org.apache.lucene.store.ChecksumIndexInput.java Source code

Introduction

Here is the source code for org.apache.lucene.store.ChecksumIndexInput.java

Source

/*
 * 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.lucene.store;

import java.io.IOException;

/** 
 * Extension of IndexInput, computing checksum as it goes. 
 * Callers can retrieve the checksum via {@link #getChecksum()}.
 */
public abstract class ChecksumIndexInput extends IndexInput {

    /** resourceDescription should be a non-null, opaque string
     *  describing this resource; it's returned from
     *  {@link #toString}. */
    protected ChecksumIndexInput(String resourceDescription) {
        super(resourceDescription);
    }

    /** Returns the current checksum value */
    public abstract long getChecksum() throws IOException;

    /**
     * {@inheritDoc}
     *
     * {@link ChecksumIndexInput} can only seek forward and seeks are expensive
     * since they imply to read bytes in-between the current position and the
     * target position in order to update the checksum.
     */
    @Override
    public void seek(long pos) throws IOException {
        final long curFP = getFilePointer();
        final long skip = pos - curFP;
        if (skip < 0) {
            throw new IllegalStateException(
                    getClass() + " cannot seek backwards (pos=" + pos + " getFilePointer()=" + curFP + ")");
        }
        skipBytes(skip);
    }
}