added Filter for set Content-Language Header of the response

dspace-server-webapp/src/main/java/org/dspace/app/rest/filter/ContentLanguageHeaderResponseFilter.java

@@ -0,0 +1,52 @@
+package org.dspace.app.rest.filter;
+
+import java.io.IOException;
+import java.util.Locale;
+import javax.servlet.Filter;
+import javax.servlet.FilterChain;
+import javax.servlet.FilterConfig;
+import javax.servlet.ServletException;
+import javax.servlet.ServletRequest;
+import javax.servlet.ServletResponse;
+import javax.servlet.http.HttpServletResponse;
+
+import org.dspace.core.I18nUtil;
+import org.springframework.stereotype.Component;
+
+/**
+ * This filter assures that when the dspace instance supports multiple languages
+ * they are noted in the Content-Language Header of the response
+ * 
+ * @author Mykhaylo Boychuk (at 4science.it)
+ */
+@Component
+public class ContentLanguageHeaderResponseFilter implements Filter {
+
+    @Override
+    public void init(FilterConfig filterConfig) throws ServletException {
+    }
+
+    @Override
+    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
+        throws IOException, ServletException {
+        chain.doFilter(request, response);
+
+        HttpServletResponse httpServletResponse = (HttpServletResponse) response;
+        if (!httpServletResponse.containsHeader("Content-Language")) {
+            Locale[] locales = I18nUtil.getSupportedLocales();
+            StringBuilder locsStr = new StringBuilder();
+            for (Locale locale : locales) {
+                if (locsStr.length() > 0) {
+                    locsStr.append(",");
+                }
+                locsStr.append(locale.getLanguage());
+            }
+            httpServletResponse.setHeader("Content-Language", locsStr.toString());
+        }
+    }
+
+    @Override
+    public void destroy() {
+    }
+
+}