Rediscovering Spring with Spring Boot(1)

Rediscovering Spring with
Spring Boot
Gunith Devasurendra
Asso. Tech Lead, CMS

Agenda
● Intro
● Using Maven
● Features and Conventions
● Spring Data with Boot
● Spring MVC with Boot
● Spring Test with Boot
● In Conclusion

Spring
● What?
● Who?
● Why?
● Why not?
● What is Boot?

Spring.. Boot?
Spring made Simple
‘Spring Boot makes it easy to create stand-alone,
production-grade Spring based Applications that you can
“just run”’
New recommended way of running Spring programs
Goals
● Faster and more accessible initial setup
● Default Configurations and the ability to Customize
● No code generation and No XML configs

System Requirements
● Java 6+ (8 recommended)
● Spring 4.1.5+
That's it! Simply include the appropriate spring-boot-*.jar
files on your classpath.
---
● But, Recommended to use Build scripts:
○ Maven (3.2+), Gradle (1.12+)
● Also, Out-of-box supported Servlet containers:
○ Tomcat 7+, Jetty 8+, Undertow 1.1

Using Maven : Parent POM & Dependency
Inherit from the spring-boot-starter-parent project to
obtain sensible defaults:
Java 6 compiler, UTF-8 code, Sensible resource filtering (ex:
for application.properties), Sensible plugin configs
spring-boot-starter-parent extends from spring-boot-
dependencies which holds a predefined set of dependencies.
● Could easily include dependencies from the parent
● Could override the versions by overriding MVN variables
<properties>
<java.version>1.8</java.version>
</properties>

Using Maven : Starter POMs
Starter POMs are a set of convenient dependency descriptors
that you can include in your application
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency> ^-- No need for version as it comes
</dependencies> from Parent POM
Has many more including:
spring-boot-starter-amqp, spring-boot-starter-batch,
spring-boot-starter-data-jpa, spring-boot-starter-data-rest,
spring-boot-starter-mail, spring-boot-starter-mobile,
spring-boot-starter-test, spring-boot-starter-logging,
spring-boot-starter-ws spring-security-oauth2

Build File Generation
https://start.spring.io/

Main Class
@Configuration
@EnableAutoConfiguration
@ComponentScan
public class Application {
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
}
Just starts up deamon. To build CLI apps, use Spring Boot
CLI
SpringApplication can be customized by calling different
setters
Ex: Command line params, add listeners, shutdown hooks
@SpringBootApplication}

Code Structure
@ComponentScan automatically picks up all Spring components
com
+- example
+- myproject
+- Application.java <- Main application class is in a
| root package above other classes
+- domain for correct @ComponentScan
| +- Customer.java
| +- CustomerRepository.java
|
+- service
| +- CustomerService.java
|
+- web
+- CustomerController.java

Defining Beans in @Configuration
Spring Boot favors Java-based @Configuration over XML
Config, which is more traditional.
@Configuration
public class AdsdaqCoreDatasourceConfiguration {
@Bean(name = “dataSourceMain”)
@ConfigurationProperties(prefix = “datasource.main”)
@Primary
public DataSource dataSourceAdServer() {
return DataSourceBuilder.create().build();
}
}
___
datasource.main.url=jdbc:mysql://localhost:3306/reviewdb
datasource.main.username=root
datasource.main.password=admin

Enabling Auto Configuration
@EnableAutoConfiguration attempts to automatically configure
the application based on the dependencies
At any point you can start to define your own @Configuration
to replace specific parts of the auto-configuration.
Ex: if you add your own DataSource bean, the default
embedded database support will back away.
There are factories defined in
[MVN_repo]orgspringframeworkbootspring-boot-autoconfigure[VER]
[JAR]META-INFspring.factories
These factories only loaded by if satisfied various
conditions (ex: WebMvcAutoConfiguration)

Spring Beans
Spring provides the following stereotypes for a Spring Bean:
| Annotation | Meaning |
+-------------+-----------------------------------------------------+
| @Component | generic stereotype for any Spring-managed component |
| @Repository | stereotype for persistence layer |
| @Service | stereotype for service layer |
| @Controller | stereotype for presentation layer (spring-mvc) |
Any object with a stereotype as above is identified as a
Spring Bean.
Spring will create them upon container startup and map them
to any @Autowired annotation on an attribute/constructor

Spring Config files
Usually Spring Configuration is stored in file
config/application.properties (or YAML)
Can hard-code values into setters in beans
app.name=MyApp
app.description=${app.name} is a Spring Boot application
This can be overridden by
● runtime variables,
● environment variables,
● profile specific files (application-local.properties),
● based on the location of application.properties,
etc.

Setting Spring Config values to Beans
app.name=MyApp
listener.enable: true
connection.username:
admin
connection.remote-
address: 192.168.1.1
@Value("${app.name}")
private String name;
@Component
@ConditionalOnProperty(prefix = "listener",
name = "enable", matchIfMissing = false)
public class SomeListener { .. }
@Component
@ConfigurationProperties(prefix="connection")
public class ConnectionSettings {
private String username;
@NotNull
private InetAddress remoteAddress;
// ... getters and setters
}

Spring Profiles
Support profiles where the application would act differently
based on the active profile.
Ex: if ‘dev’ profile is passed via env. var.
--spring.profiles.active=dev
If exists,
● Beans with @Profile("dev") will be activated
● File application-dev.properties will be activated
Good for: Dev vs Prod settings, Local Dev vs Default
settings

Logging
Spring uses Commons Logging as default.
By default logs to console unless logging.file or logging.
path is set in application.properties.
Set log levels as follows:
logging.level.root=WARN
logging.level.org.springframework.web=DEBUG
If custom logging framework specific configs are to be used
property logging.config
Log format also can be configured.

Building JAR and Running
Spring has plugins for Eclipse, IDEA etc.
Spring Boot has a Maven plugin that can package the project
as an executable jar. Add the plugin to your <plugins>
section if you want to use it:
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
Run java -jar target/myproject-0.0.1-SNAPSHOT.jar
Or mvn spring-boot:run

DB Access with Spring
If you use embeded DB, it only needs MVN dependency.
If you use a production database,
Spring will connection pooling using tomcat-jdbc by
default (via Starters)
spring.datasource.url=jdbc:mysql://localhost/test
spring.datasource.username=dbuser
spring.datasource.password=dbpass
spring.datasource.driver-class-name=com.mysql.jdbc.Driver
There are many more attributes

Data Access Using JPA and Spring Data - Entity
Using spring-boot-starter-data-jpa.
@Entity classes are ‘scanned’.
import javax.persistence.*;
@Entity
public class City implements Serializable {
@Id
@GeneratedValue
private Long id;
@Column(nullable = false)
private String name;
}
More info about JPA at Hibernate Documentation

Data Access Using JPA and Spring Data - Repository
SQL are autogenerated.
public interface CityRepository extends PagingAndSortingRepository<City, Long>
{
Page<City> findAll(Pageable pageable);
City findByNameAndCountryAllIgnoringCase(String name, String country);
@Query("select c from City c")
Stream<City> findAllByCustomQueryAndStream();
}
● Repository’s subclass CrudRepository generates default
CRUD methods in runtime.
● CrudRepository’s subclass PagingAndSortingRepository
generates paging and sorting methods

Spring Data REST
Is able to easily open a REST interface to the DB using
Spring Data REST by including a spring-boot-starter-data-
rest dependency
Auto serialization
@RepositoryRestResource(collectionResourceRel = "cities", path =
"cities")
interface CityRepository extends Repository<City, Long> {
...
}

Spring MVC
Spring Boot comes with some auto configuration.
@Controller
@RequestMapping(value="/users")
public class MyRestController {
@RequestMapping(value="/{user}/cust", method=RequestMethod.GET)
ModelAndView getUserCustomers(@PathVariable Long user) {
// ...
}
}
@RestController creates a REST service.
● Expects any static content to be in a directory called
/static (or /public or /resources or /META-INF/resources)
or at spring.resources.staticLocations
● /error mapping by default that handles all errors as a
global error page.

@RequestMapping
@RequestMapping when added to a class would be prefixed to
the @RequestMapping of the method
@RequestMapping method can be called with different
parameters and different return types and it will work
differently
Can also write @RequestMapping to be caught based on,
● RequestMethod (GET, POST..)
● HTTP parameters (ex: params="myParam=myValue")
● HTTP Headers (ex: headers="myHeader=myValue")

Spring MVC : Other features
● Templating: Auto-configuration support for: FreeMarker,
Groovy, Thymeleaf, Velocity, Mustache
○ Templates will be picked up automatically from
src/main/resources/templates
● Other REST Implementations: Support for JAX-RS and Jersey
● Embedded servlet container support: Comes with Starter
Pom. Embeds Tomcat by default. Can go for Jetty, and
Undertow servers as well
○ Can set attributes server.port (default is 8080), server.
address, server.session.timeout values
○ Can deploy as a WAR as well

Why need Spring for Tests?
Sometimes we need Spring context
Ex: DB related tests, Web related tests
Can set custom properties for tests using
@TestPropertySource
Has Transaction support, esp for Integration testing for
Auto-rollback
For TestNG, extend AbstractTransactionalTestNGSpringContextTests

Parting notes
● Can convert your classic Spring app to Spring Boot
● Many guides found in: http://spring.io/guides
● Well documented
___
Pros
● Easy to use. Will soon be the Future
Cons
● Debugging config issues can get tough. Not much help yet
from ‘Googling’

Rediscovering Spring with Spring Boot(1)

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