using the j2ee connector architecture common client interface.htm

本人收集的关于Java Connector Architecture的资料

	// to invoke the ADDACCT stored procedure
	ix.execute(iSpec,iRec);
	// Close the connection to the database.
	closeCCIConnection(con);
}catch (ResourceException ex) {
	ex.printStackTrace();
}
}
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<h3>Executing a Local Transaction</h3>
<p>
The previous sections showed how to program with the CCI from an EJB that 
uses container-managed persistence. Because the EJB container ensured that the database 
access would take place within the context of a transaction, an <code>AcctManage</code> bean using 
container-managed persistence did not have to concern itself with these matters. The container 
handled starting and ending the transaction, making sure that the database record was 
updated without interference from other processes. 
</p>
<p>
However, if your bean uses bean-managed persistence, then it must handle its own transaction. 
An enterprise bean with bean-managed persistence uses methods from the <code>LocalTransaction</code> 
interface to handle local transactions. 
</p>
<p>
Keep in mind that resource managers typically support two types of transactions: XA 
transactions and local transactions. XA transactions refer to the Java mapping of the X/Open XA 
protocol. They are often called global transactions, because they can span multiple resource 
managers. Typically, XA transactions are managed by an external transaction manager 
located on the application server. 
</p>
<p>
Local transactions, on the other hand, are managed by the resource manager itself, and you 
can use the CCI API to handle a local transaction. To ensure the integrity of the data, add a 
record to the database from within the context of a transaction. To illustrate, look at the modified 
the <code>AcctManage</code> bean's <code>insertAcct</code> method that uses the CCI to start and commit, or rollback, a 
local transaction.  
</p>
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public void insertAcct(
String acctName, int amt) {
  try {
	Connection con = getCCIConnection();
	Interaction ix = con.createInteraction();
	CciInteractionSpec iSpec = 
	                new CciInteractionSpec();
	iSpec.setFunctionName("ADDACCT");
	iSpec.setSchema(user);
	iSpec.setCatalog(null);
	RecordFactory rf = cf.getRecordFactory();
	IndexedRecord iRec = 
	     rf.createIndexedRecord(
	     "InputRecord");
	boolean flag = iRec.add(acctName);
	flag = iRec.add(new Integer(amt));

	// Obtain a reference to a transaction 
	// context
	LocalTransaction transaction = 
	                con.getLocalTransaction();
	// Start the transaction
	transaction.begin();
	try {
		ix.execute(iSpec, iRec);
		// The operation was successful; 
		// commit the transaction
		transaction.commit();
	} catch (ResourceException e) {
		// An error occurred; rollback 
		// the transaction
		transaction.rollback();
	}

	closeCCIConnection(con);
}catch(ResourceException ex) {
	ex.printStackTrace();
}
}
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<p>
As you can see, most of the code of the <code>insertAcct</code> method is identical to the container-managed 
persistence version: Both versions do the following, in the 
same order:
</p>
<ul><li>Obtain a connection to the database.</li>
<li>Create an <code>Interaction</code> object.</li>
<li>Create and define properties for an object that implements the <code>InteractionSpec</code> interface. </li>
<li>Use the <code>ConnectionFactory</code> to obtain a reference to the <code>RecordFactory</code>.</li>
<li>Create an IndexedRecord input Record and sets the values for the two elements in the 
<code>Account</code> record: account name and amount.</li>
</ul>
<p>
At this point, the bean-managed persistence version deviates from the container-managed 
version. Before invoking the <code>Interaction</code> object's <code>execute</code> method, the bean first obtains a 
reference to a transaction. To do this, it invokes the <code>Connection</code> object's
<code>getLocalTransaction</code> 
method and instantiates a new <code>LocalTransaction</code> object. The <code>LocalTransaction</code> object 
provides the context for the transaction. Then, the bean starts the transaction by invoking the 
<code>LocalTransaction</code> object's <code>begin</code> method.
</p>
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  ...
  // Obtain a reference to a transaction context
  LocalTransaction transaction = 
	              con.getLocalTransaction();
  // Start the transaction
  transaction.begin();
  ...
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<p>
The bean can now safely do its transactional work. In this case, it invokes the Interaction 
object's <code>execute</code> method to execute the stored procedure <code>ADDACCT</code> and insert the new Account 
record into the database. The call to <code>execute</code> is the same as in the container-managed 
version, except that it is made from within a <code>try</code> block to catch any errors. If the call to <code>execute</code> 
is successful, then the bean commits the transaction. Otherwise, it rolls back the transaction 
to undo its actions. When a transaction is rolled back, any changes made to the database are 
undone and the database is restored to the state it was in prior to the start of the transaction. 
</p>
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	...
	try {
		ix.execute(iSpec, iRec);
		transaction.commit();
	} catch (ResourceException e) {
		transaction.rollback();
	}
	// Close the connection
	...
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<p>
The <code>insertAcct</code> method finishes by closing the connection.
</p>
<h3>Writing a CCI Client</h3>
<p>
A client application that relies on a CCI resource adapter is very much like any other J2EE 
client application. The AcctManageClient application uses the methods of the 
<code>AcctManageEJB</code> session bean to access the Account table in the underlying database. 
AcctManageClient invokes the <code>AcctManage getAcctAmt</code> method to read account amounts from the Account 
table and the <code>insertAcct</code> method to add records to the table.
</p>
<h2>Conclusion</h2>
<p>
By now, you should have a good understanding of how to use the J2EE Connector architecture's Common 
Client Interface API. You've seen how to use the different interfaces and classes defined by the
CCI to access a resource adapter for an underlying database or EIS. You've also seen how to use
these methods to invoke procedures stored in the EIS, and to pass parameters to these procedures and
receive values back.
</p>
<p>
The Connector architecture and the CCI are currently supported by a
significant number of J2EE-compliant EIS vendors and tools vendors.  It is
anticipated that most, if not all, J2EE-compliant EIS vendors will support
this technology. As its use becomes more widespread, and particularly as
more and more tools vendors build support of the CCI into their tools, it
will become the standard for J2EE enterprise application connectivity.
</p>
<p>
<img src="/images/coffeecup13x10.gif"  width="13" height="10" alt="Coffecup Logo">
</p>
<h4>About the Author</h4>
<p>
<em><strong>Beth Stearns</strong></em> is the principal partner of ComputerEase Publishing, a
computer consulting firm she founded in 1982. Her client list includes Sun
Microsystems, Inc., Silicon Graphics, Inc., Oracle Corporation, and Xerox
Corporation. Among her publications are the "Java Native
Interface" chapter in "The Java Tutorial Continued" book in the Addison
Wesley Java series, "The EJB Programming Guide" for Inprise Corporation,
and  "Understanding
EDT", a guide to Digital Equipment Corporation's text editor.  Most
recently, she is co-author with Vlada Matena of the forthcoming Addison
Wesley Java series book, "Applying Enterprise JavaBeans: Component-Based
Development for the J2EE Platform."
</p>
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