Ant: The Definitive Guide

The Task Life Cycle

Complex tasks, which perform operations on many files, rely on nested tasks, and use multiple libraries (e.g., the optional ejbjar task), require an in-depth understanding of a task’s relationship with Ant. Consider this a warning. This section delves into the dark and dirty details involving the life cycle of a task. If you feel that your custom tasks will not meet the complexity level described here, skip this section and move on to our example. You can always come back and read this section later. Understanding the engine and the task life cycle is important for becoming an expert task writer, but it is not a requirement for writing custom tasks that are relatively simple.

Ant processes all tasks identically. Ant sets attributes and processes nested elements at fixed intervals. We can predict how a task operates and design it accordingly. A task’s life can be broken down into two primary phases of time: parse-time and runtime. The parse-time phase begins when Ant reads the task from the XML (think of the engine as interpreting the XML, element by element). The runtime phase begins when the parse-time phase completes successfully.

The Parse Phase

Ant parses a task after its XML parser loads the element. The task’s name, attributes, and nested elements are wrapped into a single XML element object and stored in Ant’s in-memory DOM.^[35] During parse-time, operations can fail if the task XML is poorly formed or if actions taken within a task’s constructor throw ...