The SpringApplication
class provides a convenient way to bootstrap a Spring application
that will be started from a main()
method. In many situations you can just delegate to
the static SpringApplication.run
method:
public static void main(String[] args) { SpringApplication.run(MySpringConfiguration.class, args); }
When your application starts you should see something similar to the following:
. ____ _ __ _ _ /\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \ ( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \ \\/ ___)| |_)| | | | | || (_| | ) ) ) ) ' |____| .__|_| |_|_| |_\__, | / / / / =========|_|==============|___/=/_/_/_/ :: Spring Boot :: v1.1.5.RELEASE 2013-07-31 00:08:16.117 INFO 56603 --- [ main] o.s.b.s.app.SampleApplication : Starting SampleApplication v0.1.0 on mycomputer with PID 56603 (/apps/myapp.jar started by pwebb) 2013-07-31 00:08:16.166 INFO 56603 --- [ main] ationConfigEmbeddedWebApplicationContext : Refreshing org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@6e5a8246: startup date [Wed Jul 31 00:08:16 PDT 2013]; root of context hierarchy 2014-03-04 13:09:54.912 INFO 41370 --- [ main] .t.TomcatEmbeddedServletContainerFactory : Server initialized with port: 8080 2014-03-04 13:09:56.501 INFO 41370 --- [ main] o.s.b.s.app.SampleApplication : Started SampleApplication in 2.992 seconds (JVM running for 3.658)
By default INFO
logging messages will be shown, including some relevant startup details
such as the user that launched the application.
The banner that is printed on start up can be changed by adding a banner.txt
file
to your classpath, or by setting banner.location
to the location of such a file.
If the file has an unusual encoding you can set banner.encoding
(default is UTF-8).
If the SpringApplication
defaults aren’t to your taste you can instead create a local
instance and customize it. For example, to turn off the banner you would write:
public static void main(String[] args) { SpringApplication app = new SpringApplication(MySpringConfiguration.class); app.setShowBanner(false); app.run(args); }
Note | |
---|---|
The constructor arguments passed to |
It is also possible to configure the SpringApplication
using an application.properties
file. See Chapter 21, Externalized Configuration for details.
For a complete list of the configuration options, see the
SpringApplication
Javadoc.
If you need to build an ApplicationContext
hierarchy (multiple contexts with a
parent/child relationship), or if you just prefer using a “fluent” builder API, you
can use the SpringApplicationBuilder
.
The SpringApplicationBuilder
allows you to chain together multiple method calls, and
includes parent
and child
methods that allow you to create a hierarchy.
For example:
new SpringApplicationBuilder() .showBanner(false) .sources(Parent.class) .child(Application.class) .run(args);
Note | |
---|---|
There are some restrictions when creating an |
In addition to the usual Spring Framework events, such as
ContextRefreshedEvent
,
a SpringApplication
sends some additional application events. Some events are actually
triggered before the ApplicationContext
is created.
You can register event listeners in a number of ways, the most common being
SpringApplication.addListeners(...)
method.
Application events are sent in the following order, as your application runs:
ApplicationStartedEvent
is sent at the start of a run, but before any
processing except the registration of listeners and initializers.
ApplicationEnvironmentPreparedEvent
is sent when the Environment
to be used in
the context is known, but before the context is created.
ApplicationPreparedEvent
is sent just before the refresh is started, but after bean
definitions have been loaded.
ApplicationFailedEvent
is sent if there is an exception on startup.
Tip | |
---|---|
You often won’t need to use application events, but it can be handy to know that they exist. Internally, Spring Boot uses events to handle a variety of tasks. |
A SpringApplication
will attempt to create the right type of ApplicationContext
on
your behalf. By default, an AnnotationConfigApplicationContext
or
AnnotationConfigEmbeddedWebApplicationContext
will be used, depending on whether you
are developing a web application or not.
The algorithm used to determine a “web environment” is fairly simplistic (based on the
presence of a few classes). You can use setWebEnvironment(boolean webEnvironment)
if
you need to override the default.
It is also possible to take complete control of the ApplicationContext
type that will
be used by calling setApplicationContextClass(...)
.
Tip | |
---|---|
It is often desirable to call |
If you want access to the raw command line arguments, or you need to run some specific code
once the SpringApplication
has started you can implement the CommandLineRunner
interface. The run(String... args)
method will be called on all Spring beans
implementing this interface.
import org.springframework.boot.* import org.springframework.stereotype.* @Component public class MyBean implements CommandLineRunner { public void run(String... args) { // Do something... } }
You can additionally implement the org.springframework.core.Ordered
interface or use the
org.springframework.core.annotation.Order
annotation if several CommandLineRunner
beans are defined that must be called in a specific order.
Each SpringApplication
will register a shutdown hook with the JVM to ensure that the
ApplicationContext
is closed gracefully on exit. All the standard Spring lifecycle
callbacks (such as the DisposableBean
interface, or the @PreDestroy
annotation) can
be used.
In addition, beans may implement the org.springframework.boot.ExitCodeGenerator
interface if they wish to return a specific exit code when the application ends.