By default, the value of the property is set to true if the timestamp of the source file s is not more recent than the timestamp of the corresponding target file s. You can set the value to something other than the default by specifying the value attribute. Normally, this task is used to set properties that are useful to avoid target execution depending on the relative age of the specified files. Make follows the chain of dependencies and walks down the recursion chain until it finds a target with up-to-date prerequisites, a target with no prerequisites, or a target whose prerequisites have no rules.
Once it reaches the end of the chain it walks back down the recursion chain by executing the commands found in each target's rule.
Ant and make differ in the way they look at the build process. Make requires you to state resources and nonresources dependencies and the build commands required to transform them.
Ant wants you to state build steps and the order between them like an assembly line. The tasks themselves can do dependency checking or not, whereas make has an explicit dependency checking mechanism provided to the make builder by the user via the makefile file. Also versus Ant, make is not platform independent. Both views have their advantages and disadvantages; it would be nice to combine the ideas behind both of them. After our review of concepts and definitions, now I want to propose some techniques and guidelines for quickening your builds and optimizing them for incremental builds.
Please note that I briefly introduce most of these techniques; this article is only a starting point. For more information on the tools used, refer to Resources. Make sure that a correct and logical dependency remains among your build targets, but prevents the execution of unnecessary targets when a chain of dependent targets are run. Omitting dependencies between targets to optimize the build is a bad practice because it forces programmers to remember to invoke a series of targets in a particular order to get a decent build See " Top 15 Ant Best Practices by Eric M.
Burke ONJava. Let the build file remember the correct dependency and conduct an optimized build on its own. Getting back to our sample bottom-up build process, every time we do a build, we don't need to run the SQL commands, Middlegen, XDoclet and so on.
Nevertheless, we want to keep the correct dependencies between targets. However, in some cases, dependency checking itself takes a long time e. If possible, we want to skip these kinds of targets completely.
Here, I introduce a simple technique that you can use to skip unnecessary targets: Check the last execution timestamp of the target to be skipped against its depending targets' last execution timestamps to determine whether that target's output is up-to-date.
This rule works only when all inputs of A are produced by B and C, and no manual modifications are completed on B or C's outputs between target executions. To add this functionality, we use the Ant touch task to either create a temporary file or update that temporary file's modification timestamp each time the unnecessary target or its depending targets execute. Then, before the unnecessary target's execution, we check the timestamp of the file created during the last target execution against the timestamps of the files created during the last executions of the depending targets via the uptodate task.
Open Source Tools for Developers: Why They Matter From a developer's point of view use of open-source tools has advantages beyond the obvious economic ones. The file new. If so, then the property new. If so, which should not be the case , then the old. How It Works I hope it is clear to you what is intended - the files are first created, then checked against each other using the uptodate task to see which is newer, and finally a message or messages is printed out according to the conditional targets is.
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