（參考并轉(zhuǎn)載自http://blog.donews.com/Ralph/archive/2004/11/18/174646.aspx）
關(guān)于分布式事務(wù)，我覺(jué)得有必要了解清楚以下幾點(diǎn)：
（1）目前流行的分布式事務(wù)協(xié)議DTP，
（2）Java如何定義實(shí)現(xiàn)規(guī)范
（3）常用的第三方JTA以及使用配置方法
1.分布式事務(wù)的協(xié)議：DTP 和 Two - Phase Commit Protocol
在分布式事務(wù)管理領(lǐng)域，X/Open的DTP模型是業(yè)界最被廣泛接受分布式事務(wù)管理模型。幾乎所有的事務(wù)處理產(chǎn)品，關(guān)系數(shù)據(jù)庫(kù)以及消息產(chǎn)品都支持該DTP模型中定義的接口。下面是對(duì)DTP模型的一段描述：
X/Open’s
DTP model defines three components: application programs, resource
managers(such as RDBMS), and a transaction manager. This model also
specifies functional interfaces between application programs and the
transaction manager (known as the TX interface), and between the
transaction manager and the resource managers (the XA interface). With
products complying to these interfaces, one can implement transactions
with the two phase commit and recovery protocol to preserve atomicity
of transactions.
DTP 模型中有一個(gè)非常重要的模型，叫Two - Phase Commit
Protocol。該協(xié)議作用于transaction manager和resource managers之間，保證所有的resource
managers要么都commit, 要么都abort。
具體的TPC protocol執(zhí)行過(guò)程如下：
The first
phase of this protocol is the preparation phase, during which the
transaction manager conducts a voting among all the resource managers
registered for the target transaction. The transaction manager calls
the prepare method on each resource manager, which will return a
X_READONLY or XA_OK constant. The first value implies that the
operations conducted on the target resource are read only, and there
are no operations to be committed. The second value indicates that the
resource manager is ready to commit the operations. In case the
resource manager wants the transaction to be rolled back, it throws an
appropriate XAException.
The second phase is a commit or recover
phase. Depending on whether all resource managers are ready for a
commit or not, one of these phases will be invoked by the transaction
manager. In case all the resource managers return a X_OK in the first
phase, the transaction manager calls the commit method on each resource
manager. Please note that the two phase protocol is not fool-proof, and
the commit calls may throw appropriate XAException in return. In such a
case, the transaction manager should initiate the recovery phase. In
case the voting determines a rollback, the transaction calls the
recover on each prepared resource manager.
2. Java Transaction Service
sun并未提供Java Persistence API的實(shí)現(xiàn)，只是定義了一套接口和規(guī)范。Java的事務(wù)實(shí)現(xiàn)構(gòu)架遵循了DTP模型，主要有兩部分組成：JTS(Java Transaction Service)和JTA(Java Transaction API)。JTS主要規(guī)定了DTP模型中transaction manager的實(shí)現(xiàn)方式，而JTA則定義了application programs, transaction manager及resource manager之間的接口。
JTA可以分為三類(lèi)， 分別為針對(duì)application接口，transaction manager接口和resource manager接口。
（1）application接口包括：
javax.transaction.Synchronization：An
object intended to participate in a synchronization protocol with the
transaction manager should implement this interface. This mechanism is
based on the Observer pattern. This interface has two methods -
beforeCompletion and afterCompletion to be called before starting and
after completing, respectively, the two phase commit operation.
（2）transaction manager接口：
javax.transaction.Status:
Defines the flags for the status of a transaction. The
javax.transaction.Transaction, javax.transaction.TransactionManager,
and javax.transaction.UserTransaction interfaces provide a getStatus
method that returns one of the above status flags.
javax.transaction.Transaction:
An object of this type is created for each global transaction. This
interface provides methods for transaction completion(commit and
rollback), resource enlistment (enlistResource) and delistment
(delistResource), registration of synchronization objects
(registerSynchronization), and query of status of the transaction
(getStatus).
javax.transaction.TransactionManager: This
interface is implemented by the JTS and allows an application server to
communicate with the transaction manager to demarcate transactions
(begin, commit, rollback, suspend and resume), set the transaction for
rollback (setRollbackOnly), get the associated Transaction object
(getTransaction), set the transaction timeout interval
(setTransactionTimeout) and query the status of the transaction
(getStatus).
javax.transaction.UserTransaction: This interface
allows application components to manage transaction boundaries
explicitly. This interface provides methods to begin and end
transactions (begin, commit, and rollback), set the transaction for
rollback (setRollbackOnly), set the transaction timeout interval
(setTransactionTimeout), and get the status of the transaction
(getStatus). The application server should provide an interface to
create an object of this type.
javax.transaction.xa.Xid: This
interface is a Java mapping of the X/Open transaction identifier xid
structure. The transaction manager uses an object of this type to
associate a resource manager with a transaction.
（3）resource manager接口：
javax.transaction.xa.XAResource:
This is a Java mapping of the X/Open XA interface, and is implemented
by resource managers operating with the JTS. This interface provides
methods to start (start) and end (end) work on behalf of a specified
transaction, to prepare a transaction with the current resource
(prepare), to end transactions with the current resource (commit,
forget, recover, and rollback), to compare the current resource manager
with another resource manager (isSameRM), and to get and set the
transaction timeout (getTransactionTimeout, setTransactionTimeout).
使用JTA進(jìn)行分布式事務(wù)編程有兩種方法，一種是通過(guò)javax.transaction.UserTransaction,另一種是通過(guò)javax.transaction.TransactionManager。但這兩種方法之間的區(qū)別不是很清楚？
運(yùn)用javax.transaction.UserTransaction(以Weblogic6.1為例)：
//get UserTransaction
//in websphere, jndi name is “java:comp/UserTransaction”
UserTransaction userTrans = (UserTransaction)getInitialContext().lookup("javax.transaction.UserTransaction");
//begin transaction
userTrans.begin();
//transactional operations
…
//end transaction
userTrans.commit();
運(yùn)用javax.transaction.TransactionManager(以Weblogic6.1為例)：
//get UserTransaction
UserTransaction transManager = (UserTransaction)getInitialContext().lookup("javax.transaction.TransactionManager");
//begin transaction
Transaction trans = transManager.begin();
//transactional operations
…
//end transaction
transManager.commit();
Transaction
對(duì)象封裝了事務(wù)上下文，通過(guò)該對(duì)象的enlistResource()，delistResource()方法可以添加刪除參與事務(wù)的resource
manager, 通過(guò)registerSynchronization()方法可以注冊(cè)監(jiān)聽(tīng)對(duì)象。
3. AtomikosTransactionsEssentials簡(jiǎn)介
關(guān)于這一點(diǎn)可以參考：http://momoko8443.javaeye.com/blog/190994