The new spring.io website provides a whole series of "Getting Started" guides to help you learn Spring. You can read more about the guides in the Chapter 1, Getting Started with Spring section in this document. The new website also provides a comprehensive overview of the many additional projects that are released under the Spring umbrella.

If you are a Maven user you may also be interested in the helpful bill of materials POM file that is now published with each Spring Framework release.

All deprecated packages, and many deprecated classes and methods have been removed with version 4.0. If you are upgrading from a previous release of Spring, you should ensure that you have fixed any deprecated calls that you were making to outdated APIs.

For a complete set of changes, check out the API Differences Report.

Note that optional third-party dependencies have been raised to a 2010/2011 minimum (i.e. Spring 4 generally only supports versions released in late 2010 or later now): notably, Hibernate 3.6+, EhCache 2.1+, Quartz 1.8+, Groovy 1.8+, and Joda-Time 2.0+. As an exception to the rule, Spring 4 requires the recent Hibernate Validator 4.3+, and support for Jackson has been focused on 2.0+ now (with Jackson 1.8/1.9 support retained for the time being where Spring 3.2 had it; now just in deprecated form).

Spring Framework 4.0 provides support for several Java 8 features. You can make use of lambda expressions and method references with Spring’s callback interfaces. There is first-class support for java.time (JSR-310), and several existing annotations have been retrofitted as @Repeatable. You can also use Java 8’s parameter name discovery (based on the -parameters compiler flag) as an alternative to compiling your code with debug information enabled.

Spring remains compatible with older versions of Java and the JDK: concretely, Java SE 6 (specifically, a minimum level equivalent to JDK 6 update 18, as released in January 2010) and above are still fully supported. However, for newly started development projects based on Spring 4, we recommend the use of Java 7 or 8.

Java EE version 6 or above is now considered the baseline for Spring Framework 4, with the JPA 2.0 and Servlet 3.0 specifications being of particular relevance. In order to remain compatible with Google App Engine and older application servers, it is possible to deploy a Spring 4 application into a Servlet 2.5 environment. However, Servlet 3.0+ is strongly recommended and a prerequisite in Spring’s test and mock packages for test setups in development environments.

	Note
	If you are a WebSphere 7 user, be sure to install the JPA 2.0 feature pack. On WebLogic 10.3.4 or higher, install the JPA 2.0 patch that comes with it. This turns both of those server generations into Spring 4 compatible deployment environments.

On a more forward-looking note, Spring Framework 4.0 supports the Java EE 7 level of applicable specifications now: in particular, JMS 2.0, JTA 1.2, JPA 2.1, Bean Validation 1.1, and JSR-236 Concurrency Utilities. As usual, this support focuses on individual use of those specifications, e.g. on Tomcat or in standalone environments. However, it works equally well when a Spring application is deployed to a Java EE 7 server.

Note that Hibernate 4.3 is a JPA 2.1 provider and therefore only supported as of Spring Framework 4.0. The same applies to Hibernate Validator 5.0 as a Bean Validation 1.1 provider. Neither of the two are officially supported with Spring Framework 3.2.

Beginning with Spring Framework 4.0, it is possible to define external bean configuration using a Groovy DSL. This is similar in concept to using XML bean definitions but allows for a more concise syntax. Using Groovy also allows you to easily embed bean definitions directly in your bootstrap code. For example:

def reader = new GroovyBeanDefinitionReader(myApplicationContext)
reader.beans {
    dataSource(BasicDataSource) {
        driverClassName = "org.hsqldb.jdbcDriver"
        url = "jdbc:hsqldb:mem:grailsDB"
        username = "sa"
        password = ""
        settings = [mynew:"setting"]
    }
    sessionFactory(SessionFactory) {
        dataSource = dataSource
    }
    myService(MyService) {
        nestedBean = { AnotherBean bean ->
            dataSource = dataSource
        }
    }
}

For more information consult the GroovyBeanDefinitionReader javadocs.

There have been several general improvements to the core container:

Deployment to Servlet 2.5 servers remains an option, but Spring Framework 4.0 is now focused primarily on Servlet 3.0+ environments. If you are using the Spring MVC Test Framework you will need to ensure that a Servlet 3.0 compatible JAR is in your test classpath.

In addition to the WebSocket support mentioned later, the following general improvements have been made to Spring’s Web modules:

A new spring-websocket module provides comprehensive support for WebSocket-based, two-way communication between client and server in web applications. It is compatible with JSR-356, the Java WebSocket API, and in addition provides SockJS-based fallback options (i.e. WebSocket emulation) for use in browsers that don’t yet support the WebSocket protocol (e.g. Internet Explorer < 10).

A new spring-messaging module adds support for STOMP as the WebSocket sub-protocol to use in applications along with an annotation programming model for routing and processing STOMP messages from WebSocket clients. As a result an @Controller can now contain both @RequestMapping and @MessageMapping methods for handling HTTP requests and messages from WebSocket-connected clients. The new spring-messaging module also contains key abstractions formerly from the Spring Integration project such as Message, MessageChannel, MessageHandler, and others to serve as a foundation for messaging-based applications.

For further details, including a more thorough introduction, see the Chapter 25, WebSocket Support section.

In addition to pruning of deprecated code within the spring-test module, Spring Framework 4.0 introduces several new features for use in unit and integration testing.