160 lines
8.6 KiB
Plaintext
160 lines
8.6 KiB
Plaintext
[[overview]]
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= Spring Framework Overview
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:toc: left
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:toclevels: 1
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:docinfo1:
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Spring makes it easy to create Java enterprise applications. It provides everything you
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need to embrace the Java language in an enterprise environment, with support for Groovy
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and Kotlin as alternative languages on the JVM, and with the flexibility to create many
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kinds of architectures depending on an application's needs. As of Spring Framework 5.1,
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Spring requires JDK 8+ (Java SE 8+) and provides out-of-the-box support for JDK 11 LTS.
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Java SE 8 update 60 is suggested as the minimum patch release for Java 8, but it is
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generally recommended to use a recent patch release.
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Spring supports a wide range of application scenarios. In a large enterprise, applications
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often exist for a long time and have to run on a JDK and application server whose upgrade
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cycle is beyond developer control. Others may run as a single jar with the server embedded,
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possibly in a cloud environment. Yet others may be standalone applications (such as batch
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or integration workloads) that do not need a server.
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Spring is open source. It has a large and active community that provides continuous feedback
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based on a diverse range of real-world use cases. This has helped Spring to successfully
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evolve over a very long time.
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[[overview-spring]]
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== What We Mean by "Spring"
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The term "Spring" means different things in different contexts. It can be used to refer to
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the Spring Framework project itself, which is where it all started. Over time, other Spring
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projects have been built on top of the Spring Framework. Most often, when people say
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"Spring", they mean the entire family of projects. This reference documentation focuses on
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the foundation: the Spring Framework itself.
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The Spring Framework is divided into modules. Applications can choose which modules they need.
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At the heart are the modules of the core container, including a configuration model and a
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dependency injection mechanism. Beyond that, the Spring Framework provides foundational
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support for different application architectures, including messaging, transactional data and
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persistence, and web. It also includes the Servlet-based Spring MVC web framework and, in
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parallel, the Spring WebFlux reactive web framework.
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A note about modules: Spring's framework jars allow for deployment to JDK 9's module path
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("Jigsaw"). For use in Jigsaw-enabled applications, the Spring Framework 5 jars come with
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"Automatic-Module-Name" manifest entries which define stable language-level module names
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("spring.core", "spring.context" etc) independent from jar artifact names (the jars follow
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the same naming pattern with "-" instead of ".", e.g. "spring-core" and "spring-context").
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Of course, Spring's framework jars keep working fine on the classpath on both JDK 8 and 9+.
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[[overview-history]]
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== History of Spring and the Spring Framework
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Spring came into being in 2003 as a response to the complexity of the early
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https://en.wikipedia.org/wiki/Java_Platform,_Enterprise_Edition[J2EE] specifications.
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While some consider Java EE and Spring to be in competition, Spring is, in fact, complementary
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to Java EE. The Spring programming model does not embrace the Java EE platform specification;
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rather, it integrates with carefully selected individual specifications from the EE umbrella:
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* Servlet API (https://jcp.org/en/jsr/detail?id=340[JSR 340])
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* WebSocket API (https://www.jcp.org/en/jsr/detail?id=356[JSR 356])
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* Concurrency Utilities (https://www.jcp.org/en/jsr/detail?id=236[JSR 236])
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* JSON Binding API (https://jcp.org/en/jsr/detail?id=367[JSR 367])
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* Bean Validation (https://jcp.org/en/jsr/detail?id=303[JSR 303])
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* JPA (https://jcp.org/en/jsr/detail?id=338[JSR 338])
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* JMS (https://jcp.org/en/jsr/detail?id=914[JSR 914])
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* as well as JTA/JCA setups for transaction coordination, if necessary.
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The Spring Framework also supports the Dependency Injection
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(https://www.jcp.org/en/jsr/detail?id=330[JSR 330]) and Common Annotations
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(https://jcp.org/en/jsr/detail?id=250[JSR 250]) specifications, which application developers
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may choose to use instead of the Spring-specific mechanisms provided by the Spring Framework.
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As of Spring Framework 5.0, Spring requires the Java EE 7 level (e.g. Servlet 3.1+, JPA 2.1+)
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as a minimum - while at the same time providing out-of-the-box integration with newer APIs
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at the Java EE 8 level (e.g. Servlet 4.0, JSON Binding API) when encountered at runtime.
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This keeps Spring fully compatible with e.g. Tomcat 8 and 9, WebSphere 9, and JBoss EAP 7.
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Over time, the role of Java EE in application development has evolved. In the early days of
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Java EE and Spring, applications were created to be deployed to an application server.
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Today, with the help of Spring Boot, applications are created in a devops- and
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cloud-friendly way, with the Servlet container embedded and trivial to change.
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As of Spring Framework 5, a WebFlux application does not even use the Servlet API directly
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and can run on servers (such as Netty) that are not Servlet containers.
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Spring continues to innovate and to evolve. Beyond the Spring Framework, there are other
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projects, such as Spring Boot, Spring Security, Spring Data, Spring Cloud, Spring Batch,
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among others. It’s important to remember that each project has its own source code repository,
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issue tracker, and release cadence. See https://spring.io/projects[spring.io/projects] for
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the complete list of Spring projects.
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[[overview-philosophy]]
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== Design Philosophy
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When you learn about a framework, it’s important to know not only what it does but what
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principles it follows. Here are the guiding principles of the Spring Framework:
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* Provide choice at every level. Spring lets you defer design decisions as late as possible.
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For example, you can switch persistence providers through configuration without changing
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your code. The same is true for many other infrastructure concerns and integration with
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third-party APIs.
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* Accommodate diverse perspectives. Spring embraces flexibility and is not opinionated
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about how things should be done. It supports a wide range of application needs with
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different perspectives.
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* Maintain strong backward compatibility. Spring’s evolution has been carefully managed
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to force few breaking changes between versions. Spring supports a carefully chosen range
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of JDK versions and third-party libraries to facilitate maintenance of applications and
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libraries that depend on Spring.
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* Care about API design. The Spring team puts a lot of thought and time into making APIs
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that are intuitive and that hold up across many versions and many years.
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* Set high standards for code quality. The Spring Framework puts a strong emphasis on
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meaningful, current, and accurate javadoc. It is one of very few projects that can claim
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clean code structure with no circular dependencies between packages.
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[[overview-feedback]]
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== Feedback and Contributions
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For how-to questions or diagnosing or debugging issues, we suggest using StackOverflow,
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and we have a https://spring.io/questions[questions page] that lists the suggested tags to use.
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If you're fairly certain that there is a problem in the Spring Framework or would like
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to suggest a feature, please use the https://github.com/spring-projects/spring-framework/issues[GitHub Issues].
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If you have a solution in mind or a suggested fix, you can submit a pull request on
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https://github.com/spring-projects/spring-framework[Github]. However, please keep in mind
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that, for all but the most trivial issues, we expect a ticket to be filed in the issue
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tracker, where discussions take place and leave a record for future reference.
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For more details see the guidelines at the
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https://github.com/spring-projects/spring-framework/blob/master/CONTRIBUTING.md[CONTRIBUTING],
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top-level project page.
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[[overview-getting-started]]
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== Getting Started
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If you are just getting started with Spring, you may want to begin using the Spring
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Framework by creating a https://projects.spring.io/spring-boot/[Spring Boot]-based
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application. Spring Boot provides a quick (and opinionated) way to create a
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production-ready Spring-based application. It is based on the Spring Framework, favors
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convention over configuration, and is designed to get you up and running as quickly
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as possible.
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You can use https://start.spring.io/[start.spring.io] to generate a basic project or follow
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one of the https://spring.io/guides["Getting Started" guides], such as
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https://spring.io/guides/gs/rest-service/[Getting Started Building a RESTful Web Service].
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As well as being easier to digest, these guides are very task focused, and most of them
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are based on Spring Boot. They also cover other projects from the Spring portfolio that
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you might want to consider when solving a particular problem.
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