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Introducing Transactions
This topic includes the following sections:
Overview of Transactions in WebLogic Enterprise Applications
This topic includes the following sections:
ACID Properties of Transactions
One of the most fundamental features of the WebLogic Enterprise system is transaction management. Transactions are a means to guarantee that database transactions are completed accurately and that they take on all the ACID properties (atomicity, consistency, isolation, and durability) of a high-performance transaction. WebLogic Enterprise protects the integrity of your transactions by providing a complete infrastructure for ensuring that database updates are done accurately, even across a variety of resource managers (RMs). If any one of the operations fails, the entire set of operations is rolled back.
Supported Programming Models
WebLogic Enterprise supports transactions in two different programming models:
WebLogic Enterprise supports two transaction API models:
WebLogic Enterprise provides a C++ interface to the OTS and a Java interface to the OTS and the JTS. The JTS is the Sun Microsystems, Inc. Java interface for transaction services, and is based on the OTS. The OTS and the JTS are accessed through the org.omg.CosTransactions.Current environmental object. For information about using the TransactionCurrent environmental object, see the C++ Bootstrap Object Programming Reference or the Java Bootstrap Object Programming Reference.
Only the application-level demarcation interface (javax.transaction.UserTransaction) is supported. For information about JTA, see the following sources:
Support for Business Transactions
OTS, JTS, and JTA each provide the following support for your business transactions:
Distributed Transactions and the Two-Phase Commit Protocol
WebLogic Enterprise supports distributed transactions and the two-phase commit protocol for enterprise applications. A distributed transaction is a transaction that updates multiple resource managers (such as databases) in a coordinated manner. The two-phase commit protocol (2PC) is a method of coordinating a single transaction across one or more resource managers. It guarantees data integrity by ensuring that transactional updates are committed in all of the participating databases, or are fully rolled back out of all the databases, reverting to the state prior to the start of the transaction.
When to Use Transactions
Transactions are appropriate in the situations described in the following list. Each situation describes a transaction model supported by the WebLogic Enterprise system.
For example, consider a travel agent application. The client application needs to arrange for a journey to a distant location; for example, from Strasbourg, France, to Alice Springs, Australia. Such a journey would inevitably require multiple individual flight reservations. The client application works by reserving each individual segment of the journey in sequential order; for example, Strasbourg to Paris, Paris to New York, New York to Los Angeles. However, if any individual flight reservation cannot be made, the client application needs a way to cancel all the flight reservations made up to that point.
For example, consider an Internet-based online shopping cart application. Users of the client application browse through an online catalog and make multiple purchase selections. When the users are done choosing all the items they want to buy, they proceed to check out and enter their credit card information to make the purchase. If the credit card check fails, the shopping application needs a way to cancel all the pending purchase selections in the shopping cart, or roll back any purchase transactions made during the conversation.
For example, consider a banking application. The client invokes the transfer operation on a teller object. The transfer operation requires the teller object to make the following invocations on the bank database:
If the credit invocation on the bank database fails, the banking application needs a way to roll back the previous debit invocation.
What Happens During a Transaction
This topic includes the following sections:
Transactions in WebLogic Enterprise CORBA Applications
Figure 1-1 illustrates how transactions work in a WebLogic Enterprise CORBA application.
Figure 1-1 How Transactions Work in a WebLogic Enterprise CORBA Application
For CORBA applications, a basic transaction works in the following way:
Transactions in WebLogic Enterprise EJB Applications
Figure 1-2 illustrates how transactions work in a WebLogic Enterprise EJB application.
Figure 1-2 How Transactions Work in a WebLogic Enterprise EJB Application
WebLogic Enterprise supports two types of transactions in WebLogic Enterprise EJB applications:
The sequence of transaction events differs between container-managed and bean-managed transactions.
Container-managed Transactions
For EJB applications with container-managed transactions, a basic transaction works in the following way:
Note: Calling the EJBContext.SetRollbackOnly method is allowed only for methods that have a meaningful transaction context.
You can control transaction timeouts by setting the trans-timeout-seconds element in the weblogic-ejb-extensions.xml file. For more information about the weblogic-ejb-extensions.xml file, see the WebLogic Enterprise EJB XML Reference. You can also change this setting with the WebLogic Enterprise EJB Deployer, as described in Using the WebLogic Enterprise EJB Deployer.
Bean-managed Transactions
For EJB applications with bean-managed transaction demarcations, a basic transaction works in the following way:
Transactions in WebLogic Enterprise RMI Applications
Figure 1-3 illustrates how transactions work in a WebLogic Enterprise RMI application.
Figure 1-3 How Transactions Work in a WebLogic Enterprise RMI Application
For RMI client and server applications, a basic transaction works in the following way:
Obtaining the object reference begins a conversational state between the application and that object. The conversational state continues until the transaction is completed (committed or rolled back). Once instantiated, RMI objects remain active in memory until they are released (typically during server shutdown). For the duration of the transaction, the WebLogic Enterprise infrastructure does not perform any deactivation or activation.
For guidelines about using transactions in RMI applications, see Transactions in RMI Applications.
Transactions Sample Code
This topic includes the following sections:
Transactions Sample CORBA Application
In the Transactions sample CORBA application, the operation of registering for courses is executed within the scope of a transaction. The transaction model used in the Transactions sample application is a combination of the conversational model and the model in which a single client invocation makes multiple individual operations on a database.
Workflow for the Transactions Sample Application
The Transactions sample application works in the following way:
Figure 1-4 illustrates how the Transactions sample application works.
Figure 1-4 Transactions Sample Application
The Transactions sample application shows two ways in which a transaction can be rolled back:
Thus, the Transactions sample application also shows how to implement user-defined CORBA exceptions. For example, if the student tries to register for a course that would exceed the maximum number of courses for which the student can register, the server application returns the TooManyCredits exception. When the client application receives this exception, the client application rolls back the transaction automatically.
Note: For information about how transactions are implemented in CORBA/Java WebLogic Enterprise applications, see the Transactions Sample in the WebLogic Enterprise online documentation.
This topic describes the following development steps for writing a WebLogic Enterprise application that contains transaction processing code:
The Transactions sample application is used to demonstrate these development steps. The source files for the Transactions sample application are located in the \samples\corba\university directory of the WebLogic Enterprise software. For information about building and running the Transactions sample application, see the Transactions Sample in the WebLogic Enterprise online documentation.
The XA Bankapp sample application demonstrates how to use transactions in Java WebLogic Enterprise applications. The source files for the XA Bankapp sample application are located in the \samples\corba\bankapp_java\XA directory of the WebLogic Enterprise software. For information about building and running the XA Bankapp sample application, see the Bankapp Sample Using XA in the WebLogic Enterprise online documentation.
Step 1: Writing the OMG IDL
You need to specify interfaces involved in transactions in Object Management Group (OMG) Interface Definition Language (IDL) just as you would any other CORBA interface. You must also specify any user exceptions that might occur from using the interface.
For the Transactions sample application, you would define in OMG IDL the Registrar interface and the register_for_courses() operation. The register_for_courses() operation has a parameter, NotRegisteredList, which returns to the client application the list of courses for which registration failed. If the value of NotRegisteredList is empty, then the client application commits the transaction. You also need to define the TooManyCredits user exception.
Listing 1-1 includes the OMG IDL for the Transactions sample application.
Listing 1-1 OMG IDL for the Transactions Sample Application
#pragma prefix "beasys.com"
module UniversityT
{
typedef unsigned long CourseNumber;
typedef sequence<CourseNumber> CourseNumberList;
struct CourseSynopsis
{
CourseNumber course_number;
string title;
};
typedef sequence<CourseSynopsis> CourseSynopsisList;
interface CourseSynopsisEnumerator
{
//Returns a list of length 0 if there are no more entries
CourseSynopsisList get_next_n(
in unsigned long number_to_get, // 0 = return all
out unsigned long number_remaining
);
void destroy();
};
typedef unsigned short Days;
const Days MONDAY = 1;
const Days TUESDAY = 2;
const Days WEDNESDAY = 4;
const Days THURSDAY = 8;
const Days FRIDAY = 16;
}
//Classes restricted to same time block on all scheduled days,
//starting on the hour
struct ClassSchedule
{
Days class_days; // bitmask of days
unsigned short start_hour; // whole hours in military time
unsigned short duration; // minutes
};
struct CourseDetails
{
CourseNumber course_number;
double cost;
unsigned short number_of_credits;
ClassSchedule class_schedule;
unsigned short number_of_seats;
string title;
string professor;
string description;
};
typedef sequence<CourseDetails> CourseDetailsList;
typedef unsigned long StudentId;
struct StudentDetails
{
StudentId student_id;
string name;
CourseDetailsList registered_courses;
};
enum NotRegisteredReason
{
AlreadyRegistered,
NoSuchCourse
};
struct NotRegistered
{
CourseNumber course_number;
NotRegisteredReason not_registered_reason;
};
typedef sequence<NotRegistered> NotRegisteredList;
exception TooManyCredits
{
unsigned short maximum_credits;
};
//The Registrar interface is the main interface that allows
//students to access the database.
interface Registrar
{
CourseSynopsisList
get_courses_synopsis(
in string search_criteria,
in unsigned long number_to_get,
out unsigned long number_remaining,
out CourseSynopsisEnumerator rest
);
CourseDetailsList get_courses_details(in CourseNumberList
courses);
StudentDetails get_student_details(in StudentId student);
NotRegisteredList register_for_courses(
in StudentId student,
in CourseNumberList courses
) raises (
TooManyCredits
);
};
// The RegistrarFactory interface finds Registrar interfaces.
interface RegistrarFactory
{
Registrar find_registrar(
);
};
Step 2: Defining Transaction Policies for the Interfaces
Transaction policies are used on a per-interface basis. During design, it is decided which interfaces within a WebLogic Enterprise application will handle transactions. Table 1-1 describes the CORBA transaction policies.
Transaction Policy |
Description |
---|---|
always |
The interface must always be part of a transaction. If the interface is not part of a transaction, a transaction will be automatically started by the TP Framework. |
ignore |
The interface is not transactional. However, requests made to this interface within a scope of a transaction are allowed. The AUTOTRAN parameter, specified in the UBBCONFIG file for this interface, is ignored. |
never |
The interface is not transactional. Objects created for this interface can never be involved in a transaction. The WebLogic Enterprise system generates an exception (INVALID_TRANSACTION) if an interface with this policy is involved in a transaction. |
optional |
The interface may be transactional. Objects can be involved in a transaction if the request is transactional. This transaction policy is the default. |
During development, you decide which interfaces will execute in a transaction by assigning transaction policies in the following ways:
In the Transactions sample application, the transaction policy of the Registrar interface is set to always.
Step 3: Writing the Server Application
When using transactions in server applications, you need to write methods that implement the interface's operations. In the Transactions sample application, you would write a method implementation for the register_for_courses() operation.
If your WebLogic Enterprise application uses a database, you need to include in the server application code that opens and closes an XA Resource Manager. These operations are included in the Server::initialize() and Server::release() operations of the Server object. Listing 1-2 shows the portion of the code for the Server object in the Transactions sample application that opens and closes the XA Resource Manager.
Note: For a complete example of a C++ server application that implements transactions, see the Transactions Sample in the WebLogic Enterprise online documentation. For an example of a Java server application that implements transactions, see Bankapp Sample Using XA in the WebLogic Enterprise online documentation.
Listing 1-2 C++ Server Object in Transactions Sample Application
CORBA::Boolean Server::initialize(int argc, char* argv[])
{
TRACE_METHOD("Server::initialize");
try {
open_database();
begin_transactional();
register_fact();
return CORBA_TRUE;
}
catch (CORBA::Exception& e) {
LOG("CORBA exception : " <<e);
}
catch (SamplesDBException& e) {
LOG("Can't connect to database");
}
catch (...) {
LOG("Unexpected database error : " <<e);
}
catch (...) {
LOG("Unexpected exception");
}
cleanup();
return CORBA_FALSE;
}
void Server::release()
{
TRACE_METHOD("Server::release");
cleanup();
}
static void cleanup()
{
unregister_factory();
end_transactional();
close_database();
}
//Utilities to manage transaction resource manager
CORBA::Boolean s_became_transactional = CORBA_FALSE;
static void begin_transactional()
{
TP::open_xa_rm();
s_became_transactional = CORBA_TRUE;
}
static void end_transactional()
{
if(!s_became_transactional){
return//cleanup not necessary
}
try {
TP::close_xa_rm ();
}
catch (CORBA::Exception& e) {
LOG("CORBA Exception : " << e);
}
catch (...) {
LOG("unexpected exception");
}
s_became_transactional = CORBA_FALSE;
}
Step 4: Writing the Client Application
The client application needs code that performs the following tasks:
Listing 1-3 illustrates the portion of the CORBA C++ client applications in the Transactions sample application that illustrates the development steps for transactions.
For an example of a CORBA Java client application that uses transactions, see Bankapp Sample Using XA in the WebLogic Enterprise online documentation. For an example of using transactions in an ActiveX client application, see Transactions in CORBA Client Applications.
Listing 1-3 Transactions Code for CORBA C++ Client Applications
CORBA::Object_var var_transaction_current_oref =
Bootstrap.resolve_initial_references("TransactionCurrent");
CosTransactions::Current_var transaction_current_oref=
CosTransactions::Current::_narrow(var_transaction_current_oref.in());
//Begin the transaction
var_transaction_current_oref->begin();
try {
//Perform the operation inside the transaction
pointer_Registar_ref->register_for_courses(student_id, course_number_list);
...
//If operation executes with no errors, commit the transaction:
CORBA::Boolean report_heuristics = CORBA_TRUE;
var_transaction_current_ref->commit(report_heuristics);
}
catch (...) {
//If the operation has problems executing, rollback the
//transaction. Then throw the original exception again.
//If the rollback fails,ignore the exception and throw the
//original exception again.
try {
var_transaction_current_ref->rollback();
}
catch (...) {
TP::userlog("rollback failed");
}
throw;
}
Step 5: Creating a Configuration File
You need to add the following information to the configuration file for a transactional WebLogic Enterprise application:
Listing 1-4 includes the portions of the configuration file that define this information for the Transactions sample application.
Listing 1-4 Configuration File for Transactions Sample Application
*RESOURCES
IPCKEY 55432
DOMAINID university
MASTER SITE1
MODEL SHM
LDBAL N
SECURITY APP_PW
*MACHINES
BLOTTO
LMID = SITE1
APPDIR = C:\TRANSACTION_SAMPLE
TUXCONFIG=C:\TRANSACTION_SAMPLE\tuxconfig
TLOGDEVICE=C:\APP_DIR\TLOG
TLOGNAME=TLOG
TUXDIR="C:\WLEdir"
MAXWSCLIENTS=10
*GROUPS
SYS_GRP
LMID = SITE1
GRPNO = 1
ORA_GRP
LMID = SITE1
GRPNO = 2
OPENINFO = "ORACLE_XA:Oracle_XA+SqlNet=ORCL+Acc=P
/scott/tiger+SesTm=100+LogDir=.+MaxCur=5"
CLOSEINFO = ""
TMSNAME = "TMS_ORA"
TMSCOUNT = 2
*SERVERS
DEFAULT:
RESTART = Y
MAXGEN = 5
TMSYSEVT
SRVGRP = SYS_GRP
SRVID = 1
TMFFNAME
SRVGRP = SYS_GRP
SRVID = 2
CLOPT = "-A -- -N -M"
TMFFNAME
SRVGRP = SYS_GRP
SRVID = 3
CLOPT = "-A -- -N"
TMFFNAME
SRVGRP = SYS_GRP
SRVID = 4
CLOPT = "-A -- -F"
TMIFRSVR
SRVGRP = SYS_GRP
SRVID = 5
UNIVT_SERVER
SRVGRP = ORA_GRP
SRVID = 1
RESTART = N
ISL
SRVGRP = SYS_GRP
SRVID = 6
CLOPT = -A -- -n //MACHINENAME:2500
*SERVICES
For information about the transaction log and defining parameters in the Configuration file, see Administering Transactions.
Transactions Sample EJB Code
This topic provides a walkthrough of sample code fragments from a class in an EJB application. This topic includes the following sections:
The code fragments demonstrate using the UserTransaction object for bean-managed transaction demarcation. The deployment descriptor for this bean specifies the transaction type (transaction-type element) for transaction demarcation (Bean).
Note: These code fragments do not derive from any of the sample applications that ship with WebLogic Enterprise. They merely illustrate the use of the UserTransaction object within an EJB application.
Importing Packages
Listing 1-5 shows importing the necessary packages for transactions, including:
Listing 1-5 Importing Packages
import javax.naming.*;
import javax.transaction.UserTransaction;
import javax.transaction.SystemException;
import javax.transaction.HeuristicMixedException
import javax.transaction.HeuristicRollbackException
import javax.transaction.NotSupportedException
import javax.transaction.RollbackException
import javax.transaction.IllegalStateException
import javax.transaction.SecurityException
Initializing the UserTransaction Object
Listing 1-6 shows initializing an instance of the UserTransaction object to null.
Listing 1-6 Initializing the UserTransaction Object
UserTransaction tx = null;
Using JNDI to Return an Object Reference to the UserTransaction Object
Listing 1-7 shows searching the JNDI tree to return an object reference to the UserTransaction object for the appropriate WebLogic Enterprise domain.
Listing 1-7 Performing a JDNI Lookup
try {
Context ctx = getInitialContext();
tx = (UserTransaction)ctx.lookup("java:comp/UserTransaction");
Starting a Transaction
Listing 1-8 shows starting a transaction by calling the javax.transaction.UserTransaction.begin method. Database operations that occur after this method invocation and prior to completing the transaction exist within the scope of this transaction.
Listing 1-8 Starting a Transaction
tx.begin();
Completing a Transaction
Listing 1-9 shows completing the transaction depending on whether an exception was thrown during any of the database operations that were attempted within the scope of this transaction:
Listing 1-9 Completing a Transaction
if(gotException){
try{
tx.rollback();
}catch(Exception e){}
}
elseif{
tx.commit();
}
This topic provides a walkthrough of sample code fragments from a class in an RMI application. This topic includes the following sections:
The code fragments demonstrate using the UserTransaction object for RMI transactions. For guidelines about using transactions in RMI applications, see Transactions in RMI Applications.
Note: These code fragments do not derive from any of the sample applications that ship with WebLogic Enterprise. They merely illustrate the use of the UserTransaction object within an RMI application.
Importing Packages
Listing 1-10 shows importing the necessary packages, including the following packages used to handle transactions:
Listing 1-10 Importing Packages
import javax.naming.*;
import java.rmi.*;
import javax.transaction.UserTransaction;
import javax.transaction.SystemException;
import javax.transaction.HeuristicMixedException
import javax.transaction.HeuristicRollbackException
import javax.transaction.NotSupportedException
import javax.transaction.RollbackException
import javax.transaction.IllegalStateException
import javax.transaction.SecurityException
Initializing the UserTransaction Object
Listing 1-11 shows initializing an instance of the UserTransaction object to null.
Listing 1-11 Initializing the UserTransaction Object
UserTransaction tx = null;
Using JDNI to Return an Object Reference to the UserTransaction Object
Listing 1-12 shows searching the JNDI tree to return an object reference to the UserTransaction object for the appropriate WebLogic Enterprise domain.
Note: Obtaining the object reference begins a conversational state between the application and that object. The conversational state continues until the transaction is completed (committed or rolled back). Once instantiated, RMI objects remain active in memory until they are released (typically during server shutdown). For the duration of the transaction, the WebLogic Enterprise infrastructure does not perform any deactivation or activation.
Listing 1-12 Performing a JDNI Lookup
try {
Context ctx = getInitialContext();
tx = (UserTransaction)ctx.lookup("java:comp/UserTransaction");
Starting a Transaction
Listing 1-13 shows starting a transaction by calling the javax.transaction.UserTransaction.begin method. Database operations that occur after this method invocation and prior to completing the transaction exist within the scope of this transaction.
Listing 1-13 Starting a Transaction
tx.begin();
Completing a Transaction
Listing 1-14 shows completing the transaction depending on whether an exception was thrown during any of the database operations that were attempted within the scope of this transaction:
Listing 1-14 Completing a Transaction
if(gotException){
try{
tx.rollback();
}catch(Exception e){}
}
elseif{
tx.commit();
}
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