Earlier versions of EJBs were very difficult to unit test. In fact, it was difficult to run EJBs outside the container (as of version 2.1). The only way to test them was to deploy them in a container.

Spring Framework brought in the concept of Dependency Injection (DI). We will discuss dependency injection in complete detail in Chapter 2, Dependency Injection.

The dependency injection enables unit testing by making it easy to replace the dependencies with their mocks. We do not need to deploy the entire application to unit test it.

Simplifying unit testing has multiple benefits:

Before Spring Framework, typical J2EE (or Java EE, as it is called now) applications contained a lot of plumbing code. For example: getting a database connection, exception handling code, transaction management code, logging code, and a lot more.

Let's take a look at a simple example of executing a query using prepared statement:

    PreparedStatement st = null;
    try {
          st = conn.prepareStatement(INSERT_TODO_QUERY);
          st.setString(1, bean.getDescription());
          st.setBoolean(2, bean.isDone());
          st.execute();
        } 
    catch (SQLException e) {
          logger.error("Failed : " + INSERT_TODO_QUERY, e);
     } finally {
                if (st != null) {
           try {
           st.close();
          } catch (SQLException e) {
           // Ignore - nothing to do..
          }
       }
     }

In the preceding example, there are four lines of business logic and more than 10 lines of plumbing code.

With Spring Framework, the same logic can be applied in a couple of lines:

    jdbcTemplate.update(INSERT_TODO_QUERY, 
    bean.getDescription(), bean.isDone());

Spring Framework is modular. It is built as a set of independent modules built on top of the core Spring modules. Most of the Spring modules are independent--you can use one of them without having to use others.

Let's look at a few examples:

Spring Framework does not want to be the jack-of-all-trades. While focusing on its core job of reducing coupling between different parts of the application and making them testable, Spring provides great integration with frameworks of your choice. This means you have flexibility in your architecture--if you do not want to use a specific framework, you can easily replace it with another.

The first version of Spring Framework focused on making applications testable. However, as time moved on, there were new challenges. Spring Framework managed to evolve and stay ahead of the curve with the flexibility and modules that are offered. A couple of examples are listed as follows:

Another important thing Spring brings in is the umbrella of Spring Projects. Spring Framework is just one of the many projects under Spring Projects. We will discuss the different Spring Projects in a separate section. The following examples illustrate how Spring managed to stay ahead of times with new Spring Projects: