What is spring framework

Spring Framework Overview

Spring makes it easy to create Java enterprise applications. It provides everything you need to embrace the Java language in an enterprise environment, with support for Groovy and Kotlin as alternative languages on the JVM, and with the flexibility to create many kinds of architectures depending on an application’s needs. As of Spring Framework 5.1, Spring requires JDK 8+ (Java SE 8+) and provides out-of-the-box support for JDK 11 LTS. Java SE 8 update 60 is suggested as the minimum patch release for Java 8, but it is generally recommended to use a recent patch release.

Spring supports a wide range of application scenarios. In a large enterprise, applications often exist for a long time and have to run on a JDK and application server whose upgrade cycle is beyond developer control. Others may run as a single jar with the server embedded, possibly in a cloud environment. Yet others may be standalone applications (such as batch or integration workloads) that do not need a server.

Spring is open source. It has a large and active community that provides continuous feedback based on a diverse range of real-world use cases. This has helped Spring to successfully evolve over a very long time.

1. What We Mean by «Spring»

The term «Spring» means different things in different contexts. It can be used to refer to the Spring Framework project itself, which is where it all started. Over time, other Spring projects have been built on top of the Spring Framework. Most often, when people say «Spring», they mean the entire family of projects. This reference documentation focuses on the foundation: the Spring Framework itself.

The Spring Framework is divided into modules. Applications can choose which modules they need. At the heart are the modules of the core container, including a configuration model and a dependency injection mechanism. Beyond that, the Spring Framework provides foundational support for different application architectures, including messaging, transactional data and persistence, and web. It also includes the Servlet-based Spring MVC web framework and, in parallel, the Spring WebFlux reactive web framework.

A note about modules: Spring’s framework jars allow for deployment to JDK 9’s module path («Jigsaw»). For use in Jigsaw-enabled applications, the Spring Framework 5 jars come with «Automatic-Module-Name» manifest entries which define stable language-level module names («spring.core», «spring.context», etc.) independent from jar artifact names (the jars follow the same naming pattern with «-» instead of «.», e.g. «spring-core» and «spring-context»). Of course, Spring’s framework jars keep working fine on the classpath on both JDK 8 and 9+.

2. History of Spring and the Spring Framework

Spring came into being in 2003 as a response to the complexity of the early J2EE specifications. While some consider Java EE and Spring to be in competition, Spring is, in fact, complementary to Java EE. The Spring programming model does not embrace the Java EE platform specification; rather, it integrates with carefully selected individual specifications from the EE umbrella:

Why Spring?

Spring makes programming Java quicker, easier, and safer for everybody. Spring’s focus on speed, simplicity, and productivity has made it the world’s most popular Java framework.

“We use a lot of the tools that come with the Spring framework and reap the benefits of having a lot of the out of the box solutions, and not having to worry about writing a ton of additional code—so that really saves us some time and energy.”

Spring is everywhere

Spring’s flexible libraries are trusted by developers all over the world. Spring delivers delightful experiences to millions of end-users every day—whether that’s streaming TV, online shopping, or countless other innovative solutions. Spring also has contributions from all the big names in tech, including Alibaba, Amazon, Google, Microsoft, and more.

Spring is flexible

Spring’s flexible and comprehensive set of extensions and third-party libraries let developers build almost any application imaginable. At its core, Spring Framework’s Inversion of Control (IoC) and Dependency Injection (DI) features provide the foundation for a wide-ranging set of features and functionality. Whether you’re building secure, reactive, cloud-based microservices for the web, or complex streaming data flows for the enterprise, Spring has the tools to help.

Spring is productive

Spring Boot transforms how you approach Java programming tasks, radically streamlining your experience. Spring Boot combines necessities such as an application context and an auto-configured, embedded web server to make microservice development a cinch. To go even faster, you can combine Spring Boot with Spring Cloud’s rich set of supporting libraries, servers, patterns, and templates, to safely deploy entire microservices-based architectures into the cloud, in record time.

Spring is fast

Our engineers care deeply about performance. With Spring, you’ll notice fast startup, fast shutdown, and optimized execution, by default. Increasingly, Spring projects also support the reactive (nonblocking) programming model for even greater efficiency. Developer productivity is Spring’s superpower. Spring Boot helps developers build applications with ease and with far less toil than other competing paradigms. Embedded web servers, auto-configuration, and “fat jars” help you get started quickly, and innovations like LiveReload in Spring DevTools mean developers can iterate faster than ever before. You can even start a new Spring project in seconds, with the Spring Initializr at start.spring.io.

Spring is secure

Spring has a proven track record of dealing with security issues quickly and responsibly. The Spring committers work with security professionals to patch and test any reported vulnerabilities. Third-party dependencies are also monitored closely, and regular updates are issued to help keep your data and applications as safe as possible. In addition, Spring Security makes it easier for you to integrate with industry-standard security schemes and deliver trustworthy solutions that are secure by default.

Spring is supportive

The Spring community is enormous, global, diverse, and spans folks of all ages and capabilities, from complete beginners to seasoned pros. No matter where you are on your journey, you can find the support and resources you need to get you to the next level: quickstarts, guides & tutorials, videos, meetups, support, or even formal training and certification.

What can Spring do?

Microservices

Quickly deliver production‑grade features with independently evolvable microservices.

Reactive

Spring’s asynchronous, nonblocking architecture means you can get more from your computing resources.

Cloud

Your code, any cloud—we’ve got you covered. Connect and scale your services, whatever your platform.

Web apps

Frameworks for fast, secure, and responsive web applications connected to any data store.

Serverless

The ultimate flexibility. Scale up on demand and scale to zero when there’s no demand.

Event Driven

Integrate with your enterprise. React to business events. Act on your streaming data in realtime.

Batch

Automated tasks. Offline processing of data at a time to suit you.

Get ahead

VMware offers training and certification to turbo-charge your progress.

Get support

Spring Runtime offers support and binaries for OpenJDK™, Spring, and Apache Tomcat® in one simple subscription.

Upcoming events

Check out all the upcoming events in the Spring community.

Spring Framework

A key element of Spring is infrastructural support at the application level: Spring focuses on the «plumbing» of enterprise applications so that teams can focus on application-level business logic, without unnecessary ties to specific deployment environments.

Support Policy and Migration

For information about minimum requirements, guidance on upgrading from earlier versions and support policies, please check out the official Spring Framework wiki page

Features

Core technologies: dependency injection, events, resources, i18n, validation, data binding, type conversion, SpEL, AOP.

Data Access: transactions, DAO support, JDBC, ORM, Marshalling XML.

Integration: remoting, JMS, JCA, JMX, email, tasks, scheduling, cache.

Languages: Kotlin, Groovy, dynamic languages.

SpringOnePlatform 2017 talks

Quickstart Your Project

Documentation

Tutorials

OSS support

Free security updates and bugfixes with support from the Spring community. See VMware Tanzu OSS support policy.

Commercial support

Business support from Spring experts during the OSS timeline, plus extended support after OSS End-Of-Life.
Publicly available releases for critical bugfixes and security issues when requested by customers.

Future release

Generation not yet released, timeline is subject to changes.

About commercial support (*)

Get ahead

VMware offers training and certification to turbo-charge your progress.

Get support

Spring Runtime offers support and binaries for OpenJDK™, Spring, and Apache Tomcat® in one simple subscription.

Upcoming events

Check out all the upcoming events in the Spring community.

Overview of Spring Framework

1. Getting Started with Spring

This reference guide provides detailed information about the Spring Framework. It provides comprehensive documentation for all features, as well as some background about the underlying concepts (such as «Dependency Injection») that Spring has embraced.

If you are just getting started with Spring, you may want to begin using the Spring Framework by creating a Spring Boot based application. Spring Boot provides a quick (and opinionated) way to create a production-ready Spring based application. It is based on the Spring Framework, favors convention over configuration, and is designed to get you up and running as quickly as possible.

You can use start.spring.io to generate a basic project or follow one of the «Getting Started» guides like the Getting Started Building a RESTful Web Service one. As well as being easier to digest, these guides are very task focused, and most of them are based on Spring Boot. They also cover other projects from the Spring portfolio that you might want to consider when solving a particular problem.

2. Introduction to the Spring Framework

The Spring Framework is a Java platform that provides comprehensive infrastructure support for developing Java applications. Spring handles the infrastructure so you can focus on your application.

Spring enables you to build applications from «plain old Java objects» (POJOs) and to apply enterprise services non-invasively to POJOs. This capability applies to the Java SE programming model and to full and partial Java EE.

Examples of how you, as an application developer, can benefit from the Spring platform:

Make a Java method execute in a database transaction without having to deal with transaction APIs.

Make a local Java method an HTTP endpoint without having to deal with the Servlet API.

Make a local Java method a message handler without having to deal with the JMS API.

Make a local Java method a management operation without having to deal with the JMX API.

2.1. Dependency Injection and Inversion of Control

A Java application — a loose term that runs the gamut from constrained, embedded applications to n-tier, server-side enterprise applications — typically consists of objects that collaborate to form the application proper. Thus the objects in an application have dependencies on each other.

Although the Java platform provides a wealth of application development functionality, it lacks the means to organize the basic building blocks into a coherent whole, leaving that task to architects and developers. Although you can use design patterns such as Factory, Abstract Factory, Builder, Decorator, and Service Locator to compose the various classes and object instances that make up an application, these patterns are simply that: best practices given a name, with a description of what the pattern does, where to apply it, the problems it addresses, and so forth. Patterns are formalized best practices that you must implement yourself in your application.

The Spring Framework Inversion of Control (IoC) component addresses this concern by providing a formalized means of composing disparate components into a fully working application ready for use. The Spring Framework codifies formalized design patterns as first-class objects that you can integrate into your own application(s). Numerous organizations and institutions use the Spring Framework in this manner to engineer robust, maintainable applications.

«The question is, what aspect of control are [they] inverting?» Martin Fowler posed this question about Inversion of Control (IoC) on his site in 2004. Fowler suggested renaming the principle to make it more self-explanatory and came up with Dependency Injection.

2.2. Framework Modules

The Spring Framework consists of features organized into about 20 modules. These modules are grouped into Core Container, Data Access/Integration, Web, AOP (Aspect Oriented Programming), Instrumentation, Messaging, and Test, as shown in the following diagram.

The following sections list the available modules for each feature along with their artifact names and the topics they cover. Artifact names correlate to artifact IDs used in Dependency Management tools.

2.2.1. Core Container

The spring-core and spring-beans modules provide the fundamental parts of the framework, including the IoC and Dependency Injection features. The BeanFactory is a sophisticated implementation of the factory pattern. It removes the need for programmatic singletons and allows you to decouple the configuration and specification of dependencies from your actual program logic.

The Context ( spring-context ) module builds on the solid base provided by the Core and Beans modules: it is a means to access objects in a framework-style manner that is similar to a JNDI registry. The Context module inherits its features from the Beans module and adds support for internationalization (using, for example, resource bundles), event propagation, resource loading, and the transparent creation of contexts by, for example, a Servlet container. The Context module also supports Java EE features such as EJB, JMX, and basic remoting. The ApplicationContext interface is the focal point of the Context module. spring-context-support provides support for integrating common third-party libraries into a Spring application context, in particular for caching (EhCache, JCache) and scheduling (CommonJ, Quartz).

The spring-expression module provides a powerful Expression Language for querying and manipulating an object graph at runtime. It is an extension of the unified expression language (unified EL) as specified in the JSP 2.1 specification. The language supports setting and getting property values, property assignment, method invocation, accessing the content of arrays, collections and indexers, logical and arithmetic operators, named variables, and retrieval of objects by name from Spring’s IoC container. It also supports list projection and selection as well as common list aggregations.

2.2.2. AOP and Instrumentation

The separate spring-aspects module provides integration with AspectJ.

The spring-instrument module provides class instrumentation support and classloader implementations to be used in certain application servers. The spring-instrument-tomcat module contains Spring’s instrumentation agent for Tomcat.

2.2.3. Messaging

2.2.4. Data Access/Integration

The Data Access/Integration layer consists of the JDBC, ORM, OXM, JMS, and Transaction modules.

The spring-jdbc module provides a JDBC-abstraction layer that removes the need to do tedious JDBC coding and parsing of database-vendor specific error codes.

The spring-tx module supports programmatic and declarative transaction management for classes that implement special interfaces and for all your POJOs (Plain Old Java Objects).

The spring-orm module provides integration layers for popular object-relational mapping APIs, including JPA and Hibernate. Using the spring-orm module you can use these O/R-mapping frameworks in combination with all of the other features Spring offers, such as the simple declarative transaction management feature mentioned previously.

The spring-oxm module provides an abstraction layer that supports Object/XML mapping implementations such as JAXB, Castor, JiBX and XStream.

The spring-jms module (Java Messaging Service) contains features for producing and consuming messages. Since Spring Framework 4.1, it provides integration with the spring-messaging module.

2.2.5. Web

The spring-web module provides basic web-oriented integration features such as multipart file upload functionality and the initialization of the IoC container using Servlet listeners and a web-oriented application context. It also contains an HTTP client and the web-related parts of Spring’s remoting support.

The spring-webmvc module (also known as the Web-Servlet module) contains Spring’s model-view-controller (MVC) and REST Web Services implementation for web applications. Spring’s MVC framework provides a clean separation between domain model code and web forms and integrates with all of the other features of the Spring Framework.

2.2.6. Test

The spring-test module supports the unit testing and integration testing of Spring components with JUnit or TestNG. It provides consistent loading of Spring ApplicationContext s and caching of those contexts. It also provides mock objects that you can use to test your code in isolation.

2.3. Usage scenarios

The building blocks described previously make Spring a logical choice in many scenarios, from embedded applications that run on resource-constrained devices to full-fledged enterprise applications that use Spring’s transaction management functionality and web framework integration.

Spring’s declarative transaction management features make the web application fully transactional, just as it would be if you used EJB container-managed transactions. All your custom business logic can be implemented with simple POJOs and managed by Spring’s IoC container. Additional services include support for sending email and validation that is independent of the web layer, which lets you choose where to execute validation rules. Spring’s ORM support is integrated with JPA and Hibernate; for example, when using Hibernate, you can continue to use your existing mapping files and standard Hibernate SessionFactory configuration. Form controllers seamlessly integrate the web-layer with the domain model, removing the need for ActionForms or other classes that transform HTTP parameters to values for your domain model.

Sometimes circumstances do not allow you to completely switch to a different framework. The Spring Framework does not force you to use everything within it; it is not an all-or-nothing solution. Existing front-ends built with Struts, Tapestry, JSF or other UI frameworks can be integrated with a Spring-based middle-tier, which allows you to use Spring transaction features. You simply need to wire up your business logic using an ApplicationContext and use a WebApplicationContext to integrate your web layer.

The Spring Framework also provides an access and abstraction layer for Enterprise JavaBeans, enabling you to reuse your existing POJOs and wrap them in stateless session beans for use in scalable, fail-safe web applications that might need declarative security.

2.3.1. Dependency Management and Naming Conventions

Dependency management and dependency injection are different things. To get those nice features of Spring into your application (like dependency injection) you need to assemble all the libraries needed (jar files) and get them onto your classpath at runtime, and possibly at compile time. These dependencies are not virtual components that are injected, but physical resources in a file system (typically). The process of dependency management involves locating those resources, storing them and adding them to classpaths. Dependencies can be direct (e.g. my application depends on Spring at runtime), or indirect (e.g. my application depends on commons-dbcp which depends on commons-pool ). The indirect dependencies are also known as «transitive» and it is those dependencies that are hardest to identify and manage.

Each release of the Spring Framework will publish artifacts to the following places:

In a public Maven repository hosted specifically for Spring. In addition to the final GA releases, this repository also hosts development snapshots and milestones. The jar file names are in the same form as Maven Central, so this is a useful place to get development versions of Spring to use with other libraries deployed in Maven Central. This repository also contains a bundle distribution zip file that contains all Spring jars bundled together for easy download.

So the first thing you need to decide is how to manage your dependencies: we generally recommend the use of an automated system like Maven, Gradle or Ivy, but you can also do it manually by downloading all the jars yourself.

Below you will find the list of Spring artifacts. For a more complete description of each module, see Framework Modules.

What is Spring Framework? An Unorthodox Guide

You can use this guide to understand what Spring framework is and how its core features like dependency injection or aspected oriented programming work. Also, a comprehensive FAQ.

(Editor’s note: At

6700 words, you probably don’t want to try reading this on a mobile device. Bookmark it and come back later. And even on a desktop, eat read this elephant one bite at a time.)

Introduction

The complexity of the Spring ecosystem

A lot of companies are using Spring, but then you go to spring.io and see that the Spring universe actually consists of 21 different, active projects. Ouch!

Furthermore, if you started programming with Spring in the last couple of years, there is a very high chance that you went directly into Spring Boot or Spring Data.

However, this guide is solely about one, the most important one, of these projects: Spring Framework. Why?

Because it is essential to learn that Spring Framework is the basis for all other projects. Spring Boot, Spring Data, Spring Batch all build on top of Spring.

This has two implications:

Without proper Spring framework knowledge, you will sooner or later get lost. You won’t fully grok e.g. Spring Boot, no matter how unimportant you think that core knowledge is.

15 minutes reading this guide, which covers the most important 80% of Spring framework, will pay-off a million times in your professional career.

What is Spring Framework?

The short answer:

At its core, Spring framework is really just a dependency injection container, with a couple of convenience layers (think: database access, proxies, aspect-oriented programming, RPC, a web mvc framework) added on top. It helps you build Java application faster and more conveniently.

Now, that doesn’t really help, does it?

Luckily, there’s also a long answer:

The remainder of this document.

Dependency Injection Basics

In case you already know what dependency injection is, feel free to skip straight to Spring’s Dependency Injection Container. Otherwise, read on.

What is a dependency?

Imagine you are writing a Java class that lets you access a users table in your database. You would call these classes DAOs (data access object) or Repositories. So, you are going to write a UserDAO class.

Your UserDAO has only one method which lets you find users in your database table by their respective IDs.

To execute the appropriate SQL query, your UserDAO needs a database connection. And in the Java world, you (usually) get that database connection from another class, called a DataSource. So, your code now would look something like this:

The question is now, where does your UserDao get its dataSource dependency from? The DAO obviously depends on a valid DataSource to fire those SQL queries.

How to instantiate dependencies with new()

The naive approach would be to simply create a new DataSource through a constructor, every time you need one. So, to connect to a MySQL database your UserDAO could look like this:

We want to connect to a MySQL database; hence we are using a MysqlDataSource and hardcoding url/username/password here for easier reading.

We use our newly created DataSource for the query.

This works, but let’s see what happens when we extend our UserDao class with another method, findByFirstName.

Unfortunately, that method also needs a DataSource to work with. We can add that new method to our UserDAO and apply some refactorings, by introducing a newDataSource method.

findById has been rewritten to use the new newDataSource() method.

findByFirstName has been added and also uses the new newDataSource() method.

This is our newly extracted method, able to create new DataSources.

This approach works, but has two drawbacks:

What happens if we want to create a new ProductDAO class, which also executes SQL statements? Your ProductDAO would then also have a DataSource dependency, which now is only available in your UserDAO class. You would then have another similar method or extract a helper class that contains your DataSource.

How to ‘manage’ dependencies in a global Application class

To accommodate these issues, you could think about writing a global Application class, that looks something like this:

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