sap的用户出口总共有三代:
1、第一代
sap提供一个空代码的子过程，在这个子过程中用户可以添加自己的代码，控制自己的需求。这类增强都需要修改sap的标准代码。
示例：USEREXIT.. in SAPMV45A
2、第二代
sap提供的是CUSTOMER-FUNCTION，它是通过SMOD和CMOD完成实现。参见我的http://blog.csdn.net/CompassButton/archive/2006/08/31/1150258.aspx
3、第三代
sap提供的第三代的用户出口就是BADI，他的调用方式是CALL METHOD (instance)，（相关的TCODE是SE18和SE19），你可以通过EXIT_HANDLER这个单词查找BADI。
另外还有一种出口叫BTE
相关TCODE: FIBF
Business Transaction Events (Open FI)
The Open FI enhancement technique was developed in the Financial Accounting component. Open FI is based upon the following principles:
Application developers must define their interface in a function module, an assignment table is read in the accompanying (generated) code, and the customer modules assigned are called dynamically.
This technique differentiates between enhancements that are only allowed to have one implementation and enhancements that can call multiple implementations in any sequence desired. Both industry-specific and country-specific enhancements may be defined.
The concepts behind the Business Add-Ins enhancement technique and Open FI are basically the same. However, the two enhancement techniques do differ from each other in the following points:
- Open FI can only be used to make program enhancements, that is, you can only enhance source code using Open FI. You cannot enhance user interface elements with Open FI like you can with Business Add-Ins.
- Open FI assumes that enhancement will only take place on three levels (SAP - partners - customers), whereas with Business Add-Ins you can create and implement enhancements in as many software layers as you like.
- Open FI uses function modules for program enhancements. With Business Add-Ins, ABAP Objects is used to enhance programs.