Using ABAP

63 Pages·2005·0.9 MB·English

NetWeaver Developer’s Guide
Release: SAP NetWeaver 2004s

Using ABAP
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Contents

1 USING ABAP.....................................................................................................................1
2 GETTING INVOLVED........................................................................................................2
2.1 The Origins of ABAP – an Overview.........................................................................2
2.2 ABAP and Its Infrastructure.......................................................................................3
2.3 ABAP and the SAP NW Application Server..............................................................4
3 GO AND CREATE.............................................................................................................5
3.1 Creating a Database Table and Data Elements.......................................................6
3.2 Creating a Database Table – Part 1.........................................................................6
3.3 Creating Data Elements............................................................................................7
3.4 Creating a Database Table – Part 2.........................................................................8
3.5 Defining the Basic Attributes of a Global Class......................................................10
3.6 Methods, Types, and Attributes of a Global Class..................................................11
4 CORE DEVELOPMENT TASKS.....................................................................................16
4.1 UI Technology.........................................................................................................17
4.2 Advantages of ABAP Objects.................................................................................18
4.2.1 Why You Should Use ABAP Objects...........................................................18
4.2.2 Using ABAP Objects - Best Practices..........................................................20
4.3 Sharing Data...........................................................................................................20
4.3.1 Shared Objects - Basic Features.................................................................21
4.3.2 Shared Objects - Advanced Features..........................................................22
4.3.3 Best Practices...............................................................................................23
4.4 Exception Handling.................................................................................................24
4.4.1 Class-Based Exceptions in ABAP................................................................24
4.4.2 Basic Features..............................................................................................24
4.4.3 Planning Exception Handling and Delegating Exceptions...........................25
4.4.4 The Three Exception Classes in ABAP........................................................27
4.4.5 Defining an Exception Class........................................................................29
4.4.6 New Exceptions and Former Concepts of Error Handling...........................30
4.5 Developing Persistence..........................................................................................30
4.5.1 The Standard Path to Persistence...............................................................31
4.5.2 Other Persistence Options...........................................................................33
4.5.3 All or Nothing – Database and SAP Transactions.......................................34
4.5.4 Exclusive Database Access - Lock Concept of the SAP NW AS.................35
4.5.5 Restricting Access - Authorization Concept of the SAP NW AS..................36
4.6 Using Connectivity and Interoperability...................................................................37
4.6.1 The Integration Strategy of SAP and Web Services....................................38
4.6.2 How Web Services Function........................................................................38
4.6.3 Generating Interfaces and Proxies – The Outside-In Approach..................40
4.6.4 XML-Based Process Integration with the Exchange Infrastructure..............41
4.7 Making Enhancements............................................................................................42
4.7.1 How Do Modification-Free Enhancements Work?.......................................42
4.7.2 Enhancement Framework Details Based on an Example............................44
4.7.3 New BAdIs....................................................................................................47
4.7.4 The Switch Framework.................................................................................49
5 ENSURING QUALITY......................................................................................................53
5.1 ABAP Unit Tests.....................................................................................................53
5.2 Effective Testing with ABAP Unit............................................................................56
5.3 The Philosophy of Unit Tests..................................................................................57
5.4 Unit Tests and Transports.......................................................................................59
5.5 Advantages of ABAP Unit Tests.............................................................................59
October 2005

1 Using ABAP

Being able to use ABAP effectively requires more than just knowledge of the keywords. As a
programmer, you need to have a basic understanding of the architecture of the SAP
NetWeaver Application Server ABAP and how specific fundamental concepts are
implemented in ABAP and its infrastructure.
The aim of this guide is to enable you to use the possibilities of ABAP and the NW Application
Server ABAP as effectively as possible. It is to provide you with guidelines on how best to
solve certain standard tasks, which are part of any business programming.
Determining the best method to solve a problem in ABAP also means finding the most useful
of the various possibilities this language provides. In ABAP, there are often a number of
different ways of achieving the same goal. This is the price that has to be paid for evolutionary
development and downward compatibility. If old constructs are still required in a new release,
because they appear in important application programs, they remain part of the language.
Programmers can continue to use them, but should be aware in which cases there are now
more effective ways of solving a specific task.
Not only does the ABAP Developer Guider provide programmers with an overview of working
with ABAP, but also show the best solution to standard problems of business programming. In
any cases where there are multiple, equally useful solutions, this guide is to provide
information on their advantages and disadvantages.
The section Getting Involved [Seite 2] introduces the basic features of the ABAP language
and the SAP NetWeaver Application Server ABAP. You will learn how ABAP and its tools
support the entire lifecycle of an application and what tailor-made, business programming
features the language offers. You will also be familiarized with the three-layer architecture of
the server and learn why you do not develop locally with ABAP but always centrally on the
server.
Programming is a practical experience, and the best way to get an impression of the
possibilities of a language and its infrastructure is to write a small program in this language
and thus understand its development. The tutorial in the section Go and Create [Seite 5]
shows how easily you can use ABAP to create a database table – declaratively and with
metadata control – with the relevant fields and attributes. A simple ABAP Objects program
manages the data of this table.
With the knowledge gained from these two sections, you are ready to understand how
specific basic programming concepts are implemented in ABAP. The section Core
Development Tasks [Seite 16] provides an overview of the following topics:
• UI Technology: [Seite 17] The standard Web user interface is Web Dynpro. For special
requirements, Business Server Pages can be configured.
• ABAP Objects [Seite 18] offers a number of advantages, even if you want to continue
using procedural programming. If you want to use new ABAP features, you have to use
object-oriented interfaces anyway.
• Sharing Data: [Seite 20] With ABAP shared objects, you can aggregate data once at a
central location and the different users and programs can then access this data without
the need for copying.
• Exception Handling: [Seite 24] With the class-based exception concept of ABAP, you
can define a special control flow for a specific error situation and provide the user with
information about the error.
• Developing Persistency: [Seite 30] For permanent storage of data in ABAP, you use
relational database tables by means of database-independent Open SQL, which is
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integrated in ABAP. However, you can also store selected objects transparently or
access the integrated database or other databases using proprietary SQL.
• Using Connectivity and Interoperability: [Seite 37] The Exchange Infrastructure and
Web services are the means by which developers can implement a service-oriented
architecture. With Web services, you can provide and consume services independently
of implementation or protocol. Furthermore, you can do so within NetWeaver and in the
communication with other systems. With the features of the Exchange Infrastructure,
you can enable, manage, and adapt integration scenarios between systems.
• Making Enhancements: [Seite 42] With the Enhancement Framework, you can
enhance programs, function modules, and global classes without modification as well
as replace existing code. The Switch Framework enables you activate only specific
development objects or enhancements in a system.
Testing is an essential part of the software development cycle. The ABAP development
environment also provides support for this. The section Ensuring Quality [Seite 53]
introduces the basic features of ABAP Unit, a framework with which you can take advantage
of unit testing in ABAP. The relevant tools are fully integrated in the standard development
environment (SE80, SE24, SE37, SE38) and the code required for testing is implemented in
ABAP Objects.

2 Getting Involved
When you program with ABAP on the application server, you profit from a range of services,
which in other languages would have to be programmed manually with a great amount of
effort. Many of these services have resulted from the fact that the SAP NW Application Server
is the outcome of a long development period. You are thus benefiting from the experience of
many programmers, whose suggestions for improvement are implemented in the server
today.
The following provides you with an overview of the origins of ABAP, its infrastructure, and the
underlying server architecture. You are thus provided with information introducing you to
ABAP and its infrastructure.
If you are used to languages like C or Java, some aspects of programming with ABAP will at
first appear unfamiliar, some will seem unusual, and some may even appear impractical. If
you use the possibilities of the language effectively, you will soon see that many aspects of
business programming can be done with ABAP very simply. In this language, much has
already been anticipated and created.

2.1 The Origins of ABAP – an Overview
As a programming language of SAP, ABAP (Advanced Business Application Programming)
has contributed in no small way to the success of SAP’s application software. Since the
seventies, when the language was a macro assembler, ABAP has been consistently
optimized for business programming. With the introduction of the R/3 System in the nineties,
the ABAP language – now in its fourth generation – became the basis of the entire system, in
which all applications and large parts of Basis (as it was referred to at the time) were
implemented.
A further, significant step forward was the development of ABAP Objects with Release 4.6. In
keeping with SAP’s philosophy of safeguarding the existing billions’ worth of investments
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made by customers in ABAP, ABAP Objects is an object-based enhancement of the
procedural ABAP language available up to that point. Thanks to this evolutionary strategy with
its high level of downward compatibility, the many millions of lines of productive, procedural
ABAP coding still run on the NetWeaver Application Server – the name for the technological
basis of SAP since Release 6.10.
ABAP is thus not only a mature language that has proven itself in the practical field, but – on
the basis of its evolutionary strategy – it continues to be suited to the requirements of
business programming. The requests, suggestions, and requirements of the software
developers involved have flowed into this language over the years. With the quality of its
application programs, it has made SAP a world leader in the development of business
software.
Up to the year 2000, ABAP was the sole language in which SAP programmed its successful
business software. Since then, the SAP NetWeaver AS combines an ABAP and a J2EE
server. SAP uses the opportunities provided by both technologies for its products, but still
continues to invest in the further development of ABAP.

2.2 ABAP and Its Infrastructure
There are more advantages to programming with ABAP than simply using a sophisticated
programming language, and there are very good reasons for this. You require more than just
the programming language to write business applications successfully. Efficient programming
not only involves the writing of source code, especially in the case of very large projects. A
single program with its code is only a building block in a component, which in turn is part of a
solution. Furthermore, it is not just the creation of the solution that is relevant, but its entire
lifecycle, especially considering that, on average, maintenance costs make up some 60% of
software costs.
When you write an ABAP program, it is, from the outset, integrated in an environment that
supports its entire lifecycle. The ABAP Development Workbench, the programming
environment of the SAP NW AS ABAP, supports the entire software development cycle with
tools for:
• Programming in the ABAP language
• Efficient debugging
• Static and dynamic tests of different scales
• Performance analyses
• Organizing large projects
• Updates and importing patches
• Source code management
• Connectors to Java and .NET world
With regard to the actual programming, ABAP has the following features:
• Tailor-made data types for business programming – for example, the internal table, in
which you can dynamically create tables with row types structured to any depth and
can search their rows for specific fields.
• Object-oriented exception handling
• Support for dynamic programming; from dynamic data generation to dynamic creation
of types and entire programs
• Simple management of multilingual texts
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October 2005

• Integration of the DML part of SQL into the language
• Creation of database tables via the definition of metadata
• Definition of various types of data structures, which are then available throughout the
server
• Conversion of XML data into ABAP structures
• Simple handling of transactions – that is, program units – which can only be executed
fully or not all, in order to ensure data integrity
• Possibility to prepare program enhancements so that customers can enhance
programs without modification – that is, without the changes being lost after an update
or having to be merged manually
• Possibility to publish procedures as Web services or access Web services as a user

2.3 ABAP and the SAP NW Application Server
Overview
If you have experience in programming or languages such as Java and C, you have probably
asked yourself why, in the context of ABAP, we speak of the programming environment of the
server. In ABAP, you program on the server from the outset. You do not develop the
programs locally on your PC, nor do you store the sources in a versioning system or deploy
the programs on the server at a later stage.
To program with ABAP, you therefore require access to and developer authorization for the
SAP NW Application Server ABAP. You write your programs using the ABAP Editor of the
ABAP Workbench, which is also part of the server. Once you activate your source code,
platform-independent byte code is generated, which the runtime environment interprets for
the program execution.
However, the SAP NW Application Server ABAP not only contains the programming
environment with its tools and those for supporting the software lifecycle. ABAP programs
always run on the SAP NW AS ABAP and the architecture of the environment in which they
run must be taken into account when designing these programs. For this purpose, you first
require some information about this architecture.
The Layers of the SAP NW Application Server
The SAP NW Application Server ABAP consists of three layers: presentation, application, and
database. The database layer of a system is made up of a central database with a database
management system and the database itself. It not only contains the user data, but also the
entire program code of the SAP NW AS and application programs, all administrative data, and
Customizing settings.
The application layer lies between the database layer and the presentation layer. It consists of
one or more application servers (more than 100 servers possible) and a single message
server, which is responsible for communication and load distribution within this layer. The
programs that process the business logic of an application run in this layer. Technically, the
actual processing takes place in work processes, which represent operating system
processes. A fixed database connection is assigned to each work process. There is no fixed
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October 2005

assignment of users to work processes. A lengthy user session can utilize different work
processes sequentially.
The kernel and the Basis services make up the part of the application layer that is specific to
both the operating system and the database. They are responsible for user and process
management, database access, communication with other systems, as well as system
monitoring and administration. The software processes or virtual machines, that interpret the
platform-independent byte code as operating system-specific machine language commands,
run in the kernel.
The presentation layer represents the interface with the user and is responsible for the screen
display. This layer receives user entries – that is, mouse-clicks and keyboard input – and
passes them on to the application layer. Furthermore, it receives data from the application
layer and displays it to the user.
The purpose of this layering is high performance and scalability. The layer division is purely
logical. It does not imply over how many machines the system is distributed. All three layers
can actually run on a single computer. However, in the case of large, production applications
of customers, this is more of a theoretical possibility, since it would counteract the scalability
of the three-level architecture. For demonstration purposes, such as in the case of the mini
Basis, it is possible to install all three layers on a single PC. In a production operation, the
database usually has a separate machine, as it contains all program, Customizing, and user
data. The application layer is spread across several machines, depending on the anticipated
load, while the presentation layer runs on the workstations of the individual users.
What Does All this Mean for the Programmer?
The layers communicate with one another via network connections, meaning that
programmers need not concern themselves with these connections. When you write
application programs, these run in the application layer in work processes. Therefore, there is
always an open database connection. The specifications of the individual database are of just
as little concern to you as the operating system. The kernel is responsible for the
communication with all supported operating systems and databases. Therefore, you can
program platform-independently.

3 Go and Create
In the following sections, you will learn how you can easily use the ABAP Dictionary to create
a table in the database and a system-wide class that manages this data.
You create the database table with its fields and the desired attributes via metadata in the
ABAP Dictionary. When you activate the object, the table is created on the database. The
field types created in the ABAP Dictionary are then available system-wide. You can access
them from your ABAP program if you use ABAP Objects to program corresponding service
methods for accessing the table.

3.1 Creating a Database Table and Data Elements
Before discussing the theory, let us first look at an example that displays how simple it is to
program in ABAP. The aim of the development is to have a small program that stores names
on the database, finds them again, and lists them on the screen. The first thing you require is
a database table in which the names can be stored.
Using ABAP 5