Java is a robust language and when combined with a framework, Java can provide the best solutions for any domain be it e-commerce, banking, cloud computing, finance, big data, stock market, IT, and more.

If you are just starting with Java, see Java live in action with this blog that will run you through all the important concepts you need to know to start working with the frameworks.

What Are Java Frameworks?

A body of pre-written code acting as a template or skeleton, which a developer can then use and reuse to create an application by filling in their code as needed to get the app to work as they intend refers to as a Framework. Reuse of frameworks enables developers to program their application without the manual overhead of creating every line of code from scratch. 
A Java framework is specific to the Java programming language, used as a platform for developing software applications and Java programs.
Java frameworks may include predefined classes and functions used to process, input, and manage hardware devices, as well as interact with system software. It depends on the type of framework, the programmer’s skill level, what they’re trying to accomplish, and their preferences.

Why frameworks?

Frameworks give a structure to your applications. For example, if we have a proper framework for testing, we can automate a lot of things and get accurate and consistent results. Same way if there are frameworks for ORM, web applications, logging, data management etc. it will make a developer’s life simple and help them concentrate more on business logic rather than worrying about common pieces of code used across a domain or application.

Best Java Frameworks

Although there are many frameworks built on Java, here are some very commonly used frameworks of different types – web applications, network applications, logging, testing, ORM, etc. Note that each of these has its own benefits and can work best for different business use cases. We cannot say which is better because they are all good in different scenarios.

Spring

With its concept of Dependency Injection and aspect-oriented programming features, Spring took the development world by storm. It is an open-source framework used for Enterprise applications.

With Spring, developers can create loosely coupled modules where-in dependencies are handled by the framework rather than depending on the libraries in the code.

Spring framework is exhaustive and covers a lot of features including security and configuration, which are easy to learn. Further, since it is the most popular web framework, you can find a lot of documentation and an active community.

With everything configured, your code will be clean and easy to comprehend.

Main concepts:

• Dependency Injection (DI) (Inversion of Control) – In this principle, rather than the application taking control of the flow sequentially, it gives the control to an external controller who drives the flow. The external controller is the events. When some event happens, the application flow continues. This gives flexibility to the application. In Spring, IoC is done by DI which are of three types – setter injection, method injection and constructor injection.
• Beans and Spring Context – In Spring, objects are called as beans and there is a BeanFactory that manages and configures these beans. You can think of the beanfactory as a container that instantiates, configures and manages the beans. Most applications use xml (beans.xml) for the configuration. ApplicationContext which a superset of BeanFactory is used for more complex applications that need event propagation, declarative mechanisms and integration with aspect-oriented features of Spring.
• Read about some more major spring concepts here.

Struts

Apache Struts is another robust open-source framework for web applications. It follows the MVC (Model-View-Controller) model and extends the JSP API. In a traditional servlet-JSP approach, if a user submits let’s say a form with his details, the information then goes to a servlet for processing or the control goes over to next JSP (Java Server Pages – where you can write Java code in an HTML). This becomes confusing for complex applications as the ‘View’ or presentation layer should ideally not have business logic.

Struts separate the View, Controller and the Model (data) and provides the binding between each through a configuration file struts-config.xml.

The controller is an ActionServlet where you can write templates for the View and the user data is maintained using ActionForm JavaBean. The Action object is responsible for forwarding the application flow.

• Dependency Injection (DI) (Inversion of Control) – In this principle, rather than the application taking control of the flow sequentially, it gives the control to an external controller who drives the flow. The external controller is the events. When some event happens, the application flow continues. This gives flexibility to the application. In Spring, IoC is done by DI which are of three types – setter injection, method injection and constructor injection.
• Beans and Spring Context – In Spring, objects are called as beans and there is a BeanFactory that manages and configures these beans. You can think of the beanfactory as a container that instantiates, configures and manages the beans. Most applications use xml (beans.xml) for the configuration. ApplicationContext which a superset of BeanFactory is used for more complex applications that need event propagation, declarative mechanisms and integration with aspect-oriented features of Spring.
• Read about some more major spring concepts here.

The View is maintained by a rich set of tag libraries.

Struts are easy to set up and provides much more flexibility and extensibility over the traditional MVC approach using servlets and JSP alone. It can be a good starting point for your career as a web developer.

Hibernate

Though Hibernate is not a full-stack framework, it completely changed the way we looked at the database. Implementation of Java Persistence API (JPA), Hibernate is an Object-Relational-Mapping (ORM) database for Java applications. Just like SQL, queries in Hibernate are called HQL (Hibernate Query Language).

Hibernate directly maps Java classes to corresponding database tables and vice versa.

The main file in hibernate is the hibernate.cfg.xml file that contains information about mapping Java classes with database configuration.

Hibernate solves the two major problems with JDBC – JDBC doesn’t support object-level relationship and if you ever decide to migrate to a different database, the older queries may not work – meaning a lot of changes – i.e. time and money!

Hibernate provides an abstraction layer so that the code is loosely coupled with the database. Stuff like establishing a database connection, performing CRUD operations are taken care of by Hibernate – so developers need not implement that, hence making the code independent of the database used.

Choose one or more from these beginner and advanced courses to get a complete overview of Hibernate and JPA.

Apache Wicket

If you have already worked with JSP, the learning wicket will be a cakewalk. A simple Java web frameworks, Wicket has a component-oriented structure and all you need to know is Java and HTML. Absolutely no XMLs or configuration files!

The main feature of Wicket is it POJO model wherein components are simple (Plain Old) Java Objects having OOP features. These components are bundled together as reusable packages with images, buttons, forms, links, pages, containers, behaviours and more so that developers can customize them.

Wicket is light-weight and you can build applications really fast. It is also easy to unit test code written in Wicket.