Lecture 1 - Why bother?

Specification: A detailed precise presentation or plan or proposal for something.

Architecture: The manner in which components of a computer or computer system are organised and integrated.

Engineering: The design and manufacture of complex products.

Current Situation

We have new complexities:

  • Large scale, distributed systems e.g. Internet-centric computing.
  • Cheap microsystems, therefore a massive distribution. e.g. a car has 100s of microprocessors.
  • Internet and web applications.

There is no silver bullet and software engineering is less clear cut than theoretical computer science. We use techniques, methods and tools, that can reduce the complexity of constructing systems.

Software Engineering is the practical application of scientific methods to the specification, design and implementation of programs and systems. We focus on Semi-formal methods.

A language is formal when:

  • It has a formal language (syntax)
  • whose meaning (semantics) is described in a mathematically precise way.

A development method is formal when:

  • it is based on a formal language and
  • there are semantically consistent transformation/proof rules.

UML is a semi-formal method: Often syntax with a mere hint of semantics.


The goal of development is to solve problems in the real world. Structuring and abstraction are critical as the real world is complex. Models are built in the early development phases with a goal of specifying the requirements and precisely whilst avoiding a premature commitment to algorithms or data-structures.

The goal of models is to specify the requirements clearly and precisely whilst not prematurely committing into any algorithm or data-structure.

  • Structuring serves to organise/decompose the problem/solution.
  • Abstraction aims to eliminate insignificant details.

Classical approaches to Structuring and abstraction are:

  • Functional Decomposition: Decomposition independent tasks.
  • Parameterisation and generic development: reusability.
  • Model simplification: To improve understanding of tasks and possible solutions.
  • Information-hiding: Interfaces and property-oriented descriptions.

Interfaces must be clearly described. An interface is an imagined or actual border between two functional entities with fixed rules for the transfer of data. They have:

  • Syntactic properties: The available rules, the types of their arguments etc.
  • Semantic properties: A description of the entities behaviour. The goal is support proper use of the entity.

Interfaces also provide the basis for communicating and explaining (sub)systems between the specifier, implementer, and user.

Lecture 1B - Model-Driven Development (MDD)

Envisages development of software systems as a process consisting of the construction and transformation of software models and semi-automated generation of executable code from models rather than focusing on manual construction of low level code.

It aims to make production of software systems more reliable and efficient by freeing developers from complexity of implementation on particular platforms and by retaining core functionality of a system despite changing technologies. This is very relevant for web applications because the technology for them changes often.

Model Driven Architecture (MDA)

Model Driven Architecture aims to support cost-effective adaption of a system to new technologies and environments by separating technology-independent models of data and functionality of a system from technology-specific models.

Key concepts:

  • Platform-Independent Models (PIMs)
  • Platform-Specific Models (PSMs)
  • Model Transformations

A Platform Independent Model can transform into a Platform Specific Model which transforms into a language implementation.

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A Platform-Independent Model (PIM) is a system specification or design model that models a system in terms of domain concepts and implementation-independent constructs. It expresses business rules that are the core definition of functionalities of a system. If a PIM is defined in a manner that abstracts from particular algorithms and computation procedures, then it can be referred to as a Computation Independent Model.

A Platform-Specific Model (PSM) is a system specification or design model of the system tailored to a specific software platform and programming language such and J2EE and Java or C++. It defines the functionalities of a system in sufficient enough detail to be directly programmed from the model.

A Model Transformation produces a new model from an existing model. This can be to:

  • improve the quality of the a model by removing redundancies
  • refine a PIM towards a PSM
  • refine a PSM to an implementation

UML Notation

  • Use Case Diagrams: Show services used by a system and which users/agents these services interact with.
  • Class Diagrams and Object Diagrams: Describe the structure of entities involved in a system and relationships between these entities.
  • State machine diagrams: Describe the behaviour of objects and execution steps of individual operations on objects.
  • Object Constraint Language (OCL)
  • Interactions Diagrams
  • Activity Diagrams
  • Deployment Diagrams


  • Rectangles denote classes or instances.
  • Ovals denote functions.
  • Names of Classes are not underlined.
  • Names of instances are underlined.
  • An edge between two nodes denotes a relationship between the corresponding entities.

Use Case Diagrams

Use Case Diagrams represent the functionality of the system from a user’s point of view.

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Use cases are a scenario-based technique in the UML which identify the actors in an interaction and which describe the interaction itself. That is, a use case is a set of scenarios tied together by a common user goal (which might succeed or fail). A set of use cases should describe all possible interactions with the system. Sequence diagrams may be used to add detail to use cases by showing the sequence of event processing in the system.

  • Actor: Models an external entity which communicates with the system. They have a unique name and an optional description. e.g. Client: A person in the train.
  • Use Case: A use case represents a kind of task provided by the system as an event flow. A use case consists of:
    • Unique name
    • Participating actors
    • Entry conditions
    • Flow of events
    • Exit conditions
    • Special requirements

Each Use case has:

  • A primary actor, which calls on the system to deliver a service. It is the actor with the goal that the use-case attempts to satisfy, and are usually, but not always the initiator of the use-case. e.g. Client is the initiating actor of Withdraw.
  • A pre-condition (or entry-condition) that describes what the system should ensure is true before the system allows the use case to begin. e.g. Withdraw:Client must have opened a bank account and received a bank card with pin.
  • A guarantee (or exit condition) that describes what the system will ensure at the end of the use case. Success guarantees hold after a successful scenario; minimal guarantees hold after any scenario. Success guarantees hold after a successful scenario. Minimal guarantees hold after any scenario.
  • A trigger that specifies the event that gets the use case started.

Each step in a use case is an element of interaction between an actor and the system. The step should be a simple statement and clearly show who is carrying out the step. The step should show the intent of the actor, not the mechanics of what the actor does. The User Interface is not described in the use case.


  1. actor:Authenticate
  2. system: ATM displays options
  3. actor: Client selects “Withdraw”
  4. system: ATM queries amount
  5. actor: Client enters amount
  6. system: ATM returns bank card
  7. system: ATM outputs specific amount

Reusing use cases

Common behaviour can be factorised using the <<include>> stereotype. e.g. Withdraw includes the Authenticate use case.

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  • Convenient
  • Shorter descriptions
  • Common functionality = reusable components
  • Integration of existing components


  • May lead to functional decomposition rather than an object-oriented model.
  • Requires more UML skills.

Sources to elicit use cases

  • Client
  • User
  • Existing Documents
  • Task Observations

Types of Scenarios

  • Visionary Scenarios: Scenarios that reference future systems.
  • As-is Scenarios: Scenarios that reference current systems. A user describes such system.
  • Evaluation scenarios: The actor performs tasks against the system which is to be evaluated.
  • Training Scenarios: Tasks which aid a novice user for the goal of using/learning.

Class Diagrams

Class Diagrams represent the structure of the system.

Class identification approaches

  • Application Domain Approach: Asking the application domain expert to define objects.
  • Syntactic Approach: Analyse all the use cases to define objects.
  • Design Pattern Approach: Apply design patterns.
  • Component-Based Approach: Use existing solution classes.

Object kinds

  • Entity Object: object that represents application domain context.
  • Boundary Object: object that handles user-system interactions.
  • Control object: object that is responsible of control tasks (coordination of entity and boundary objects) that is executed via the server.

Sequence Diagrams

Sequence Diagrams represent the behaviour of a system as messages (interactions) between different objects.

Statechart Diagrams

Statechart diagrams represent the behaviour of a single object with interesting dynamic behaviour.

Show the interactions of a system.

The state represents the value of a object. e.g. Individual Web pages.

The transition the event that causes a change of state. e.g. Actions performed on the web pages which can be links or submitted forms.

Object Constraint Language (OCL)

OCL enables developers to describe properties of classes, associations and state machines in detail using a textual language.

Lecture 2

Object Models

Object models describe the system in terms of object classes and their associations.

An Object class is an abstraction over a set of objects with common attributes and the services (operations) provided by each object.

  • Natural ways of reflecting the real-world entities manipulated by the system.
  • More abstract entities are more difficult to model using this approach.
  • Object class identification is recognised as a difficult process requiring a deep understanding of the application domain.
  • Object classes reflecting domain entities are reusable across systems

objects are the main unit of abstraction. Objects carry out activities. The interface to objects is event oriented.

  • A clear diamond represents an aggregation that denotes a ”consists-of” hierarchy.

  • A solid diamond represents a composition that denotes a strong aggregation where the life time of the component is controlled by the aggregate. i.e. “The whole controls/destroys the parts”. The component cannot exist without the aggregate.

An abstract class cannot be directly instantiated. An abstract operation has no implementation, but is a pure declaration so that clients can bind to the abstract class. NOTE: It can be indicated by italicizing its name.

An asbtract operaton has no implementation but is a pure declaration so that clients can bind to the abstract class.

An interface is a class that has no implementation. An interface defines which messages an object can receive.

A Class describes objects with similar strucutre and behaviour.

A Class diagram describes the kind of objects in a system and their different static relationships. They represent the structure of a system.

Actor vs Class vs Object

  • Actor: An entity outside the system to be modeled, interacting with the system.
  • Class: An abstraction modeling an entity in the application or solution domain.
  • Object: A specific instance of a class.


syntax: visibility name : type multiplicity = default {property-string}

e.g. - name: String [1] = "Untitled" {readOnly}

  • Visibility can be:
    • + public
    • - private
    • ~ package
    • # protected
  • Property is additional, e.g.:
    • readOnly indicates that clients may not modify the property.
    • frozen indicates that the property is immutable.


Objects of a class collaborate with objects of other classes.

UML supports modeling different relationships between objects or classes.

AssociationDenotes a relationship between 2 classes.alt text
GeneralisationA relationship between a more general description and a more specific variety.alt text
DependencyIf changes to one model may change another.alt text
RealisationRelationship between a specification and its implementation.alt text
UsageSituation where one element requires another for proper functioning.alt text

Generalization expresses a kind-of relationship. It is implemented by inheritance, where child classes inherit the attributes and operations of the parent class.


syntax: visibility name (parameter-list) : return-type {property-string}

Derived properties

Can be calculated based on other values. Notation: /property -- {constraint}.

Reference Objects and Value objects

A reference object is one that has an identity. e.g. a Customer. All changes to the object will be made available to all users.

A value object holds a value that is immutable.

Multiple Classification

  • Classification: The relationships between an object and its type.
    • Single Classification: The object belongs to a single type.
    • Multiple Classification: The object may be described by several types. (Not usually possible in OO as each object must have one type even if it has multiple inheritance.)

Association Classes

Allow one to add attributes, operations and other features to associations.

Lecture 3 - Web Application Development

Model-driven Development is relevant to web application development because there are many rapidly-evolving technologies involved in these applications, which create a corresponding obligation for web applications to be flexible and easily upgraded to these new or enhanced technologies.

Model-driven architecture provides flexibility by defining PIMs that specify business data and business rules of a system, independently of particular technologies.

Development of web applications involves 3 forms of development:

  1. Development of software that
    • receives information from users
    • processes information
    • returns information to clients
  2. Development of visual appearance and behaviour of web pages.
  3. Deciding on information content of web pages, choice of words to use, what information to emphasise, etc.

Properties that are important for web applications

  • Portability: When the system is transported to a new environment, it should behave the same as when it was running in the old environment.
  • Usability: The users must not put unreasonable effort into using the system to achieve provided functionality.
  • Accessibility: The system must be easily accessible by disabled users.

Web Services

Software functions that can be executed from remote applications. It enables integration of applications that are in remote locations so that these applications can behave like they are running in the same location.

Reasons to transform a task into a web service:

  • If it needs to access remote data or business-to-business interactions.
  • If it is a common sub-task in several business process.
  • If it does not require fine-grained interchange of data.
  • If it is not performance critical.

Lecture 4 - Interaction State Diagrams

History Connector

Describes which state was last active.

Switch connector

From analysis to design models

For relational database implementation, the following transformations are used:

  • Remove inheritance by merging subclasses into their superclass. The classes can be represented in separate tables by forming a foreign key relationship from sub to super class.
  • Introduce primary keys for all persistent entities that do not already have an {identity} attribute.
  • Replace many-to-many associations with foreign-key associations.
  • Replace many-to-one associations with foreign keys.

Lecture 5

Different Architectural Styles for Presentation tier

Pure Servlet

Servlets respond to requests, call DBI/business tier and use auxiliary classes to generate response pages.

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Pure JSP

JSPs respond to requests, call DBI/business tier and generate response pages.

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Like pure servlet approach, but using JSPs to construct response pages, on redirect from servlets.

Find Diagram with JSP/Servlet only

Similar to MVC, replace Controllers with Servlets.

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Lecture 6 - Enterprise Information Systems (EIS)

An EIS is a software system which holds core business data for a company or organisation and which performs operations involving this data.

These are usually large and complex systems, typically involving distributed processing and data.

5 Tier Architecture

  1. Client tier: Has responsibility to display information and receive information from the user to transmit to the presentation tier.
  2. Presentation tier: Has responsibility of managing presentation of information to clients and controlling what sequence of interaction should be followed.
    • Insulates the business tier from UI changes.
  3. Business tier: Contains components implementing the business rules and data of the application.
    • Should be the most stable part of EIS.
  4. Integration tier: Manages data retrieval, using interfaces such as JDBC. It insulates the higher tiers from direct knowledge of how data is stored and retrieved.
    • Insulates the business tier from changes in persistence engines.
  5. Resource tier: Contains persistent data storage, such as database, and external resources such as credit card authorisation services.


  • Session Bean: Is a business component that is dedicated to a single client that lives only for the duration of the client’s session. Is is not persistent. It can be used to model stateful or stateless interactions between the client and business tier components.
    • Stateless: Provide a service by a single method call. They do not hold client-specific state so can be shared between them.
    • Stateful: Provide an unsharable service to a single client. The cannot be shared and hold several related operations.

Session Beans should be introduced when the mix of business and view/control logic in the presentation tier becomes too complex. Or when business functionality needs to be made available to multiple applications.

  • Entity Bean: A coarse-grained business component which provides an object view of persistent data. It is multiuser and long-lived. They act as an object-oriented facade for data of a system which may actually be stored as relational tables.

Entity beans should be introduced when persistent business components become complex, and require transaction management.

Container Managed Persistence

J2EE/Java EE provides automated synchronisation of entity bean data and stored data in the resource tier.

  • Less code to write.
  • Greater portability.

Sequence diagram:

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Bean Managed Persistence

Synchronisation is performed manually by the programmer in the bean using JDBC.

  • Greater scope for customisation of database interface code.

Sequence diagram:

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Separation of Code

Controller and view components are used for presentation processing.

Session beans are for business processing.

Entity beans are for complex business data.

EIS Presentation Patterns

1. Intercepting Filter

The intercepting filter’s purpose is to provide a flexible and configurable means to add filtering, pre and post processing, to presentation-tier request/response handling.


  • Is the clients IP address from a trusted network? (IP checker)
  • Does the client have a valid session (Session checker)
  • Is the client’s browser supported (Browser checker)


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Class Diagram:

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2. Front Controller

The front controller’s purpose is to provide a central entry point for an application that controls and manages web request handling. The controller component can control navigation and dispatching.

It makes it easier to impose consistent security, data and checks on requests.


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3. Composite View

The composite view’s purpose is to manage views which are composed from multiple subviews.

Complex web pages are often built from multiple parts. e.g. Navigation, Header, Footer.

Class Diagram:

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EIS Business Patterns

4. Value Object

The value object’s purpose is to improve the efficiency of access to persistent data by grouping data and transferring data as a group of attribute values of each object.

It is inefficient to invoke an Entity Bean’s getAttribute() value one-by-one. It also reduces data transfer costs.

Class Diagram:

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5. Session Facade

The session facade’s purpose is to encapsulate the details of complex interactions between business objects. A session facade for a group of business objects manages these objects and provides a simplified coarse-grained set of operations to clients.


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6. Composite Entity

The composite entity’s purpose is to manage a set of interrelated persistent objects to improve efficiency.

This pattern groups related objects into a single entity bean.

Class Diagram:

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7. Value List Handler

The value list handler’s purpose is to manage a list of data items/objects to be presented to clients.

The result data lists produced by database searches can be very large, so it is impractical to represent the whole set in memory at once.

Class Diagram:

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EIS Integration Patterns

8. Data Access Object

The data access object’s purpose is to abstract details from particular persistent storage mechanisms, hiding these details from the business layer.

Class Diagram:

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Lecture 7 - EJB


  • Implements the beans remote interface
  • When client invokes this interface, the interface delegates to the bean instance, which is in the pool.

Implementation of Enterprise Information Systems

Java 2 Enterprise Edition J2EE is a Java framework for distributed enterprise systems which includes:

  • Servlets, JDBC and JSP
  • Enterprise Java Beans (EJB): representing distributed business components, possibly with persistent data.
  • Java Message Service (JMS): An API to communicate with message-oriented middleware (MOM) to provide messaging services between systems.
  • Java Naming and Directory Interface (JNDI): An interface to support naming and directory services, such as the Java RMI registry for locating remote methods.
  • JavaMail an API for platform-independent mailing and messaging in Java.

J2EE uses the 5-tier architecture.

Typical J2EE System Architecture

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Enterprise Java Beans (EJB)

The two forms of EJB are:

  • Session bean: a business component.
  • Entity bean: A coarse-grained business component.


  • Remote Interface: Lists business operations specific to the bean.
  • Home Interface: Lists lifecycle operations (creation, deletion) and methods (such as findByPrimaryKey) to return particular bean objects.
  • Local interface: Listing business operations that can be accessed by local clients. i.e. those executing in the same JVM as the EJB.
  • Local home interface: Listing lifecycle and finder methods for local clients.

Session EJB lifecycle


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Sequence Diagram:

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Entity EJB lifecycle


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Web Services

Web services are software functions that can be invoked by clients across the internet. They support integration of applications at different network locations, enabling these applications to function as if they were part of a single large software system.

Web services are examples of services in a Service-Oriented Architecture (SOA), and can be used to provide functionalities offered in cloud computing.

Web Service Architecture

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Web Service Design Patterns

Broker Design Pattern: Source application needs to call multiple target services. (e.g. to find price of an item supplied by alternative suppliers). Pattern introduces a broker service to perform this distributed call.

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Router Design Pattern: Source application needs to call one specific service, depending on various criteria/rules. Pattern introduces router service which applies these rules to select correct target service.

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EJB example classes

Using Container Managed Persistence (CMP)

The injected EntityManager comes from the Container. Calling entityManager.persist() is where it is used.

<pre><code class="java"> package; import; import; import javax.ejb.Stateless; import javax.persistence.*; import java.util.List; @Stateless public class MemberManager { @PersistenceContext private EntityManager entityManager; /** * Saves a Member * @param member the Member to save * @return Member */ public Member save(Member member) { if (!this.entityManager.contains(member)) { member = this.entityManager.merge(member); } this.entityManager.persist(member); return member; } /** * Returns a Member given by its username * @param username the username to search for * @return Member * @throws MemberNotFoundException */ public Member findByUsername(String username) throws MemberNotFoundException { Query q = this.entityManager.createNamedQuery("Member.findByUsername"); q.setParameter("username", username); try { return (Member)q.getSingleResult(); } catch (NoResultException e) { throw new MemberNotFoundException(); } } /** * Returns all of the members that a given member is allowed to see * @param member Member * @return List<Member> */ public List<Member> findAllForMember(Member member) { Query q = this.entityManager.createNamedQuery("Member.findAllForMember"); q.setParameter("member", member); return (List<Member>)q.getResultList(); } } </code></pre>

An Entity Bean

Note that this will also be used for ValueObjects. I have NamedQueries that are computed SQL statements so, you can see this as something that provides a view of the persistent data, but isnt an instance of the persistent data itself.

<pre><code class="java"> package; import javax.persistence.*; import javax.validation.constraints.NotNull; import javax.validation.constraints.Size; import; import; import java.util.HashSet; import java.util.Set; @Entity @NamedQueries({ @NamedQuery(name = "Member.findAll", query = "SELECT m from Member m"), @NamedQuery(name = "Member.findByUsername", query = "SELECT m from Member m WHERE m.username = :username"), @NamedQuery(name = "Member.findAllLoggedIn", query = "SELECT m from Member m WHERE m.loggedIn = true"), @NamedQuery( name = "Member.findAllForMember", query = "SELECT m from Member m WHERE m <> :member " + "AND m.loggedIn = true " + "AND m.visibility <> 2 " + "AND (m.visibility = 0) " + "OR (m.visibility = 1 AND :member IN (SELECT a FROM m.friends a))" ) }) public class Member implements Serializable { public static int EVERYONE = 0; public static int FRIENDS_ONLY = 1; public static int NOBODY = 2; @NotNull @Size(min = 1, max = 255) @Id private String username; @NotNull @Size(min = 1, max = 255) private String password; @NotNull private boolean loggedIn = false; @NotNull private int visibility = Member.EVERYONE; @OneToMany(fetch = FetchType.EAGER) private Set<Member> friends = new HashSet<>(); /** * Returns the username * @return String */ public String getUsername() { return this.username; } /** * Sets the username * @param username The username */ public void setUsername(String username) { this.username = username; } /** * Returns the password * @return String */ public String getPassword() { return this.password; } /** * Sets the password * @param password The password */ public void setPassword(String password) { this.password = password; } /** * Returns whether or not the Member is logged in * @return boolean */ public boolean isLoggedIn() { return this.loggedIn; } /** * Sets whether or not the Member is logged in * @param loggedIn True if the member is logged in, false otherwise */ public void setLoggedIn(Boolean loggedIn) { this.loggedIn = loggedIn; } /** * Returns the Visibility level of the Member * @return int */ public int getVisibility() { return this.visibility; } /** * Returns the possible Visibility levels for a Member * @return int[] */ public static int[] getVisibilities() { return new int[]{Member.EVERYONE, Member.FRIENDS_ONLY, Member.NOBODY}; } /** * Returns a human-readable string representation of the Visbility * @return String */ public String getReadableVisibility() { switch (this.getVisibility()) { case 0: return "Everyone"; case 1: return "Friends Only"; case 2: return "Nobody"; default: return "N/A"; } } /** * Sets the visibility for the Member * @param visibility The integer representation of a Visibility */ public void setVisibility(int visibility) { this.visibility = visibility; } /** * Returns the Friends * @return Set<Member> */ public Set<Member> getFriends() { return this.friends; } /** * Adds a given Member as a Friend to the Member * @param friend the Member to add */ public void addFriend(Member friend) { this.friends.add(friend); } /** * Removes a given Member as a Friend from the Member * @param friend the Member to remove */ public void removeFriend(Member friend) { this.friends.remove(friend); } public String toString() { return String.format( "Member(username: %s, loggedIn: %s)", this.getUsername(), this.isLoggedIn() ); } @Override public boolean equals(Object object) { if (object == this) return true; if (!(object instanceof Member)) return false; Member other = (Member) object; return other.getUsername().equals(this.getUsername()); } @Override public int hashCode() { int hash = 7; hash = 31 * hash + this.username.hashCode(); return hash; } /** * Serialize the Member without Friends to solve recursive serialization * @param out the output stream * @throws IOException */ private void writeObject( out) throws IOException { out.writeObject(this.getUsername()); out.writeObject(this.isLoggedIn()); out.writeObject(this.getVisibility()); } /** * Serialize the Member without Friends to solve recursive serialization * @param in the input stream * @throws IOException * @throws ClassNotFoundException */ private void readObject( in) throws IOException, ClassNotFoundException { this.username = (String) in.readObject(); this.loggedIn = (boolean) in.readObject(); this.visibility = (int) in.readObject(); } } </code></pre>

Intercepting Filter

<pre><code class="java"> package; import; import; import; import javax.inject.Inject; import javax.servlet.*; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import javax.servlet.http.HttpSession; import; public class AuthFilter implements Filter { @Inject private AuthTokenManager authTokenManager; @Override public void init(FilterConfig filterConfig) throws ServletException { } @Override public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException { HttpSession session = ((HttpServletRequest)servletRequest).getSession(); String token = (String)session.getAttribute("auth_token"); Member member = (Member)session.getAttribute("member"); if (!this.authTokenManager.isValidAuthToken(token, member)) { String contextPath = ((HttpServletRequest)servletRequest).getContextPath(); ((HttpServletResponse)servletResponse).sendRedirect(String.format("%s/auth/login.xhtml", contextPath)); } filterChain.doFilter(servletRequest, servletResponse); } @Override public void destroy() { } } </code></pre>