ServerInitializer

ServerInitializer負責初始化server. 其實現(xiàn)ServletContextListener缩滨，也就是在web啟動的時候會進行初始化的動作九杂。

/**
 * Initializes the Sqoop server. This listener is also responsible for
 * cleaning up any resources occupied by the server during the system shutdown.
 */
public class ServerInitializer implements ServletContextListener {

  private static final Logger LOG = Logger.getLogger(ServerInitializer.class);

  public void contextDestroyed(ServletContextEvent arg0) {
    SqoopServer.destroy();
  }

  public void contextInitialized(ServletContextEvent arg0) {
    try {
      SqoopServer.initialize();
    } catch (Throwable ex) {
      // We are assuming that by default we are running as the only app inside
      // the tomcat and hence we want to try kill entire tomcat on our load failure.
      if("true".equals(System.getProperty(ConfigurationConstants.KILL_TOMCAT_ON_FAILURE, "true"))) {
        LOG.error("Sqoop server failed to start", ex);
        System.exit(1);
      }

      throw new RuntimeException("Sqoop server failed to start.", ex);
    }
  }
}

sqoop_server的源代碼

/**
 * Entry point for initializing and destroying Sqoop server
 */
public class SqoopServer {

  private static final Logger LOG = Logger.getLogger(SqoopServer.class);

  public static void destroy() {
  ....
  }

  public static void initialize() {
    try {
      LOG.info("Booting up Sqoop server");
      SqoopConfiguration.getInstance().initialize();
      AuthenticationManager.getInstance().initialize();
      AuthorizationManager.getInstance().initialize();
      AuditLoggerManager.getInstance().initialize();
      RepositoryManager.getInstance().initialize();
      ConnectorManager.getInstance().initialize();
      Driver.getInstance().initialize();
      JobManager.getInstance().initialize();
      LOG.info("Sqoop server has successfully boot up");
    } catch (Exception ex) {
      LOG.error("Server startup failure", ex);
      throw new RuntimeException("Failure in server initialization", ex);
    }
  }
}

sqoop_server類分為兩個部分， initialize方法負責初始化相應(yīng)的資源。destroy方法負責釋放資源官脓。destroy的代碼和initialize的是相對應(yīng)的。為了節(jié)省空間，故略去相對應(yīng)的destroy的代碼揪惦。

從上面的代碼中，可以看出 sqoop_server的初始化過程包括對以下對象的初始化：

• SqoopConfiguration對象罗侯， 其保存sqoop的相關(guān)配置信息
• AuthenticationManager對象器腋， 其負責
• AuthorizationManager對象， 其負責
• AuditLoggerManager對象， 其負責
• RepositoryManager對象纫塌， 其負責
• ConnectorManager對象再愈， 其負責
• Driver對象， 其負責
• JobManager對象护戳， 其負責

后面的文章將分別對各個對象進行詳細分析翎冲。 這里暫不敘述。