ANT programming samples (Java sources would be placed into src/sample/ directory of your project. Ant files would be placed into test/ directory of your project. Before trying to run the other build files, you should try to run build_greeting.xml.)

build_dir.xml

<?xml version="1.0"?>
<project default="main">
	<property name="export" location="../export"/>
	
	<target name="main">
		<taskdef name="dir" classname="sample.Dir" classpath="${export}/sample.jar" />
		<echo>Default</echo>
		<dir/>
		<echo>Specified base directory to src</echo>
		<dir dir="${basedir}/../src" />
		<echo>Specified "include" element</echo>		
		<dir dir="${basedir}/..">
			<include name="**/*.class"/>
		</dir>
	</target>
</project>

build_failure.xml

<?xml version="1.0"?>
<project default="main">
	<property name="export" location="../export"/>
	<property name="sample" location="SAMPLE"/>
	
	<target name="main">
		<taskdef name="failure" classname="sample.Failure" classpath="${export}/sample.jar" />
		<failure/>
		<failure failonerror="true"/>
		<failure/>
	</target>
</project>

build_greeting.xml

<?xml version="1.0"?>
<project default="main">
	<property name="src" location="../src"/>
	<property name="output" location="../output"/>
	<property name="export" location="../export"/>
	
	<target name="main" depends="jar">
		<taskdef name="greeting" classname="sample.Greeting" classpath="${export}/sample.jar" />
		<!-- You may use classpath element instead of classpass attribute. -->
		<greeting/>
	</target>
	
	<target name="jar" depends="compile">
		<jar destfile="${export}/sample.jar" basedir="${output}" />
	</target>
	
	<target name="compile">
		<mkdir dir="${output}"/>
		<mkdir dir="${export}"/>
		<javac srcdir="${src}" destdir="${output}">
			<include name="**/*.java"/>
		</javac>
	</target>
	
</project>

build_log.xml

<?xml version="1.0"?>
<project default="main">
	<property name="export" location="../export"/>
	
	<target name="main">
		<taskdef name="log" classname="sample.Log" classpath="${export}/sample.jar" />
		<log/>
		<log>Log task samples:</log>
		<log loglevel="4">((DEBUG))</log>
		<log loglevel="3">...VERBOSE.</log>
		<log loglevel="2">INFO.</log>
		<log loglevel="1">WARN!</log>
		<log loglevel="0">ERROR!!</log>
	</target>
</project>

build_nest.xml

<?xml version="1.0"?>
<project default="main">
	<property name="export" location="../export"/>
	
	<target name="main">
		<taskdef name="nest" classname="sample.Nest" classpath="${export}/sample.jar" />
		<nest name="root">
			<nested name="a1">
				<nested name="b1">
				</nested>
				<nested name="b2">
				</nested>
			</nested>
			<nested name="a2">
				<nested name="b3">
					<nested name="c1">
					</nested>
				</nested>
			</nested>
		</nest>
	</target>
</project>

build_prop.xml

<?xml version="1.0"?>
<project default="main">
	<property name="export" location="../export"/>
	<property name="sample" location="SAMPLE"/>
	
	<target name="main">
		<taskdef name="prop" classname="sample.DumpProperties" classpath="${export}/sample.jar" />
		<echo>Display single property value</echo>
		<prop key="sample"/>
		<echo>Dump all properties</echo>
		<prop/>
	</target>
</project>

build_run.xml

<?xml version="1.0"?>
<project default="main">
	<property name="export" location="../export"/>
	
	<target name="main">
		<taskdef name="run" classname="sample.Run" classpath="${export}/sample.jar" />
		<run executable="C:\\Windows\\system32\\notepad.exe">
			<arg arg="${basedir}/build_run.xml"/>
		</run>
	</target>
</project>

Dir.java

package sample;

import java.io.File;
import java.util.Arrays;

import org.apache.tools.ant.BuildException;
import org.apache.tools.ant.DirectoryScanner;
import org.apache.tools.ant.taskdefs.MatchingTask;

public class Dir extends MatchingTask {
	
	private File dir = new File(System.getProperty("user.dir"));//Default
	
	//Invoked by ANT system
	public void setDir(File dir){
		this.dir = dir;
	}
	
	//Invoked by ANT system
	public void execute() throws BuildException {
		DirectoryScanner scanner = this.getDirectoryScanner(this.dir);
		String[] files = scanner.getIncludedFiles();
		
		System.out.println("At \""+this.dir+"\":");
		Arrays.stream(files).map(s->new File(this.dir, s)).forEach(f->System.out.println("\t\""+this.dir.toPath().relativize(f.toPath())+"\" : "+f.length()+" bytes"));
	}
}

DumpProperties.java

package sample;

import java.util.Map;

import org.apache.tools.ant.Task;

public class DumpProperties extends Task {
	
	private static void print(String key, Object value) {
		System.err.println(String.format("\tkey: \"%s\", value: \"%s\"", key, value));
	}

	private String key = null;//Default

	//Invoked by ANT system
	public void setKey(String key){
		this.key = key;
	}
	
	//Invoked by ANT system
	public void execute(){
		@SuppressWarnings("unchecked")
		Map<String,Object> props = this.getProject().getProperties();
		if(key != null){
			print(key, props.get(key));
			return;
		}
		props.entrySet().stream().forEach(e->print(e.getKey(), e.getValue()));
	}
}

Failure.java

package sample;

import org.apache.tools.ant.BuildException;
import org.apache.tools.ant.Project;
import org.apache.tools.ant.Task;

public class Failure extends Task {
	private static final String message = "Task \"failure\" should fail anytime.";
	
	private boolean failonerror = false;//Default

	//Invoked by ANT system
	public void setFailOnerror(boolean failonerror){
		this.failonerror = failonerror;
	}
	
	//Invoked by ANT system
	public void execute() throws BuildException {
		this.log(message, Project.MSG_INFO);
		if(failonerror){
			this.log("Going to terminate whole build.", Project.MSG_ERR);

			throw new BuildException(message);
		}
		this.log("Ignore failure.", Project.MSG_WARN);
	}
}

Greeting.java

package sample;

public class Greeting {
	//Invoked by ANT system
	public void execute(){
		System.out.println("Hello.");
	}
}

Log.java

package sample;

import org.apache.tools.ant.BuildException;
import org.apache.tools.ant.Project;
import org.apache.tools.ant.Task;

public class Log extends Task {
	private int loglevel = Project.MSG_INFO;//Default
	private String content = "";//default

	//Invoked by ANT system
	public void addText(String content){
		this.content = this.content + content;
	}
	
	//Invoked by ANT system
	public void setLoglevel(int loglevel){
		this.loglevel = loglevel;
	}
	
	//Invoked by ANT system
	public void execute() throws BuildException {
		if(content.length() < 1){
			this.log("Log levels:", Project.MSG_INFO);
			this.log("\tMSG_ERR:  "+Project.MSG_ERR, Project.MSG_INFO);
			this.log("\tMSG_WARN:  "+Project.MSG_WARN, Project.MSG_INFO);
			this.log("\tMSG_INFO:  "+Project.MSG_INFO, Project.MSG_INFO);
			this.log("\tMSG_VERBOSE:  "+Project.MSG_VERBOSE, Project.MSG_INFO);
			this.log("\tMSG_DEBUG:  "+Project.MSG_DEBUG, Project.MSG_INFO);
			return;
		}
		this.log("Log task: ["+this.content+"]", this.loglevel);
	}
}

Nest.java

package sample;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.stream.Collectors;

import org.apache.tools.ant.BuildException;
import org.apache.tools.ant.Task;

public class Nest extends Task {
	private static String expand(List<Nested> nesteds){
		return nesteds.stream().map(n->n.getName()+"("+expand(n.getNested())+")").collect(Collectors.joining(", "));
	}
	
	public class Nested{
		private String name = null;//Default
		private final List<Nested> nesteds = new ArrayList<>();//Default
		
		public Nested(){
			//Nothing to do.
		}

		//Invoked by ANT system
		public void setName(String name){
			this.name = name;
		}
		
		public String getName(){
			if(this.name == null){
				throw new IllegalStateException("\"name\" attribute of \"nested\" element should not be null.");
			}
			return this.name;
		}

		//Invoked by ANT system
		public Nested createNested(){
			Nested nested = new Nested();
			this.nesteds.add(nested);
			return nested;
		}
		
		public List<Nested> getNested(){
			return Collections.unmodifiableList(this.nesteds);
		}
	}
	
	private String name = null;
	private List<Nested> nesteds = new ArrayList<>();//Default
	
	//Invoked by ANT system
	public void setName(String name){
		this.name = name;
	}
	
	public String getName(){
		if(this.name == null){
			throw new IllegalStateException("\"name\" attribute of \"nested\" element should not be null.");
		}
		return this.name;
	}

	//Invoked by ANT system
	public Nested createNested(){
		Nested nested = new Nested();
		this.nesteds.add(nested);
		return nested;
	}
	
	public List<Nested> getNested(){
		return Collections.unmodifiableList(this.nesteds);
	}
	
	//Invoked by ANT system
	public void execute() throws BuildException {
		System.out.println(expand(this.getNested()));
	}
}

Run.java

package sample;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import org.apache.tools.ant.BuildException;
import org.apache.tools.ant.Project;
import org.apache.tools.ant.Task;
import org.apache.tools.ant.taskdefs.Execute;
import org.apache.tools.ant.types.Commandline;

public class Run extends Task{
	public class Arg{
		private String arg = null;
		
		public void setArg(String arg){
			this.arg = arg;
		}
		
		//Invoked by ANT system
		public String getArg(){
			return this.arg;
		}
	}
	
	private String exe = null;
	private List<Arg> args = new ArrayList<>();

	//Invoked by ANT system
	public void setExecutable(String exe){
		this.exe = exe;
	}
	
	//Invoked by ANT system
	public Arg createArg(){
		Arg arg = new Arg();
		this.args.add(arg);
		return arg;
	}
	
	//Invoked by ANT system
	public void execute() throws BuildException{
		Commandline cmdln = new Commandline();
		cmdln.setExecutable(this.exe);
		args.stream().filter(a->(a.getArg()!=null)).map(Arg::getArg).forEach(a->cmdln.createArgument().setValue(a));
		
		this.log("Going to execute: \""+cmdln.toString()+"\"", Project.MSG_INFO);
		
		Execute runner = new Execute();
		runner.setCommandline(cmdln.getCommandline());
		
		try{
			runner.execute();
		}catch(IOException e){
			this.log("Execution failed.", e, Project.MSG_ERR);
			throw new BuildException("Execution failed.", e);
		}
	}
}