/*
* Copyright 2002-2006 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.jdbc.datasource.lookup;
import org.springframework.core.Constants;
import org.springframework.transaction.TransactionDefinition;
import org.springframework.transaction.support.DefaultTransactionDefinition;
import org.springframework.transaction.support.TransactionSynchronizationManager;
/**
* DataSource that routes to one of various target DataSources based on the
* current transaction isolation level. The target DataSources need to be
* configured with the isolation level name as key, as defined on the
* {@link org.springframework.transaction.TransactionDefinition TransactionDefinition interface}.
*
* <p>This is particularly useful in combination with JTA transaction management
* (typically through Spring's {@link org.springframework.transaction.jta.JtaTransactionManager}).
* Standard JTA does not support transaction-specific isolation levels. Some JTA
* providers support isolation levels as a vendor-specific extension (e.g. WebLogic),
* which is the preferred way of addressing this. As alternative (e.g. on WebSphere),
* the target database can be represented through multiple JNDI DataSources, each
* configured with a different isolation level (for the entire DataSource).
* The present DataSource router allows to transparently switch to the
* appropriate DataSource based on the current transaction's isolation level.
*
* <p>The configuration can for example look like this, assuming that the target
* DataSources are defined as individual Spring beans with names
* "myRepeatableReadDataSource", "mySerializableDataSource" and "myDefaultDataSource":
*
* <pre>
* <bean id="dataSourceRouter" class="org.springframework.jdbc.datasource.lookup.IsolationLevelDataSourceRouter">
* <property name="targetDataSources">
* <map>
* <entry key="ISOLATION_REPEATABLE_READ" value-ref="myRepeatableReadDataSource"/>
* <entry key="ISOLATION_SERIALIZABLE" value-ref="mySerializableDataSource"/>
* </map>
* </property>
* <property name="defaultTargetDataSource" ref="myDefaultDataSource"/>
* </bean></pre>
*
* Alternatively, the keyed values can also be data source names, to be resolved
* through a {@link #setDataSourceLookup DataSourceLookup}: by default, JNDI
* names for a standard JNDI lookup. This allows for a single concise definition
* without the need for separate DataSource bean definitions.
*
* <pre>
* <bean id="dataSourceRouter" class="org.springframework.jdbc.datasource.lookup.IsolationLevelDataSourceRouter">
* <property name="targetDataSources">
* <map>
* <entry key="ISOLATION_REPEATABLE_READ" value="java:comp/env/jdbc/myrrds"/>
* <entry key="ISOLATION_SERIALIZABLE" value="java:comp/env/jdbc/myserds"/>
* </map>
* </property>
* <property name="defaultTargetDataSource" value="java:comp/env/jdbc/mydefds"/>
* </bean></pre>
*
* Note: If you are using this router in combination with Spring's
* {@link org.springframework.transaction.jta.JtaTransactionManager},
* don't forget to switch the "allowCustomIsolationLevels" flag to "true".
* (By default, JtaTransactionManager will only accept a default isolation level
* because of the lack of isolation level support in standard JTA itself.)
*
* <pre>
* <bean id="transactionManager" class="org.springframework.transaction.jta.JtaTransactionManager">
* <property name="allowCustomIsolationLevels" value="true"/>
* </bean></pre>
*
* @author Juergen Hoeller
* @since 2.0.1
* @see #setTargetDataSources
* @see #setDefaultTargetDataSource
* @see org.springframework.transaction.TransactionDefinition#ISOLATION_READ_UNCOMMITTED
* @see org.springframework.transaction.TransactionDefinition#ISOLATION_READ_COMMITTED
* @see org.springframework.transaction.TransactionDefinition#ISOLATION_REPEATABLE_READ
* @see org.springframework.transaction.TransactionDefinition#ISOLATION_SERIALIZABLE
* @see org.springframework.transaction.jta.JtaTransactionManager
*/
public class IsolationLevelDataSourceRouter extends AbstractRoutingDataSource {
/** Constants instance for TransactionDefinition */
private static final Constants constants = new Constants(TransactionDefinition.class);
/**
* Supports Integer values for the isolation level constants
* as well as isolation level names as defined on the
* {@link org.springframework.transaction.TransactionDefinition TransactionDefinition interface}.
*/
protected Object resolveSpecifiedLookupKey(Object lookupKey) {
if (lookupKey instanceof Integer) {
return (Integer) lookupKey;
}
else if (lookupKey instanceof String) {
String constantName = (String) lookupKey;
if (constantName == null || !constantName.startsWith(DefaultTransactionDefinition.PREFIX_ISOLATION)) {
throw new IllegalArgumentException("Only isolation constants allowed");
}
return constants.asNumber(constantName);
}
else {
throw new IllegalArgumentException(
"Invalid lookup key - needs to be isolation level Integer or isolation level name String: " + lookupKey);
}
}
protected Object determineCurrentLookupKey() {
return TransactionSynchronizationManager.getCurrentTransactionIsolationLevel();
}
}