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(Exchange)} method to let the copied stream start from the start. If the implementation 033 * does not support copy, then return <tt>null</tt>. 034 */ 035public interface StreamCache { 036 037 long DEFAULT_SPOOL_THRESHOLD = 128 * 1024; 038 039 /** 040 * Resets the StreamCache for a new stream consumption. 041 */ 042 void reset(); 043 044 /** 045 * Writes the stream to the given output 046 * 047 * @param os the destination to write to 048 * @throws java.io.IOException is thrown if write fails 049 */ 050 void writeTo(OutputStream os) throws IOException; 051 052 /** 053 * Create a copy of the stream. If possible use the same cached data in the 054 * copied instance. 055 * <p/> 056 * This method is useful for parallel processing. 057 * <p/> 058 * Implementations note: A copy of the stream is recommended to read from the start 059 * of the stream. 060 * 061 * @param exchange exchange in which the stream cache object is used; 062 * can be used to delete resources of the stream cache when the exchange is completed 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(Exchange exchange) 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}