Make Agents Yourself

h1. SpeADL for Dynamic Architectures Tutorial

{{>toc}}

This is a tutorial for SpeADL: understanding ecosystems and species, defining a simple ecosystem, composing species together with uses.

h2. Objectives

The objective of this tutorial to understand the abstractions of species and uses.

We will create a Logging ecosystem that contains Logger species.

Then we will create a Banking ecosystem that contains Account species that need to log what happens.

Finally we will create a Bank ecosystem that compose Account species with Logger species thanks to the use abstraction.

h2. Prerequisites

It is needed to understand the content of the [[SpeADL Minus Tutorial|SpeADL⁻ tutorial]] before doing this one.

h2. Creating a New Project and Organisation

Create a Java project.

We will use again an organisation of the package and namespaces as explained in [[MAY Best Practices#Project Organisation|this best practice]].

h2. The Logging Ecosystem

Logging will be an ecosystem, and its particularity is that it will be able to create Loggers: while logging is the subsystem responsible of all logging, each logger will be responsible of logging one particular aspect of the system identified by a _name_.

We will have multiple implementation for the Logging ecosystem:

* One with only one file where to log with each line prepended with the name.

* One with one file per Logger all in the same directory.

In any case, a port will be provided by Logging to create standalone instances of Logger.

h3. Defining the Ecosystem and the Species

Create a SpeADL file named _logging.speadl_ in the package _tutorial2.logging_.

Define in it the ecosystem and the species in the right namespace as well as the needed interface:

<pre>

import tutorial2.logging.interfaces.ILog

namespace tutorial2.logging {

	ecosystem Logging {		

		provides create: ICreateLogger

		species Logger(name: String) {

			provides log: ILog

		}

	}

}

</pre>

<pre>

package tutorial2.logging.interfaces;

public interface ILog {

	public void addLine(String line);

}

public interface ICreateLogger {

	public Logging.Logger.Component createStandaloneLogger(String name);

}

</pre>

h3. Implementing the Ecosystem and the Species, First One

Create a new Java class in _tutorial2.logging.impl_ named _LoggingImplOne_ that extends _Logging_, that takes the a _File_ as a parameter to the constructor to store the logs, and resolve the error with the Quick Fixes of Eclipse:

<pre>

package tutorial2.logging.impl;

import java.io.File;

import java.io.FileNotFoundException;

import java.io.FileWriter;

import java.io.IOException;

import java.io.PrintWriter;

import tutorial2.logging.Logging;

import tutorial2.logging.interfaces.ICreateLogger;

public class LoggingImplOne extends Logging {

	private PrintWriter logWriter;

	public LoggingImplOne(File logFile) {

		// if an exception happens, nothing can be done about it

		// we just let logStream be null and

		// the operations of logging won't be done

		try {

			this.logWriter = new PrintWriter(new FileWriter(logFile), true);

		} catch (FileNotFoundException e) {

			System.err.println("An error happened with the file, nothing will be logged.");

			this.logWriter = null;

		} catch (IOException e) {

			System.err.println("An error happened with the file, nothing will be logged.");

			this.logWriter = null;

		}

	}

	@Override

	protected ICreateLogger make_create() {

		// TODO Auto-generated method stub

		return null;

	}

	@Override

	protected Logger make_Logger(String name) {

		// TODO Auto-generated method stub

		return null;

	}

}

</pre>

As we can see, the species we defined needs to be implemented and this implementation needs to be returned by the method _Logger make_Logger(String name)_.

Let's define an inner class inside _LoggingImplOne_ to do that, it will take as a parameter to the constructor the _name_ of the Logger and that will exploit the _logWriter_ to do the actual logging.

<pre>

public class LoggingImplOne extends Logging {

	private PrintWriter logWriter;

	// ...

	@Override

	protected Logger make_Logger(String name) {

		return new LoggerImpl(name);

	}

	private class LoggerImpl extends Logger implements ILog {

		private final String name;

		public LoggerImpl(String name) {

			this.name = name;

		}

		@Override

		protected ILog make_log() {

			return this;

		}

		@Override

		public void addLine(String line) {

			if (logWriter != null) {

				logWriter.println("["+name+"] "+ line);

			}

		}

	}

}

</pre>

Then let's implement the create port by exploiting the method *newLogger(String name)* present in the extended class that enables to instantiate a species:

<pre>

public class LoggingImplOne extends Logging {

	// ...

	@Override

	protected ICreateLogger make_create() {

		return new ICreateLogger() {

			@Override

			public Logger.Component createStandaloneLogger(String name) {

				return newLogger(name);

			}

		};

	}

	// ...

}

</pre>

We now have a complete implementation for the Logging ecosystem.

Let's test it with a very simple program that we put in the package _tutorial2.logging.tests_*:

<pre>

package tutorial2.logging.tests;

import java.io.File;

import tutorial2.logging.Logging;

import tutorial2.logging.Logging.Logger;

import tutorial2.logging.impl.LoggingImplOne;

public class LoggingTest {

	public static void main(String[] args) {

		Logging.Component logging = new LoggingImplOne(new File("/tmp/tutorial2-logging-test.txt")).newComponent();

		// create new Loggers

		Logger.Component l1 = logging.create().createStandaloneLogger("a");

		Logger.Component l2 = logging.create().createStandaloneLogger("b");

		Logger.Component l3 = logging.create().createStandaloneLogger("c");

		// log things to them

		l1.log().addLine("1 a says hi");

		l1.log().addLine("2 test test");

		l2.log().addLine("3 b says hoy");

		l1.log().addLine("4 blabla");

		l3.log().addLine("5 hop");

	}

}

</pre>

Execute it and confirm that the file _/tmp/tutorial2-logging-test.txt_ contains the following:

<pre>

[a] 1 a says hi

[a] 2 test test

[b] 3 b says hoy

[a] 4 blabla

[c] 5 hop

</pre>

h3. Implementing the Ecosystem and the Species, Second One

We can now define a second implementation that stores the logs of each Logger in its own file:

<pre>

package tutorial2.logging.impl;

import java.io.File;

import java.io.FileNotFoundException;

import java.io.FileWriter;

import java.io.IOException;

import java.io.PrintWriter;

import tutorial2.logging.Logging;

import tutorial2.logging.interfaces.ICreateLogger;

import tutorial2.logging.interfaces.ILog;

public class LoggingImplTwo extends Logging {

	private final File logDir;

	public LoggingImplTwo(File logDir) {

		this.logDir = logDir;

		this.logDir.mkdirs();

	}

	@Override

	protected Logger make_Logger(String name) {

		return new LoggerImpl(new File(logDir, name+".txt"));

	}

	@Override

	protected ICreateLogger make_create() {

		return new ICreateLogger() {

			@Override

			public Logger.Component createStandaloneLogger(String name) {

				return newLogger(name);

			}

		};

	}

	private class LoggerImpl extends Logger implements ILog {

		private PrintWriter logWriter;

		public LoggerImpl(File logFile) {

			// if an exception happens, nothing can be done about it

			// we just let logStream be null and

			// the operations of logging won't be done

			try {

				this.logWriter = new PrintWriter(new FileWriter(logFile), true);

			} catch (FileNotFoundException e) {

				System.err.println("An error happened with the file, nothing will be logged.");

				this.logWriter = null;

			} catch (IOException e) {

				System.err.println("An error happened with the file, nothing will be logged.");

				this.logWriter = null;

			}

		}

		@Override

		protected ILog make_log() {

			return this;

		}

		@Override

		public void addLine(String line) {

			if (logWriter != null) {

				logWriter.println(line);

			}

		}

	}

}

</pre>

It can be tested with the previous class by changing the first line instantiating the component:

<pre>

Logging.Component logging = new LoggingImplTwo(new File("/tmp/tutorial2-logging-test/")).newComponent();

</pre>

Execute it and confirm that the _/tmp/tutorial2-logging-test/_ directory contains one file per Logger with the correct content.

h2. The Banking Ecosystem 

Banking will also be an ecosystem, it will contain Account that are species with a particularity: they have required ports!

Because of that, they can't simply be created but must be composed with other components or species to be usable.

h3. Defining the Ecosystem and the Species

Create a SpeADL file named _banking.speadl_ in the package _tutorial2.banking_ and define a _Banking_ ecosystem in _tutorial2.banking_ namespace:

<pre>

import tutorial2.banking.interfaces.IAccountOperations

import tutorial2.banking.interfaces.IAccountStatus

import tutorial2.logging.interfaces.ILog

namespace tutorial2.banking {

	ecosystem Banking {

		species Account(owner: String) {

			provides operations: IAccountOperations

			provides status: IAccountStatus

			requires log: ILog

		}

	}

}

</pre>

Then the interfaces in _tutorial2.banking.interfaces_:

<pre>

package tutorial2.banking.interfaces;

public interface IAccountOperations {

	public void deposit(int value);

	public void withdraw(int value);

}

public interface IAccountStatus {

	public int getBalance();

}

</pre>

h3. Implementing the Ecosystem and the Species

We now  can define an implementation named _BankingImpl_ in the package _tutorial2.banking.impl_.

It exploits the provided ports and the required ports of the species, but also the required port of the ecosystem:

<pre>

package tutorial2.banking.impl;

import java.util.concurrent.atomic.AtomicInteger;

import tutorial2.banking.Banking;

import tutorial2.banking.interfaces.IAccountOperations;

import tutorial2.banking.interfaces.IAccountStatus;

public class BankingImpl extends Banking {

	@Override

	protected Account make_Account(final String owner) {

		return new Account() {

			private final AtomicInteger balance = new AtomicInteger();

			@Override

			protected void start() {

				eco_requires().elog().addLine("Added a new account for "+owner);

			}

			@Override

			protected IAccountOperations make_operations() {

				return new IAccountOperations() {

					@Override

					public void withdraw(int value) {

						provides().operations().deposit(-value);

						requires().log().addLine(value+" were withdrawn, current balance: "+provides().status().getBalance());

					}

					@Override

					public void deposit(int value) {

						balance.addAndGet(value);

						requires().log().addLine(value+" were deposited, current balance: "+provides().status().getBalance());

					}

				};

			}

			@Override

			protected IAccountStatus make_status() {

				return new IAccountStatus() {

					@Override

					public int getBalance() {

						return balance.get();

					}

				};

			}

		};

	}

}

</pre>

Notice the calls to *provides()* and *requires()*.

Now let's add a bit more log for when a species is instantiated: it must be logged in a file specific to the ecosystem and not to the species.

Let's add a required port to the ecosystem _Banking_:

<pre>

requires elog: ILog

</pre>

Then let's add a *start()* method to the implementation of  _Account_ in _BankingImpl_:

<pre>

	@Override

	protected void start() {

		eco_requires().elog().addLine("Added a new account for "+owner);

	}

</pre>

Notice the use of  *eco_requires()* from within the species to access the ports of the ecosystem.

h2. Composing with Uses into a Bank Application

Now that we have the two functionality we need, we can build our application to compose them together.

In order to do that, we need to define an ecosystem with a species that "uses" the other two.

Let's define the ecosystem _Bank_ in a SpeADL file named _bank.speadl_ in the package and namespace _tutorial2.bank_:

<pre>

import tutorial2.banking.Banking

import tutorial2.banking.interfaces.IAccountOperations

import tutorial2.banking.interfaces.IAccountStatus

import tutorial2.logging.Logging

import tutorial2.logging.interfaces.ILog

namespace tutorial2.bank {

	ecosystem Bank {

		provides elog: ILog

		part l: Logging

		part b: Banking {

			bind elog to elog

		}

		species LoggedAccount(owner: String) {

			provides operations: IAccountOperations = ba.operations

			provides status: IAccountStatus = ba.status

			use ll: l.Logger(owner)

			use ba: b.Account(owner) {

				bind log to ll.log

			}

		}

	}

}

</pre>

Notice that