Tutorial: Hello World with Ant

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.

Content

• Preparing the project
• Enhance the build file
• Enhance the build file
• Using external libraries

Preparing the project

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");
    }
}

Four steps to a running application

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

Enhance the build file

The first and second point would be adressed with properties, the thirs 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

Using external libraries

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

• it is not part of the JDK (1.4+) and we want to show how to use external libs
• it can run under JDK 1.2 (as Ant)
• it's highly configurable
• it's from Apache :-)

We store our external libraries in a new directory lib. Log4J can be downloaded 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. 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 red 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?

• [java] Ant task running at the moment
• 0 sorry don't know - some Log4J stuff
• [main] the running thread from our application
• INFO log level of that statement
• oata.HelloWorld source of that statement
• - sorry don't know - some Log4J stuff
• Hello World the message

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

    ...
    <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>
    ...