Question

State which of the following are true and which are false. If false, explain why. a) Data associated with an entity EJB typically is stored in a relational database. b) The remote interface for an entity EJB represents the database table with which the EJB is associated. c) Entity EJBs that use bean-managed persistence require the deployer to specify SQL queries for inserting, updating, deleting and querying data from the database. d) The create methods in the home interface for an entity EJB insert new records into the underlying database. e) Entity EJBs should obtain necessary resources in method ejbcreate. f) Entity EJBs that use container-managed persistence must implement interface CMPEntityBean, whereas those that use bean-managed persistence must implement interface EntityBean

Short answer

a) True; b) False; c) True; d) True; e) False; f) True.

Step-by-step solution

Understanding Entity EJB Storage

Statement a proposes that data associated with an entity EJB is typically stored in a relational database. Entity EJBs are designed to represent persistent data that is most commonly stored in a relational database. Hence, this statement is indeed true.

Remote Interface Representation

Statement b claims that the remote interface for an entity EJB represents the database table associated with the EJB. This is false. The remote interface provides a client view to access the EJB's methods but does not directly represent the database table.

Bean-managed Persistence (BMP)

Statement c suggests that for entity EJBs using bean-managed persistence, the deployer must specify SQL queries. In BMP, the developer writes the code to access the database, including detailed SQL, so this statement is true.

Create Methods and Database Records

Statement d mentions that create methods in the home interface for an entity EJB insert new records into the database. This is true as these methods are responsible for creating a new instance and inserting it into the database.

Resource Acquisition in ejbCreate

Statement e suggests that entity EJBs should obtain necessary resources in method ejbCreate. This statement is false because ejbCreate is meant to initialize bean-related resources rather than obtain database connections or other external resources.

Persistence Type Implementation

Statement f asserts different interface implementations based on persistence type: CMPEntityBean for container-managed persistence and EntityBean for bean-managed persistence. This is true since container-managed persistence does not require CMPEntityBean implementation, but interfaces follow specific requirements for persistence management.

Key concepts

Relational Database

A relational database is a digital database based on the relational model of data. This model organizes data into one or more tables (or "relations") of rows and columns, with a unique key identifying each row. These databases are powerful tools for structuring data in a way that can be easily accessed and managed. The compatibility with Structured Query Language (SQL) makes relational databases particularly popular because SQL is a standard language used for database management and manipulation across many different systems.

Entity Enterprise JavaBeans (EJBs) are often tied with relational databases when it comes to persisting data. They map objects in a Java application to the records and fields in a relational database, allowing for a smoother transfer and manipulation of data between the application and its storage. This connection to relational databases makes it easier for developers to manage large amounts of structured data using Entity EJBs as entities often represent data that is persistent and structured.

Bean-managed Persistence

Bean-managed persistence (BMP) is a strategy used in Java EE to manage entity EJB persistence where the developers themselves are responsible for coding the database access logic. This requires an understanding of JDBC (Java Database Connectivity) and the ability to write SQL queries to perform CRUD operations: Create, Read, Update, and Delete.

Here are the responsibilities under BMP:

• Write detailed SQL queries: Developers must write and manage SQL queries to interact with the database.
• Handle database connections: The developer manages database connections, ensuring they are closed after use to maintain optimum performance and resource management.
• Implement custom transaction management: Manages how applications and transactions access and manipulate data across multiple databases.

BMP provides great flexibility and control, but it is essential for developers to have a strong grasp of SQL and database management skills to avoid errors and ensure efficient database operations.

Container-managed Persistence

In contrast to bean-managed persistence, container-managed persistence (CMP) is managed by the enterprise bean container, taking a lot of load off the developers' shoulders. With CMP, the container generates SQL statements automatically and manages database transactions based on the abstract definitions and mappings provided by entities and container configuration.

Key features of CMP include:

• Minimal developer involvement in SQL: Developers do not need to write explicit SQL queries for CRUD operations, allowing them to focus more on business logic.
• Automated database transactions: The container is responsible for managing transactions, reducing the likelihood of transaction management errors.
• Simplified codebase: With less code to manage, the codebase remains more maintainable and readable.

CMP is advantageous for developers who prefer not to delve deeply into SQL or database transactions, offering a simpler approach without sacrificing functionality.

Remote Interface

A remote interface in the context of Java EE represents the client-view of an Enterprise JavaBean (EJB). It allows clients to interact with the EJB remotely, typically across a network. This capability makes distributed computing possible by enabling applications to scale across different systems while still being cohesive.

Characteristics of a remote interface include:

• Eases remote invocation: Through the remote interface, a client can invoke business methods on EJBs as if they were local, hiding the complexity of remote method invocation.
• Defines business methods: The remote interface specifies the business methods that a client can call. These methods are implemented by the enterprise bean itself.
• Security and transaction capabilities: While it provides remote access, it also handles security checks and enforces transactional constraints.

Despite its benefits, a remote interface adds complexity in deployment and configuration, making it more suited to applications needing strong scalability and distribution.

SQL Queries

SQL queries form the basis for database interaction in relational databases. SQL, or Structured Query Language, is used to perform CRUD operations on the data stored in a relational database.

Here are some of the core SQL operations:

• SELECT: Retrieves data from one or more tables, allowing filtering, sorting, and aggregation.
• INSERT: Adds new records into a table.
• UPDATE: Modifies existing records with new data.
• DELETE: Removes records from a table based on specified conditions.

In the realm of EJBs, understanding SQL is especially crucial for those using bean-managed persistence, where developers explicitly define queries to manipulate data. Mastering SQL offers precise control over database interactions, which is essential for both performance and data integrity.