Java EE (EJB, Servlets, JSP) Quiz

The question asks which option is NOT a session management method. HTTP Redirects (sendRedirect) is not considered a core session management technique; it's a redirection mechanism. The standard session management methods are Cookies, Hidden Form Fields, URL Rewriting, and HttpSession.

To solve this question, the user needs to know the basic concept of thread safety in Java and how it applies to local variables in methods like service(), doPost() and doGet().

The answer to this question is:

A. True

Explanation:

Local variables declared within a method are thread-safe because they are confined to the method and are not shared between threads. Each thread, when executing the method, will have its own copy of the local variables declared within the method. As a result, other threads cannot modify the values of these local variables, ensuring thread safety.

Therefore, the correct answer is option A, true.

For sendRedirect(), you must use encodeRedirectURL(). The encodeURL() method is for regular URLs (links in HTML, form actions). encodeRedirectURL() specifically handles the session encoding rules required for redirect responses.

The getParameterValues() method of the ServletRequest interface returns an array of String objects containing all of the values that the given request parameter has, or null if the parameter does not exist. The other methods do not exist or return single values.

If a transaction is initiated by a client (Required attribute) and the bean method throws a system (unchecked) exception, the EJB container intercepts it, rolls back the transaction, and throws a TransactionRolledBackException to the client. Checked exceptions do not cause auto-rollback by default.

To maintain client state, the user needs to know the different options available and which option is best suited to the given scenario.

A. Cookies: Cookies are small text files that are stored on the client's computer. They can be used to store client state information, such as user preferences or session IDs. While cookies can be effective for maintaining state, they have some limitations, such as a limited storage capacity and the potential for security vulnerabilities.

B. Entity Beans: Entity beans are used to represent persistent data in a Java Enterprise Edition (JEE) application. They are not designed to maintain client state.

C. HttpSession attributes: HttpSession attributes are used to store client-specific information on the server side. They are associated with a particular user session and can be used to maintain client state across multiple requests. This makes HttpSession attributes a good option for maintaining client state in a JEE application.

D. Stateful session beans: Stateful session beans are designed to maintain state across multiple requests. They are associated with a particular client and can be used to store client-specific information. This makes stateful session beans a good option for maintaining client state in a JEE application.

E. URL Rewriting: URL rewriting is a technique for adding session IDs to URLs. This allows the server to identify the client and maintain state across multiple requests. While URL rewriting can be effective for maintaining state, it has some limitations, such as the potential for security vulnerabilities and the impact on URL readability.

Based on the given scenario, the best option for maintaining client state is D. Stateful session beans, as they are designed to maintain state across multiple requests and are associated with a particular client. Option C. HttpSession attributes is also a good option since it can be used to maintain client state across multiple requests. Option A. Cookies and option E. URL Rewriting can also be used to maintain state but are less suited to the given scenario.

The Answer is: D. Stateful session beans

Message Driven Beans (MDBs) do not have client view interfaces (local or remote) because they do not receive direct synchronous calls from clients; instead, they act as asynchronous message consumers listening to JMS queues or topics.

The SessionFacade pattern hides complexity, provides a simple interface, and reduces network traffic by consolidating remote calls. However, it manages transactions on the server side; allowing the client to control fine-grained transactions contradicts the pattern's goal of abstraction.

When you use only the type attribute in jsp:useBean (without class or beanName), the container will look for an existing bean with the specified scope and type. If no existing bean is found, no new instance is created. This prevents instantiation when you only want to reference existing beans.

In a unidirectional one-to-many CMR relationship where A owns the relationship to B, only bean A's local interface exposes the relationship methods (abstract getter/setter for the collection of B). Bean B has no knowledge of the relationship in unidirectional CMR.

In bean-managed transactions (BMT), stateful session beans manage their own transactions using UserTransaction methods. The getRollbackOnly() method is specific to container-managed transactions (CMT) and is not available in BMT context. getUserTransaction() and getStatus() are valid methods that can be called in BMT.

The method signature shows RemoteException in the throws clause, which is only present in remote interfaces (local interfaces don't throw RemoteException). The create method with parameters can be used by stateful session beans to initialize state during creation, whereas stateless session beans typically have no-arg create methods.

The Value Object (or Transfer Object) pattern reduces network traffic by grouping multiple attributes into a single object transfer, minimizing remote calls. Business Delegate abstracts business service lookups, DAO abstracts data persistence, and MVC decouples model, view, and controller components.

Top-level classes in Java cannot be declared static. However, nested classes (inner classes) inside another class can be declared as static. Static nested classes are different from inner classes - they don't have access to instance members of the enclosing class.

Static inner classes (nested static classes) behave like regular classes - their members are NOT static by default. They can have both instance and static members, just like any other Java class. The 'static' keyword on the class only means it doesn't require an instance of the enclosing class.

Anonymous inner classes can be created within interfaces in specific contexts. While interfaces cannot have instance initializers, anonymous classes can be defined inside static contexts like static field initialization or static blocks within the interface. This is a valid though rarely used Java feature.

Java supports dynamic class creation at runtime through bytecode generation libraries like ASM, BCEL, or through the Java Compiler API. Classes can be generated programmatically with custom methods, fields, and interface implementations. This is used in frameworks, proxies, and dynamic programming.

Java has both static and dynamic dispatch. Static dispatch occurs for private, static, and final methods - these are resolved at compile time based on the declared type. Dynamic dispatch (virtual method invocation) occurs for overridden instance methods, resolved at runtime based on the actual object type.