Spring Transaction Management

• Declarative Transaction Management

• Declarative transaction management is the most common Spring implementation as it has the least impact on application code.
• The XML declarative approach configures the transaction attributes in a Spring bean configuration file. Declarative transaction management in Spring has the advantage of being less invasive. 
•  There is no need for changing application code when using declarative transactions.       All you have to do is to modify the application context.
• Methods
•  XML based
• Annotations based
• Steps
• Step 1: Define a transaction manager in spring.xml
• <bean class="org.springframework.jdbc.datasource.DataSourceTransactionManager" id="txManager"/>
• Step 2: Turn on support for transaction annotations in spring.xml
• <tx:annotation-driven transaction-manager="txManager"/>
•  Step 3: Add the @Transactional annotation to the createEmployee Method      @Transactional
• public int createEmployee(Employee employee) {

..

• Annotation attributes
• Transaction readOnly
• If you don’t explicitly set readOnly attribute to true, you will have read/write transactions.Its always better to explicitly specify the readOnly attribute, as we have noticed some massive performance improvements with Hibernate because of this.
• Transaction propagation
• Transaction propagation is REQUIRED by default, which means that the same transaction will propagate from a transactional caller to transactional callee. It will create a new transaction or reuse the one if available. For example, if a read-only transaction calls a read-write transaction method, the whole transaction will be read-only.
• Depending on the transaction propagation attribute (like for REQUIRES_NEW), sometimes the existing transaction is suspended/paused at some point, a new one is always started and eventually committed, and after that the first transaction is resumed.
• Isolation Level
• Isolation level defines a contract between transactions.
• Read Uncommitted – Allows dirty reads, when a transaction is not yet committed by a thread and another thread is reading the dirty data.
• Read Committed – Does not allow dirty reads. Only lets a thread to read values which have already been committed by other running transactions in another threads.
• Repeatable Read – If the same data is read twice in the same transaction, it will always be the same. This level guarantees that any data once read cannot change.
• Serializable – Transactions occur with locking at all levels (read, range and write locking), because of which they are executed in a fixed sequence. It doesn’t allow concurrent transactions and leads to a performance hit.

•  Programmatic Transaction Management
• Spring provides Support for programmatic transaction management by using TransactionTemplate or PlatformTransactionManager implementation.