Robust Data Synchronization with IBM Tivoli Directory Integrator

Appendix C. Handling exceptions and errors 467

Mode-specific On Error

If an error occurs during a Connector Interface operation, then the On Error Hook

for the Connector mode is invoked

7

. This Hook is not mandatory, so having it not

enabled will not cause additional exceptions to be thrown.

After the mode-specific

On Error Hook is executed (or skipped, if not enabled)

flow continues to the

Default On Error Hook.

Default On Error

Although other error Hooks can precede it - like On Connection Failure or

Mode-Specific On Error described in the previous sections - this is the error

Hook that is ultimately called for any error-exception thrown during Connector or

Function operation.

If this Hook is not enabled then the AssemblyLine aborts with the error and the

AL's

On Failure Hook is invoked. However, if Default On Error is enabled, the

exception is effectively "swallowed" and control is passed to the next AL

component.

Logging

An important part of any error handling scheme is logging. Of course, logging

has other uses as well; like passing data to other applications, or writing an

AssemblyLine audit trail. As a result, this chapter will deal with logging in more

general terms than just error handling.

TDI uses a Java API for logging called

Log4j. This flexible framework provides a

rich set of features that TDI leverages in such a way as to pass this flexibility on

to you. It is not necessary that you know how Log4j works to do logging in TDI.

However, any knowledge you do have can be directly applied to your solutions.

So without going into the gritty details, logging in log4j can be thought of in three

parts:

logger, appender, and layout.

The first part (

logger) refers to the mechanism that enables logging, and this bit

handled for you by TDI.

The second term (

appender) is also a job for TDI. This work is carried out a

logging component called, not surprisingly, an Appender. TDI provides a range of

appenders that each supports a specific log system or mechanism.

7

This is also true of connection failures as well, although the On Connection Failure (and possibly

Reconnect feature, if enabled) is executed first.

468 Robust Data Synchronization with IBM Tivoli Directory Integrator

Finally, layout defines the format in which your log messages are written. You

define the layout for an Appender by setting its parameters.

More information about this topic can be found in the Logging and debugging

section of the IBM Tivoli Directory Integrator 6.0: Administrator Guide,

SC32-1716.

Figure C-4 The IDI File Roller appender

The window in Figure C-4 is of the IDI File Roller Appender, and the top two

parameters are specific to this component. Here you tell the Appender what file

to use as well as how many backup copies it should maintain. The next two

parameters - Layout and Pattern - are how the log messages are to be written.

Finally, the Log Level parameter instructs the logger feature in TDI which

message priority levels to enable for this Appender. There are five levels to

choose from: DEBUG, INFO, WARN, ERROR, and FATAL; in ascending order of

priority. This parameter controls how verbose the Appender will be and setting

one level will enable that priority plus all those that are higher. For example, if you

set the log level to FATAL, then only this level of messages will be written by the

Appender. However, setting it to WARN means that it will handle ERROR and

FATAL as well.

Logging can be defined at the Config level, as well as for specific AssemblyLines.

Setting up how all AssemblyLines in a Config will do their logging is done under

the Config folder of the Config Browser as shown in Figure C-5. Here you will see

an Item called Logging.

Appendix C. Handling exceptions and errors 469

Figure C-5 Setup logging - config level

Selecting this item brings up a Logging Details window where you can add and

remove Appenders that will be applied to all ALs.

In addition to Config-level settings, each AssemblyLine offers a Logging tab

where you can specify further Appenders for this task. This is shown in our final

capture in Figure C-6.

Figure C-6 Setup logging tab

470 Robust Data Synchronization with IBM Tivoli Directory Integrator