The Ant Command Line
We've already discussed a few of the Ant command-line switches and arguments, but we need to spend a little time covering all of them. There really aren't that many, but they can fundamentally change the way Ant works.
The general format of an Ant command line looks like Listing 3.77.
Listing 3.77 General Form of Ant Command Line
ant [options] [target...]
Notice that you can specify multiple targets on the command line and they will be executed in the order you gave them. This is optional, and if no targets are given, the default target will be executed.
The options that Ant supports are
-help prints a usage message.
-version prints the version of Ant and exits.
-projecthelp displays the names and descriptions of targets in the build file.
-quiet suppresses most output messages to the console.
-verbose displays more information about what the build is doing.
-debug displays more information than you probably want about what the build is doing.
-emacs prints console output in a format that Emacs can parse.
-logfile <filename> sends all console output to the given filename.
-logger <log class> uses the specified class to log messages.
-listener <listener class> uses the specified class to process build events.
-buildfile <build filename> uses the specified build file instead of build.xml.
-find [build filename] searches for a build.xml file (or the specified filename.
-Dkey=value sets a Java property for Ant to use.
-propertyfile <filename> sets properties for every line in the specified file.
inputhandler <inputhandler class> uses the specified class to process interactive user input.
We'll now discuss each of these with a bit of explanation. We'll begin with -projecthelp because -help and -version are self-explanatory.
This switch is extremely useful, especially with a new project or if you've just gotten a build file from someone else. It will print the names and descriptions of each target in the file, indicating which target is the default. Listing 3.78 shows the output using the build file for Ant itself.
Listing 3.78 Shows -projecthelp Output
Buildfile: build.xml Main targets: allclean --> cleans up everything bootstrap --> creates a bootstrap build build --> compiles the source code clean --> cleans up build and dist directories dist --> creates a complete distribution dist-lite --> creates a minimum distribution to run Apache Ant distribution --> creates the full Apache Ant distribution interactive-tests --> runs interactive tests jars --> creates the Apache Ant jars javadocs --> creates the API documentation main --> creates a minimum distribution in ./dist main_distribution --> creates the zip and tar distributions run-single-test --> -runs the single unit test defined in the testcase property src-dist --> creates a source distribution test --> run JUnit tests test-jar --> creates the Apache Ant Test Utilties jar test-javadocs --> creates the API documentation for test utilities Default target: main
You can see from the last line that if you do not specify a target to execute, the target called main will be run.
Notice that each of the targets has some descriptive text after the name. This is taken from the description attribute of each target. If you don't specify any description attributes, Ant will display all of your targets in response to a -projecthelp. As soon as you specify one target with a description attribute, Ant will display only those targets that have a description. So, after you start setting descriptions, you have to take it to completion if you want your project help to be useful. You can omit descriptions for targets that are purely internal to the build and should never be called by a user.
-quiet, -verbose, and -debug
These three switches control how much or how little information is sent to the logger or console. -quiet will output only errors, which is quite a bit less text than running Ant without -quiet. -verbose will print several hundred lines of information, showing properties, classpaths, and other settings; -debug prints an even more in-depth listing. If you're having problems with a build, try using one of these two switches to increase the amount of output. One interesting thing that will be displayed when using -verbose or -debug is that FileSets will display the files they are processing and whether or not they have been selected.
If you are executing Ant from within Emacs, you must use this switch to cause Ant to alter its output so that Emacs can parse it. If you do this, Emacs will be able to take you to the source of errors in your source file. Otherwise, you'll have to manually navigate to these locations.
By default, Ant logs everything to the console. You can redirect this output to a file by specifying the -logfile switch and giving a filename to log to. If there is already a file with that name, it will be overwritten.
-logger <log class>, -listener <listener class>
-logger enables you to replace the DefaultLogger with a different logger. -listener enables you to replace the event listener. Consult the "Listeners and Loggers" section earlier in this chapter for more details and a list of available loggers and listeners.
-buildfile <build filename>
By default Ant looks for a file called build.xml in the current directory. If you want to specify a different file, either in the current directory or elsewhere, pass it as the parameter to the -buildfile switch.
-find [build filename]
The -find switch is similar to -buildfile in that it lets you give an alternative build file to execute. However, instead of telling Ant specifically where the file is, the -find switch forces Ant to search for the alternative build file. If you don't give a filename, Ant will search for build.xml. The search rules are contrary to what you might expect, however. You would generally expect a find to start in the current directory and work down. The -find switch actually searches from the current directory up. In other words, it would first look for the build file in the current directory, and then it would move to its parent, and then its parent, and so forth, either until it found a build file or reached the drive root.
The -D switch is identical to the Java -D switch; it enables you to set properties from the command line. For example, if you had a target that executes only if the release.build property has been set, you could run Ant as in Listing 3.79 to set this property.
Listing 3.79 Setting a Property from the Command Line
ant -Drelease.build=true build
It is important to note that properties set on the command line take precedence over those set by <property> tasks or in properties files. This is useful to occasionally change a property that needs to be at its default most of the time.
This switch is equivalent to specifying a loadproperties task inside your build file. It will load all the key/value pairs from this properties file as properties that can be used in your build.
-inputhandler <inputhandler class>
This switch is a bit more esoteric than the others. Its purpose is to specify a different class to handle user input during the <input> task. This task enables you to prompt your user for input to answer build questions, and so on. The input task is covered in Chapter 4.