support clear_cache and cache_size methods in StringInterpolation, adjust specs

Fixes #4325

logstash-core-event-java/lib/logstash/event.rb

@@ -2,6 +2,7 @@
 
 require "logstash/namespace"
 require "logstash/json"
+require "logstash/string_interpolation"
 
 # transcient pipeline events for normal in-flow signaling as opposed to
 # flow altering exceptions. for now having base classes is adequate and

logstash-core-event-java/lib/logstash/string_interpolation.rb

@@ -0,0 +1,18 @@
+# encoding: utf-8
+
+module LogStash
+  module StringInterpolation
+    extend self
+
+    # clear the global compiled templates cache
+    def clear_cache
+      Java::ComLogstash::StringInterpolation.get_instance.clear_cache;
+    end
+
+    # @return [Fixnum] the compiled templates cache size
+    def cache_size
+      Java::ComLogstash::StringInterpolation.get_instance.cache_size;
+    end
+  end
+end
+

logstash-core-event-java/src/main/java/com/logstash/StringInterpolation.java

@@ -29,6 +29,14 @@ public class StringInterpolation {
         this.cache = new ConcurrentHashMap<>();
     }
 
+    public void clearCache() {
+        this.cache.clear();
+    }
+
+    public int cacheSize() {
+        return this.cache.size();
+    }
+
     public String evaluate(Event event, String template) throws IOException {
         TemplateNode compiledTemplate = (TemplateNode) this.cache.get(template);
 

logstash-core-event/lib/logstash/string_interpolation.rb

@@ -4,7 +4,7 @@ require "forwardable"
 
 module LogStash
   module StringInterpolation
-    extend self 
+    extend self
 
     # Floats outside of these upper and lower bounds are forcibly converted
     # to scientific notation by Float#to_s
@@ -27,6 +27,16 @@ module LogStash
       compiled.evaluate(event)
     end
 
+    # clear the global compiled templates cache
+    def clear_cache
+      CACHE.clear
+    end
+
+    # @return [Fixnum] the compiled templates cache size
+    def cache_size
+      CACHE.size
+    end
+
     private
     def not_cachable?(template)
       template.index("%").nil?

logstash-core-event/spec/logstash/event_spec.rb

@@ -506,11 +506,11 @@ describe LogStash::Event do
     let(:event2) { LogStash::Event.new({ "host" => "bar", "message" => "foo"}) }
 
     it "should cache only one template" do
-      LogStash::StringInterpolation::CACHE.clear
+      LogStash::StringInterpolation.clear_cache
       expect {
         event1.to_s
         event2.to_s
-      }.to change { LogStash::StringInterpolation::CACHE.size }.by(1)
+      }.to change { LogStash::StringInterpolation.cache_size }.by(1)
     end
 
     it "return the string containing the timestamp, the host and the message" do