Databases Reference
In-Depth Information
CHAPTER 2
Extending Pipe Assemblies
Example 3: Customized Operations
Cascading provides a wide range of built-in
operations
to perform on workflows. For
many apps, the Cascading API is more than sufficient. However, you may run into cases
where a slightly different transformation is needed. Each of the Cascading operations
can be extended by subclassing in Java. Let's extend the Cascading app from
“Example
2: The Ubiquitous Word Count” on page 8
to show how to customize an operation.
Modifying a conceptual flow diagram is a good way to add new requirements for a
Cascading app.
Figure 2-1
shows how this iteration of
Word Count
can be modified to
clean up the token stream. A new class for this example will go right after the
Token
ize
operation so that it can scrub each tuple. In terms of Cascading patterns, this op‐
eration needs to be used in an
Each
operator, so we must implement it as a
Function
.
Figure 2-1. Conceptual flow diagram for
“Example 3: Customized Operations”
