Grails is a rapid web application development framework inspired by the popular Ruby on Rails framework (RoR). Groovy is a dynamic programming language for Java’s Virtual Machine (JVM) and Java Development Kit (JDK) and is used as a primary programming language in Grails. A compelling feature of Groovy is that it can be used in place of Java, or used alongside Java, as per the needs of the development. 

Note: Groovy is an open source language licensed under Apache 2.0 and Grails is built on proven Operational Support Systems (OSS) framework which includes a combination of Spring, Hibernate and Jetty.

Groovy and Grails favors convention over configuration with modern web application best practices like: 

• Convention over configuration 
• Don’t Repeat Yourself (DRY)
• Agile Software Development
• Ajax
• Web services (REST, SOAP etc)
• Built-in Unit testing support

Some of the reasons for using Groovy and Grails in Web Application Development include:

Faster to kickstart a new project: While using traditional Java web application platforms for projects, developers have to spend weeks creating the initial code for the infrastructure. But with the help of Groovy and Grails, a prototype working web application can be engineered with web user interface and database access support in a couple of hours. This enhances the productivity of the developers and they can concentrate on improving the overall quality of the project.

Utilization of Java platform: Java offers tremendous scope for developers in creating ground-breaking web applications. Groovy and Grails can easily be integrated with Java applications. Grails offers an industrious web application framework which reduces the steps in Java Development Framework. It is very easy for the developers to utilize Java library in an easier and faster way with Groovy. The use of Groovy and Grails reduces the development cycle phases and saves precious time. 

Do Not Repeat Yourself (DRY) principle: With the help of Grail’s DRY principle, developers can easily accommodate changes in their code. Since the code is not repeated, developers can concentrate on improving the quality of the project. Grail also assists developers in easily documenting their code. This enables them in getting quick resolution to the problems and helps the novice Grails developers in their team.

Nowadays, it has become a trend in the information technology industry to use various forms of agile development process. However it is extremely difficult for inexperienced developers to take advantage of the Java framework using traditional Java methods to practice Agile methods. Hence, it is important for developers to use Groovy and Grails to exploit the benefits of Java in developing web applications.