Author: Jan Matèrne

# 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

Ok, the build works - but it is not as nice as it should: many time you are referencing the same directories, main-class and jar-name are hard coded, and while invocation you have to remember the right order of build steps.

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

For another layout ... have a look inside Log4J's documentation about using other PatternLayout's.

## Configuration files

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.

Copyright © 2005 The Apache Software Foundation. All rights Reserved.