hadoop IsActiveServlet 源码
haddop IsActiveServlet 代码
文件路径：/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/http/IsActiveServlet.java
/**
* 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.hadoop.http;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
/**
* Used by Load Balancers to detect the active NameNode/ResourceManager/Router.
*/
public abstract class IsActiveServlet extends HttpServlet {
/** Default serial identifier. */
private static final long serialVersionUID = 1L;
public static final String SERVLET_NAME = "isActive";
public static final String PATH_SPEC = "/isActive";
public static final String RESPONSE_ACTIVE =
"I am Active!";
public static final String RESPONSE_NOT_ACTIVE =
"I am not Active!";
/**
* Check whether this instance is the Active one.
* @param req HTTP request
* @param resp HTTP response to write to
*/
@Override
public void doGet(
final HttpServletRequest req, final HttpServletResponse resp)
throws IOException {
// By default requests are persistent. We don't want long-lived connections
// on server side.
resp.addHeader("Connection", "close");
if (!isActive()) {
// Report not SC_OK
resp.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED,
RESPONSE_NOT_ACTIVE);
return;
}
resp.setStatus(HttpServletResponse.SC_OK);
resp.getWriter().write(RESPONSE_ACTIVE);
resp.getWriter().flush();
}
/**
* @return true if this instance is in Active HA state.
*/
protected abstract boolean isActive();
}
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