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What Is Application Modernization?

A short introduction to application modernization and some different ways to approach it.

Application modernization - sometimes called legacy modernization or legacy application modernization - is the process of updating existing Java applications for newer technology and approaches.

Commonly part of an overall digital transformation strategy, application modernization typically updates applications reliant on a monolithic architecture, on-premises hosting, waterfall development processes, legacy frameworks and platforms, or some combination of these factors.

Applications modernization is an essential task for IT leaders if business-critical applications are going to support today’s business needs.

Why modernize?

Over time, the performance of legacy applications declines. Whilst legacy systems are often critical for business operation, the fact is that they can’t keep up with today’s technology. They become expensive to maintain, difficult to update, are inefficient, and can have severe performance issues. Security can also become an issue when it becomes hard to make changes with confidence.

if you are going to keep up with demand, retain your customers, and remain competitive, you need to make a change. The question for IT leaders is how to scope application modernization for the best balance of cost, effort and benefit. 

The importance of Java

Among the enterprise applications most often in need of modernization are those written in Java. Java has been used to build enterprise software for nearly 30 years, and over that time, a staggering amount of code has been written - much of which is still in use today.

According to the Diffblue Java Application Modernization Survey, 96% of businesses consider Java applications to be extremely or very important to their organizations.  Most organizations with more than 3000 employees have at least 100 Java applications.

Only 5% of firms will migrate any applications away from Java, however. In fact, survey respondents said they plan to modernize more than 80% of all their Java applications.

Different types of application modernization

Application modernization has become something of an umbrella term for a variety of different things which improve the performance of legacy software. Some common types of application modernization are:

Cloud migration

Moving legacy systems to the cloud allows businesses to scale computer power (and the amount they spend) according to demand, avoiding the fixed cost and risk of under-utilization inherent in on-premises data centers. Though the idea that cloud hosting is cheaper is no longer universally accepted, many businesses are still planning to migrate to public cloud, private cloud, or a hybrid of the two.


A microservices architecture distributes the functionality of an overall application into a loosely coupled range of separate components that communicate with each other, typically via APIs. Microservices accelerate software change as each component is discrete in scope and can be independently updated and deployed, but they increase overall system complexity and can make effective testing more difficult.


Containers are a cloud-centric method for packaging, deploying, and running software in a way that enables it to operate consistently across different hardware, environments, and platforms. Containerizing and application increases scalability and portability. Containers can be easily created and destroyed as required, helping to reduce hosting and compute costs if managed effectively.

Orchestration and automation

Adopting new approaches to software development is seen as a key part of application modernization for many enterprises. Automation, commonly in the form of Continuous Integration (CI) pipelines leveraging numerous different tools, enables greater code velocity and reduces cycle times, allowing greater agility. Orchestration is the coordination of these automated operational tasks.

Application modernization strategies

Choosing the right application modernization approach ultimately comes down to many factors, such as architecture, cost, risk, and security. There are a number of legacy application approaches available, depending on your business and what you want to achieve. The five main strategy options are:


Rehosting moves an existing application from a legacy environment to newer infrastructure, typically in the cloud. This is also known as “lift and shift” where the application is moved as it is, with few changes to its underlying code, functions, or features.


Replatforming sees the application components migrate to a new runtime platform to take advantage of new or different capabilities. Modifications are typically limited to those necessary for compatibility with the new platform, with modification of functionality or features again kept to a minimum.


Rearchitecting involves material alterations to the design and structure of existing code, typically to improve performance and reduce technical debts without changing the application behavior. Shifting to microservices or cloud-native architecture can both be examples of this scenario, in that technical and cost benefits accrue even if the end user experience doesn’t change.


A complex and expensive option, rebuilding involves rewriting or redesigning the application component from scratch whilst keeping its scope and specifications. As such, it is usually only undertaken when there is little other choice.


Replacing involves disposing of the legacy application component entirely and replacing it with a new solution that better meets the business needs, for example, switching tooling developed in-house for modern SaaS alternatives.

Unit testing in application modernization

Whichever approach you ultimately decide on, modernization by definition almost always requires some level of code refactoring.

Whether it’s a relatively small adjustment in a cloud migration or a substantial amount of change in a full-blown codebase redesign, every such change comes with risks, which makes comprehensive unit testing is vital. However, poor unit test coverage is a common trait of applications in need of modernization.

That’s not an easy situation to change. Legacy code is often fragile, hard to understand and poorly documented - which makes unit test writing a difficult, time-consuming task. 

Tens of thousands could be needed, requiring years of developer effort. In fact, according to the Diffblue survey, Java modernization efforts are expected to divert 45% of available developer resources for five years or more. Maintaining code quality is the single biggest barrier to success in such projects.

But there is a better way.

Diffblue Cover: AI for code 

Diffblue Cover gives enterprises and Java developers the means to unlock more value from unit testing by writing Java unit tests autonomously at large scale.

Cover’s AI for code technology can write a full suite of regression unit tests in hours rather than years, enabling faster, safely, more cost-effective modernization that helps Java applications to support business needs more effectively.

It also comes with a suite of supporting tools that help organizations make unit testing efforts even more effective. Key features include:

Diffblue Cover Core

Cover Core at the heart of the Diffblue Cover. It autonomously writes and maintains Java unit tests at massive scale. Learn more here.

Diffblue Cover Reports

Cover Reports uses Cover Core’s analysis of Java code to provide detailed insight into unit test coverage. It allows you to identify risk and allocate resources effectively through a range of detailed dashboards. Learn more here.

Diffblue Cover Optimize

Cover Optimize speeds up unit development by selectively running only the unit tests that apply to your code change. Learn more here.

Diffblue Cover Refactor

Cover Refactor automatically improves existing code by making it more testable. Cover Core then does the rest. Learn more here.

Take the next step

Autonomous unit test writing and maintenance enables you to accelerate application modernization by providing the foundational unit test coverage necessary to protect core business logic during your modernization project, and automatically updating those tests whenever a code change is made.

To find out more about how Diffblue Cover can support application modernization, contact us today to book a demo.