Execute before or after a spring transactional method

Spring provides a mechanism through which you can plugin some code which gets executed after the transaction is complete. We need to provide an implementation of the org.springframework.transaction.support.TransactionSynchronization interface which can be registered using TransactionSynchronizationManager. This could be useful in scenario where your code does not have a control over when the transaction starts and ends. For e.g. Your service code always joins an existing transaction started by the calling method (using REQUIRED PROPAGATION LEVEL).

Lets have a look at some sample code. Below sample captures one of the bulk report upload use case where each record in a database has a corresponding report (physical file). When the existing records are replaced with new records their corresponding reports would have to be deleted after the transaction successfully commits.

public class ServiceBean {

    @Transactional
    public void copyNewRecords(Collection<RecordInfo> recordInfo) {
        //read old file names
        //register the TransactionSynchronization object
        TransactionSynchronizationManager.registerSynchronization(new FileDeletionHandler(oldFileLists);
        //copy new records and their corresponding files
    }
}

public class FileDeletionHandler implements TransactionSynchronization {
    private List<File> filesToBeDeleted;

    public FileDeletionHandler(List<File> filesToBeDeleted) {
        this.filesToBeDeleted = filesToBeDeleted;
    }

    @Override
    public void suspend() {

    }

    @Override
    public void resume() {

    }

    @Override
    public void flush() {

    }

    @Override
    public void beforeCommit(boolean readOnly) {
    }

    @Override
    public void beforeCompletion() {
    }

    @Override
    public void afterCommit() {
        for(File file : filesToBeDeleted) {
            file.delete();
        }
    }

    @Override
    public void afterCompletion(int status) {
        //status could be either TransactionSynchronization.STATUS_COMMITTED or TransactionSynchronization.STATUS_ROLLED_BACK
        //or TransactionSynchronization.STATUS_UNKNOWN
    }
}

If you want to execute some code when the transaction rolls back, you could implement that in the afterCompletion() method and have a conditional check on the passed status parameter.

If you have a look at the TransactionSynchronizationManager implementation, you will notice that a List<TransactionSynchronization> objects are maintained in a ThreadLocal variable. This variable is initialized just after the transaction starts (using initSynchronization() method) and cleared when the transaction is suspended or ends.

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