We can expect
JAVA_HOME is set, right?

OT: I realized that our current Rake build system depends on
'default.build.properties' not 'build.properties'.

build.xml

@@ -7,6 +7,7 @@
 
   <property name="jruby.gem.home.1.8" location="${basedir}/lib/ruby/gems/1.8"/>
 
+  <property environment="env"/>
   <!-- First try to load machine-specific properties. -->
   <property file="build.properties"/>
 
@@ -97,7 +98,6 @@
   </condition>
 
   <tstamp><format property="build.date" pattern="yyyy-MM-dd"/></tstamp>
-  <property environment="env"/>
 
   <!-- Use JAVA_OPTS env var if set, -ea (supported by all JVMs) otherwise -->
   <condition property="java.opts" value="${env.JAVA_OPTS}"><isset property="env.JAVA_OPTS"/></condition>

default.build.properties

@@ -58,7 +58,7 @@ javac.version=1.5
 jruby.compile.memory=256M
 jruby.launch.memory=512M
 jruby.test.memory=512M
-jruby.test.jvm=java
+jruby.test.jvm=${env.JAVA_HOME}/bin/java
 rake.args=
 ruby.executable=/usr/bin/ruby
 install4j.executable=/Applications/install4j 4/bin/install4jc

rakelib/helpers.rake

@@ -15,8 +15,17 @@ def load_build_properties_into_constants
 
   # two-pass so substitutions can appear above where the var is defined
   constant_names.each do |name|
-    Object.const_get(name).chop!.gsub!(/\$\{([^}]+)\}/) do |embed|
-      Object.const_get($1.gsub!(".", "_").upcase!)
+    Object.const_get(name).chop!.gsub!(/\$\{([^}]+)\}/) do
+      embed = $1
+      const = embed.gsub(".", "_").upcase
+      if Object.constants.include?(const)
+        Object.const_get(const)
+      elsif /^env\.(.*)$/ =~ embed # for ${env.JAVA_HOME}
+        ENV[$1]
+      else
+        warn("no definition for #{const} in default.build.properties")
+        const
+      end
     end
     puts "#{name} = #{Object.const_get(name)}" if Rake.application.options.trace
   end