#349 add a OkHttpClient instance

docs/extensions-howto.md

@@ -72,6 +72,7 @@ alf.io provides some objects and properties to the script in the script scope:
 * **log** Log4j logger
 * **extensionLogger** a logger that write in the extension_log table. It implement the [ExtensionLogger](https://github.com/alfio-event/alf.io/blob/master/src/main/java/alfio/extension/ExtensionLogger.java) interface.
 * **restTemplate** Spring Framework's [RestTemplate](https://docs.spring.io/spring/docs/4.3.13.RELEASE/javadoc-api/org/springframework/web/client/RestTemplate.html)
+* **httpClient** instance of a [OkHttpClient](http://square.github.io/okhttp/)
 * **GSON** Google's [JSON parser/generator](http://static.javadoc.io/com.google.code.gson/gson/2.8.2/com/google/gson/Gson.html)
 * **returnClass** `java.lang.Class<?>` the expected result type
 * **extensionParameters** a map containing the parameters of an extension

src/main/java/alfio/extension/ScriptingExecutionService.java

@@ -22,6 +22,7 @@
 import com.github.benmanes.caffeine.cache.Caffeine;
 import com.github.benmanes.caffeine.cache.RemovalListener;
 import lombok.extern.log4j.Log4j2;
+import okhttp3.OkHttpClient;
 import org.springframework.stereotype.Service;
 import org.springframework.web.client.RestTemplate;
 
@@ -46,6 +47,9 @@
 @Log4j2
 public class ScriptingExecutionService {
 
+    private static final OkHttpClient HTTP_CLIENT = new OkHttpClient();
+    private static final RestTemplate REST_TEMPLATE = new RestTemplate();
+
     private final static Compilable engine = (Compilable) new ScriptEngineManager().getEngineByName("nashorn");
     private final Cache<String, CompiledScript> compiledScriptCache = Caffeine.newBuilder()
         .expireAfterAccess(12, TimeUnit.HOURS)
@@ -101,7 +105,8 @@ private static <T> T executeScript(String name, CompiledScript script, Map<Strin
             engineScope.put("log", log);
             engineScope.put("extensionLogger", extensionLogger);
             engineScope.put("GSON", Json.GSON);
-            engineScope.put("restTemplate", new RestTemplate());
+            engineScope.put("restTemplate", REST_TEMPLATE);
+            engineScope.put("httpClient", HTTP_CLIENT);
             engineScope.put("returnClass", clazz);
             engineScope.putAll(params);
             T res = (T) script.eval(newContext);