Design Patterns - Builder

Design Patterns | Builder

References
Example

References
- Definition: (source: http://en.wikipedia.org/wiki/Builder_pattern)
  
  The intent of the Builder design pattern is to separate the construction of a complex object from its representation.
  By doing so the same construction process can create different representations.
- Class diagram: (source: http://en.wikipedia.org/wiki/Builder_pattern)

Example

The Product:

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public interface Session {
    public String sendRequest(final String request);
}

The Concrete Product:

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public class HttpSession implements Session {
    public String sendRequest(final String request) {
        return "http response";
    }
}

The Builder:

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public interface SessionBuilder {
    public Session getSession();
​
    public void createSession();
​
    public void configureSession();
}

The Concrete Builder:

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public class HttpSessionBuilder implements SessionBuilder {
    private Session session;
​
    public Session getSession() {
        return session;
    }
​
    public void createSession() {
        this.session = new HttpSession();
        // do something else with the created session ...
    }
​
    public void configureSession() {
        // configure the session ...
    }
}

The Director:

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public class SessionDirector {
    private SessionBuilder sessionBuilder;
​
    public SessionDirector(final SessionBuilder sessionBuilder) {
        this.sessionBuilder = sessionBuilder;
    }
​
    public Session build() {
        sessionBuilder.createSession();
        sessionBuilder.configureSession();
        return sessionBuilder.getSession();
    }
}

A simple class to test the Builder design pattern:

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public class BuilderPatternTest {
    public static void main(String[] args) {
        // create the builder
        final SessionBuilder sessionBuilder = new HttpSessionBuilder();
​
        // create the director
        final SessionDirector sessionDirector = new SessionDirector(sessionBuilder);
​
        // create the session
        final Session session = sessionDirector.build();
​
        // call methods
        final String response = session.sendRequest("request");
        System.out.println(response);
    }
}