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- Herausgeber: Packt Publishing
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
Develop cloud native applications with microservices using Spring Boot, Spring Cloud, and Spring Cloud Data Flow
About This Book
- Explore the new features and components in Spring
- Evolve towards micro services and cloud native applications
- Gain powerful insights into advanced concepts of Spring and Spring Boot to develop applications more effectively
- Understand the basics of Kotlin and use it to develop a quick service with Spring Boot
Who This Book Is For
This book is for an experienced Java developer who knows the basics of Spring, and wants to learn how to use Spring Boot to build applications and deploy them to the cloud.
What You Will Learn
- Explore the new features in Spring Framework 5.0
- Build microservices with Spring Boot
- Get to know the advanced features of Spring Boot in order to effectively develop and monitor applications
- Use Spring Cloud to deploy and manage applications on the Cloud
- Understand Spring Data and Spring Cloud Data Flow
- Understand the basics of reactive programming
- Get to know the best practices when developing applications with the Spring Framework
- Create a new project using Kotlin and implement a couple of basic services with unit and integration testing
In Detail
Spring 5.0 is due to arrive with a myriad of new and exciting features that will change the way we've used the framework so far. This book will show you this evolution—from solving the problems of testable applications to building distributed applications on the cloud.
The book begins with an insight into the new features in Spring 5.0 and shows you how to build an application using Spring MVC. You will realize how application architectures have evolved from monoliths to those built around microservices. You will then get a thorough understanding of how to build and extend microservices using Spring Boot. You will also understand how to build and deploy Cloud-Native microservices with Spring Cloud. The advanced features of Spring Boot will be illustrated through powerful examples. We will be introduced to a JVM language that's quickly gaining popularity - Kotlin. Also, we will discuss how to set up a Kotlin project in Eclipse.
By the end of the book, you will be equipped with the knowledge and best practices required to develop microservices with the Spring Framework.
Style and approach
This book follows an end-to-end tutorial approach with lots of examples and sample applications, covering the major building blocks of the Spring framework.
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Veröffentlichungsjahr: 2017
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Mastering Spring 5.0
Copyright © 2017 Packt Publishing
All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without the prior written permission of the publisher, except in the case of brief quotations embedded in critical articles or reviews.
Every effort has been made in the preparation of this book to ensure the accuracy of the information presented. However, the information contained in this book is sold without warranty, either express or implied. Neither the author, nor Packt Publishing, and its dealers and distributors will be held liable for any damages caused or alleged to be caused directly or indirectly by this book.
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First published: June 2017
Production reference: 1240617
ISBN 978-1-78712-317-5
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Credits
AuthorRanga Rao Karanam
Copy EditorStuti Srivastava
Reviewer
Jarosław Krochmalski
Project Coordinator
Prajakta Naik
Commissioning Editor
Kunal Parikh
Proofreader
Safis Editing
Acquisition Editor
Denim Pinto
Indexer
Rekha Nair
ContentDevelopmentEditor
Siddhi Chavan
Graphics
Abhinash Sahu
Technical Editor
Supriya Thabe
Production Coordinator
Shraddha Falebhai
About the Author
Ranga Rao Karanam is a programmer, trainer, and architect. His areas of interest include Cloud Native Applications, microservices, evolutionary design, high-quality code, DevOps, BDD, TDD, and refactoring. He loves consulting for start-ups on developing scalable, component-based Cloud Native applications, and following modern development practices such as BDD, continuous delivery, and DevOps. He loves the freedom the Spring Framework brings to developing enterprise Java applications.
Ranga started in28minutes with the vision of creating high-quality courses on developing Cloud Native Java applications. He is looking forward to enhancing his already considerable success--75,000 students on Udemy and 35,000 subscribers on YouTube.
Ranga likes to play cricket and go hiking. His dream is to spend a year hiking the Himalayas.
About the Reviewer
Jarosław Krochmalski is a passionate software designer and developer who specializes in the financial business domain. He has over 12 years of experience in software development. He is a clean-code and software craftsmanship enthusiast. He is a Certified ScrumMaster and a fan of Agile. His professional interests include new technologies in web application development, design patterns, enterprise architecture, and integration patterns. He likes to experiment with NoSQL and cloud computing. Jaroslaw has been working with IDEA since its first release and has observed the IDE grow and mature. He has been designing and developing software professionally since 2000 and has been using Java as his primary programming language since 2002. In the past, he worked for companies such as Kredyt Bank (KBC) and Bank BPS on many large-scale projects, such as international money orders, express payments, and collection systems. He currently works as a consultant for the Danish company 7N as an infrastructure architect for the Nykredit bank. You can reach him via Twitter at @jkroch or by email at [email protected].
He has authored the books, IntelliJ Idea Essentials, Developing with Docker, and Docker and Kubernetes for Java Developers by Packt, and he has reviewed another book by Packt, Spring Essentials.
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Table of Contents
Preface
What this book covers
What you need for this book
Who this book is for
Conventions
Reader feedback
Customer support
Downloading the example code
Errata
Piracy
Questions
Evolution to Spring Framework 5.0
Spring Framework
Problems with EJB
Why is Spring Framework popular?
Simplified unit testing
Reduction in plumbing code
How does Spring Framework do this magic?
Architectural flexibility
Keep up with changing times
Spring modules
Spring Core Container
Cross-cutting concerns
Web
Business
Data
Spring Projects
Spring Boot
Spring Cloud
Spring Data
Spring Batch
Spring Security
Spring HATEOAS
New features in Spring Framework 5.0
Baseline upgrades
JDK 9 runtime compatibility
Usage of JDK 8 features in Spring Framework code
Reactive programming support
Functional web framework
Java modularity with Jigsaw
Kotlin support
Dropped features
Spring Boot 2.0 new features
Summary
Dependency Injection
Understanding dependency injection
Understanding dependencies
The Spring IoC container
Defining beans and wiring
Creating a Spring IoC container
Java configuration for the application context
A quick review
Launching the application context with Java configuration
The console log
The XML configuration for the application context
Defining the XML Spring configuration
Launching an application context with the XML configuration
Writing JUnit using the Spring context
Unit testing with mocks
Container managed beans
Dependency injection types
The setter injection
The constructor injection
Constructor versus setter injection
Spring bean scopes
Java versus XML configuration
The @Autowired annotation in depth
The @Primary annotation
The @Qualifier annotation
Other important Spring annotations
Exploring Contexts and dependency injection
An example of CDI
Summary
Building a Web Application with Spring MVC
Java web application architecture
Model 1 architecture
Model 2 architecture
Model 2 Front Controller architecture
Basic flows
Basic setup
Adding dependency for Spring MVC
Adding DispatcherServlet to web.xml
Creating Spring context
Flow 1 - Simple controller flow without View
Creating a Spring MVC controller
Running the web application
Unit testing
Setting up the Controller to test
Writing the Test method
Flow 2 - Simple controller flow with a View
Spring MVC controller
Creating a View - a JSP
View resolver
Unit testing
Setting up the Controller to test
Writing the Test method
Flow 3 - Controller redirecting to a View with Model
Spring MVC controller
Creating a View
Unit testing
Setting up the Controller to test
Writing the Test method
Flow 4 - Controller redirecting to a View with ModelAndView
Spring MVC controller
Creating a View
Unit testing
Flow 5 - Controller redirecting to a View with a form
Creating a command or form backing object
The Controller method to show the form
Creating the View with a form
Controller get method to handle form submit
Unit testing
Flow 6 - Adding validation to the previous flow
Hibernate Validator dependency
Simple validations on the bean
Custom validations
Unit testing
Controller setup
The Test method
An overview of Spring MVC
Important features
How it works
Important concepts behind Spring MVC
RequestMapping
Examples of request mapping
Example 1
Example 2
Example 3
Request Mapping methods - supported method arguments
RequestMapping methods - supported return types
View resolution
Configuring JSP view resolver
Configuring Freemarker
Handler mappings and Interceptors
Defining a HandlerInterceptor
Mapping HandlerInterceptor to handlers
Model attributes
Session attributes
Putting an attribute in the session
Reading an attribute from the session
Removing an attribute from the session
InitBinders
The @ControllerAdvice annotation
Spring MVC - advanced features
Exception handling
Common exception handling across controllers
The error view
Specific exception handling in a Controller
Internationalization
Message bundle setup
Configuring a SessionLocaleResolver
Configuring a CookieLocaleResolver
Integration testing Spring controllers
Serving static resources
Exposing static content
Caching static content
Enabling GZip compression of static content
Integrating Spring MVC with Bootstrap
Bootstrap WebJar as Maven dependency
Configure Spring MVC resource handler to deliver WebJar static content
Using Bootstrap resources in JSP
Spring Security
Adding Spring Security dependency
Configuring a filter to intercept all requests
Logout
Summary
Evolution toward Microservices and Cloud-Native Applications
Typical web application architecture with Spring
Web layer
Web application - rendering an HTML View
RESTful services
Business layer
Data layer
Integration layer
Cross-cutting concerns
Problems solved by Spring
Loose coupling and testability
Plumbing code
Lightweight architecture
Architecture flexibility
Simplified implementation of cross-cutting concerns
Design patterns for free
Application development goals
Speed
Safety
Reliability
Availability
Security
Performance
High resilience
Scalability
Challenges with monolithic applications
Long release cycles
Difficult to scale
Adapting new technologies
Adapting new methodologies
Adapting modern development practices
Understanding microservices
What is a microservice?
The microservice architecture
Microservice characteristics
Small and lightweight microservices
Interoperability with message-based communication
Capability-aligned microservices
Independently deployable units
Stateless
Automated build and release process
Event-driven architecture
Approach 1 - sequential approach
Approach 2 - event-driven approach
Independent teams
Microservice advantages
Faster time to market
Technology evolution
Availability and scaling
Team dynamics
Microservice challenges
Increased need for automation
Defining the boundaries of subsystems
Visibility and monitoring
Fault tolerance
Eventual consistency
Shared capabilities (enterprise level)
Increased need for operations teams
Cloud-Native applications
Twelve-Factor App
Maintain one code base
Dependencies
Config
Backing services
Build, release, run
Stateless
Port binding
Concurrency
Disposability
Environment parity
Logs as event streams
No distinction of admin processes
Spring projects
Spring Boot
Spring Cloud
Summary
Spring Framework
Problems with EJB
Why is Spring Framework popular?
Simplified unit testing
Reduction in plumbing code
How does Spring Framework do this magic?
Architectural flexibility
Keep up with changing times
Spring modules
Spring Core Container
Cross-cutting concerns
Web
Business
Data
Spring Projects
Spring Boot
Spring Cloud
Spring Data
Spring Batch
Spring Security
Spring HATEOAS
New features in Spring Framework 5.0
Baseline upgrades
JDK 9 runtime compatibility
Usage of JDK 8 features in Spring Framework code
Reactive programming support
Functional web framework
Java modularity with Jigsaw
Kotlin support
Dropped features
Spring Boot 2.0 new features
Summary
Building Microservices with Spring Boot
What is Spring Boot?
Building a quick prototype for a microservice
Primary goals
Nonfunctional features
Spring Boot Hello World
Configure spring-boot-starter-parent
spring-boot-starter-parent
Configure pom.xml with the required starter projects
Understanding starter projects
Configuring spring-boot-maven-plugin
Creating your first Spring Boot launch class
SpringApplication class
The @SpringBootApplication annotation
Running our Hello World application
Auto-configuration
Starter projects
What is REST?
First REST service
Simple method returning string
Unit testing
Integration testing
Simple REST method returning an object
Executing a request
Unit testing
Integration testing
Get method with path variables
Executing a request
Unit testing
Integration testing
Creating a todo resource
Request methods, operations, and URIs
Beans and services
Retrieving a Todo list
Executing the service
Unit testing
Integration testing
Retrieving details for a specific Todo
Executing the service
Unit testing
Integration testing
Adding a Todo
Postman
Executing the POST service
Unit testing
Integration testing
Spring Initializr
Creating your first Spring Initializr project
pom.xml
FirstSpringInitializrApplication.java class
FirstSpringInitializrApplicationTests class
A quick peek into auto-configuration
Summary
Extending Microservices
Exception handling
Spring Boot default exception handling
Nonexistent resource
Resource throwing an exception
Throwing a custom exception
Customizing the exception message
Response status
HATEOAS
Sending HATEOAS links in response
Spring Boot starter HATEOAS
Validation
Enabling validation on ;the controller method
Defining validations on the bean
Unit testing validations
Documenting REST services
Generating ;a Swagger specification
Swagger UI
Customizing Swagger documentation using annotations
Securing REST services with Spring Security
Adding Spring Security starter
Basic authentication
Integration testing
Unit testing
OAuth 2 authentication
High-level ;flow
Implementing OAuth 2 authentication for our service
Setting up authorization and resource servers
Executing OAuth requests
Obtaining an access token
Executing the request using the access token
Integration test
Internationalization
Caching
Spring-boot-starter-cache
Enabling caching
Caching data
JSR-107 caching annotations
Auto-detection order
Summary
Advanced Spring Boot Features
Externalised configuration
Customizing frameworks through application.properties
Logging
Embedded server configuration
Spring MVC
Spring starter security
Data Sources, JDBC and JPA
Other configuration options
Custom properties in application.properties
Configuration properties - type-safe Configuration Management
Profiles
Profiles-based Bean configuration
Other options ;for application configuration values
YAML configuration
Embedded servers
Switching to Jetty and Undertow
Building a WAR file
Developer tools
Live reload
Spring Boot Actuator
HAL Browser
Configuration properties
Environment details
Health
Mappings
Beans
Metrics
Auto-configuration
Debugging
Deploying ;an application to Cloud
Cloud Foundry
Summary
Spring Data
Background - data stores
Spring Data
Spring Data Commons
Repository
The CrudRepository interface
The PagingAndSortingRepository interface
Spring Data JPA
Spring Data JPA example
New project with Starter Data JPA
Entities
The SpringBootApplication class
Populating some data
A simple repository
Unit test
The CrudRepository interface
Unit test
The PagingAndSortingRepository interface
Unit tests
Query methods
Queries
Named Parameters
Named Query
Native query
Spring Data Rest
The GET method
The POST method
The search resource
Big Data
MongoDB
Unit test
Summary
Spring Cloud
Introducing Spring Cloud
Spring Cloud Netflix
Demo microservices setup
Microservice A
Service consumer
Ports
Centralized microservice configuration
Problem statement
Solution
Options
Spring Cloud Config
Implementing Spring Cloud Config Server
Setting up Spring Cloud Config Server
Connecting Spring Cloud Config Server to a local Git repository
Creating an environment-specific configuration
Spring Cloud Config Client
Spring Cloud Bus
The need for Spring Cloud Bus
Propogating configuration changes using Spring Cloud Bus
Implementation
Declarative REST Client - Feign
Load balancing
Ribbon
Implementation
The Name server
Limitations of hard coding microservice URLs
Workings of Name server
Options
Implementation
Setting up a Eureka Server
Registering microservices with Eureka
Connecting the service consumer microservice with Eureka
API Gateways
Implementing client-side load balancing with Zuul
Setting up a new Zuul API Gateway Server
Zuul custom filters
Invoking microservices through Zuul
Configuring service consumer to use Zuul API gateway
Distributed tracing
Distributed tracing options
Implementing Spring Cloud Sleuth and Zipkin
Integrating microservice components with Spring Cloud Sleuth
Setting up Zipkin Distributed Tracing Server
Integrating microservice components with Zipkin
Hystrix - fault tolerance
Implementation
Summary
Spring Cloud Data Flow
Message-based asynchronous communication
Complexities of asynchronous communication
Spring projects for asynchronous messages
Spring Integration
Spring Cloud Stream
Spring Cloud Data Flow
Spring Cloud Stream
Spring Cloud Stream architecture
Event processing - stock trading example
Model for stock trading example
The source application
Processor
Sink
Spring Cloud Data Flow
High-level architecture
Implementing Spring Cloud Data Flow
Setting up Spring Cloud Data Flow server
Setting up Data Flow Shell project
Configuring the apps
Configuring the stream
Deploying the stream
Log messages - setting up connections to the message factory
Log messages - the flow of events
Spring Cloud Data Flow REST APIs
Spring Cloud Task
Summary
Reactive Programming
The Reactive Manifesto
Characteristics of Reactive Systems
Reactive use case - a stock price page
The traditional approach
The reactive approach
Comparison between the traditional and reactive approaches
Reactive programming in Java
Reactive streams
Reactor
Mono
Flux
Spring Web Reactive
Creating a project using Spring Initializr
Creating a Reactive Controller
Creating an HTML view
Launching SpringReactiveExampleApplication
Reactive databases
Integrating Spring Boot Reactive MongoDB Starter
Creating a model object - a stock document
Creating a ReactiveCrudRepository
Initialising stock data using the Command Line Runner
Creating Reactive methods in Rest Controller
Updating the view to subscribe to the event stream
Launching SpringReactiveExampleApplication
Summary
Spring Best Practices
Maven standard directory layout
Layered architecture
Recommended practices
Separate API and impl for important layers
Exception handling
Spring's approach to exception handling
The recommended approach
Keeping your Spring configuration light
Using the basePackageClasses attribute in ComponentScan
Not using version numbers in schema references
Preferring constructor injection over setter injection for mandatory dependencies
Managing dependency versions for Spring Projects
Unit testing
The business layer
Web layer
The data layer
Other best practices
Integration testing
Spring Session
Example
Adding dependencies for Spring Session
Configuring Filter to replacing HttpSession with Spring Session
Enabling filtering for Tomcat by extending AbstractHttpSessionApplicationInitializer
Caching
Adding the Spring Boot Starter Cache dependency
Adding caching annotations
Logging
Logback
Log4j2
Framework independent configuration
Summary
Working with Kotlin in Spring
Kotlin
Kotlin versus Java
Variables and type inference
Variables and immutability
Type system
Functions
Arrays
Collections
No c
Data class
Creating a Kotlin project in Eclipse
Kotlin plugin
Creating a Kotlin project
Creating a Kotlin class
Running a Kotlin class
Creating a Spring Boot project using Kotlin
Dependencies and plugins
Spring Boot application class
Spring Boot application test class
Implementing a REST service using Kotlin
Simple method returning a string
Unit testing
Integration testing
Simple REST method returning an object
Executing a request
Unit testing
Integration testing
Get method with path variables
Executing a request
Unit testing
Integration testing
Summary
Preface
Spring 5.0 is due to arrive with a myriad of new and exciting features that will change the way we've used the framework so far. This book will show you this evolution--from solving the problems of testable applications to building distributed applications on the Cloud. The book begins with an insight into the new features in Spring 5.0, and shows you how to build an application using Spring MVC. You will then get a thorough understanding of how to build and extend microservices using the Spring Framework. You will also understand how to build and deploy Cloud applications. You will realize how application architectures have evolved from monoliths to those built around microservices. The advanced features of Spring Boot will also be covered and displayed through powerful examples. By the end of this book, you will be equipped with the knowledge and best practices to develop applications with the Spring Framework.
What this book covers
Chapter 1, Evolution to Spring Framework 5.0, takes you through the evolution of the Spring Framework, ranging from its initial versions to Spring 5.0. Initially, Spring was used to develop testable applications using dependency injection and core modules. Recent Spring Projects, such as Spring Boot, Spring Cloud, Spring Cloud Data Flow--deal with application infrastructure and moving applications to Cloud. We get an overview of different Spring modules and projects.
Chapter 2, Dependency Injection, dives deep into dependency injection. We will look at different kinds of dependency injection methods available in Spring, and how auto-wiring makes your life easy. We will also take a quick look into unit testing.
Chapter 3, Building a Web Application with Spring MVC, gives a quick overview of building a web application with Spring MVC.
Chapter 4, Evolution toward Microservices and Cloud-Native Applications, explains the evolution of application architectures in the last decade. We will understand why microservices and Cloud Native applications are needed and get a quick overview of the different Spring projects that help us build Cloud-Native applications.
Chapter 5, Building Microservices with Spring Boot, discusses how Spring Boot takes away the complexity in creating production-grade Spring-based applications. It makes it easy to get started with Spring-based projects and provides easy integration with third-party libraries. In this chapter, we will take the students on a journey with Spring Boot. We will start with implementing a basic web service and then move on to adding caching, exception handling, HATEOAS, and internationalization, while making use of different features from the Spring Framework.
Chapter 6, Extending Microservices, focuses on adding more advanced features to the microservices that we built in Chapter 4, Evolution toward Microservices and Cloud-Native Applications.
Chapter 7, Advanced Spring Boot Features, takes a look at the advanced features in Spring Boot. You will learn how to monitor a microservice with a Spring Boot Actuator. Then, you will deploy the microservice to Cloud. You will also learn how to develop more effectively with the developer tools provided by Spring Boot.
Chapter 8, Spring Data, discusses the Spring Data module. We will develop simple applications to integrate Spring with JPA and Big Data technologies.
Chapter 9, Spring Cloud, discusses the distributed systems in the Cloud that have common problems, configuration management, service discovery, circuit breakers, and intelligent routing. In this chapter, you will learn how Spring Cloud helps you develop solutions for these common patterns. These solutions should work well on the Cloud as well as developer local systems.
Chapter 10, Spring Cloud Data Flow, talks about the Spring Cloud Data Flow, which offers a collection of patterns and best practices for microservices-based distributed streaming and batch data pipelines. In this chapter, we will understand the basics of Spring Cloud Data Flow and use it to build basic data flow use cases.
Chapter 11, Reactive Programming, explores programming with asynchronous data streams. In this chapter, we will understand Reactive programming and take a quick look at the features provided by the Spring Framework.
Chapter 12, Spring Best Practices, helps you understand best practices in developing enterprise applications with Spring related to unit testing, integration testing, maintaining Spring configuration, and more.
Chapter 13,Working with Kotlin in Spring, introduces you to a JVM language gaining quick popularity--Kotlin. We will discuss how to setup a Kotlin project in Eclipse. We will create a new Spring Boot project using Kotlin and implement a couple of basic services with unit and integration testing.
What you need for this book
To be able to run examples from this book, you will need the following tools:
Java 8
Eclipse IDE
Postman
We will use Maven embedded into Eclipse IDE to download all the dependencies that are needed.
Who this book is for
This book is for experienced Java developers who knows the basics of Spring, and wants to learn how to use Spring Boot to build applications and deploy them to the Cloud.
Conventions
In this book, you will find a number of text styles that distinguish between different kinds of information. Here are some examples of these styles and an explanation of their meaning.
Code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, and user input are shown as follows: "Configure spring-boot-starter-parent in your pom.xml file".
A block of code is set as follows:
<properties> <mockito.version>1.10.20</mockito.version></properties>
Any command-line input or output is written as follows:
mvn clean install
New terms and important words are shown in bold. Words that you see on the screen, for example, in menus or dialog boxes, appear in the text like this: "Provide the details and click onGenerate Project."
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Questions
If you have a problem with any aspect of this book, you can contact us at [email protected], and we will do our best to address the problem.
Evolution to Spring Framework 5.0
The first version of Spring Framework 1.0 was released in March 2004. For more than a decade and a half, Spring Framework remained the framework of choice to build Java applications.
In the relatively young and dynamic world of Java frameworks, a decade is a long time.
In this chapter, we start with understanding the core features of Spring Framework. We will look at why the Spring Framework became popular and how it adapted to remain the framework of choice. After taking a quick look at the important modules in the Spring Framework, we will jump into the world of Spring Projects. We will end the chapter by looking at the new features in Spring Framework 5.0.
This chapter will answer the following questions:
Why is Spring Framework popular?
How has Spring Framework adapted to the evolution of application architectures?
What are the important modules in Spring Framework?
Where does Spring Framework fit in the umbrella of Spring Projects?
What are the new features in Spring Framework 5.0?
Spring Framework
The Spring website (https://projects.spring.io/spring-framework/) defines Spring Framework as follows: The Spring Framework provides a comprehensive programming and configuration model for modern Java-based enterprise applications.
Spring Framework is used to wire enterprise Java applications. The main aim of Spring Framework is to take care of all the technical plumbing that is needed in order to connect the different parts of an application. This allows programmers to focus on the crux of their jobs--writing business logic.
Problems with EJB
Spring Framework was released in March 2004. When the first version of Spring Framework was released, the popular way of developing an enterprise application was using Enterprise Java Beans (EJB) 2.1.
Developing and deploying EJBs was a cumbersome process. While EJBs made the distribution of components easier, developing, unit testing, and deploying them was not easy. The initial versions of EJBs (1.0, 2.0, 2.1) had a complex Application Programmer Interface (API), leading to a perception (and truth in most applications) that the complexity introduced far outweighed the benefits:
Difficult to unit test. Actually, difficult to test outside the EJB Container.
Multiple interfaces need to be implemented with a number of unnecessary methods.
Cumbersome and tedious exception handling.
Inconvenient deployment descriptors.
Spring Framework was introduced as a lightweight framework aimed at making developing Java EE applications simpler.
Why is Spring Framework popular?
The first version of Spring Framework was released in March 2004. In the subsequent decade and a half, the use and popularity of Spring Framework only grew.
The important reasons behind the popularity of Spring Framework are as follows:
Simplified unit testing--because of dependency injection
Reduction in plumbing code
Architectural flexibility
Keeping up with changing times
Let's discuss each of these in detail.
Simplified unit testing
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:
Programmers are more productive
Defects are found earlier so they are less costly to fix
Applications have automated unit tests, which can run in
Continuous Integration
builds, preventing future defects
How does Spring Framework do this magic?
In the preceding example, Spring JDBC (and Spring, in general) converts most checked exceptions into unchecked exceptions. Typically, when a query fails, there is not a lot we can do--other than to close the statement and fail the transaction. Instead of implementing exception handling in every method, we can have centralized exception handling and inject it in using Spring Aspect-Oriented Programming (AOP).
Spring JDBC removes the need to create all the plumbing code involved in getting a connection, creating a prepared statement, and so on. The jdbcTemplate class can be created in the Spring context and injected into the Data Access Object (DAO) class wherever it is needed.
Similar to the preceding example, Spring JMS, Spring AOP, and other Spring modules help in reducing a lot of plumbing code.
Spring Framework lets the programmer focus on the primary job of a programmer-- writing business logic.
Avoiding all the plumbing code also has another great benefit--reduced duplication in code. Since all code for transaction management, exception handling, and so on (typically, all your cross-cutting concerns) is implemented at one place, it is easier to maintain.
Architectural flexibility
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:
In the web layer, Spring offers a framework of its own--Spring MVC. However, Spring has great support for Struts, Vaadin, JSF, or any web framework of your choice.
Spring Beans can provide lightweight implementation for your business logic. However, Spring can be integrated with EJBs as well.
In the data layer, Spring simplifies JDBC with its Spring JDBC module. However, Spring has great support for any of your preferred data layer frameworks--JPA, Hibernate (with or without JPA), or iBatis.
You have the option of implementing your cross-cutting concerns (logging, transaction management, security, and so on) with Spring AOP. Or, you can integrate with a fully fledged AOP implementation such as AspectJ.
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.
Keep up with changing times
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:
Annotations were introduced in Java 5. Spring Framework (version 2.5 – Nov 2007) was ahead of Java EE in introducing an annotation-based controller model for Spring MVC. Developers using Java EE had to wait until Java EE 6 (Dec 2009 – 2 years) before having comparable functionality.
Spring Framework introduced a number of abstractions ahead of Java EE to keep the application decoupled from specific implementation. Caching API provides a case in point. Spring provided a transparent caching support in Spring 3.1. Java EE came up with
JSR-107
for JCache (in 2014)--support for which was provided in Spring 4.1.
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:
Spring Batch
defines a new approach to building Java Batch applications. We had to wait until Java EE 7 (June 2013) to have comparable batch application specification in Java EE.
As architecture evolved toward Cloud and microservices, Spring came up with new Cloud-oriented Spring Projects. Spring Cloud helps in simplifying the development and deployment of microservices. Spring Cloud Data Flow provides orchestrations around microservice applications.
Spring modules
The modularity of Spring Framework is one of the most important reasons for its widespread used. Spring Framework is highly modular with more than 20 different modules--having clearly defined boundaries.
The following figure shows different Spring modules--organized by the layer of application they are typically used in:
We will start with discussing the Spring Core Container before moving on to other modules grouped by the application layer they are typically used in.
Spring Core Container
Spring Core Container provides the core features of Spring Framework--dependency injection, IoC (Inversion of Control) container, and the application context. We will learn more about DI and IoC Container in Chapter 2, Dependency Injection.
Important core Spring modules are listed in the following table:
Module/Artifact
Use
spring-core
Utilities used by other Spring modules.
spring-beans
Support for Spring beans. In combination with spring-core provides the core feature of Spring Framework--dependency injection. Includes implementation of BeanFactory.
spring-context
Implements ApplicationContext, which extends BeanFactory and provides support to load resources and internationalization, among others.
spring-expression
Extends
EL
(
Expression Language
from JSP) and provides a language for bean property (including arrays and collections) access and manipulations.
Cross-cutting concerns
Cross-cutting concerns are applicable to all application layers--logging and security, among others. AOP is typically used to implement cross-cutting concerns.
Unit tests and integration tests fit this category since they are applicable to all layers.
Important Spring modules related to cross-cutting concerns are listed as follows:
Module/Artifact
Use
spring-aop
Provides basic support for Aspect-Oriented Programming--with method interceptors and pointcuts.
spring-aspects
Provides integration with the most popular and fully featured AOP framework, AspectJ.
spring-instrument
Provides basic instrumentation support.
spring-test
Provides basic support for unit testing and integration testing.
Web
Spring provides its own MVC framework, Spring MVC, other than providing great integration with popular web frameworks such as Struts.
Important artifacts/modules are listed as follows:
spring-web
: Provides basic web features, such as multi-part file upload. Provides support for integration with other web frameworks, such as Struts.
spring-webmvc
: Provides a fully featured web MVC framework--Spring MVC, which includes features to implement REST services as well.
We will cover Spring MVC and develop web applicaitions and rest services with it in Chapter 3, Building Web Application with Spring MVC and Chapter 5, Building Microservices with Spring Boot.
Business
The business layer is focused on executing the business logic of the applications. With Spring, business logic is typically implemented in Plain Old Java Object (POJO).
Spring Transactions (spring-tx) provides declarative transaction management for POJO and other classes.
Data
The data layer in applications typically talks to the database and/or the external interfaces. Some of the important Spring modules related to the data layer are listed in the following table:
Module/Artifact
Use
spring-jdbc
Provides abstraction around JDBC to avoid boilerplate code.
spring-orm
Provides integration with ORM frameworks and specifications-- JPA and Hibernate, among others.
spring-oxm
Provides an object to XML mapping integration. Supports frameworks such as JAXB, Castor, and so on.
spring-jms
Provides abstraction around JMS to avoid boilerplate code.
Spring Projects
While Spring Framework provides the base for core features of enterprise applications (DI, web, data), other Spring Projects explore integration and solutions to other problems in the enterprise space--deployment, Cloud, Big Data, Batch and Security, among others.
Some of the important Spring Projects are listed as follows:
Spring Boot
Spring Cloud
Spring Data
Spring Batch
Spring Security
Spring HATEOAS
Spring Boot
Some of the challenges while developing microservices and web applications are as follows:
Making framework choices and deciding compatible framework versions
Providing mechanisms for externalizing configuration--properties that can change from one environment to another
Health checks and monitoring--providing alerts if a specific part of the application is down
Deciding the deployment environment and configuring the application for it
Spring Boot solves all these problems out of the box by taking an opinionated view of how applications have to be developed.
We will look at Spring Boot in depth in two chapters--Chapter 5, Building Microservices with Spring Boot and Chapter 7, Advanced Spring Boot Features.
Spring Cloud
It is not an exaggeration to say The world is moving to the Cloud.
Cloud Native microservices and applications are the order of the day. We will discuss this in detail in Chapter 4, Evolution toward Microservices and Cloud-Native Applications.
Spring is taking rapid strides toward making application development for the Cloud simpler with Spring Cloud.
Spring Cloud provides solutions for common patterns in distributed systems. Spring Cloud enables developers to quickly create applications that implement common patterns. Some of the common patterns implemented in Spring Cloud are listed as follows:
Configuration management
Service discovery
Circuit breakers
Intelligent routing
We will discuss Spring Cloud and its varied range features in more detail in Chapter 9, Spring Cloud.
Spring Data
There are multiple sources of data in today's world--SQL (relational) and a variety of NOSQL databases. Spring Data tries to provide a consistent data-access approach to all these different kinds of databases.
Spring Data provides integration with a varied range of specifications and/or data stores:
JPA
MongoDB
Redis
Solr
Gemfire
Apache Cassandra
Some of the important features are listed as follows:
Provides abstractions around repository and object mappings--by determining queries from method names
Simple Spring integration
Integration with Spring MVC controllers
Advanced automatic auditing features--created by, created date, last changed by, and last changed date
We will discuss Spring Data in more detail in Chapter 8, Spring Data.
Spring Batch
Enterprise applications today process large volumes of data using batch programs. The needs of these applications are very similar. Spring Batch provides solutions for high- volume batch programs with high performance requirements.
Important features in Spring Batch are as follows:
The ability to start, stop, and restart jobs--including the ability to restart failed jobs from the point where they failed
The ability to process data in chunks
The ability to retry steps or to skip steps on failure
Web-based administration interface
Spring Security
Authentication is the process of identifying the user. Authorization is the process of ensuring that a user has access to perform the identified action on the resource.
Authentication and authorization are critical parts of Enterprise applications, both web applications and web services. Spring Security provides declarative authentication and authorization for Java based applications.
Important features in Spring Security are as follows:
Simplified authentication and authorization
Great integration with Spring MVC and Servlet APIs
Support to prevent common security attacks--
cross-site forgery request
(
CSRF
) and Session Fixation
Modules available for integration with SAML and LDAP
We will discuss how to secure web applications with Spring Security in Chapter 3, Building Web Application with Spring MVC.
We will discuss how to secure REST Services with Basic and OAuth authentication mechanisms using Spring Security in Chapter 6, Extending Microservices.
Spring HATEOAS
HATEOAS stands for Hypermedia as The Engine of Application State. Though it sounds complex, it is quite a simple concept. Its main aim is to decouple the server (the provider of the service) from the client (the consumer of the service).
The service provider provides the service consumer with information about what other actions can be performed on the resource.
Spring HATEOAS provides a HATEOAS implementation--especially for the REST services implemented with Spring MVC.
Important features in Spring HATEOAS are as follows:
Simplified definition of links pointing to service methods, making the links less fragile
Support for JAXB (XML-based) and JSON integration
Support for service consumer (client side)
We will discuss how to use HATEOAS in Chapter 6, Extending Microservices.
New features in Spring Framework 5.0
Spring Framework 5.0 is the first major upgrade in Spring Framework, almost four years after Spring Framework 4.0. In this time frame, one of the major developments has been the evolution of the Spring Boot project. We will discuss the new features in Spring Boot 2.0 in the next section.
One of the biggest features of Spring Framework 5.0 is Reactive Programming. Core reactive programming features and support for reactive endpoints are available out of the box with Spring Framework 5.0. The list of important changes includes the following:
Baseline upgrades
JDK 9 runtime compatibility
Usage of JDK 8 features in the Spring Framework code
Reactive programming support
A functional web framework
Java modularity with Jigsaw
Kotlin support
Dropped features
Baseline upgrades
Spring Framework 5.0 has JDK 8 and Java EE 7 baseline. Basically, it means that previous JDK and Java EE versions are not supported anymore.
Some of the important baseline Java EE 7 specifications for Spring Framework 5.0 are listed as follows:
Servlet 3.1
JMS 2.0
JPA 2.1
JAX-RS 2.0
Bean Validation 1.1
There are many changes to the minimum supported versions of several Java frameworks. The following list contains some of the minimum supported versions of prominent frameworks:
Hibernate 5
Jackson 2.6
EhCache 2.10
JUnit 5
Tiles 3
The following list shows the supported server versions:
Tomcat 8.5+
Jetty 9.4+
WildFly 10+
Netty 4.1+ (for web reactive programming with Spring Web Flux)
Undertow 1.4+ (for web reactive programming with Spring Web Flux)
Applications using earlier versions of any of the preceding specifications/frameworks need to be upgraded at least to the previously listed versions before they can use Spring Framework 5.0.
JDK 9 runtime compatibility
JDK 9 is expected to be released mid-2017. Spring Framework 5.0 is expected to have runtime compatibility with JDK 9.
Usage of JDK 8 features in Spring Framework code
The Spring Framework 4.x baseline version is Java SE 6. This means that it supports Java 6, 7, and 8. Having to support Java SE 6 and 7 puts constraints on the Spring Framework code. The framework code cannot use any of the new features in Java 8. So, while the rest of the world upgraded to Java 8, the code in Spring Framework (at least the major parts) was restricted to using earlier versions of Java.
With Spring Framework 5.0, the baseline version is Java 8. Spring Framework code is now upgraded to use the new features in Java 8. This will result in more readable and performant framework code. Some of the Java 8 features used are as follows:
Java 8 default methods in core Spring interfaces
Internal code improvements based on Java 8 reflection enhancements
Use of functional programming in the framework code--lambdas and streams
Reactive programming support
Reactive programming is one of the most important features of Spring Framework 5.0.
Microservices architectures are typically built around event-based communication. Applications are built to react to events (or messages).
Reactive programming provides an alternate style of programming focused on building applications that react to events.
While Java 8 does not have built-in suppport for reactive programming, there are a number of frameworks that provide support for reactive programming:
Reactive Streams
: Language-neutral attempt to define reactive APIs.
Reactor
: Java implementation of Reactive Streams provided by the Spring Pivotal team.
Spring WebFlux
: Enables the development of web applications based on reactive programming. Provides a programming model similar to Spring MVC.
We will discuss Reactive Programming and how you can implement it with Spring Web Flux in Chapter 11, Reactive Programming.
Java modularity with Jigsaw
Until Java 8, the Java platform was not modular. A couple of important problems resulted out of this:
Platform Bloat
: Java modularity has not been a cause of concern in the last couple of decades. However, with
Internet of Things
(
IOT
) and new lightweight platforms such as Node.js, there is an urgent need to address the bloat of the Java platform. (Initial versions of JDK were less than 10 MB in size. Recent versions of JDK need more than 200 MB.)
JAR Hell
: Another important concern is the problem of JAR Hell. When Java ClassLoader finds a class, it will not see whether there are other definitions for the class available. It immediately loads the first class that is found. If two different parts of the application need the same class from different jars, there is no way for them to specify the jar from which the class has to be loaded.
Open System Gateway initiative (OSGi) is one of the initiatives, started way back in 1999, to bring modularity into Java applications.
Each module (referred to as bundle) defines the following:
imports
: Other bundles that the module uses
exports
: Packages that this bundle exports
Each module can have its own life cycle. It can be installed, started, and stopped on its own.
Jigsaw is an initiative under Java Community Process (JCP), started with Java 7, to bring modularity into Java. It has two main aims:
Defining and implementing a modular structure for JDK
Defining a module system for applications built on the Java platform
Jigsaw is expected to be part of Java 9 and Spring Framework 5.0 is expected to include basic support for Jigsaw modules.
