Advanced Java Servlets

• Advance Java includes more specialized and complex Java topics beyond the basics
• Designed for developing enterprise-level applications

Servlets

• Java classes extending server capabilities, typically web servers
• Servlets respond to incoming requests, commonly HTTP requests
• Platform-independent Java classes that run on any server supporting the Servlet specification
• The javax.servlet and javax.servlet.http packages provide interfaces and classes for writing servlets
• Common tasks include handling form data, managing sessions, and generating dynamic content

Servlet Lifecycle

• Consists of initialization, request handling, and destruction
• Initialization: init() method, called once when the servlet is loaded
• Request handling: service() method, called for each request
• service() method dispatches requests to doGet(), doPost(), doPut(), doDelete(), etc., based on the HTTP method
• Destruction: destroy() method, called when the servlet is taken out of service

Servlet Configuration

• Configured using the web.xml deployment descriptor file or annotations
• web.xml maps URL patterns to servlet classes
• Specifies initialization parameters for servlets
• Annotations like @WebServlet, @WebInitParam, and @WebListener provide an alternative configuration approach

JavaServer Pages (JSP)

• Server-side scripting technology for embedding Java code within HTML pages
• JSPs are compiled into servlets by the JSP container
• Simplifies the creation of dynamic web content
• Uses special tags (e.g., <% ... %>, <%= ... %>, <jsp: ... %>) to insert Java code and control page rendering

JSP Lifecycle

• Involves translation, compilation, class loading, instantiation, initialization, request processing, and destruction
• Translation converts the JSP into a servlet source code
• Compilation compiles the servlet source code into a servlet class
• The servlet container loads the servlet class and creates an instance of the servlet
• jspInit() method is called for initialization
• _jspService() method handles requests
• jspDestroy() method is called during destruction

JSP Implicit Objects

• Provides implicit objects automatically available within the JSP page
• Includes request, response, session, application, out, page, pageContext, config, and exception
• Allows easy access to request parameters, session data, application context, output stream, etc.

JSP Standard Tag Library (JSTL)

• Collection of pre-defined JSP tags providing common functionality
• Simplifies JSP development by providing tags for core tasks, formatting, XML processing, database access, and more
• Core tags include <c:out>, <c:set>, <c:if>, <c:forEach>, etc.
• Promotes code reuse and reduces the amount of Java code in JSPs

Java Database Connectivity (JDBC)

• API for connecting to and interacting with relational databases from Java
• Provides a standard way to perform database operations like querying, updating, and deleting data
• JDBC drivers are required to connect to specific database systems (e.g., MySQL, Oracle, PostgreSQL)
• The JDBC API includes interfaces and classes for establishing connections, executing SQL statements, and processing results

JDBC Steps

• Load the JDBC driver using Class.forName()
• Establish a connection to the database using DriverManager.getConnection()
• Create a statement using Connection.createStatement() or Connection.prepareStatement()
• Execute the query using Statement.executeQuery() or PreparedStatement.executeUpdate()
• Process the result set using ResultSet.next() and ResultSet.getXXX() methods
• Close the connection, statement, and result set in a finally block to release resources

Prepared Statements

• Precompiled SQL statements that can be executed multiple times with different parameters
• Prevents SQL injection attacks by properly escaping input values
• Improves performance by reducing the overhead of parsing and compiling SQL statements for each execution
• Parameters are set using PreparedStatement.setXXX() methods, such as setInt(), setString(), setDate()

Transactions

• Sequence of database operations treated as a single unit of work
• Ensures data consistency by providing atomicity, consistency, isolation, and durability (ACID) properties
• JDBC supports transactions through the Connection.setAutoCommit(), Connection.commit(), and Connection.rollback() methods
• setAutoCommit(false) disables automatic committing of changes, allowing multiple operations to be grouped into a transaction
• commit() saves all changes made during the transaction
• rollback() reverts all changes made during the transaction

Java Naming and Directory Interface (JNDI)

• API for accessing naming and directory services
• Allows Java applications to look up resources such as database connections, JMS queues, and enterprise beans using logical names
• Abstracts the underlying naming and directory implementation, providing a uniform way to access different services

JNDI Context

• Uses a context-based approach for looking up resources
• The initial context is obtained using InitialContext
• Resources are bound to names within the context using Context.bind()
• Resources are looked up using Context.lookup()
• Commonly used in enterprise applications to manage and access shared resources

Enterprise JavaBeans (EJB)

• Managed Java components that run in an EJB container within an application server
• Provides a component-based architecture for developing distributed enterprise applications
• Simplifies development by providing services such as transaction management, security, concurrency, and dependency injection

EJB Types

• Session beans encapsulate business logic and are typically used to perform tasks on behalf of a client
• Entity beans represent persistent data and are mapped to database tables
• Message-driven beans (MDBs) asynchronously process messages from JMS queues or topics

Session Beans

• Stateless session beans do not maintain client-specific state
• Stateful session beans maintain client-specific state across multiple method calls
• Singleton session beans are instantiated only once per application and provide a shared, thread-safe resource

Entity Beans

• Entity beans represent persistent data stored in a database
• Can be managed by the container (container-managed persistence or CMP) or by the bean itself (bean-managed persistence or BMP)
• JPA (Java Persistence API) is commonly used for defining and managing entity beans

Message-Driven Beans (MDBs)

• MDBs asynchronously process messages from JMS queues or topics
• They are activated when a message arrives and perform a specific task
• Commonly used for implementing event-driven architectures

Dependency Injection and Annotations

• Dependency injection (DI) is a design pattern that allows objects to be created with dependencies supplied from an external source
• Annotations like @Inject, @EJB, and @Resource are used to inject dependencies into EJB components
• DI simplifies configuration and promotes loose coupling between components

Java Persistence API (JPA)

• JPA is a standard API for object-relational mapping (ORM) in Java
• Allows developers to map Java objects to database tables and perform database operations using object-oriented concepts
• JPA providers (e.g., Hibernate, EclipseLink) implement the JPA specification and provide the runtime environment

JPA Entities

• Entities are Java classes that represent database tables
• Annotated with @Entity to indicate that they are persistent objects
• Fields are mapped to database columns using annotations like @Id, @Column, @ManyToOne, @OneToMany, etc.

EntityManager

• Primary interface for interacting with the persistence context
• Used to persist, update, delete, and retrieve entities
• EntityManagerFactory is used to create EntityManager instances
• Queries are defined using JPQL (Java Persistence Query Language) or native SQL

Hibernate

• Popular open-source JPA provider
• Provides advanced features such as caching, lazy loading, and optimistic locking
• Uses a configuration file (e.g., hibernate.cfg.xml) or annotations to map entities to database tables

Spring Framework

• Comprehensive application framework for building enterprise Java applications
• Provides features such as dependency injection, aspect-oriented programming (AOP), transaction management, and MVC framework
• Simplifies development by providing a consistent and modular programming model

Spring Modules

• Spring Core provides the basic DI and IoC (Inversion of Control) container
• Spring MVC provides a framework for building web applications
• Spring Data simplifies data access with repositories
• Spring Security provides authentication and authorization features

Spring Boot

• Simplifies the creation of Spring-based applications by providing auto-configuration and embedded servers
• Reduces boilerplate code and makes it easy to create standalone, production-ready applications
• Uses convention over configuration to automatically configure application components

Web Services

• Software systems that communicate over a network using standard protocols
• Enables interoperability between different platforms and technologies
• SOAP (Simple Object Access Protocol) and REST (Representational State Transfer) are common web service architectures

SOAP Web Services

• SOAP is a protocol for exchanging structured information in web services
• SOAP messages are typically transported over HTTP, SMTP, or other protocols
• WSDL (Web Services Description Language) is used to describe the capabilities and interface of a SOAP web service

RESTful Web Services

• REST is an architectural style for building web services
• RESTful web services use HTTP methods (GET, POST, PUT, DELETE) to perform operations on resources
• Resources are identified by URIs (Uniform Resource Identifiers)
• RESTful web services typically exchange data in JSON or XML format

Java API for RESTful Web Services (JAX-RS)

• JAX-RS is a Java API for creating RESTful web services
• Annotations like @Path, @GET, @POST, @PUT, @DELETE, and @Produces are used to define resource endpoints and specify media types
• JAX-RS implementations (e.g., Jersey, RESTEasy) provide the runtime environment for deploying and running RESTful web services

Java Message Service (JMS)

• JMS is an API for sending and receiving messages in a distributed environment
• Enables asynchronous communication between applications
• JMS providers (e.g., ActiveMQ, RabbitMQ) implement the JMS specification and provide the messaging infrastructure

JMS Concepts

• Messages are the units of communication in JMS
• Destinations (queues and topics) are used to send and receive messages
• Message producers send messages to destinations
• Message consumers receive messages from destinations

Servlets are Java classes that enhance server capabilities, responding to HTTP requests. They're platform-independent, using javax.servlet and javax.servlet.http. Servlets handle form data, sessions, and dynamic content, managed through initialization, request handling, and destruction.