This document provides a step by step tutorial for starting Java programming with Apache 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 split into several subdirectories for the individual steps: classes for our compiled files and jar for our own JAR-file.
We have to create only the src directory. (Because I am working on Windows, here is the Windows syntax—translate to your shell):
md src
The following simple Java class just prints a fixed message out to STDOUT, so just write this code into src\oata\HelloWorld.java.
package oata;
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello World");
}
}
Now just try to compile and run that:
md build\classes javac -sourcepath src -d build\classes src\oata\HelloWorld.java java -cp build\classes oata.HelloWorldwhich will result in
Hello World
Creating a jar-file is not very difficult. But creating a startable jar-file needs more steps: create a manifest-file containing the start class, creating the target directory and archiving the files.
echo Main-Class: oata.HelloWorld>myManifest md build\jar jar cfm build\jar\HelloWorld.jar myManifest -C build\classes . java -jar build\jar\HelloWorld.jar
Note: Do not have blanks around the >-sign in the echo Main-Class instruction because it would falsify it!
After finishing the Java-only step 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".
By default Ant uses build.xml as the name for a buildfile, so our .\build.xml 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
While having a look at the buildfile, we will see some similar steps between Ant and the Java-only commands:
| Java-only | Ant |
|---|---|
md build\classes
javac
-sourcepath src
-d build\classes
src\oata\HelloWorld.java
echo Main-Class: oata.HelloWorld>mf
md build\jar
jar cfm
build\jar\HelloWorld.jar
mf
-C build\classes
.
java -jar build\jar\HelloWorld.jar |
<mkdir dir="build/classes"/>
<javac
srcdir="src"
destdir="build/classes"/>
<!-- automatically detected -->
<!-- obsolete; done via manifest tag -->
<mkdir dir="build/jar"/>
<jar
destfile="build/jar/HelloWorld.jar"
basedir="build/classes">
<manifest>
<attribute name="Main-Class" value="oata.HelloWorld"/>
</manifest>
</jar>
<java jar="build/jar/HelloWorld.jar" fork="true"/> |
Now that we have a working buildfile, we could do some enhancements: many times you are referencing the same directories, main-class and jar-name are hardcoded, and while invoking you have to remember the right order of build steps.
The first and second point would be addressed 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
Somebody told us not to use System-statements. For output, we should use a Logging
API—customizable to a high degree (including switching off during usual life (= not development) execution). We
use Log4J for that, 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-1.2.17.jar into that directory. After that we have to modify our Java source file 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"); // the old SysO-statement
}
}
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 on 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 (or to be more precise: all libraries (jar-files) which are somewhere under .\lib) 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 jar-name 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 moment0 sorry, don't know—some Log4J stuff[main] the running thread from our applicationINFO log level of that statementoata.HelloWorld source of that statement- separatorHello World the messageFor another layout ... have a look inside Log4J's documentation about using other PatternLayouts.
Why we have used Log4J? "It's highly configurable"? No—all is hardcoded! But that is not the fault of
Log4J—it's ours. We had coded BasicConfigurator.configure(); which implies a simple, but
hardcoded configuration. More comfortable would be using a property file. In the Java source file, delete
the BasicConfiguration line from the main() method (and the
related import statement). Log4J will search then for a configuration as described in its 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="${src.dir}" excludes="**/*.java"/>
</copy>
</target>
...
This copies all resources (as long as they haven't the suffix .java) to the build directory, so we could start the application from that directory and these files will included into the jar.
In this step we will introduce the usage of the JUnit [3] test framework in combination with Ant. Because Ant has a built-in JUnit 4.13.1 you could start directly using it. Write a test class in src\oata\HelloWorldTest.java:
package oata;
import org.junit.Test;
import static org.junit.Assert.fail;
public class HelloWorldTest {
@Test
public void testNothing() {
}
@Test
public void testWillAlwaysFail() {
fail("An error message");
}
}
Because we don't have real business logic to test, this test class is very small: just showing how to start. For
further information see the JUnit documentation [3] and the manual of junit task. Now we
add a junit instruction to our buildfile:
...
<path id="application" location="${jar.dir}/${ant.project.name}.jar"/>
<target name="run" depends="jar">
<java fork="true" classname="${main-class}">
<classpath>
<path refid="classpath"/>
<path refid="application"/>
</classpath>
</java>
</target>
<target name="junit" depends="jar">
<junit printsummary="yes">
<classpath>
<path refid="classpath"/>
<path refid="application"/>
</classpath>
<batchtest fork="yes">
<fileset dir="${src.dir}" includes="**/*Test.java"/>
</batchtest>
</junit>
</target>
...
We reuse the path to our own jar file as defined in run
-target by giving it an id and making it
globally available. The printsummary=yes
lets us see more detailed information than just a "FAILED"
or "PASSED" message. How much tests failed? Some errors? printsummary lets us know. The classpath is set up
to find our classes. To run tests the batchtest here is used, so you could easily add more test classes in
the future just by naming them *Test.java. This is a common naming scheme.
After a ant junit you'll get:
...
junit:
[junit] Running oata.HelloWorldTest
[junit] Tests run: 2, Failures: 1, Errors: 0, Skipped: 0, Time elapsed: 0,01 sec
[junit] Test oata.HelloWorldTest FAILED
BUILD SUCCESSFUL
...
We can also produce a report. Something that you (and others) could read after closing the shell ... There are two
steps: 1. let <junit> log the information and 2. convert these log files to something readable
(browsable).
...
<property name="report.dir" value="${build.dir}/junitreport"/>
...
<target name="junit" depends="jar">
<mkdir dir="${report.dir}"/>
<junit printsummary="yes">
<classpath>
<path refid="classpath"/>
<path refid="application"/>
</classpath>
<formatter type="xml"/>
<batchtest fork="yes" todir="${report.dir}">
<fileset dir="${src.dir}" includes="**/*Test.java"/>
</batchtest>
</junit>
</target>
<target name="junitreport">
<junitreport todir="${report.dir}">
<fileset dir="${report.dir}" includes="TEST-*.xml"/>
<report todir="${report.dir}"/>
</junitreport>
</target>
Because we would produce a lot of files and these files would be written to the current directory by default, we
define a report directory, create it before running the junit
and redirect the logging to it. The log format is
XML so junitreport
could parse it. In a second target junitreport
should create a browsable HTML report
for all generated XML log files in the report directory. Now you can open the ${report.dir}\index.html and
see the result (looks something like JavaDoc).
Personally I use two different targets
for <junit> and <junitreport>. Generating the HTML report needs some time and you
don't need the HTML report just for testing, e.g. if you are fixing an error or a integration server is doing a job.