Is there a list of beans provided by Spring Boot and its different modules? For example, I only recently discovered that Spring Boot already provides a configurable Jackson ObjectMapper bean. I would have never known that if not for reading up on an unrelated issue I was dealing with. Now I'm working with Spring JMS and am afraid that I am reinventing the wheel because Spring Boot may already have what I need and I just don't know about it. How are these beans discovered? They don't seem to be cataloged in any Spring documentation.
I would recommend starting with the reference documentation. While it doesn't list every bean that may be auto-configured, it does have documentation describing each feature area that may be auto-configured. For example, there are sections on Jackson's ObjectMapper and on JMS.
Each starter that Spring Boot offers is also a good indication of what it can auto-configure. Each first-party starter is listed in the documentation.
Related
And most important, what's the reason behind the "Auto" prefix? Classes annotated with #Configuration rather than #AutoConfiguration are less automatic or something?
#Configuration is a spring framework annotation and not strictly bound to spring-boot. It was introduced when spring started to allow programmatic creation of spring-beans as to move forward from xml definitions of beans.
#AutoConfiguration is a spring-boot specific annotation not commonly available in spring framework. The reason it exists, is for external providers that cooperate with spring-boot to be able to mark some classes in some libraries they provide with this annotation as to inform spring-boot that those classes could be parsed and make some initializations during start up of spring application automatically.
So if some regular programmer that develops some application happens to have kafka in dependencies then some beans will automatically be created and added in application context and will be ready for the programmer to use, although he has not defined any configuration for them. Spring-boot already knows this as the kafka provider has already informed by marking some class in the jar they provide with the annotation #AutoConfiguration.
For this reason #AutoConfiguration has some more powerful configurations available as before, after, beforeName, afterName as to allow the provider to specify when the configuration is applied during application startup if some order is necessary.
So this annotation is not to be used from some regular programmer that develops an application using spring-boot. It is for someone that develops a library that other users might use with spring-boot. One such example is kafka library.
For this to work in a spring-boot project #EnableAutoConfiguration is needed as well, to enable auto configuration.
From spring documentation
Spring Boot auto-configuration attempts to automatically configure
your Spring application based on the jar dependencies that you have
added. For example, if HSQLDB is on your classpath, and you have not
manually configured any database connection beans, then Spring Boot
auto-configures an in-memory database.
#Configuration instead is to be used from some regular programmer that develops an application using spring-boot or spring-framework as to inform the framework for which beans should be created and how.
#AutoConfiguration was introduced in 2.7 with the idea to mark all auto-configurations with its dedicated annotation and move away from spring.factories for auto-configuration imports in 3.0 as described in Github issue.
According to Spring documentation:
[#AutoConfiguration] indicates that a class provides configuration that can be
automatically applied by Spring Boot. Auto-configuration classes are
regular #Configuration with the exception that
Configuration#proxyBeanMethods() proxyBeanMethods is always false.
Usually, #AutoConfiguration classes automatically configure an application based on the dependencies that are present on the classpath. Those classes are generally marked as #ConditionalOnClass and #ConditionalOnMissingBean annotations that detect the presence or absence of specific classes.
Additionally, if a configuration needs to be applied in a specific order, you can use the before, beforeName, after, and afterName attributes on the #AutoConfiguration, unlike #Configuration which doesn't provide those attributes.
Here, several questions have been asked by many developers about difference between Spring-Rest and JAX-RS.
And, I have also learned that Spring is not following any specification and Spring framework has their own implementation then
Why Spring allows all that Annotations which are supported/used by JAX-RS by default?
Spring does not support JAX-RS annotations. If there is a situation where you think they do, then you are mistaken or it's just a coincidence. Period. If you will add any JAX-RS annotations in my Spring MVC program, nothing will happen. Annotations are just metadata. They are not programs. If Spring does not recognize the metadata, it will ignore it. But if you use a JAX-RS annotation in place of a Spring annotation that is used for the same purpose, respective of their framework, then you will not get the expected Spring behavior. So basically, if you are using Spring MVC, remove any JAX-RS dependencies so you don't mistakenly use them.
I've found quite a huge pile of topics that give the answer for the opposite question: "Why choose Spring Boot over Spring?", but I guess somebody can give an example that will justify Spring selection over Spring Boot.
You can found several cons on Spring boot over Spring, mainly missing learning steps in Spring and support and if using monolithic application
If you are new to Spring and want to learn how the dependency injection, AOP programming, and proxies work, starting with Spring Boot is not a good choice. Spring Boot hides the most of these details from you.
If you are not familiarized with other projects of the Spring ecosystem (Spring Integration, Spring AMQP, Spring Security, etc), using them from Spring Boot will make you miss a lot of concepts
In a large and monolithic based applications, I wouldn’t encourage you to use Spring Boot
Also can increase deployment size
Spring boot may unnecessarily increase the deployment binary size with unused dependencies.
I want to understand what is the exact meaning of term "autowiring" and AOP in Spring Framework.
From the official Spring Framework Reference:
The Spring container can autowire relationships between collaborating
beans. You can allow Spring to resolve collaborators (other beans)
automatically for your bean by inspecting the contents of the
ApplicationContext.
Which basically means you can leave it up to the Spring Framework to initialize your beans and ensure they're there when you need them. For example, lets say I have a number of Things in my app. Now, if I want to get all the Things and have them placed in a List<Thing>, in Spring (assuming I've configured it properly), I can simply use this code:
#Autowired
private List<Thing> things;
With no additional effort on my part I have the list I needed.
The question concerning Aspect Oriented Programming (AOP) as it relates to Spring would be quite a bit to put in a post. The simple explanation can be seen in the official Spring Framework Reference:
Aspect-Oriented Programming (AOP) complements Object-Oriented
Programming (OOP) by providing another way of thinking about program
structure. The key unit of modularity in OOP is the class, whereas in
AOP the unit of modularity is the aspect. Aspects enable the
modularization of concerns such as transaction management that cut
across multiple types and objects. (Such concerns are often termed
crosscutting concerns in AOP literature.)
One of the key components of Spring is the AOP framework. While the
Spring IoC container does not depend on AOP, meaning you do not need
to use AOP if you don’t want to, AOP complements Spring IoC to provide
a very capable middleware solution.
That section is very detailed and worth a read if you're interested in AOP.
Autowiring is a mechanism of resolving dependencies in Spring IoC container, as per Spring Reference. So instead of directly specifying the dependency (in XML or in Java configuration), you can depend on container itself to provide you with candidate(s). Spring itself should abort if you find more than one matching dependency (unless you are looking for a collection of beans).
There are many people who advised me to use Spring Boot instead of Spring to develop REST web services.
I want to know what exactly the difference between the two is?
In short
Spring Boot reduces the need to write a lot of configuration and boilerplate code.
It has an opinionated view on Spring Platform and third-party libraries so you can get started with minimum effort.
Easy to create standalone applications with embedded Tomcat/Jetty/Undertow.
Provides metrics, health checks, and externalized configuration.
You can read more here http://projects.spring.io/spring-boot/
Unfortunately and I mean this out of personal frustration with Spring boot, I have yet to see any real quantified list, where the differences are explicitly outlined.
There is only qualifications such as the rubbish sentence "...opinionated view..." which are bandied about.
What is clear, is that SpringBoot has wrapped up groups of Spring annotations into its own set of annotations, implicitly.
Further obfuscating, and making the need for anyone starting out in SpringBoot to have to commit to memory what a particular SpringBoot annotation represents.
My reply therefore is of no quantifiable benefit to the original question, which is analogous to that of the SpringBoot authors.
Those behind Spring IMO deliberately set-out to obfuscate, which reflects the obtuseness of their JavaDoc and API's (see SpringBatch API's as an example, if you think I am flaming) that makes one wonder the value of their open-source ethos.
My quest for figuring out SpringBoot continues.
Update. 22-08-2022
Read this (https://docs.spring.io/spring-boot/docs/current/reference/html/using.html#using.auto-configuration) and you will figure out for yourself what "opinionated" means.
There are over 140 Config classes that Springboot can use for this opinionated view, depending on what is on your classpath.
yes, on your classpath.
Finally and bizzarely, the annotation #SpringBootApplication is a configuration annotation as it includes it.
Go figure :=)
Basically, Spring Boot is an opinionated instance of a Spring application.
Spring Boot is a rapid application development platform. It uses various components of Spring, but has additional niceties like the ability to package your application as a runnable jar, which includes an embedded tomcat (or jetty) server. Additionally, Spring Boot contains a LOT of auto-configuration for you (the opinionated part), where it will pick and choose what to create based on what classes/beans are available or missing.
I would echo their sentiment that if you are going to use Spring I can't think of any reasons to do it without Spring Boot.
Spring Boot is opinionated view of Spring Framework projects.Let's analyse it through one program taken from Spring Boot Documentation.
#RestController
#EnableAutoConfiguration
public class Example {
#RequestMapping("/")
String home() {
return "Hello World!";
}
public static void main(String[] args) throws Exception {
SpringApplication.run(Example.class, args);
}
}
It's a very basic REST API and you need to add Spring-boot-starter-web in your POM.xml for the same. Since you have added starter-web dependency, the annotation
#EnableAutoConfiguration guesses that you want to develop a web application and sets up Spring accordingly.
Spring Boot auto-configuration attempts to automatically configure your Spring application based on the jar dependencies that you have added. For example, if HSQLDB is on your classpath, and you have not manually configured any database connection beans, then Spring Boot auto-configures an in-memory database.
It's opinionated like maven. Maven creates a project structure for you which it thinks is the general pattern of projects like it adds src/main/java folder or resource folder for you.
Spring boot helps in faster development. It has many starter projects that helps you get going quite faster. It also includes many non functional features like: embedded servers, security, metrics, health checks etc. In short, it makes, spring based application development easier with minimally invading code(Less configuration files, less no of annotations).
Reference: https://docs.spring.io/spring-boot/docs/current-SNAPSHOT/reference/htmlsingle/#boot-documentation-about
For developing common Spring applications or starting to learn Spring, I think using Spring Boot would be recommended. It considerably eases the job, is production ready and is rapidly being widely adopted.
Spring Boot is supposedly opinionated, i.e. it heavily advocates a certain style of rapid development, but it is designed well enough to accommodate exceptions to the rule, if you will. In short, it is a convention over configuration methodology that is willing to understand your need to break convention when warranted
For Spring Framework, you need to configure your project using XML configuration or Java configuration.
But for Spring Boot, these are preconfigured according to Spring team's view for rapid development. That is why Spring Boot is said to be an "opinionated view" of Spring Framework. It follows Convention over Configuration design paradigm.
Note: These configurations include view resolvers for MVC, transaction managers, way of locating container managed beans (Spring beans) and many more. And of course you can override any of these preconfigurations according to your need.
Spring Boot supports embedded servlet containers like Tomcat, Jetty or Undertow to create standalone applications, which Spring Framework doesn't.
Spring eliminate boilerplate code.
Spring-boot eliminates boilerplate configurations.
more