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Using Transactions
This topic includes the following sections:
Note: This topic describes using the C++ interface to the CORBAservices Object Transaction service. For a complete description of all the transaction features available in the WebLogic Enterprise product and instructions for implementing the transaction features, see Using Transactions in the WebLogic Enterprise online documentation.
Overview of the Transaction Service
One of the most fundamental features of the WebLogic Enterprise product 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. The WebLogic Enterprise system 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.
The WebLogic Enterprise system includes the following:
The WebLogic Enterprise product provides a C++ interface to the OTS and a Java interface to the OTS via 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 TransactionCurrent environmental object. For information about using the TransactionCurrent environmental object, see CORBA C++ Programming Reference or CORBA Java Programming Reference in the WebLogic Enterprise online documentation.
Only the application-level demarcation interface (javax.transaction.UserTransaction) is supported. For information about JTA, refer to the following:
OTS, JTS, and JTA each provide the following support for your business transactions:
What Happens During a Transaction
Figure 6-1 illustrates how transactions work in a WebLogic Enterprise CORBA application.
Figure 6-1 How Transactions Work in a WebLogic Enterprise CORBA Application
A basic transaction works in the following way:
Transactions Sample Application
In the Transactions sample 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 invokes multiple individual operations on a database.
The Transactions sample application works in the following way:
Figure 6-2 illustrates how the Transactions sample application works.
Figure 6-2 Transactions Sample Application
The Transactions sample application shows two ways in which a transaction can be rolled back:
Note: For information about how transactions are implemented in WebLogic Enterprise CORBA Java applications, see the description of the XA Bankapp sample application in Using Transactions in the WebLogic Enterprise online documentation.
Development Steps
This topic describes the development steps for writing a WebLogic Enterprise CORBA application that includes transactions. Table 6-1 lists the development steps.
Table 6-1 Development Steps for WebLogic Enterprise CORBA Applications That Have Transactions
Step |
Description |
---|---|
1 |
Write the OMG IDL code for the transactional CORBA interface. |
2 |
Define the transaction policies for the CORBA interface in the Implementation Configuration file (ICF) for C++ WebLogic Enterprise CORBA applications, or in the Server Description File for Java WebLogic Enterprise CORBA client applications. |
3 |
Write the client application. |
4 |
Write the server application. |
5 |
Create a configuration file. |
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 Samples in the WebLogic Enterprise online documentation.
The XA Bankapp sample application demonstrates how to use transactions in Java WebLogic Enterprise CORBA applications. The source files for the XA Bankapp sample application are located in the \samples\corba\bankapp_java directory of the WebLogic Enterprise software. For information about building and running the XA Bankapp sample application, see Samples in the WebLogic Enterprise online documentation.
Step 1: Write the OMG IDL Code
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 may 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, the client application commits the transaction. You also need to define the TooManyCredits user exception.
Listing 6-1 includes the OMG IDL code for the Transactions sample application.
Listing 6-1 OMG IDL Code 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: Define 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. The transaction policies are:
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, as follows:
In the Transactions sample application, the transaction policy of the Registrar interface is set to always.
Step 3: Write the CORBA Client Application
The CORBA client application needs code that performs the following tasks:
Listing 6-2 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 the XA Bankapp sample application in Guide to the Java Sample Applications in the WebLogic Enterprise online documentation.
Listing 6-2 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 4: Write 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 CORBA application uses a database, you need to include code in the server application 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 6-3 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 application in Using Transactions in the WebLogic Enterprise online documentation.
For an example of a Java server application that implements transactions, see the description of the XA Bankapp sample application in Using Transactions in the WebLogic Enterprise online documentation.
Listing 6-3 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 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 5: Create a Configuration File
You need to add the following information to the configuration file for a transactional WebLogic Enterprise CORBA application.
Listing 6-4 includes the portions of the configuration file that define this information for the Transactions sample application.
Listing 6-4 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"
OPENINFO = "ORACLE_XA:Oracle_XA+Acc=P/scott/tiger
+SesTm=100+LogDir=.+MaxCur=5"
CLOSEINFO = ""
TMSNAME = "TMS_ORA"
*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 Creating a Configuration File in the WebLogic Enterprise online documentation.
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