001/**
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.camel;
018
019import java.io.IOException;
020import java.io.OutputStream;
021
022/**
023 * Tagging interface to indicate that a type is capable of caching the underlying data stream.
024 * <p/>
025 * This is a useful feature for avoiding message re-readability issues.
026 * This interface is mainly used by the {@link org.apache.camel.spi.StreamCachingStrategy}
027 * for determining if/how to wrap a stream-based message.
028 * <p/>
029 * The Camel routing engine uses the {@link org.apache.camel.processor.CamelInternalProcessor.StreamCachingAdvice}
030 * to apply the stream cache during routing.
031 * <p/>
032 * It is recommended in the {@link #copy()} method to let the copied stream start from the start. If the implementation
033 * does not support copy, then return <tt>null</tt>.
034 *
035 * @version 
036 */
037public interface StreamCache {
038
039    long DEFAULT_SPOOL_THRESHOLD = 128 * 1024;
040
041    /**
042     * Resets the StreamCache for a new stream consumption.
043     */
044    void reset();
045
046    /**
047     * Writes the stream to the given output
048     *
049     * @param os the destination to write to
050     * @throws java.io.IOException is thrown if write fails
051     */
052    void writeTo(OutputStream os) throws IOException;
053
054    /**
055     * Create a copy of the stream. If possible use the same cached data in the
056     * copied instance.
057     * <p/>
058     * This method is useful for parallel processing.
059     * <p/>
060     * Implementations note: A copy of the stream is recommended to read from the start
061     * of the stream.
062     *
063     * @return a copy, or <tt>null</tt> if copy is not possible
064     * @throws java.io.IOException is thrown if the copy fails
065     */
066    StreamCache copy() throws IOException;
067
068    /**
069     * Whether this {@link StreamCache} is in memory only or
070     * spooled to persistent storage such as files.
071     */
072    boolean inMemory();
073
074    /**
075     * Gets the length of the cached stream.
076     * <p/>
077     * The implementation may return <tt>0</tt> in cases where the length
078     * cannot be computed, or if the implementation does not support this.
079     *
080     * @return number of bytes in the cache.
081     */
082    long length();
083
084}