"Simple" Factory (padrão de desenho)

O padrão "simple" factory fornece uma forma de criar objectos a partir de uma descrição externa.

O processo de criação de objectos a partir de texto é um processo semelhante à compilação e implica interpretar esse texto e construir a semântica.

Utilização de Método Independente da Linguagem

<java5>

       public void readImportFile(String name) throws IOException {
               BufferedReader reader = new BufferedReader(new FileReader(name));
               String line;
               while ((line = reader.readLine()) != null) {
                       String[] fields = line.split("\\|");
                       try {
                               registerFromFields(fields);
                       } catch (UnknownDataException e) {
                               System.err.printf("WARNING: unknown data %s\n", e.getMessage());
                               e.printStackTrace();
                       } catch (PublicationExistsException e) {
                               e.printStackTrace();
                       } catch (UnknownAgentException e) {
                               e.printStackTrace();
                       } catch (ClientExistsException e) {
                               e.printStackTrace();
                       } catch (InvalidIdentifierException e) {
                               e.printStackTrace();
                       }
               }
               reader.close();
       }

</java5>

<java5>

       public void registerFromFields(String[] fields) throws UnknownDataException,
                       PublicationExistsException, UnknownAgentException, ClientExistsException,
                       InvalidIdentifierException {
               // Regular expression pattern to match an agent.
               Pattern patAgent = Pattern.compile("^(PERSON|ORGANIZATION)");
               // Regular expression pattern to match a message.
               Pattern patMessage = Pattern.compile("^(MESSAGE)");
               // Regular expression pattern to match a publication.
               Pattern parPublication = Pattern.compile("^(IMAGE|NOTE|URI)");
               // Regular expression pattern to match a publication.
               Pattern parConnection = Pattern.compile("^(CONNECTION)");

               if (patAgent.matcher(fields[0]).matches()) {
                       registerAgent(fields);
               } else if (patMessage.matcher(fields[0]).matches()) {
                       registerMessage(fields);
               } else if (parPublication.matcher(fields[0]).matches()) {
                       registerPublication(fields);
               } else if (parConnection.matcher(fields[0]).matches()) {
                       registerConnection(fields);
               } else {
                       throw new UnknownDataException(fields[0]);
               }
       }

</java5>

<java5>

       /**
        * @param fields
        *            0 - type; 1 - id/null; 2 - agent; other - pub-specific
        * @throws PublicationExistsException
        *             we throw it because we may be called from outside (i.e., we
        *             are not responsible for communicating the problem to the
        *             end-user)
        * @throws UnknownAgentException
        *             we throw it because we may be called from outside (i.e., we
        *             are not responsible for communicating the problem to the
        *             end-user)
        * @throws UnknownDataException
        *             we throw it because we may be called from outside (i.e., we
        *             are not responsible for communicating the problem to the
        *             end-user)
        */
       public void registerPublication(String... fields) throws PublicationExistsException,
                       UnknownAgentException, UnknownDataException {
               int pubId = (fields[1] != null) ? Integer.parseInt(fields[1]) : getUUID();
               int agtId = Integer.parseInt(fields[2]);
               if (fields[0].equals("IMAGE")) {
                       Image image = new Image(pubId, fields[3], fields[4]);
                       Agent owner = fetchAgent(agtId);
                       owner.addPublication(pubId, image);
                       setLastUUID(pubId);
                       changed();
               } else if (fields[0].equals("NOTE")) {
                       TextNote note = new TextNote(pubId, fields[3], fields[4]);
                       Agent owner = fetchAgent(agtId);
                       owner.addPublication(pubId, note);
                       setLastUUID(pubId);
                       changed();
               } else if (fields[0].equals("URI")) {
                       URI uri = new URI(pubId, fields[3], fields[4]);
                       Agent owner = fetchAgent(agtId);
                       owner.addPublication(pubId, uri);
                       setLastUUID(pubId);
                       changed();
               } else {
                       throw new UnknownDataException(fields[0]);
               }
       }

</java5>

<java5>

       /**
        * Format: type|id-or-null|name|email|phone
        * 
        * @param fields
        * @throws ClientExistsException
        *             we throw it because we may be called from outside (i.e., we
        *             are not responsible for communicating the problem to the
        *             end-user)
        * @throws UnknownDataException
        *             we throw it because we may be called from outside (i.e., we
        *             are not responsible for communicating the problem to the
        *             end-user)
        */
       @SuppressWarnings("nls")
       public void registerAgent(String... fields) throws ClientExistsException, UnknownDataException {
               int id = (fields[1] != null) ? Integer.parseInt(fields[1]) : getUUID();
               if (fields[0].equals("PERSON")) {
                       Person person = new Person(id, fields[2], fields[3], fields[4]);
                       addAgent(id, person);
                       setLastUUID(id);
                       changed();
               } else if (fields[0].equals("ORGANIZATION")) {
                       Organization organization = new Organization(id, fields[2], fields[3], fields[4]);
                       addAgent(id, organization);
                       setLastUUID(id);
                       changed();
               } else {
                       throw new UnknownDataException(fields[0]);
               }
       }

</java5>

<java5>

       /**
        * This method DOES NOT check message permissions when registering messages
        * with agents inboxes/outboxes. It must be private.
        * 
        * @param fields
        * @throws UnknownAgentException
        * @throws UnknownDataException
        * @throws InvalidIdentifierException
        */
       @SuppressWarnings("nls")
       private void registerMessage(String... fields) throws UnknownAgentException,
                       UnknownDataException, InvalidIdentifierException {
               if (fields[0].equals("MESSAGE")) {
                       int msgId = Integer.parseInt(fields[1]);
                       Sender sender = fetchAgent(Integer.parseInt(fields[2]));
                       List<Recipient> recipients = new ArrayList<Recipient>();
                       for (String recipientId : fields[3].split(",")) {
                               Recipient recipient = fetchAgent(Integer.parseInt(recipientId));
                               recipients.add(recipient);
                       }
                       assertValidIdentifier(msgId);
                       EmailMessage message = new EmailMessage(msgId, fields[2], sender, fields[3],
                                       recipients, fields[4], fields[5], "", null);
                       sendMessage(message);
                       setLastUUID(msgId);
                       changed();
               } else {
                       throw new UnknownDataException(fields[0]);
               }
       }

</java5>

Connections between agents

Unrelated exceptions that are detected in this function are simply forwarded.

<java5>

       private void registerConnection(String[] fields) throws NumberFormatException,
                       UnknownAgentException, UnknownDataException {
               if (fields[0].equals("CONNECTION")) {
                       Agent a1 = fetchAgent(Integer.parseInt(fields[1]));
                       Agent a2 = fetchAgent(Integer.parseInt(fields[2]));
                       boolean a1Accepting = (Integer.parseInt(fields[3]) != 0);
                       boolean a2Accepting = (Integer.parseInt(fields[4]) != 0);
                       a1.addConnection(new Connection(a1, a2, a1Accepting, a2Accepting));
                       a2.addConnection(new Connection(a2, a1, a2Accepting, a1Accepting));
                       changed();
               } else {
                       throw new UnknownDataException(fields[0]);
               }
       }

</java5>

Utilização de Informação de Tipos em Tempo de Execução

Neste caso, apresenta-se a criação dinâmica de objectos de um determinado tipo, a partir de descrições textuais desses objectos.

Este exemplo utiliza informação de tipos em tempo de execução. Note-se que este tipo de abordagem apenas é possível em linguagens que providenciem este tipo de informação em tempo de execução, como é o caso do Java.

• Informação de Tipos em Tempo de Execução (Java)