How to find a block containing a transaction using transaction hash only? Well, the title says it all.
I have  a transaction hash and I want to find this transaction in the blockchain.
I am working with bitcoinj.

I am probably missing something very obvious here, but I cannot find how to do it.
The transaction does not know the block in which it was integrated.

https://en.bitcoin.it/wiki/Protocol_specification#tx

There are many services around like blockchain.info or blockexplorer.com which stores the blockchain and have indexed all transactions, which you can search.