Java jersey2: use a shared Client instance

modules/swagger-codegen/src/main/resources/Java/libraries/jersey2/ApiClient.mustache

@@ -45,6 +45,7 @@ import {{invokerPackage}}.auth.OAuth;
 
 {{>generatedAnnotation}}
 public class ApiClient {
+  private Client client;
   private Map<String, Client> hostMap = new HashMap<String, Client>();
   private Map<String, String> defaultHeaderMap = new HashMap<String, String>();
   private boolean debugging = false;
@@ -69,6 +70,8 @@ public class ApiClient {
     // Set default User-Agent.
     setUserAgent("Java-Swagger");
 
+    buildClient();
+
     // Setup authentications (key: authentication name, value: authentication).
     authentications = new HashMap<String, Authentication>();{{#authMethods}}{{#isBasic}}
     authentications.put("{{name}}", new HttpBasicAuth());{{/isBasic}}{{#isApiKey}}
@@ -203,6 +206,7 @@ public class ApiClient {
    */
   public ApiClient setDebugging(boolean debugging) {
     this.debugging = debugging;
+    buildClient();
     return this;
   }
 
@@ -419,13 +423,6 @@ public class ApiClient {
   public <T> T invokeAPI(String path, String method, List<Pair> queryParams, Object body, Map<String, String> headerParams, Map<String, Object> formParams, String accept, String contentType, String[] authNames, TypeRef returnType) throws ApiException {
     updateParamsForAuth(authNames, queryParams, headerParams);
 
-    final ClientConfig clientConfig = new ClientConfig();
-    clientConfig.register(MultiPartFeature.class);
-    if (debugging) {
-      clientConfig.register(LoggingFilter.class);
-    }
-    Client client = ClientBuilder.newClient(clientConfig);
-
     WebTarget target = client.target(this.basePath).path(path);
 
     if (queryParams != null) {
@@ -537,6 +534,15 @@ public class ApiClient {
     }
   }
 
+  private void buildClient() {
+    final ClientConfig clientConfig = new ClientConfig();
+    clientConfig.register(MultiPartFeature.class);
+    if (debugging) {
+      clientConfig.register(LoggingFilter.class);
+    }
+    this.client = ClientBuilder.newClient(clientConfig);
+  }
+
   private Map<String, List<String>> buildResponseHeaders(Response response) {
     Map<String, List<String>> responseHeaders = new HashMap<String, List<String>>();
     for (Entry<String, List<Object>> entry: response.getHeaders().entrySet()) {