| 1 | /* |
| 2 | * Copyright 2006-2012 the original author or authors. |
| 3 | * |
| 4 | * Licensed under the Apache License, Version 2.0 (the "License"); |
| 5 | * you may not use this file except in compliance with the License. |
| 6 | * You may obtain a copy of the License at |
| 7 | * |
| 8 | * http://www.apache.org/licenses/LICENSE-2.0 |
| 9 | * |
| 10 | * Unless required by applicable law or agreed to in writing, software |
| 11 | * distributed under the License is distributed on an "AS IS" BASIS, |
| 12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 13 | * See the License for the specific language governing permissions and |
| 14 | * limitations under the License. |
| 15 | */ |
| 16 | package org.springframework.batch.support.transaction; |
| 17 | |
| 18 | import java.io.IOException; |
| 19 | import java.io.UnsupportedEncodingException; |
| 20 | import java.io.Writer; |
| 21 | import java.nio.ByteBuffer; |
| 22 | import java.nio.channels.FileChannel; |
| 23 | |
| 24 | import org.springframework.batch.item.WriteFailedException; |
| 25 | import org.springframework.transaction.support.TransactionSynchronizationAdapter; |
| 26 | import org.springframework.transaction.support.TransactionSynchronizationManager; |
| 27 | |
| 28 | /** |
| 29 | * Wrapper for a {@link FileChannel} that delays actually writing to or closing the |
| 30 | * buffer if a transaction is active. If a transaction is detected on the call |
| 31 | * to {@link #write(String)} the parameter is buffered and passed on to the |
| 32 | * underlying writer only when the transaction is committed. |
| 33 | * |
| 34 | * @author Dave Syer |
| 35 | * @author Michael Minella |
| 36 | * |
| 37 | */ |
| 38 | public class TransactionAwareBufferedWriter extends Writer { |
| 39 | |
| 40 | private static final String BUFFER_KEY_PREFIX = TransactionAwareBufferedWriter.class.getName() + ".BUFFER_KEY"; |
| 41 | |
| 42 | private static final String CLOSE_KEY_PREFIX = TransactionAwareBufferedWriter.class.getName() + ".CLOSE_KEY"; |
| 43 | |
| 44 | private final String bufferKey; |
| 45 | |
| 46 | private final String closeKey; |
| 47 | |
| 48 | private FileChannel channel; |
| 49 | |
| 50 | private final Runnable closeCallback; |
| 51 | |
| 52 | // default encoding for writing to output files - set to UTF-8. |
| 53 | private static final String DEFAULT_CHARSET = "UTF-8"; |
| 54 | |
| 55 | private String encoding = DEFAULT_CHARSET; |
| 56 | |
| 57 | private boolean forceSync = false; |
| 58 | |
| 59 | /** |
| 60 | * Create a new instance with the underlying file channel provided, and a callback |
| 61 | * to execute on close. The callback should clean up related resources like |
| 62 | * output streams or channels. |
| 63 | * |
| 64 | * @param channel channel used to do the actuall file IO |
| 65 | * @param closeCallback callback to execute on close |
| 66 | */ |
| 67 | public TransactionAwareBufferedWriter(FileChannel channel, Runnable closeCallback) { |
| 68 | super(); |
| 69 | this.channel = channel; |
| 70 | this.closeCallback = closeCallback; |
| 71 | this.bufferKey = BUFFER_KEY_PREFIX + "." + hashCode(); |
| 72 | this.closeKey = CLOSE_KEY_PREFIX + "." + hashCode(); |
| 73 | } |
| 74 | |
| 75 | public void setEncoding(String encoding) { |
| 76 | this.encoding = encoding; |
| 77 | } |
| 78 | |
| 79 | /** |
| 80 | * Flag to indicate that changes should be force-synced to disk on flush. |
| 81 | * Defaults to false, which means that even with a local disk changes could |
| 82 | * be lost if the OS crashes in between a write and a cache flush. Setting |
| 83 | * to true may result in slower performance for usage patterns involving |
| 84 | * many frequent writes. |
| 85 | * |
| 86 | * @param forceSync the flag value to set |
| 87 | */ |
| 88 | public void setForceSync(boolean forceSync) { |
| 89 | this.forceSync = forceSync; |
| 90 | } |
| 91 | |
| 92 | /** |
| 93 | * @return |
| 94 | */ |
| 95 | private StringBuffer getCurrentBuffer() { |
| 96 | |
| 97 | if (!TransactionSynchronizationManager.hasResource(bufferKey)) { |
| 98 | |
| 99 | TransactionSynchronizationManager.bindResource(bufferKey, new StringBuffer()); |
| 100 | |
| 101 | TransactionSynchronizationManager.registerSynchronization(new TransactionSynchronizationAdapter() { |
| 102 | @Override |
| 103 | public void afterCompletion(int status) { |
| 104 | clear(); |
| 105 | } |
| 106 | |
| 107 | @Override |
| 108 | public void beforeCommit(boolean readOnly) { |
| 109 | try { |
| 110 | if(!readOnly) { |
| 111 | complete(); |
| 112 | } |
| 113 | } |
| 114 | catch (IOException e) { |
| 115 | throw new FlushFailedException("Could not write to output buffer", e); |
| 116 | } |
| 117 | } |
| 118 | |
| 119 | private void complete() throws IOException { |
| 120 | StringBuffer buffer = (StringBuffer) TransactionSynchronizationManager.getResource(bufferKey); |
| 121 | if (buffer != null) { |
| 122 | String string = buffer.toString(); |
| 123 | byte[] bytes = string.getBytes(encoding); |
| 124 | int bufferLength = bytes.length; |
| 125 | ByteBuffer bb = ByteBuffer.wrap(bytes); |
| 126 | int bytesWritten = channel.write(bb); |
| 127 | if(bytesWritten != bufferLength) { |
| 128 | throw new IOException("All bytes to be written were not successfully written"); |
| 129 | } |
| 130 | if (forceSync) { |
| 131 | channel.force(false); |
| 132 | } |
| 133 | if (TransactionSynchronizationManager.hasResource(closeKey)) { |
| 134 | closeCallback.run(); |
| 135 | } |
| 136 | } |
| 137 | } |
| 138 | |
| 139 | private void clear() { |
| 140 | if (TransactionSynchronizationManager.hasResource(bufferKey)) { |
| 141 | TransactionSynchronizationManager.unbindResource(bufferKey); |
| 142 | } |
| 143 | if (TransactionSynchronizationManager.hasResource(closeKey)) { |
| 144 | TransactionSynchronizationManager.unbindResource(closeKey); |
| 145 | } |
| 146 | } |
| 147 | |
| 148 | }); |
| 149 | |
| 150 | } |
| 151 | |
| 152 | return (StringBuffer) TransactionSynchronizationManager.getResource(bufferKey); |
| 153 | |
| 154 | } |
| 155 | |
| 156 | /** |
| 157 | * Convenience method for clients to determine if there is any unflushed |
| 158 | * data. |
| 159 | * |
| 160 | * @return the current size (in bytes) of unflushed buffered data |
| 161 | */ |
| 162 | public long getBufferSize() { |
| 163 | if (!transactionActive()) { |
| 164 | return 0L; |
| 165 | } |
| 166 | try { |
| 167 | return getCurrentBuffer().toString().getBytes(encoding).length; |
| 168 | } catch (UnsupportedEncodingException e) { |
| 169 | throw new WriteFailedException("Could not determine buffer size because of unsupported encoding: " + encoding, e); |
| 170 | } |
| 171 | } |
| 172 | |
| 173 | /** |
| 174 | * @return |
| 175 | */ |
| 176 | private boolean transactionActive() { |
| 177 | return TransactionSynchronizationManager.isActualTransactionActive(); |
| 178 | } |
| 179 | |
| 180 | /* |
| 181 | * (non-Javadoc) |
| 182 | * |
| 183 | * @see java.io.Writer#close() |
| 184 | */ |
| 185 | @Override |
| 186 | public void close() throws IOException { |
| 187 | if (transactionActive()) { |
| 188 | if (getCurrentBuffer().length() > 0) { |
| 189 | TransactionSynchronizationManager.bindResource(closeKey, Boolean.TRUE); |
| 190 | } |
| 191 | return; |
| 192 | } |
| 193 | closeCallback.run(); |
| 194 | } |
| 195 | |
| 196 | /* |
| 197 | * (non-Javadoc) |
| 198 | * |
| 199 | * @see java.io.Writer#flush() |
| 200 | */ |
| 201 | @Override |
| 202 | public void flush() throws IOException { |
| 203 | if (!transactionActive() && forceSync) { |
| 204 | channel.force(false); |
| 205 | } |
| 206 | } |
| 207 | |
| 208 | /* |
| 209 | * (non-Javadoc) |
| 210 | * |
| 211 | * @see java.io.Writer#write(char[], int, int) |
| 212 | */ |
| 213 | @Override |
| 214 | public void write(char[] cbuf, int off, int len) throws IOException { |
| 215 | |
| 216 | if (!transactionActive()) { |
| 217 | char [] subArray = new char[len]; |
| 218 | System.arraycopy(cbuf, off, subArray, 0, len); |
| 219 | byte[] bytes = new String(subArray).getBytes(encoding); |
| 220 | int length = bytes.length; |
| 221 | ByteBuffer bb = ByteBuffer.wrap(bytes); |
| 222 | int bytesWritten = channel.write(bb); |
| 223 | if(bytesWritten != length) { |
| 224 | throw new IOException("Unable to write all data. Bytes to write: " + len + ". Bytes written: " + bytesWritten); |
| 225 | } |
| 226 | return; |
| 227 | } |
| 228 | |
| 229 | StringBuffer buffer = getCurrentBuffer(); |
| 230 | buffer.append(cbuf, off, len); |
| 231 | } |
| 232 | } |