001/**************************************************************** 002 * Licensed to the Apache Software Foundation (ASF) under one * 003 * or more contributor license agreements. See the NOTICE file * 004 * distributed with this work for additional information * 005 * regarding copyright ownership. The ASF licenses this file * 006 * to you under the Apache License, Version 2.0 (the * 007 * "License"); you may not use this file except in compliance * 008 * with the License. You may obtain a copy of the License at * 009 * * 010 * http://www.apache.org/licenses/LICENSE-2.0 * 011 * * 012 * Unless required by applicable law or agreed to in writing, * 013 * software distributed under the License is distributed on an * 014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY * 015 * KIND, either express or implied. See the License for the * 016 * specific language governing permissions and limitations * 017 * under the License. * 018 ****************************************************************/ 019 020package org.apache.james.mime4j.storage; 021 022import java.io.IOException; 023import java.io.OutputStream; 024 025/** 026 * This class implements an output stream that can be used to create a 027 * {@link Storage} object. An instance of this class is obtained by calling 028 * {@link StorageProvider#createStorageOutputStream()}. The user can then write 029 * data to this instance and invoke {@link #toStorage()} to retrieve a 030 * {@link Storage} object that contains the data that has been written. 031 * <p> 032 * Note that the <code>StorageOutputStream</code> does not have to be closed 033 * explicitly because {@link #toStorage()} invokes {@link #close()} if 034 * necessary. Also note that {@link #toStorage()} may be invoked only once. One 035 * <code>StorageOutputStream</code> can create only one <code>Storage</code> 036 * instance. 037 */ 038public abstract class StorageOutputStream extends OutputStream { 039 040 private byte[] singleByte; 041 private boolean closed; 042 private boolean usedUp; 043 044 /** 045 * Sole constructor. 046 */ 047 protected StorageOutputStream() { 048 } 049 050 /** 051 * Closes this output stream if it has not already been closed and returns a 052 * {@link Storage} object which contains the bytes that have been written to 053 * this output stream. 054 * <p> 055 * Note that this method may not be invoked a second time. This is because 056 * for some implementations it is not possible to create another 057 * <code>Storage</code> object that can be read from and deleted 058 * independently (e.g. if the implementation writes to a file). 059 * 060 * @return a <code>Storage</code> object as described above. 061 * @throws IOException 062 * if an I/O error occurs. 063 * @throws IllegalStateException 064 * if this method has already been called. 065 */ 066 public final Storage toStorage() throws IOException { 067 if (usedUp) 068 throw new IllegalStateException( 069 "toStorage may be invoked only once"); 070 071 if (!closed) 072 close(); 073 074 usedUp = true; 075 return toStorage0(); 076 } 077 078 @Override 079 public final void write(int b) throws IOException { 080 if (closed) 081 throw new IOException("StorageOutputStream has been closed"); 082 083 if (singleByte == null) 084 singleByte = new byte[1]; 085 086 singleByte[0] = (byte) b; 087 write0(singleByte, 0, 1); 088 } 089 090 @Override 091 public final void write(byte[] buffer) throws IOException { 092 if (closed) 093 throw new IOException("StorageOutputStream has been closed"); 094 095 if (buffer == null) 096 throw new NullPointerException(); 097 098 if (buffer.length == 0) 099 return; 100 101 write0(buffer, 0, buffer.length); 102 } 103 104 @Override 105 public final void write(byte[] buffer, int offset, int length) 106 throws IOException { 107 if (closed) 108 throw new IOException("StorageOutputStream has been closed"); 109 110 if (buffer == null) 111 throw new NullPointerException(); 112 113 if (offset < 0 || length < 0 || offset + length > buffer.length) 114 throw new IndexOutOfBoundsException(); 115 116 if (length == 0) 117 return; 118 119 write0(buffer, offset, length); 120 } 121 122 /** 123 * Closes this output stream. Subclasses that override this method have to 124 * invoke <code>super.close()</code>. 125 * <p> 126 * This implementation never throws an {@link IOException} but a subclass 127 * might. 128 * 129 * @throws IOException 130 * if an I/O error occurs. 131 */ 132 @Override 133 public void close() throws IOException { 134 closed = true; 135 } 136 137 /** 138 * Has to implemented by a concrete subclass to write bytes from the given 139 * byte array to this <code>StorageOutputStream</code>. This method gets 140 * called by {@link #write(int)}, {@link #write(byte[])} and 141 * {@link #write(byte[], int, int)}. All the required preconditions have 142 * already been checked by these methods, including the check if the output 143 * stream has already been closed. 144 * 145 * @param buffer 146 * buffer containing bytes to write. 147 * @param offset 148 * start offset in the buffer. 149 * @param length 150 * number of bytes to write. 151 * @throws IOException 152 * if an I/O error occurs. 153 */ 154 protected abstract void write0(byte[] buffer, int offset, int length) 155 throws IOException; 156 157 /** 158 * Has to be implemented by a concrete subclass to create a {@link Storage} 159 * object from the bytes that have been written to this 160 * <code>StorageOutputStream</code>. This method gets called by 161 * {@link #toStorage()} after the preconditions have been checked. The 162 * implementation can also be sure that this methods gets invoked only once. 163 * 164 * @return a <code>Storage</code> object as described above. 165 * @throws IOException 166 * if an I/O error occurs. 167 */ 168 protected abstract Storage toStorage0() throws IOException; 169 170}