High-Level overview of the popular Spring Framework.
Introduction
Mostly, Spring refers to the entire family of Spring projects built upon the Spring Framework or the Spring Ecosystem. The point of using Spring Framework is essentially to create an easier alternative to create Java Enterprise applications than Java EE. However, currently Spring offers much more than the original Java EE due to its consistent evolution. Nowadays, with the help of Spring Boot, the Spring applications could be created in a DevOps and Cloud friendly manner with the embedded Servlet Container. The Spring Framework 5 offers WebFlux application that does not even use the Servlet API directly and can run on servers that are not Servlet containers. The Spring also comes along with a number of other projects like Spring Security, Spring Data, Spring Cloud, etc.
The Spring Family
The Spring Projects are built upon the creation of the Spring Framework, which originally aims at addressing the complexity of developing Java Enterprise applications using Java EE framework. The Spring Framework makes it easy for Web Development, Data Access, and reduces the boiler-plate code that might clutter the application. A good variety of Spring Projects tailored to specific demands are then developed based on the Spring Framework. Out of which Spring Boot is a big game changer with features like auto-configuration and massive simplification of deployment process, etc.
Spring started as a response to the complexity of J2EE (now Java EE), however, nowadays it's so much more than an simple alternative to Java EE, it's in fact complimentary to Java EE and makes use several of the standard specifications like the Java Persistence API. In short,
Spring makes it easier to develop Java Enterprise applications.
Spring is flexible, modular, backwards compatible and has a large and active community, Spring also continually innovates and evolves with state-of-the-art technologies resolving the challenges people might encounter every single day.
Understanding Spring Boot
Spring Boot Makes Getting Started with Spring Quick and Easy
Learning new technologies can be hard and overwhelming. Spring Boot makes it easier to get started with Spring without the need of understanding all the details. One more good thing about Spring Boot is that it is Fully-Featured and heavily used in industries.
Key Features
Spring Boot makes it possible to build Web and Non-Web applications. Built on top of the Spring Framework, Spring Boot has a number of notable features that make it unique and easy to use:
Auto-Configuration: Spring Boot will automatically set up the application based on the specifications provided
Standalone: you don’t need to deploy the application on the web server or a special environment, you can just run the application with one command
Opinionated: Spring Boot has a chosen way of doing things by default.
Intelligent Auto-Configuration
Auto-Configuration is a feature of Spring Boot that provides a Best Guess configuration of the application, as per the documentation:
… attempts to automatically configure your Spring application based on the … dependencies that you have added.
It does this by being both Contextually Aware and Smart. For instance, if Spring Boot knows that the application has a dependency that’s related to Database, it will make some reasonable assumptions so as to configure the application for database access.
Setting up Auto-Configuration is Effortless, you’ll just need to add the EnableAutoConfiguration annotation to the Spring Boot application.
@EnableAutoConfiguration
public class mySpringBootApplication {
...
}It is also easy to disable, or, non-invasive.
Spring Boot Is Standalone
As per the documentation:
Spring Boot makes it easy to create stand-alone, production-grade, Spring-based applications that you can ‘just run’.
To understand how helpful this feature is for development, let’s take a look at the procedures of how a typical Java web application is run:
Package the application
Choose and download the web server
Configure the web server
Deploy application & start the web server
For Spring Boot, it “just runs”:
Package the application
Run the application
Spring Boot Is Opinionated
As per the documentation:
“Takes an opinionated view of building production-ready Spring applications.”
When building Java web applications, you might encounter tons of choices like library choices, config choices, tooling choices, etc. Spring Boot removes this burden by:
… favors convention over configuration and is designed to get up and running as quickly as possible.”
Like what http://start.spring.io/ can do.
Spring Framework Foundations
The Spring Framework is a Software Framework as defined by Wikipedia:
is a universal, reusable software environment that provides particular functionality as part of a larger software platform to facilitate development of software applications, products and solutions.
Specifically, a software environment is universal and reusable, which Spring Framework very much meets this definition. Also, a software framework should provide particular functionality which for Spring Framework it means things like web development and data access. Moreover, a software framework should belong to a larger software platform, which is Java platform for Spring Framework. Lastly, software frameworks facilitate development software applications, products and solutions, just like how Spring Framework makes development of web applications easier.
The Spring Framework is the start of Spring today, enterprise Java Development was very complex at the time and people developed Spring Framework to make development easier. Built upon Spring Framework, applications can further utilize Spring Projects along with Spring Framework to make things even easier.
The Six Key Areas of Spring Framework
The Spring Framework is modular and could be divided into six areas as follows:
Spring Core
It is one of the most important features of the Spring Framework, it serves as the foundational module for other modules like Integration, Web, Data Access, Testing, AOP. Spring Core provides a number of different features like:
i18n internationalization support
Validation support
Data binding support
Type conversion support, etc.
But the center of Spring Core is Dependency Injection. Usually, developers create objects to represent or model real-life things, and some objects don’t exist by themselves, instead they are dependent on other objects. For instance, the Computer object has dependencies on other objects like Hard Disk or multiple Memory objects.
public class Computer {
HardDisk hd;
Memory[] ram;
}Dependency Injection is about dealing with the way objects fulfill their dependent objects.
There are two choices of fulfilling dependencies:
The object fulfills its own dependencies
The object declares what it depends on and something else fulfills the dependency
The first approach might seams easier but has the limitation of making objects tightly coupled while the second approach is much flexible since the objects are loosely coupled.
The second approach is called Dependency Injection. Spring Core is considered as a Dependency Injection Container:
Creates and maintains objects and their dependencies, which results less things for the developer to manage.
It’s also the thing that combines many individual parts of the application together, like a glue.
Spring Web
The web support of Spring Framework is provided via the Web module. The Spring Web is a framework of handling web requests in two different ways:
Spring Web MVC
Spring WebFlux
Spring Web MVC
To understand what Spring Web MVC is, let’s first take a look at the Java Servlet API which as per Wikipedia:
A Servlet is an object that receives a request and generates a response based on that request.
Traditionally, a standard request is sent via the web server and get processed through the business logic via the Servlet API and then gets returned by the response generated by the web server.
Servlet works but there are some issues with it:
A low-level API and lack of abstraction
Harder to use
Less productive
Spring Web MVC builds upon Servlet API to make development easier and more productive:
It is a higher level API and offers productivity and clear separation of concerns (MVC):
Spring WebFlux
To understand Spring WebFlux, we need to first understand what Reactive Programming:
… a declarative programming paradigm concerned with data streams and the propagation of change.
which literally means you react to change rather than wait to change.
Spring’s reactive programming framework is the Spring WebFlux:
A different way of handling web requests:
Asynchronous execution
Doesn’t block (wait), this results in better resource utilization
In a traditional flow, requests are executed step by step due to its dependency on different resources, in a reactive flow, however, request execution is carried out asynchronously and don’t need to wait for completing execution of a single request to proceed, the code will be notified after the each execution of a request completed.
Spring AOP
As per Wikipedia, Spring AOP is:
a programming paradigm that aims to increase modularity by allowing the separation of cross-cutting concerns.
A few key concepts here:
Programming paradigm: it simply means of programming or writing code
Molecularity: increasing organization
Cross-cutting concerns: they are referring to concerns that cross various aspects of layers, or tiers of the application, like security because security can’t be contained to any one area of the applications, instead it spans multiple parts of the application.
To put it another way, Aspect-Oriented Programming (AOP) is a way of programming that increases organization of code for concerns that span multiple tiers of an application.
Without AOP, solving concerns that are cross-cutting results in scattered and duplicated code across many parts of an application.
Spring AOP is an implementation of AOP in the Spring Framework, which has two main use cases:
Used to implement features in Spring
A valuable tool for developers to handle cross-cutting concerns
Example: Application Security
public void sensitiveOperation() {
// Check if user is authenticated and has the correct role.
if (...) {
// Do sensitive operations.
} else {
// Raise an unauthorized error log failed attempt redirect
// user to login page.
}
}These operations are very likely to occur in many places throughout the application. Spring AOP helps us to organize these operations into a single area that can be applied to different parts of the application.
Example: Application Security with Spring AOP
@PreAuthorize("hasRole('admin')")
public void sensitiveOperation() {
// Do sensitive operations.
}Spring Data Access
Almost every application interacts with data. The Spring Framework’s Data Access module makes it easier to develop applications that interact with data.
Example: Java Database Connection API (JDBC)
/* Code to retrieve data using JDBC. */
try {
Statement statement = conn.createStatement();
try {
/* Important retrieval logic. */
ResultSet resultSet = statement.executeQuery("SELECT COUNT(*) FROM foo");
try {
/* Important result logic. */
resultSet.next();
int count = resultSet.getInt(1);
} finally {
resultSet.close();
}
} finally {
statement.close();
}
} catch (SQLException e) {
// Handle error.
} finally {
try {
conn.close();
} catch (SQLException e) {
// Handle error.
}
}The other parts are boiler-plate code. Using Spring Framework’s Data Access module, we can reduce boiler-plate code:
int count = new JdbcTemplate(ds).queryForInt("SELECT COUNT(*) FROM foo");Database transactions with the Spring Framework’s Data Access module are extremely easy.
A transaction is a general unit of work that must happen together or not at all. Hence a database transaction is a series of database operations that must happen together or not at all.
Let’s take bank transactions as a concrete example. If we would like to transfer money from one bank account to another, we need to first deposit from bank account A and then transfer it to bank account B. If the deposit from back account A fails, but the money transfer to bank account B succeeds, then A just get free money. Similarly, if transfer succeeds, then the money from A is lost.
Let’s take look at another example:
try {
connection.setAutoCommit(false);
// Execute a series of database operations within the transaction.
connection.commit();
} catch (Exception e) {
connection.rollback();
} finally {
connection.close();
}The same code is a lot simpler with the Transactional Support from the Spring Framework:
@Transactional
public void operation() {
// Execute a series of database operations within the transaction.
}Exception Translation
Another small but useful feature of Spring Data Access module is Exception Translation. Exceptions are an event within a program that disrupt execution. Since different database vendors have different exceptions for the same class of errors. For example, the same data integrity violation error would look different in MySQL and Oracle:
MySQL: 630, 839, 840, etc.
Oracle: 1400, 1722, 2291,etc.
The Spring Data Access module takes these vendor-specific exceptions and maps/translates them into a well-known set of exceptions.
Another good thing about Spring Data Access module is that it makes testing data easier. It is easy to switch configurations for testing to use test data with embedded database instead of important production data alone.
Spring Integration
Application don’t work in isolation, integration is all about making different systems and applications work together.
Communications between applications
This is a multisided problem:
How do you expose operations to other systems?
How do you invoke or run operations in other systems
Exposing operations
There are many ways to expose operations that Spring Framework supports:
RMI (Remote Method Invocation)
Messaging Systems
Web Services: the Spring Framework makes it easy to both expose and invoke web services, as per the example banking account application shown below, it shows how to expose web services so as to retrieve bank account number by id:
// Denotes we're using a REST style web service.
@RestController
public class AccountController {
// Denotes operation and path.
@GetMapping("/account/{id}")
public Account find(@PathVariable int id) { // Associates path and value
// Look up account by id.
}
}From this example, we can see we could expose the operation of bank account number retrieval by providing the account id using REST Web Service.
Invoking Operations
The Spring Framework provides support for programmatically invoking our REST service by utilizing @RestTemplate, which:
Abstracts away tedious details
Handles
- Connecting to the web service
- Sending the command
- Handling the response from the web service
3. Super easy to use:
// @RestTemplate makes calling REST Web Services as easy as oneline.
restTemplate.getForObject("http://foo.com/account/123", Account.class);Spring Testing
Testing is a very important part of developing software, Spring Framework focuses two major areas of testing:
Unit Testing
Integration Testing
Unit Testing
As per the definition of techtarget.com, Unit Testing is:
… a software development process in which the smallest testable parts of an application, called units, are individually and independently scrutinized for proper operation.
Note that a side effect of dependency injection is that it makes explicit support for unit testing a lot easier. Since dependency injection is about dealing with the way objects fulfill their dependent objects.
Testing and Dependency Injection
The idea of Unit Testing is to test the smallest unit of code possible. When the code to test has dependencies, it might become challenging since we only want to test the code, not the dependencies. However, dependency injection makes testing a lot easier by enforcing developers to declare their dependencies so that during testing dependent code can be replaced with the code that behaves a certain way by Mocking dependencies. With the feature, we could ONLY test the code and forget about the dependencies. For example, suppose the following code snippet grands people certain permissions that based on their security clearance levels:
Example: Using Dependency Injection in Testing
public Permission getPermissions(SecurityManager securityManager) {
String securityLevel = securityManager.getSecurityLevel();
if (securityLevel.equals("CONFIDENTIAL")) {
// Give the user confidential permissions.
} else if (securityLevel.equals("SECRET")) {
// Give the user secret permissions.
} else if (securityLevel.equals("TOP_SECRET")) {
// Give the user top secret permissions.
}
}The objective is to test every condition, which is all the security levels in our case. Thanks to dependency injection, we could control how the SecurityManager (a dependency) behaves to control the test, in other words, we could control the securityLevel it returns. For example, we could control the SecurityManager to always return "CONFIDENTIAL" securityLevel to enter the first if block, “SECRET" to enter the second, and “TOP_SECRET” to enter the third.
Spring Framework comes with several built-in mocks to make testing easier and faster.
Integration Testing
As per Wikipedia, Integration Testing is:
… the phase in software testing in which individual software modules are combined and tested as a group. It occurs after unit testing…
Spring Framework supports Integration Testing by piecing together parts of an application for testing (inject dependencies and put everything together). Spring Framework also provides support for common testing scenarios like testing with data access and web application testing.
Another feature is that Spring Framework provides support for cleaning up after tests since tests modify things, and we need to reverse the modifications after the test so that the following tests will not be affected.