001/* 002 * Copyright 2002-2019 the original author or authors. 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); 005 * you may not use this file except in compliance with the License. 006 * You may obtain a copy of the License at 007 * 008 * https://www.apache.org/licenses/LICENSE-2.0 009 * 010 * Unless required by applicable law or agreed to in writing, software 011 * distributed under the License is distributed on an "AS IS" BASIS, 012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 013 * See the License for the specific language governing permissions and 014 * limitations under the License. 015 */ 016 017package org.springframework.jdbc.datasource; 018 019import java.lang.reflect.InvocationHandler; 020import java.lang.reflect.InvocationTargetException; 021import java.lang.reflect.Method; 022import java.lang.reflect.Proxy; 023import java.sql.Connection; 024import java.sql.SQLException; 025import javax.sql.DataSource; 026 027import org.apache.commons.logging.Log; 028import org.apache.commons.logging.LogFactory; 029 030import org.springframework.core.Constants; 031 032/** 033 * Proxy for a target DataSource, fetching actual JDBC Connections lazily, 034 * i.e. not until first creation of a Statement. Connection initialization 035 * properties like auto-commit mode, transaction isolation and read-only mode 036 * will be kept and applied to the actual JDBC Connection as soon as an 037 * actual Connection is fetched (if ever). Consequently, commit and rollback 038 * calls will be ignored if no Statements have been created. 039 * 040 * <p>This DataSource proxy allows to avoid fetching JDBC Connections from 041 * a pool unless actually necessary. JDBC transaction control can happen 042 * without fetching a Connection from the pool or communicating with the 043 * database; this will be done lazily on first creation of a JDBC Statement. 044 * 045 * <p><b>If you configure both a LazyConnectionDataSourceProxy and a 046 * TransactionAwareDataSourceProxy, make sure that the latter is the outermost 047 * DataSource.</b> In such a scenario, data access code will talk to the 048 * transaction-aware DataSource, which will in turn work with the 049 * LazyConnectionDataSourceProxy. 050 * 051 * <p>Lazy fetching of physical JDBC Connections is particularly beneficial 052 * in a generic transaction demarcation environment. It allows you to demarcate 053 * transactions on all methods that could potentially perform data access, 054 * without paying a performance penalty if no actual data access happens. 055 * 056 * <p>This DataSource proxy gives you behavior analogous to JTA and a 057 * transactional JNDI DataSource (as provided by the Java EE server), even 058 * with a local transaction strategy like DataSourceTransactionManager or 059 * HibernateTransactionManager. It does not add value with Spring's 060 * JtaTransactionManager as transaction strategy. 061 * 062 * <p>Lazy fetching of JDBC Connections is also recommended for read-only 063 * operations with Hibernate, in particular if the chances of resolving the 064 * result in the second-level cache are high. This avoids the need to 065 * communicate with the database at all for such read-only operations. 066 * You will get the same effect with non-transactional reads, but lazy fetching 067 * of JDBC Connections allows you to still perform reads in transactions. 068 * 069 * <p><b>NOTE:</b> This DataSource proxy needs to return wrapped Connections 070 * (which implement the {@link ConnectionProxy} interface) in order to handle 071 * lazy fetching of an actual JDBC Connection. Therefore, the returned Connections 072 * cannot be cast to a native JDBC Connection type such as OracleConnection or 073 * to a connection pool implementation type. Use a corresponding 074 * {@link org.springframework.jdbc.support.nativejdbc.NativeJdbcExtractor} 075 * or JDBC 4's {@link Connection#unwrap} to retrieve the native JDBC Connection. 076 * 077 * @author Juergen Hoeller 078 * @since 1.1.4 079 * @see DataSourceTransactionManager 080 */ 081public class LazyConnectionDataSourceProxy extends DelegatingDataSource { 082 083 /** Constants instance for TransactionDefinition */ 084 private static final Constants constants = new Constants(Connection.class); 085 086 private static final Log logger = LogFactory.getLog(LazyConnectionDataSourceProxy.class); 087 088 private Boolean defaultAutoCommit; 089 090 private Integer defaultTransactionIsolation; 091 092 093 /** 094 * Create a new LazyConnectionDataSourceProxy. 095 * @see #setTargetDataSource 096 */ 097 public LazyConnectionDataSourceProxy() { 098 } 099 100 /** 101 * Create a new LazyConnectionDataSourceProxy. 102 * @param targetDataSource the target DataSource 103 */ 104 public LazyConnectionDataSourceProxy(DataSource targetDataSource) { 105 setTargetDataSource(targetDataSource); 106 afterPropertiesSet(); 107 } 108 109 110 /** 111 * Set the default auto-commit mode to expose when no target Connection 112 * has been fetched yet (-> actual JDBC Connection default not known yet). 113 * <p>If not specified, the default gets determined by checking a target 114 * Connection on startup. If that check fails, the default will be determined 115 * lazily on first access of a Connection. 116 * @see java.sql.Connection#setAutoCommit 117 */ 118 public void setDefaultAutoCommit(boolean defaultAutoCommit) { 119 this.defaultAutoCommit = defaultAutoCommit; 120 } 121 122 /** 123 * Set the default transaction isolation level to expose when no target Connection 124 * has been fetched yet (-> actual JDBC Connection default not known yet). 125 * <p>This property accepts the int constant value (e.g. 8) as defined in the 126 * {@link java.sql.Connection} interface; it is mainly intended for programmatic 127 * use. Consider using the "defaultTransactionIsolationName" property for setting 128 * the value by name (e.g. "TRANSACTION_SERIALIZABLE"). 129 * <p>If not specified, the default gets determined by checking a target 130 * Connection on startup. If that check fails, the default will be determined 131 * lazily on first access of a Connection. 132 * @see #setDefaultTransactionIsolationName 133 * @see java.sql.Connection#setTransactionIsolation 134 */ 135 public void setDefaultTransactionIsolation(int defaultTransactionIsolation) { 136 this.defaultTransactionIsolation = defaultTransactionIsolation; 137 } 138 139 /** 140 * Set the default transaction isolation level by the name of the corresponding 141 * constant in {@link java.sql.Connection}, e.g. "TRANSACTION_SERIALIZABLE". 142 * @param constantName name of the constant 143 * @see #setDefaultTransactionIsolation 144 * @see java.sql.Connection#TRANSACTION_READ_UNCOMMITTED 145 * @see java.sql.Connection#TRANSACTION_READ_COMMITTED 146 * @see java.sql.Connection#TRANSACTION_REPEATABLE_READ 147 * @see java.sql.Connection#TRANSACTION_SERIALIZABLE 148 */ 149 public void setDefaultTransactionIsolationName(String constantName) { 150 setDefaultTransactionIsolation(constants.asNumber(constantName).intValue()); 151 } 152 153 154 @Override 155 public void afterPropertiesSet() { 156 super.afterPropertiesSet(); 157 158 // Determine default auto-commit and transaction isolation 159 // via a Connection from the target DataSource, if possible. 160 if (this.defaultAutoCommit == null || this.defaultTransactionIsolation == null) { 161 try { 162 Connection con = getTargetDataSource().getConnection(); 163 try { 164 checkDefaultConnectionProperties(con); 165 } 166 finally { 167 con.close(); 168 } 169 } 170 catch (SQLException ex) { 171 logger.warn("Could not retrieve default auto-commit and transaction isolation settings", ex); 172 } 173 } 174 } 175 176 /** 177 * Check the default connection properties (auto-commit, transaction isolation), 178 * keeping them to be able to expose them correctly without fetching an actual 179 * JDBC Connection from the target DataSource. 180 * <p>This will be invoked once on startup, but also for each retrieval of a 181 * target Connection. If the check failed on startup (because the database was 182 * down), we'll lazily retrieve those settings. 183 * @param con the Connection to use for checking 184 * @throws SQLException if thrown by Connection methods 185 */ 186 protected synchronized void checkDefaultConnectionProperties(Connection con) throws SQLException { 187 if (this.defaultAutoCommit == null) { 188 this.defaultAutoCommit = con.getAutoCommit(); 189 } 190 if (this.defaultTransactionIsolation == null) { 191 this.defaultTransactionIsolation = con.getTransactionIsolation(); 192 } 193 } 194 195 /** 196 * Expose the default auto-commit value. 197 */ 198 protected Boolean defaultAutoCommit() { 199 return this.defaultAutoCommit; 200 } 201 202 /** 203 * Expose the default transaction isolation value. 204 */ 205 protected Integer defaultTransactionIsolation() { 206 return this.defaultTransactionIsolation; 207 } 208 209 210 /** 211 * Return a Connection handle that lazily fetches an actual JDBC Connection 212 * when asked for a Statement (or PreparedStatement or CallableStatement). 213 * <p>The returned Connection handle implements the ConnectionProxy interface, 214 * allowing to retrieve the underlying target Connection. 215 * @return a lazy Connection handle 216 * @see ConnectionProxy#getTargetConnection() 217 */ 218 @Override 219 public Connection getConnection() throws SQLException { 220 return (Connection) Proxy.newProxyInstance( 221 ConnectionProxy.class.getClassLoader(), 222 new Class<?>[] {ConnectionProxy.class}, 223 new LazyConnectionInvocationHandler()); 224 } 225 226 /** 227 * Return a Connection handle that lazily fetches an actual JDBC Connection 228 * when asked for a Statement (or PreparedStatement or CallableStatement). 229 * <p>The returned Connection handle implements the ConnectionProxy interface, 230 * allowing to retrieve the underlying target Connection. 231 * @param username the per-Connection username 232 * @param password the per-Connection password 233 * @return a lazy Connection handle 234 * @see ConnectionProxy#getTargetConnection() 235 */ 236 @Override 237 public Connection getConnection(String username, String password) throws SQLException { 238 return (Connection) Proxy.newProxyInstance( 239 ConnectionProxy.class.getClassLoader(), 240 new Class<?>[] {ConnectionProxy.class}, 241 new LazyConnectionInvocationHandler(username, password)); 242 } 243 244 245 /** 246 * Invocation handler that defers fetching an actual JDBC Connection 247 * until first creation of a Statement. 248 */ 249 private class LazyConnectionInvocationHandler implements InvocationHandler { 250 251 private String username; 252 253 private String password; 254 255 private Integer transactionIsolation; 256 257 private Boolean autoCommit; 258 259 private boolean readOnly = false; 260 261 private boolean closed = false; 262 263 private Connection target; 264 265 public LazyConnectionInvocationHandler() { 266 this.autoCommit = defaultAutoCommit(); 267 this.transactionIsolation = defaultTransactionIsolation(); 268 } 269 270 public LazyConnectionInvocationHandler(String username, String password) { 271 this(); 272 this.username = username; 273 this.password = password; 274 } 275 276 @Override 277 public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { 278 // Invocation on ConnectionProxy interface coming in... 279 280 if (method.getName().equals("equals")) { 281 // We must avoid fetching a target Connection for "equals". 282 // Only consider equal when proxies are identical. 283 return (proxy == args[0]); 284 } 285 else if (method.getName().equals("hashCode")) { 286 // We must avoid fetching a target Connection for "hashCode", 287 // and we must return the same hash code even when the target 288 // Connection has been fetched: use hashCode of Connection proxy. 289 return System.identityHashCode(proxy); 290 } 291 else if (method.getName().equals("unwrap")) { 292 if (((Class<?>) args[0]).isInstance(proxy)) { 293 return proxy; 294 } 295 } 296 else if (method.getName().equals("isWrapperFor")) { 297 if (((Class<?>) args[0]).isInstance(proxy)) { 298 return true; 299 } 300 } 301 else if (method.getName().equals("getTargetConnection")) { 302 // Handle getTargetConnection method: return underlying connection. 303 return getTargetConnection(method); 304 } 305 306 if (!hasTargetConnection()) { 307 // No physical target Connection kept yet -> 308 // resolve transaction demarcation methods without fetching 309 // a physical JDBC Connection until absolutely necessary. 310 311 if (method.getName().equals("toString")) { 312 return "Lazy Connection proxy for target DataSource [" + getTargetDataSource() + "]"; 313 } 314 else if (method.getName().equals("getAutoCommit")) { 315 if (this.autoCommit != null) { 316 return this.autoCommit; 317 } 318 // Else fetch actual Connection and check there, 319 // because we didn't have a default specified. 320 } 321 else if (method.getName().equals("setAutoCommit")) { 322 this.autoCommit = (Boolean) args[0]; 323 return null; 324 } 325 else if (method.getName().equals("getTransactionIsolation")) { 326 if (this.transactionIsolation != null) { 327 return this.transactionIsolation; 328 } 329 // Else fetch actual Connection and check there, 330 // because we didn't have a default specified. 331 } 332 else if (method.getName().equals("setTransactionIsolation")) { 333 this.transactionIsolation = (Integer) args[0]; 334 return null; 335 } 336 else if (method.getName().equals("isReadOnly")) { 337 return this.readOnly; 338 } 339 else if (method.getName().equals("setReadOnly")) { 340 this.readOnly = (Boolean) args[0]; 341 return null; 342 } 343 else if (method.getName().equals("commit") || method.getName().equals("rollback")) { 344 // Ignore: no statements created yet. 345 return null; 346 } 347 else if (method.getName().equals("getWarnings") || method.getName().equals("clearWarnings")) { 348 // Ignore: no warnings to expose yet. 349 return null; 350 } 351 else if (method.getName().equals("close")) { 352 // Ignore: no target connection yet. 353 this.closed = true; 354 return null; 355 } 356 else if (method.getName().equals("isClosed")) { 357 return this.closed; 358 } 359 else if (this.closed) { 360 // Connection proxy closed, without ever having fetched a 361 // physical JDBC Connection: throw corresponding SQLException. 362 throw new SQLException("Illegal operation: connection is closed"); 363 } 364 } 365 366 // Target Connection already fetched, 367 // or target Connection necessary for current operation -> 368 // invoke method on target connection. 369 try { 370 return method.invoke(getTargetConnection(method), args); 371 } 372 catch (InvocationTargetException ex) { 373 throw ex.getTargetException(); 374 } 375 } 376 377 /** 378 * Return whether the proxy currently holds a target Connection. 379 */ 380 private boolean hasTargetConnection() { 381 return (this.target != null); 382 } 383 384 /** 385 * Return the target Connection, fetching it and initializing it if necessary. 386 */ 387 private Connection getTargetConnection(Method operation) throws SQLException { 388 if (this.target == null) { 389 // No target Connection held -> fetch one. 390 if (logger.isDebugEnabled()) { 391 logger.debug("Connecting to database for operation '" + operation.getName() + "'"); 392 } 393 394 // Fetch physical Connection from DataSource. 395 this.target = (this.username != null) ? 396 getTargetDataSource().getConnection(this.username, this.password) : 397 getTargetDataSource().getConnection(); 398 399 // If we still lack default connection properties, check them now. 400 checkDefaultConnectionProperties(this.target); 401 402 // Apply kept transaction settings, if any. 403 if (this.readOnly) { 404 try { 405 this.target.setReadOnly(true); 406 } 407 catch (Exception ex) { 408 // "read-only not supported" -> ignore, it's just a hint anyway 409 logger.debug("Could not set JDBC Connection read-only", ex); 410 } 411 } 412 if (this.transactionIsolation != null && 413 !this.transactionIsolation.equals(defaultTransactionIsolation())) { 414 this.target.setTransactionIsolation(this.transactionIsolation); 415 } 416 if (this.autoCommit != null && this.autoCommit != this.target.getAutoCommit()) { 417 this.target.setAutoCommit(this.autoCommit); 418 } 419 } 420 421 else { 422 // Target Connection already held -> return it. 423 if (logger.isDebugEnabled()) { 424 logger.debug("Using existing database connection for operation '" + operation.getName() + "'"); 425 } 426 } 427 428 return this.target; 429 } 430 } 431 432}