WebSphere Message Brokers
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Writer: Karen Cameron

Concept topic

This build: July 31, 2007 21:16:50

ExceptionList tree structure

The ExceptionList tree is a part of the logical message tree in which the message flow writes information about exceptions that occur when a message is processed.

The root of the ExceptionList tree is called ExceptionList, and the tree consists of a set of zero or more exception descriptions. The ExceptionList tree is populated by the message flow if an exception occurs. If no exception conditions occur during message flow processing, the exception list that is associated with that message consists of a root element only. This list is, in effect, an empty list of exceptions.

The ExceptionList tree can be accessed by other nodes within the message flow that receive the message after the exception has occurred. You can modify the contents of the ExceptionList tree only in the Compute node.

If an exception condition occurs, message processing is suspended and an exception is thrown. Control is passed back to a higher level, that is, an enclosing catch block. An ExceptionList is built to describe the failure condition, and the whole message, together with the LocalEnvironment and the newly-populated ExceptionList, is propagated through an exception-handling message flow path.

The child of the ExceptionList is always RecoverableException. There is normally only one child of the root, although more than one might be generated in some circumstances. The child of the ExceptionList contains a number of children, the last of which provides further information specific to the type of exception. The following list includes some of the exception types that you might see.

The structure of the exception list tree for a RecoverableException is shown below:

The exception description structure can be both repeated and nested to produce an ExceptionList tree. In this tree:

The children in the tree take the form of a number of name-value elements that give details of the exception, and zero or more name elements whose name is Insert. The NLS (National Language Support) message number identified in a name-value element identifies a WebSphere Message Broker error message. The Insert values are used to replace the variables within this message and provide further detail about the cause of the exception.

The name-value elements within the exception list shown in the figure above are described in the table below.

Name Type Description
File1 String C++ source file name
Line1 Integer C++ source file line number
Function1 String C++ source function name
Type2 String Source object type
Name2 String Source object name
Label2 String Source object label
Text1 String Additional text
Catalog3 String NLS message catalog name4
Severity3 Integer

1 = information
2 = warning
3 = error

Number3 Integer NLS message number4
Insert3 Type Integer The data type of the value:

0 = Unknown
1 = Boolean
2 = Integer
3 = Float
4 = Decimal
5 = Character
6 = Time
7 = GMT Time
8 = Date
9 = Timestamp
10 = GMT Timestamp
11 = Interval
12 = BLOB
13 = Bit Array
14 = Pointer

Text String The data value
Notes:
  1. Do not use the File, Line, Function, and Text elements for exception handling decision making. These elements ensure that information can be written to a log for use by IBM® Service personnel.
  2. The Type, Name, and Label elements define the object (usually a message flow node) that was processing the message when the exception condition occurred.
  3. The Catalog, Severity, and Number elements define an NLS message: the Insert elements that contain the two name-value elements shown define the inserts into that NLS message.
  4. NLS message catalog name and NLS message number refer to a translatable message catalog and message number.

When the message flow processing is complete, the ExceptionList tree is discarded.

The following sample uses the ExceptionList in the XML_Reservation message flow to pass error information to the Throw node, which generates an error message that includes the information from the ExceptionList: You can view samples only when you use the information center that is integrated with the Message Brokers Toolkit.
Related concepts
Message flows overview
Message tree contents after an exception
Message modeling
Related tasks
Accessing the ExceptionList tree
Developing message flows
Handling errors in message flows
Throwing an exception
Writing ESQL
Writing Java
Related reference
Built-in nodes
Compute node
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This build: July 31, 2007 21:16:50

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