Cross-platform java detection

1 files changed, 13 insertions, 0 deletions

diff --git a/Library/Homebrew/extend/os/mac/system_config.rb b/Library/Homebrew/extend/os/mac/system_config.rb
index 796134781..c0a28d3e9 100644
--- a/Library/Homebrew/extend/os/mac/system_config.rb
+++ b/Library/Homebrew/extend/os/mac/system_config.rb
@@ -23,6 +23,19 @@ class SystemConfig
       @ponk.join(", ") unless @ponk.empty?
     end
 
+    def describe_java
+      # java_home doesn't exist on all macOSs; it might be missing on older versions.
+      return "N/A" unless File.executable? "/usr/libexec/java_home"
+
+      java_xml = Utils.popen_read("/usr/libexec/java_home", "--xml", "--failfast", err: :close)
+      return "N/A" unless $CHILD_STATUS.success?
+      javas = []
+      REXML::XPath.each(REXML::Document.new(java_xml), "//key[text()='JVMVersion']/following-sibling::string") do |item|
+        javas << item.text
+      end
+      javas.uniq.join(", ")
+    end
+
     def describe_xquartz
       return "N/A" unless MacOS::XQuartz.installed?
       "#{MacOS::XQuartz.version} => #{describe_path(MacOS::XQuartz.prefix)}"