LogReader.java

/*
 * Copyright © 2014 Cask Data, Inc.
 *
 * Licensed 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 co.cask.cdap.common.logging;

import java.io.IOException;
import java.util.List;

/**
 * Represents classes that can read log.
 */
public interface LogReader {

  /**
   * Configures this reader.
   * @param config specifies what log to read
   */
  void configure(LogConfiguration config) throws IOException;

  /**
   * retrieves the tail of the log, up to size bytes, line by line.
   * @param sizeToRead limits the number of bytes to read
   * @param writePos position of the current writer. This is a hint to the
   *                 reader as to how far it can seek into the latest log.
   *                 This is necessary because we are reading into the latest
   *                 file while it is still open for write, and hence the
   *                 file system status will not give us a precise file length.
   */
  List<String> tail(int sizeToRead, long writePos) throws IOException;
}