fix for Java 8 Map merge method conflict

typo

DRYied code, comments, cleanup

added spec

specs DRYing

also test HashMap, refactor with shared_example

fixes logstash-plugins/logstash-filter-multiline#10

lib/logstash/java_integration.rb

@@ -24,24 +24,39 @@ def self.===(other)
   end
 end
 
+# map_mixin to patch LinkedHashMap and HashMap. it must be done directly on the classes,
+# using a module mixin does not work, and injecting in the Map interface does not work either
+# but injecting in the class works.
 
-# this is a temporary fix to solve a bug in JRuby where classes implementing the Map interface, like LinkedHashMap
-# have a bug in the has_key? method that is implemented in the Enumerable module that is somehow mixed in the Map interface.
-# this bug makes has_key? (and all its aliases) return false for a key that has a nil value.
-# Only LinkedHashMap is patched here because patching the Map interface is not working.
-# TODO find proper fix, and submit upstream
-# releavant JRuby files:
-# https://github.com/jruby/jruby/blob/master/core/src/main/ruby/jruby/java/java_ext/java.util.rb
-# https://github.com/jruby/jruby/blob/master/core/src/main/java/org/jruby/java/proxies/MapJavaProxy.java
-class Java::JavaUtil::LinkedHashMap
+map_mixin = lambda do
+  # this is a temporary fix to solve a bug in JRuby where classes implementing the Map interface, like LinkedHashMap
+  # have a bug in the has_key? method that is implemented in the Enumerable module that is somehow mixed in the Map interface.
+  # this bug makes has_key? (and all its aliases) return false for a key that has a nil value.
+  # Only LinkedHashMap is patched here because patching the Map interface is not working.
+  # TODO find proper fix, and submit upstream
+  # releavant JRuby files:
+  # https://github.com/jruby/jruby/blob/master/core/src/main/ruby/jruby/java/java_ext/java.util.rb
+  # https://github.com/jruby/jruby/blob/master/core/src/main/java/org/jruby/java/proxies/MapJavaProxy.java
   def has_key?(key)
     self.containsKey(key)
   end
   alias_method :include?, :has_key?
   alias_method :member?, :has_key?
   alias_method :key?, :has_key?
+
+  # Java 8 Map implements a merge method with a different signature from
+  # the Ruby Hash#merge. see https://github.com/jruby/jruby/issues/1249
+  # this can be removed when fixed upstream
+  if ENV_JAVA['java.specification.version'] >= '1.8'
+    def merge(other)
+      dup.merge!(other)
+    end
+  end
 end
 
+Java::JavaUtil::LinkedHashMap.module_exec(&map_mixin)
+Java::JavaUtil::HashMap.module_exec(&map_mixin)
+
 module java::util::Map
   # have Map objects like LinkedHashMap objects report is_a?(Array) == true
   def is_a?(clazz)

spec/lib/logstash/java_integration_spec.rb

@@ -50,6 +50,35 @@
     end
   end
 
+  context "Java::JavaUtil::Map" do
+    # this is to test the Java 8 Map interface change for the merge method
+
+    let(:merger){{:a => 1, :b => 2}}
+    let(:mergee){{:b => 3, :c => 4}}
+
+    shared_examples "map merge" do
+      it "should support merging" do
+        expect(subject.merge(mergee)).to eq({:a => 1, :b => 3, :c => 4})
+      end
+
+      it "should return a new hash and not change original hash" do
+        expect{subject.merge(mergee)}.to_not change{subject}
+      end
+    end
+
+    context "with Java::JavaUtil::LinkedHashMap" do
+      it_behaves_like "map merge" do
+        subject{Java::JavaUtil::LinkedHashMap.new(merger)}
+      end
+    end
+
+    context "with Java::JavaUtil::HashMap" do
+      it_behaves_like "map merge" do
+        subject{Java::JavaUtil::HashMap.new(merger)}
+      end
+    end
+  end
+
   context "Java::JavaUtil::Collection" do
     subject{Java::JavaUtil::ArrayList.new(initial_array)}