java Spring Shard datasource with Mysql/Oracle

If you are implementing database sharding and using Spring JDBC then you are out of luck to using declarative transactions and find a Datasource with Spring that would handle sharding. I had to implement my own Datasource manager and own annotations to use declarative kind of transactions to hide complexities from average developers.  Its very important to abstract out cross cutting concerns as sharding and transactions so that any junior developers wont be confused and start copying code left and right without understanding the impact of their changes globally. 

So the idea is that
1) You would implement a ShardDataSourceManager that would be basically pool of connection pools and you would lookup a datasource by shard id.
2)You would define your own Transactional annotations and annotate methods with it
3) You need to write an interceptor at dao layer that would read annotations on method and some context info. From the context info you would lookup shard id and lookup datasource and inject into a thread local.
4)The dao layer when it looks up datasource would look into thread local to construct a jdbc template and execute queries on it.

Here is a sample ShardDataSourceManager, ShardTransactional Annotation

public @interface ShardTransactional {
      public abstract boolean readOnly() default false;

}

public class ShardTransactionInterceptor implements MethodInterceptor {
    private static final AppLogger logger = AppLogger.getLogger(ShardTransactionInterceptor.class);
    private static ThreadLocal dataSourceThreadLocal = new ThreadLocal();
    private ShardDataSourceManager shardDataSourceManager;
   
    public ShardDataSourceManager getShardDataSourceManager() {
        return shardDataSourceManager;
    }

    public void setShardDataSourceManager(ShardDataSourceManager shardDataSourceManager) {
        this.shardDataSourceManager = shardDataSourceManager;
    }


    @Override
    public Object invoke(final MethodInvocation method) throws Throwable {
        if (method.getMethod().isAnnotationPresent(ShardTransactional.class)) {
            try {
                ShardTransactional annotation = method.getMethod().getAnnotation(ShardTransactional.class);
                User user = getParam(method, User.class);
                if (user == null) {
                    throw new IllegalStateException("All transactional methods must have user argument");
                }
                TransactionTemplate transactionTemplate = new TransactionTemplate();
                boolean readOnly = annotation.readOnly();
                transactionTemplate.setReadOnly(readOnly);
                ShardInfo shardInfo =  getShardInfo(user);
                transactionTemplate.setName("ShardTransaction");
                transactionTemplate.setTransactionManager(shardDataSourceManager.getTransactionManagerByHostId(shardInfo.getHostId(), readOnly));
                cacheDataSourceInThreadLocal(shardInfo.getHostId(),readOnly);
                return transactionTemplate.execute(new TransactionCallback