/*
 * Copyright 2002-2018 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.lang.Nullable;
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 TransactionDefinition interface. 
This is particularly useful in combination with JTA transaction management (typically through Spring's 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. 
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":
<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>
 Alternatively, the keyed values can also be data source names, to be resolved through a 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. 
<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>
 Note: If you are using this router in combination with Spring's 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.) 
<bean id="transactionManager" class="org.springframework.transaction.jta.JtaTransactionManager">
  <property name="allowCustomIsolationLevels" value="true"/>
</bean>
Author:
Juergen Hoeller
See Also:
AbstractRoutingDataSource.setTargetDataSources
AbstractRoutingDataSource.setDefaultTargetDataSource
TransactionDefinition.ISOLATION_READ_UNCOMMITTED
TransactionDefinition.ISOLATION_READ_COMMITTED
TransactionDefinition.ISOLATION_REPEATABLE_READ
TransactionDefinition.ISOLATION_SERIALIZABLE
JtaTransactionManager
Since:
2.0.1/**
 * 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 class="code">
 * &lt;bean id="dataSourceRouter" class="org.springframework.jdbc.datasource.lookup.IsolationLevelDataSourceRouter"&gt;
 *   &lt;property name="targetDataSources"&gt;
 *     &lt;map&gt;
 *       &lt;entry key="ISOLATION_REPEATABLE_READ" value-ref="myRepeatableReadDataSource"/&gt;
 *       &lt;entry key="ISOLATION_SERIALIZABLE" value-ref="mySerializableDataSource"/&gt;
 *     &lt;/map&gt;
 *   &lt;/property&gt;
 *   &lt;property name="defaultTargetDataSource" ref="myDefaultDataSource"/&gt;
 * &lt;/bean&gt;</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 class="code">
 * &lt;bean id="dataSourceRouter" class="org.springframework.jdbc.datasource.lookup.IsolationLevelDataSourceRouter"&gt;
 *   &lt;property name="targetDataSources"&gt;
 *     &lt;map&gt;
 *       &lt;entry key="ISOLATION_REPEATABLE_READ" value="java:comp/env/jdbc/myrrds"/&gt;
 *       &lt;entry key="ISOLATION_SERIALIZABLE" value="java:comp/env/jdbc/myserds"/&gt;
 *     &lt;/map&gt;
 *   &lt;/property&gt;
 *   &lt;property name="defaultTargetDataSource" value="java:comp/env/jdbc/mydefds"/&gt;
 * &lt;/bean&gt;</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 class="code">
 * &lt;bean id="transactionManager" class="org.springframework.transaction.jta.JtaTransactionManager"&gt;
 *   &lt;property name="allowCustomIsolationLevels" value="true"/&gt;
 * &lt;/bean&gt;</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. /** 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 TransactionDefinition interface. /**
	 * 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}.
	 */
	@Override
	protected Object resolveSpecifiedLookupKey(Object lookupKey) {
		if (lookupKey instanceof Integer) {
			return lookupKey;
		}
		else if (lookupKey instanceof String) {
			String constantName = (String) lookupKey;
			if (!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);
		}
	}

	@Override
	@Nullable
	protected Object determineCurrentLookupKey() {
		return TransactionSynchronizationManager.getCurrentTransactionIsolationLevel();
	}

}