[ZEPPELIN-5933] Polish jetty (apache#4621)

* Rewrite index.html handling

* Polish initialize of the Rest API

* Don't break the WebApp Classloader Isolation

* Use default SessionHandler

* Add simple session tests

zeppelin-server/src/main/java/org/apache/zeppelin/server/IndexHtmlServlet.java

@@ -0,0 +1,89 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.zeppelin.server;
+
+import java.io.IOException;
+import java.net.URL;
+import java.nio.charset.StandardCharsets;
+
+import javax.servlet.ServletException;
+import javax.servlet.http.HttpServlet;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+
+import org.apache.commons.io.IOUtils;
+import org.apache.zeppelin.conf.ZeppelinConfiguration;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class IndexHtmlServlet extends HttpServlet {
+
+  private static final Logger LOGGER = LoggerFactory.getLogger(IndexHtmlServlet.class);
+
+  /**
+   *
+   */
+  private static final long serialVersionUID = 1L;
+
+  private static final String TAG_BODY_OPENING = "<body"; // ignore bracket here to support potential html attributes
+  private static final String TAG_BODY_CLOSING = "</body>";
+  private static final String TAG_HEAD_CLOSING = "</head>";
+  private static final String TAG_HTML_CLOSING = "</html>";
+
+  final String bodyAddon;
+  final String headAddon;
+
+  public IndexHtmlServlet(ZeppelinConfiguration conf) {
+    this.bodyAddon = conf.getHtmlBodyAddon();
+    this.headAddon = conf.getHtmlHeadAddon();
+  }
+
+  @Override
+  protected void doGet(HttpServletRequest req, HttpServletResponse resp)
+    throws ServletException, IOException {
+    try {
+      URL indexResource = getServletContext().getResource("/index.html");
+      String content = IOUtils.toString(indexResource, StandardCharsets.UTF_8);
+      // read original content from resource
+      if (bodyAddon != null) {
+        if (content.contains(TAG_BODY_CLOSING)) {
+          content = content.replace(TAG_BODY_CLOSING, bodyAddon + TAG_BODY_CLOSING);
+        } else if (content.contains(TAG_HTML_CLOSING)) {
+          content = content.replace(TAG_HTML_CLOSING, bodyAddon + TAG_HTML_CLOSING);
+        } else {
+          content = content + bodyAddon;
+        }
+      }
+      // process head addon
+      if (headAddon != null) {
+        if (content.contains(TAG_HEAD_CLOSING)) {
+          content = content.replace(TAG_HEAD_CLOSING, headAddon + TAG_HEAD_CLOSING);
+        } else if (content.contains(TAG_BODY_OPENING)) {
+          content = content.replace(TAG_BODY_OPENING, headAddon + TAG_BODY_OPENING);
+        } else {
+          LOGGER.error(
+            "Unable to process Head html addon. Could not find proper anchor in index.html.");
+        }
+      }
+      resp.setContentType("text/html");
+      resp.setStatus(HttpServletResponse.SC_OK);
+      resp.getWriter().append(content);
+    } catch (IOException e) {
+      LOGGER.error("Error rendering index.html.", e);
+    }
+  }
+}

zeppelin-server/src/main/java/org/apache/zeppelin/server/RestApiApplication.java

@@ -0,0 +1,59 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.zeppelin.server;
+
+import java.util.HashSet;
+import java.util.Set;
+
+import javax.ws.rs.core.Application;
+
+import org.apache.zeppelin.rest.AdminRestApi;
+import org.apache.zeppelin.rest.ClusterRestApi;
+import org.apache.zeppelin.rest.ConfigurationsRestApi;
+import org.apache.zeppelin.rest.CredentialRestApi;
+import org.apache.zeppelin.rest.HeliumRestApi;
+import org.apache.zeppelin.rest.InterpreterRestApi;
+import org.apache.zeppelin.rest.LoginRestApi;
+import org.apache.zeppelin.rest.NotebookRepoRestApi;
+import org.apache.zeppelin.rest.NotebookRestApi;
+import org.apache.zeppelin.rest.SecurityRestApi;
+import org.apache.zeppelin.rest.SessionRestApi;
+import org.apache.zeppelin.rest.ZeppelinRestApi;
+import org.apache.zeppelin.rest.exception.WebApplicationExceptionMapper;
+
+public class RestApiApplication extends Application {
+  @Override
+  public Set<Class<?>> getClasses() {
+    Set<Class<?>> s = new HashSet<>();
+    s.add(AdminRestApi.class);
+    s.add(ClusterRestApi.class);
+    s.add(ConfigurationsRestApi.class);
+    s.add(CredentialRestApi.class);
+    s.add(HeliumRestApi.class);
+    s.add(InterpreterRestApi.class);
+    s.add(LoginRestApi.class);
+    s.add(NotebookRepoRestApi.class);
+    s.add(NotebookRestApi.class);
+    s.add(SecurityRestApi.class);
+    s.add(SessionRestApi.class);
+    s.add(ZeppelinRestApi.class);
+
+    // add ExceptionMapper
+    s.add(WebApplicationExceptionMapper.class);
+    return s;
+  }
+}