This document provides a step by step tutorial for starting java programming with Ant. It does not contain deeper knowledge about Java or Ant. This tutorial has the goal to let you see, how to do the easiest steps in Ant.
We want to separate the source from the generated files, so our java source files will be in src folder. All generated files should be under build, and there splitted into several subdirectories for the individual steps: classes for our compiled files and jar for our own JAR-file.
The later directories are created by our buildfile, so we have to create only the src directory. (Because I am working on Windows, here is the win-syntax - translate to your shell):
md src
This is not a Java tutorial, so just write this code into src/oata/HelloWorld.java - you should guess it's meaning ;-)
package oata;
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello World");
}
}
Oki-doki - now we have to think about our build process. We have to compile our code, otherwise we couldn't start the program. Oh - "start" - yes, we could provide a target for that. We should package our application. Now it's only one class - but if you want to provide a download, no one would download several hundreds files ... (think about a complex Swing GUI :) - so let us create a jar file. A startable jar file would be nice ... And it's a good practise to have a "clean" target, which deletes all the generated stuff. Many failures could be solved just by a "clean build" :-)
The buildfile describing that would be:
<project>
<target name="clean">
<delete dir="build"/>
</target>
<target name="compile">
<mkdir dir="build/classes"/>
<javac srcdir="src" destdir="build/classes"/>
</target>
<target name="jar">
<mkdir dir="build/jar"/>
<jar destfile="build/jar/HelloWorld.jar" basedir="build/classes">
<manifest>
<attribute name="Main-Class" value="oata.HelloWorld"/>
</manifest>
</jar>
</target>
<target name="run">
<java jar="build/jar/HelloWorld.jar" fork="true"/>
</target>
</project>
Now you can compile, package and run the application via
ant compile ant jar ant run
Or shorter with
ant compile jar run
The first and second point would be adressed with properties, the third with a special property - an attribute of the <project>-tag and the fourth problem can be solved using dependencies.
<project name="HelloWorld" basedir="." default="main">
<property name="src.dir" value="src"/>
<property name="build.dir" value="build"/>
<property name="classes.dir" value="${build.dir}/classes"/>
<property name="jar.dir" value="${build.dir}/jar"/>
<property name="main-class" value="oata.HelloWorld"/>
<target name="clean">
<delete dir="${build.dir}"/>
</target>
<target name="compile">
<mkdir dir="${classes.dir}"/>
<javac srcdir="${src.dir}" destdir="${classes.dir}"/>
</target>
<target name="jar" depends="compile">
<mkdir dir="${jar.dir}"/>
<jar destfile="${jar.dir}/${ant.project.name}.jar" basedir="${classes.dir}">
<manifest>
<attribute name="Main-Class" value="${main-class}"/>
</manifest>
</jar>
</target>
<target name="run" depends="jar">
<java jar="${jar.dir}/${ant.project.name}.jar" fork="true"/>
</target>
<target name="clean-build" depends="clean,jar"/>
<target name="main" depends="clean,run"/>
</project>
Now it's easier, just do a ant and you will get
Buildfile: build.xml
clean:
compile:
[mkdir] Created dir: C:\...\build\classes
[javac] Compiling 1 source file to C:\...\build\classes
jar:
[mkdir] Created dir: C:\...\build\jar
[jar] Building jar: C:\...\build\jar\HelloWorld.jar
run:
[java] Hello World
main:
BUILD SUCCESSFUL
Somehow told us not to use syso-statements. For log-Statements we should use a Logging-API - customizable on a high degree (including switching off during usual life (= not development) execution). We use Log4J, because
We store our external libraries in a new directory lib. Log4J can be downloaded [1] from Logging's Homepage. Create the lib directory and extract the log4j-1.2.9.jar into that lib-directory. After that we have to modify our java source to use that library and our buildfile so that this library could be accessed during compilation and run.
Working with Log4J is documented inside its manual. Here we use the MyApp-example from the Short Manual [2]. First we have to modify the java source to use the logging framework:
package oata;
import org.apache.log4j.Logger;
import org.apache.log4j.BasicConfigurator;
public class HelloWorld {
static Logger logger = Logger.getLogger(HelloWorld.class);
public static void main(String[] args) {
BasicConfigurator.configure();
logger.info("Hello World");
}
}
Most of the modifications are "framework overhead" which has to be done once. The blue line is our "old System-out" statement.
Don't try to run ant - you will only get lot of compiler errors. Log4J is not inside the classpath so we have to do a little work here. But do not change the CLASSPATH environment variable! This is only for this project and maybe you would break other environments (this is one of the most famous mistakes when working with Ant). We introduce Log4J into our buildfile:
<project name="HelloWorld" basedir="." default="main">
...
<property name="lib.dir" value="lib"/>
<path id="classpath">
<fileset dir="${lib.dir}" includes="**/*.jar"/>
</path>
...
<target name="compile">
<mkdir dir="${classes.dir}"/>
<javac srcdir="${src.dir}" destdir="${classes.dir}" classpathref="classpath"/>
</target>
<target name="run" depends="jar">
<java fork="true" classname="${main-class}">
<classpath>
<path refid="classpath"/>
<path location="${jar.dir}/${ant.project.name}.jar"/>
</classpath>
</java>
</target>
...
</project>
In this example we start our application not via its Main-Class manifest-attribute, because we could not provide a jarname and a classpath. So add our class in the red line to the already defined path and start as usual. Running ant would give (after the usual compile stuff):
[java] 0 [main] INFO oata.HelloWorld - Hello World
What's that?
Why we have used Log4J? "It's highly configurable"? No - all is hard coded! But that is not the debt of Log4J - it's ours. We had coded BasicConfigurator.configure(); which implies a simple, but hard coded configuration. More confortable would be using a property file. In the java source delete the BasicConfiguration-line from the main() method. Log4J will search then for a configuration as described in it's manual. Then create a new file src/log4j.properties. That's the default name for Log4J's configuration and using that name would make life easier - not only the framework knows what is inside, you too!
log4j.rootLogger=DEBUG, stdout log4j.appender.stdout=org.apache.log4j.ConsoleAppender log4j.appender.stdout.layout=org.apache.log4j.PatternLayout log4j.appender.stdout.layout.ConversionPattern=%m%n
This configuration creates an output channel ("Appender") to console named as stdout which prints the message (%m) followed by a line feed (%n) - same as the earlier System.out.println() :-) Oooh kay - but we haven't finished yet. We should deliver the configuration file, too. So we change the buildfile:
...
<target name="compile">
<mkdir dir="${classes.dir}"/>
<javac srcdir="${src.dir}" destdir="${classes.dir}" classpathref="classpath"/>
<copy todir="${classes.dir}">
<fileset dir="${src.dir}" excludes="**/*.java"/>
</copy>
</target>
...
This copies all resources (as long as they haven't the suffix ".java") to the build directory, so we could start the application from that directory and these files will included into the jar.
[1] http://www.apache.org/dist/logging/log4j/1.2.9/logging-log4j-1.2.9.zip
[2] http://logging.apache.org/log4j/docs/manual.html
Copyright © 2005 The Apache Software Foundation. All rights Reserved.