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``How-to'' guides

Spring Boot application

Troubleshoot auto-configuration

The Spring Boot auto-configuration tries it’s best to ``do the right thing'', but sometimes things fail and it can be hard to tell why.

There is a really useful AutoConfigurationReport available in any Spring Boot ApplicationContext. You will see it if you enable DEBUG logging output. If you use the spring-boot-actuator there is also an autoconfig endpoint that renders the report in JSON. Use that to debug the application and see what features have been added (and which not) by Spring Boot at runtime.

Many more questions can be answered by looking at the source code and the javadoc. Some rules of thumb:

  • Look for classes called AutoConfiguration and read their sources, in particular the @Conditional annotations to find out what features they enable and when. Add --debug to the command line or a System property -Ddebug to get a log on the console of all the autoconfiguration decisions that were made in your app. In a running Actuator app look at the autoconfig endpoint (`/autoconfig' or the JMX equivalent) for the same information.

  • Look for classes that are @ConfigurationProperties (e.g. {sc-spring-boot-autoconfigure}/web/ServerProperties.{sc-ext}[ServerProperties] and read from there the available external configuration options. The @ConfigurationProperties has a name attribute which acts as a prefix to external properties, thus ServerProperties has name="server" and its configuration properties are server.port, server.address etc. In a running Actuator app look at the configprops endpoint.

  • Look for use of RelaxedEnvironment to pull configuration values explicitly out of the Environment. It often is used with a prefix.

  • Look for @Value annotations that bind directly to the Environment. This is less flexible than the RelaxedEnvironment approach, but does allow some relaxed binding, specifically for OS environment variables (so CAPITALS_AND_UNDERSCORES are synonyms for period.separated).

  • Look for @ConditionalOnExpression annotations that switch features on and off in response to SpEL expressions, normally evaluated with place-holders resolved from the Environment.

Customize the Environment or ApplicationContext before it starts

A SpringApplication has ApplicationListeners and ApplicationContextInitializers that are used to apply customizations to the context or environment. Spring Boot loads a number of such customizations for use internally from META-INF/spring.factories. There is more than one way to register additional ones:

  • Programmatically per application by calling the addListeners and addInitializers methods on SpringApplication before you run it.

  • Declaratively per application by setting context.initializer.classes or context.listener.classes.

  • Declaratively for all applications by adding a META-INF/spring.factories and packaging a jar file that the applications all use as a library.

The SpringApplication sends some special ApplicationEvents to the listeners (even some before the context is created), and then registers the listeners for events published by the ApplicationContext as well. See 'spring-boot-features.adoc' in the ``Spring Boot features'' section for a complete list.

Build an ApplicationContext hierarchy (adding a parent or root context)

You can use the ApplicationBuilder class to create parent/child ApplicationContext hierarchies. See 'spring-boot-features.adoc' in the ``Spring Boot features'' section for more information.

Create a non-web application

Not all Spring applications have to be web applications (or web services). If you want to execute some code in a main method, but also bootstrap a Spring application to set up the infrastructure to use, then it’s easy with the SpringApplication features of Spring Boot. A SpringApplication changes its ApplicationContext class depending on whether it thinks it needs a web application or not. The first thing you can do to help it is to just leave the servlet API dependencies off the classpath. If you can’t do that (e.g. you are running 2 applications from the same code base) then you can explicitly call SpringApplication.setWebEnvironment(false), or set the applicationContextClass property (through the Java API or with external properties). Application code that you want to run as your business logic can be implemented as a CommandLineRunner and dropped into the context as a @Bean definition.

Properties & configuration

Externalize the configuration of SpringApplication

A SpringApplication has bean properties (mainly setters) so you can use its Java API as you create the application to modify its behavior. Or you can externalize the configuration using properties in spring.main.*. E.g. in application.properties you might have.

spring.main.web_environment=false
spring.main.show_banner=false

and then the Spring Boot banner will not be printed on startup, and the application will not be a web application.

Note
 The example above also demonstrates how flexible binding allows the use of underscores (_) as well as dashes (-) in property names.

Change the location of external properties of an application

By default properties from different sources are added to the Spring Environment in a defined order (see 'spring-boot-features.adoc' in the ``Spring Boot features'' section for the exact order).

A nice way to augment and modify this is to add @PropertySource annotations to your application sources. Classes passed to the SpringApplication static convenience methods, and those added using setSources() are inspected to see if they have @PropertySources, and if they do, those properties are added to the Environment early enough to be used in all phases of the ApplicationContext lifecycle. Properties added in this way have precedence over any added using the default locations, but have lower priority than system properties, environment variables or the command line.

You can also provide System properties (or environment variables) to change the behavior:

  • spring.config.name (SPRING_CONFIG_NAME), defaults to application as the root of the file name.

  • spring.config.location (SPRING_CONFIG_LOCATION) is the file to load (e.g. a classpath resource or a URL). A separate Environment property source is set up for this document and it can be overridden by system properties, environment variables or the command line.

No matter what you set in the environment, Spring Boot will always load application.properties as described above. If YAML is used then files with the ``.yml'' extension are also added to the list by default.

See {sc-spring-boot}/context/config/ConfigFileApplicationListener.{sc-ext}[ConfigFileApplicationListener] for more detail.

Use ``short'' command line arguments

Some people like to use (for example) --port=9000 instead of --server.port=9000 to set configuration properties on the command line. You can easily enable this by using placeholders in application.properties, e.g.

server.port=${port:8080}
Tip
 If you have enabled maven filtering for the application.properties you may want to avoid using ${} for the tokens to filter as it conflicts with those placeholders. You can either use @@ (i.e. @maven.token@ instead of ${maven.token}) or you can configure the maven-resources-plugin to use other delimiters.
Note
 In this specific case the port binding will work in a PaaS environment like Heroku and Cloud Foundry, since in those two platforms the PORT environment variable is set automatically and Spring can bind to capitalized synonyms for Environment properties.

Use YAML for external properties

YAML is a superset of JSON and as such is a very convenient syntax for storing external properties in a hierarchical format. E.g.

spring:
	application:
		name: cruncher
	datasource:
		driverClassName: com.mysql.jdbc.Driver
		url: jdbc:mysql://localhost/test
server:
	port: 9000

Create a file called application.yml and stick it in the root of your classpath, and also add snakeyaml to your dependencies (Maven coordinates org.yaml:snakeyaml, already included if you use the spring-boot-starter). A YAML file is parsed to a Java Map<String,Object> (like a JSON object), and Spring Boot flattens the map so that it is 1-level deep and has period-separated keys, a lot like people are used to with Properties files in Java.

The example YAML above corresponds to an application.properties file

spring.application.name=cruncher
spring.datasource.driverClassName=com.mysql.jdbc.Driver
spring.datasource.url=jdbc:mysql://localhost/test
server.port=9000

See 'spring-boot-features.adoc' in the ``Spring Boot features'' section for more information about YAML.

Set the active Spring profiles

The Spring Environment has an API for this, but normally you would set a System profile (spring.profiles.active) or an OS environment variable (SPRING_PROFILES_ACTIVE). E.g. launch your application with a -D argument (remember to put it before the main class or jar archive):

$ java -jar -Dspring.profiles.active=production demo-0.0.1-SNAPSHOT.jar

In Spring Boot you can also set the active profile in application.properties, e.g.

spring.profiles.active=production

A value set this way is replaced by the System property or environment variable setting, but not by the SpringApplicationBuilder.profiles() method. Thus the latter Java API can be used to augment the profiles without changing the defaults.

See 'spring-boot-features.adoc' in the ``Spring Boot features'' section for more information.

Change configuration depending on the environment

A YAML file is actually a sequence of documents separated by --- lines, and each document is parsed separately to a flattened map.

If a YAML document contains a spring.profiles key, then the profiles value (comma-separated list of profiles) is fed into the Spring Environment.acceptsProfiles() and if any of those profiles is active that document is included in the final merge (otherwise not).

Example:

server:
	port: 9000
---

spring:
	profiles: development
server:
	port: 9001

---

spring:
	profiles: production
server:
	port: 0

In this example the default port is 9000, but if the Spring profile development'' is active then the port is 9001, and if production'' is active then it is 0.

The YAML documents are merged in the order they are encountered (so later values override earlier ones).

To do the same thing with properties files you can use application-${profile}.properties to specify profile-specific values.

Discover built-in options for external properties

Spring Boot binds external properties from application.properties (or .yml) (and other places) into an application at runtime. There is not (and technically cannot be) an exhaustive list of all supported properties in a single location because contributions can come from additional jar files on your classpath.

A running application with the Actuator features has a configprops endpoint that shows all the bound and bindable properties available through @ConfigurationProperties.

The appendix includes an application.properties example with a list of the most common properties supported by Spring Boot. The definitive list comes from searching the source code for @ConfigurationProperties and @Value annotations, as well as the occasional use of RelaxedEnvironment.

Embedded servlet containers

Add a Servlet, Filter or ServletContextListener to an application

Servlet, Filter, ServletContextListener and the other listeners supported by the Servlet spec can be added to your application as @Bean definitions. Be very careful that they don’t cause eager initialization of too many other beans because they have to be installed in the container very early in the application lifecycle (e.g. it’s not a good idea to have them depend on your DataSource or JPA configuration). You can work around restrictions like that by initializing them lazily when first used instead of on initialization.

In the case of Filters and Servlets you can also add mappings and init parameters by adding a FilterRegistrationBean or ServletRegistrationBean instead of or as well as the underlying component.

Change the HTTP port

In a standalone application the main HTTP port defaults to 8080, but can be set with server.port (e.g. in application.properties or as a System property). Thanks to relaxed binding of Environment values you can also use SERVER_PORT (e.g. as an OS environment variable).

To switch off the HTTP endpoints completely, but still create a WebApplicationContext, use server.port=-1 (this is sometimes useful for testing).

For more details look at 'spring-boot-features.adoc' in the `Spring Boot features'' section, or the {sc-spring-boot-autoconfigure}/web/ServerProperties.{sc-ext}[`ServerProperties] source code.

Use a random unassigned HTTP port

To scan for a free port (using OS natives to prevent clashes) use server.port=0.

Discover the HTTP port at runtime

You can access the port the server is running on from log output or from the EmbeddedWebApplicationContext via its EmbeddedServletContainer. The best way to get that and be sure that it has initialized is to add a @Bean of type ApplicationListener<EmbeddedServletContainerInitializedEvent> and pull the container out of the event when it is published.

A really useful thing to do in is to autowire the EmbeddedWebApplicationContext into a test case and use it to discover the port that the app is running on. In that way you can use a test profile that chooses a random port (server.port=0) and make your test suite independent of its environment. Example:

@RunWith(SpringJUnit4ClassRunner.class)
@SpringApplicationConfiguration(classes = SampleDataJpaApplication.class)
@WebApplication
@IntegrationTest
@ActiveProfiles("test")
public class CityRepositoryIntegrationTests {

	@Autowired
	EmbeddedWebApplicationContext server;

	int port;

	@Before
	public void init() {
		port = server.getEmbeddedServletContainer().getPort();
	}

	// ...

}

Configure Tomcat

Generally you can follow the advice from 'Discover built-in options for external properties' about @ConfigurationProperties (ServerProperties is the main one here), but also look at EmbeddedServletContainerCustomizer and various Tomcat specific *Customizers that you can add in one of those. The Tomcat APIs are quite rich so once you have access to the TomcatEmbeddedServletContainerFactory you can modify it in a number of ways. Or the nuclear option is to add your own TomcatEmbeddedServletContainerFactory.

Terminate SSL in Tomcat

Use an EmbeddedServletContainerCustomizer and in that add a TomcatConnectorCustomizer that sets up the connector to be secure:

@Bean
public EmbeddedServletContainerCustomizer containerCustomizer(){
	return new MyCustomizer();
}

// ...

private static class MyCustomizer implements EmbeddedServletContainerCustomizer {

	@Override
	public void customize(ConfigurableEmbeddedServletContainer factory) {
		if(factory instanceof TomcatEmbeddedServletContainerFactory) {
			customizeTomcat((TomcatEmbeddedServletContainerFactory) factory));
		}
	}

	public void customizeTomcat(TomcatEmbeddedServletContainerFactory factory) {
		factory.addConnectorCustomizers(new TomcatConnectorCustomizer() {
			@Override
			public void customize(Connector connector) {
				connector.setPort(serverPort);
				connector.setSecure(true);
				connector.setScheme("https");
				connector.setAttribute("keyAlias", "tomcat");
				connector.setAttribute("keystorePass", "password");
				try {
					connector.setAttribute("keystoreFile",
						ResourceUtils.getFile("src/ssl/tomcat.keystore").getAbsolutePath());
				} catch (FileNotFoundException e) {
					throw new IllegalStateException("Cannot load keystore", e);
				}
				connector.setAttribute("clientAuth", "false");
				connector.setAttribute("sslProtocol", "TLS");
				connector.setAttribute("SSLEnabled", true);
			}
		});
	}

}

Enable Multiple Connectors Tomcat

Add a org.apache.catalina.connector.Connector to the TomcatEmbeddedServletContainerFactory which can allow multiple connectors eg a HTTP and HTTPS connector:

@Bean
public EmbeddedServletContainerFactory servletContainer() {
	TomcatEmbeddedServletContainerFactory tomcat = new TomcatEmbeddedServletContainerFactory();
	tomcat.addAdditionalTomcatConnectors(createSslConnector());
	return tomcat;
}

private Connector createSslConnector() {
	Connector connector = new Connector("org.apache.coyote.http11.Http11NioProtocol");
	Http11NioProtocol protocol = (Http11NioProtocol) connector.getProtocolHandler();
	try {
		File keystore = new ClassPathResource("keystore").getFile();
		File truststore = new ClassPathResource("keystore").getFile();
		connector.setScheme("https");
		connector.setSecure(true);
		connector.setPort(8443);
		protocol.setSSLEnabled(true);
		protocol.setKeystoreFile(keystore.getAbsolutePath());
		protocol.setKeystorePass("changeit");
		protocol.setTruststoreFile(truststore.getAbsolutePath());
		protocol.setTruststorePass("changeit");
		protocol.setKeyAlias("apitester");
		return connector;
	}
	catch (IOException ex) {
		throw new IllegalStateException("can't access keystore: [" + "keystore"
				+ "] or truststore: [" + "keystore" + "]", ex);
	}
}

Use Jetty instead of Tomcat

The Spring Boot starters (spring-boot-starter-web in particular) use Tomcat as an embedded container by default. You need to exclude those dependencies and include the Jetty one instead. Spring Boot provides Tomcat and Jetty dependencies bundled together as separate starters to help make this process as easy as possible.

Example in Maven:

<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-web</artifactId>
	<exclusions>
		<exclusion>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-tomcat</artifactId>
		</exclusion>
	</exclusions>
</dependency>
<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-jetty</artifactId>
</dependency>

Example in Gradle:

configurations {
	compile.exclude module: "spring-boot-starter-tomcat"
}

dependencies {
	compile("org.springframework.boot:spring-boot-starter-web:1.0.0.RC3")
	compile("org.springframework.boot:spring-boot-starter-jetty:1.0.0.RC3")
	// ...
}

Configure Jetty

Generally you can follow the advice from 'Discover built-in options for external properties' about @ConfigurationProperties (ServerProperties is the main one here), but also look at EmbeddedServletContainerCustomizer. The Jetty APIs are quite rich so once you have access to the JettyEmbeddedServletContainerFactory you can modify it in a number of ways. Or the nuclear option is to add your own JettyEmbeddedServletContainerFactory.

Use Tomcat 8

Tomcat 8 works with Spring Boot, but the default is to use Tomcat 7 (so we can support Java 1.6 out of the box). You should only need to change the classpath to use Tomcat 8 for it to work. For example, using the starter poms in Maven:

<properties>
	<tomcat.version>8.0.3</tomcat.version>
</properties>
<dependencies>
	...
	<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-web</artifactId>
	</dependency>
	...
</dependencies>

change the classpath to use Tomcat 8 for it to work.

Use Jetty 9

Jetty 9 works with Spring Boot, but the default is to use Jetty 8 (so we can support Java 1.6 out of the box). You should only need to change the classpath to use Jetty 9 for it to work.

If you are using the starter poms and parent you can just add the Jetty starter and change the version properties, e.g. for a simple webapp or service:

<properties>
	<java.version>1.7</java.version>
	<jetty.version>9.1.0.v20131115</jetty.version>
	<servlet-api.version>3.1.0</servlet-api.version>
</properties>
<dependencies>
	<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-web</artifactId>
		<exclusions>
			<exclusion>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-starter-tomcat</artifactId>
			</exclusion>
		</exclusions>
	</dependency>
	<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-jetty</artifactId>
	</dependency>
</dependencies>

Spring MVC

Write a JSON REST service

Any Spring @RestController in a Spring Boot application should render JSON response by default as long as Jackson2 is on the classpath. For example:

@RestController
public class MyController {

	@RequestMapping("/thing")
	public MyThing thing() {
			return new MyThing();
	}

}

As long as MyThing can be serialized by Jackson2 (e.g. a normal POJO or Groovy object) then http://localhost:8080/thing will serve a JSON representation of it by default. Sometimes in a browser you might see XML responses (but by default only if MyThing was a JAXB object) because browsers tend to send accept headers that prefer XML.

Customize the Jackson ObjectMapper

Spring MVC (client and server side) uses HttpMessageConverters to negotiate content conversion in an HTTP exchange. If Jackson is on the classpath you already get a default converter with a vanilla ObjectMapper. Spring Boot has some features to make it easier to customize this behavior.

The smallest change that might work is to just add beans of type com.fasterxml.jackson.databind.Module to your context. They will be registered with the default ObjectMapper and then injected into the default message converter. To replace the default ObjectMapper completely, define a @Bean of that type and mark it as @Primary.

In addition, if your context contains any beans of type ObjectMapper then all of the Module beans will be registered with all of the mappers. So there is a global mechanism for contributing custom modules when you add new features to your application.

Finally, if you provide any @Beans of type MappingJackson2HttpMessageConverter then they will replace the default value in the MVC configuration. Also, a convenience bean is provided of type HttpMessageConverters (always available if you use the default MVC configuration) which has some useful methods to access the default and user-enhanced message converters.

See also the 'Customize the @ResponseBody rendering' section and the {sc-spring-boot-autoconfigure}/web/WebMvcAutoConfiguration.{sc-ext}[WebMvcAutoConfiguration] source code for more details.

Customize the @ResponseBody rendering

Spring uses HttpMessageConverters to render @ResponseBody (or responses from @RestController). You can contribute additional converters by simply adding beans of that type in a Spring Boot context. If a bean you add is of a type that would have been included by default anyway (like MappingJackson2HttpMessageConverter for JSON conversions) then it will replace the default value. A convenience bean is provided of type HttpMessageConverters (always available if you use the default MVC configuration) which has some useful methods to access the default and user-enhanced message converters (useful, for example if you want to manually inject them into a custom RestTemplate).

As in normal MVC usage, any WebMvcConfigurerAdapter beans that you provide can also contribute converters by overriding the configureMessageConverters method, but unlike with normal MVC, you can supply only additional converters that you need (because Spring Boot uses the same mechanism to contribute its defaults). Finally, if you opt-out of the Spring Boot default MVC configuration by providing your own @EnableWebMvc configuration, then you can take control completely and do everything manually using getMessageConverters from WebMvcConfigurationSupport.

See the {sc-spring-boot-autoconfigure}/web/WebMvcAutoConfiguration.{sc-ext}[WebMvcAutoConfiguration] source code for more details.

Switch off the Spring MVC DispatcherServlet

Spring Boot wants to serve all content from the root of your application / down. If you would rather map your own servlet to that URL you can do it, but of course you may lose some of the other Boot MVC features. To add your own servlet and map it to the root resource just declare a @Bean of type Servlet and give it the special bean name dispatcherServlet (You can also create a bean of a different type with that name if you want to switch it off and not replace it).

Switch off the Default MVC configuration

The easiest way to take complete control over MVC configuration is to provide your own @Configuration with the @EnableWebMvc annotation. This will leave all MVC configuration in your hands.

Customize ViewResolvers

A ViewResolver is a core component of Spring MVC, translating view names in @Controller to actual View implementations. Note that ViewResolvers are mainly used in UI applications, rather than REST-style services (a View is not used to render a @ResponseBody). There are many implementations of ViewResolver to choose from, and Spring on its own is not opinionated about which ones you should use. Spring Boot, on the other hand, installs one or two for you depending on what it finds on the classpath and in the application context. The DispatcherServlet uses all the resolvers it finds in the application context, trying each one in turn until it gets a result, so if you are adding your own you have to be aware of the order and in which position your resolver is added.

WebMvcAutoConfiguration adds the following ViewResolvers to your context:

  • An InternalResourceViewResolver with bean id `defaultViewResolver''. This one locates physical resources that can be rendered using the `DefaultServlet (e.g. static resources and JSP pages if you are using those). It applies a prefix and a suffix to the view name and then looks for a physical resource with that path in the servlet context (defaults are both empty, but accessible for external configuration via spring.view.prefix and spring.view.suffix). It can be overridden by providing a bean of the same type.

  • A BeanNameViewResolver with id `beanNameViewResolver''. This is a useful member of the view resolver chain and will pick up any beans with the same name as the `View being resolved. It can be overridden by providing a bean of the same type, but it’s unlikely you will need to do that.

  • A ContentNegotiatingViewResolver with id viewResolver'' is only added if there are actually beans of type View present. This is a master'' resolver, delegating to all the others and attempting to find a match to the Accept'' HTTP header sent by the client. There is a useful blog about ContentNegotiatingViewResolver that you might like to study to learn more, and also look at the source code for detail. You can switch off the auto-configured ContentNegotiatingViewResolver by defining a bean named viewResolver''.

  • If you use Thymeleaf you will also have a ThymeleafViewResolver with id thymeleafViewResolver''. It looks for resources by surrounding the view name with a prefix and suffix (externalized to spring.thymeleaf.prefix and spring.thymeleaf.suffix, defaults classpath:/templates/'' and ``.html'' respectively). It can be overridden by providing a bean of the same name.

Checkout {sc-spring-boot-autoconfigure}/web/WebMvcAutoConfiguration.{sc-ext}[WebMvcAutoConfiguration] and {sc-spring-boot-autoconfigure}/thymeleaf/ThymeleafAutoConfiguration.{sc-ext}[ThymeleafAutoConfiguration]

Logging

Configure Logback for logging

Spring Boot has no mandatory logging dependence, except for the commons-logging API, of which there are many implementations to choose from. To use Logback you need to include it, and some bindings for commons-logging on the classpath. The simplest way to do that is through the starter poms which all depend on spring-boot-starter-logging. For a web application you only need spring-boot-starter-web since it depends transitively on the logging starter. For example, using Maven:

<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-web</artifactId>
</dependency>

Spring Boot has a LoggingSystem abstraction that attempts to configure logging based on the content of the classpath. If Logback is available it is the first choice. So if you put a logback.xml in the root of your classpath it will be picked up from there. Spring Boot provides a default base configuration that you can include if you just want to set levels, e.g.

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
	<include resource="org/springframework/boot/logging/logback/base.xml"/>
	<logger name="org.springframework.web" level="DEBUG"/>
</configuration>

If you look at the default logback.xml in the spring-boot jar you will see that it uses some useful System properties which the LoggingSystem takes care of creating for you. These are:

  • ${PID} the current process ID.

  • ${LOG_FILE} if logging.file was set in Boot’s external configuration.

  • ${LOG_PATH} if logging.path was set (representing a directory for log files to live in).

Spring Boot also provides some nice ANSI colour terminal output on a console (but not in a log file) using a custom Logback converter. See the default base.xml configuration for details.

If Groovy is on the classpath you should be able to configure Logback with logback.groovy as well (it will be given preference if present).

Configure Log4j for logging

Spring Boot supports Log4j for logging configuration, but it has to be on the classpath. If you are using the starter poms for assembling dependencies that means you have to exclude logback and then include log4j instead. If you aren’t using the starter poms then you need to provide commons-logging (at least) in addition to Log4j.

The simplest path to using Log4j is probably through the starter poms, even though it requires some jiggling with excludes, e.g. in Maven:

<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-web</artifactId>
   </dependency>
<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter</artifactId>
	<exclusions>
			<exclusion>
					<groupId>${project.groupId}</groupId>
					<artifactId>spring-boot-starter-logging</artifactId>
			</exclusion>
	</exclusions>
</dependency>
<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-log4j</artifactId>
</dependency>
Note
 The use of the log4j starter gathers together the dependencies for common logging requirements (e.g. including having Tomcat use java.util.logging but configure the output using Log4j). See the Actuator Log4j Sample for more detail and to see it in action.

Data Access

Configure a DataSource

To override the default settings just define a @Bean of your own of type DataSource. See 'spring-boot-features.adoc' in the `Spring Boot features'' section and the {sc-spring-boot-autoconfigure}/jdbc/DataSourceAutoConfiguration.{sc-ext}[`DataSourceAutoConfiguration] class for more details.

Use Spring Data repositories

Spring Data can create implementations for you of @Repository interfaces of various flavours. Spring Boot will handle all of that for you as long as those @Repositories are included in the same package (or a sub-package) of your @EnableAutoConfiguration class.

For many applications all you will need is to put the right Spring Data dependencies on your classpath (there is a spring-boot-starter-data-jpa for JPA and a spring-boot-starter-data-mongodb for Mongodb), create some repository interfaces to handle your @Entity objects. Examples are in the {github-code}/spring-boot-samples/spring-boot-sample-data-jpa[JPA sample] or the {github-code}/spring-boot-samples/spring-boot-sample-data-mongodb[Mongodb sample].

Spring Boot tries to guess the location of your @Repository definitions, based on the @EnableAutoConfiguration it finds. To get more control, use the @EnableJpaRepositories annotation (from Spring Data JPA).

Separate @Entity definitions from Spring configuration

Spring Boot tries to guess the location of your @Entity definitions, based on the @EnableAutoConfiguration it finds. To get more control, you can use the @EntityScan annotation, e.g.

@Configuration
@EnableAutoConfiguration
@EntityScan(basePackageClasses=City.class)
public class Application {

	//...

}

Configure JPA properties

Spring Data JPA already provides some vendor-independent configuration options (e.g. for SQL logging) and Spring Boot exposes those, and a few more for hibernate as external configuration properties. The most common options to set are:

spring.jpa.hibernate.ddl-auto: create-drop
spring.jpa.hibernate.naming_strategy: org.hibernate.cfg.ImprovedNamingStrategy
spring.jpa.database: H2
spring.jpa.show-sql: true

(Because of relaxed data binding hyphens or underscores should work equally well as property keys.) The ddl-auto setting is a special case in that it has different defaults depending on whether you are using an embedded database (create-drop) or not (none). In addition all properties in spring.jpa.properties.* are passed through as normal JPA properties (with the prefix stripped) when the local EntityManagerFactory is created.

See {sc-spring-boot-autoconfigure}/orm/jpa/HibernateJpaAutoConfiguration.{sc-ext}[HibernateJpaAutoConfiguration] and {sc-spring-boot-autoconfigure}/orm/jpa/JpaBaseConfiguration.{sc-ext}[JpaBaseConfiguration] for more details.

Use a traditional persistence.xml

Spring doesn’t require the use of XML to configure the JPA provider, and Spring Boot assumes you want to take advantage of that feature. If you prefer to use persistence.xml then you need to define your own @Bean of type LocalEntityManagerFactoryBean, and set the persistence unit name there.

See JpaBaseConfiguration for the default settings.

Database initialization

An SQL database can be initialized in different ways depending on what your stack is. Or of course you can do it manually as long as the database is a separate process.

Initialize a database using JPA

JPA has features for DDL generation, and these can be set up to run on startup against the database. This is controlled through two external properties:

  • spring.jpa.generate-ddl (boolean) switches the feature on and off and is vendor independent.

  • spring.jpa.hibernate.ddl-auto (enum) is a Hibernate feature that controls the behavior in a more fine-grained way. See below for more detail.

Initialize a database using Hibernate

You can set spring.jpa.hibernate.ddl-auto explicitly and the standard Hibernate property values are none, validate, update, create-drop. Spring Boot chooses a default value for you based on whether it thinks your database is embedded (default create-drop) or not (default none). An embedded database is detected by looking at the Connection type: hsqldb, h2 and derby are embedded, the rest are not. Be careful when switching from in-memory to a `real'' database that you don’t make assumptions about the existence of the tables and data in the new platform. You either have to set `ddl-auto explicitly, or use one of the other mechanisms to initialize the database.

In addition, a file named import.sql in the root of the classpath will be executed on startup. This can be useful for demos and for testing if you are careful, but probably not something you want to be on the classpath in production. It is a Hibernate feature (nothing to do with Spring).

Initialize a database using Spring JDBC

Spring JDBC has a DataSource initializer feature. Spring Boot enables it by default and loads SQL from the standard locations schema.sql and data.sql (in the root of the classpath). In addition Spring Boot will load a file schema-${platform}.sql where platform is the vendor name of the database (hsqldb, h2, oracle, mysql, postgresql etc.). Spring Boot enables the failfast feature of the Spring JDBC initializer by default, so if the scripts cause exceptions the application will fail to start.

To disable the failfast you can set spring.datasource.continueOnError=true. This can be useful once an application has matured and been deployed a few times, since the scripts can act as ``poor man’s migrations'' — inserts that fail mean that the data is already there, so there would be no need to prevent the application from running, for instance.

Initialize a Spring Batch database

If you are using Spring Batch then it comes pre-packaged with SQL initialization scripts for most popular database platforms. Spring Boot will detect your database type, and execute those scripts by default, and in this case will switch the fail fast setting to false (errors are logged but do not prevent the application from starting). This is because the scripts are known to be reliable and generally do not contain bugs, so errors are ignorable, and ignoring them makes the scripts idempotent. You can switch off the initialization explicitly using spring.batch.initializer.enabled=false.

Use a higher level database migration tool

Spring Boot works fine with higher level migration tools Flyway (SQL-based) and Liquibase (XML). In general we prefer Flyway because it is easier on the eyes, and it isn’t very common to need platform independence: usually only one or at most couple of platforms is needed.

Batch applications

Execute Spring Batch jobs on startup

Spring Batch auto configuration is enabled by adding @EnableBatchProcessing (from Spring Batch) somewhere in your context.

By default it executes all Jobs in the application context on startup (see {sc-spring-boot-autoconfigure}/batch/JobLauncherCommandLineRunner.{sc-ext}[JobLauncherCommandLineRunner] for details). You can narrow down to a specific job or jobs by specifying spring.batch.job.names (comma separated job name patterns).

If the application context includes a JobRegistry then the jobs in spring.batch.job.names are looked up in the registry instead of being autowired from the context. This is a common pattern with more complex systems where multiple jobs are defined in child contexts and registered centrally.

See {sc-spring-boot-autoconfigure}/batch/BatchAutoConfiguration.{sc-ext}[BatchAutoConfiguration] and @EnableBatchProcessing for more details.

Actuator

Change the HTTP port or address of the actuator endpoints

In a standalone application the Actuator HTTP port defaults to the same as the main HTTP port. To make the application listen on a different port set the external property management.port. To listen on a completely different network address (e.g. if you have an internal network for management and an external one for user applications) you can also set management.address to a valid IP address that the server is able to bind to.

For more detail look at the {sc-spring-boot-actuator}/autoconfigure/ManagementServerProperties.{sc-ext}[ManagementServerProperties] source code and 'production-ready-features.adoc' in the ``Production-ready features'' section.

Customize the ``whitelabel'' error page

The Actuator installs a `whitelabel'' error page that you will see in browser client if you encounter a server error (machine clients consuming JSON and other media types should see a sensible response with the right error code). To switch it off you can set `error.whitelabel.enabled=false, but normally in addition or alternatively to that you will want to add your own error page replacing the whitelabel one. If you are using Thymeleaf you can do this by adding an error.html template. In general what you need is a View that resolves with a name of error, and/or a @Controller that handles the /error path. Unless you replaced some of the default configuration you should find a BeanNameViewResolver in your ApplicationContext so a @Bean with id error would be a simple way of doing that. Look at {sc-spring-boot-actuator}/autoconfigure/ErrorMvcAutoConfiguration.{sc-ext}[ErrorMvcAutoConfiguration] for more options.

Security

Secure an application

If Spring Security is on the classpath then web applications will be secure by default (`basic'' authentication on all endpoints) . To add method-level security to a web application you can simply `@EnableGlobalMethodSecurity with your desired settings. Additional information can be found in the {spring-security-reference}#jc-method[Spring Security Reference].

The default AuthenticationManager has a single user (username `user'' and password random, printed at INFO level when the application starts up). You can change the password by providing a `security.user.password. This and other useful properties are externalized via {sc-spring-boot-autoconfigure}/security/SecurityProperties.{sc-ext}[SecurityProperties].

Switch off the Spring Boot security configuration

If you define a @Configuration with @EnableWebSecurity anywhere in your application it will switch off the default webapp security settings in Spring Boot. To tweak the defaults try setting properties in security.* (see {sc-spring-boot-autoconfigure}/security/SecurityProperties.{sc-ext}[SecurityProperties] for details of available settings) and SECURITY section of Common application properties.

Change the AuthenticationManager and add user accounts

If you provide a @Bean of type AuthenticationManager the default one will not be created, so you have the full feature set of Spring Security available (e.g. various authentication options).

Spring Security also provides a convenient AuthenticationManagerBuilder which can be used to build an AuthenticationManager with common options. The recommended way to use this in a webapp is to inject it into a void method in a WebSecurityConfigurerAdapter, e.g.

@Configuration
public class SecurityConfiguration extends WebSecurityConfigurerAdapter {

	@Autowired
	public void configureGlobal(AuthenticationManagerBuilder auth) throws Exception {
			auth.inMemoryAuthentication()
				.withUser("barry").password("password").roles("USER"); // ...  etc.
	}

	// ... other stuff for application security

}

Enable HTTPS

Ensuring that all your main endpoints are only available over HTTPS is an important chore for any application. If you are using Tomcat as a servlet container, then Spring Boot will add Tomcat’s own RemoteIpValve automatically if it detects some environment settings, and you should be able to rely on the HttpServletRequest to report whether it is secure or not (even downstream of the real SSL termination). The standard behavior is determined by the presence or absence of certain request headers (x-forwarded-for and x-forwarded-proto), whose names are conventional, so it should work with most front end proxies. You can switch on the valve by adding some entries to application.properties, e.g.

server.tomcat.remote_ip_header=x-forwarded-for
server.tomcat.protocol_header=x-forwarded-proto

(The presence of either of those properties will switch on the valve. Or you can add the RemoteIpValve yourself by adding a TomcatEmbeddedServletContainerFactory bean.)

Spring Security can also be configured to require a secure channel for all (or some requests). To switch that on in a Spring Boot application you just need to set security.require_https to true in application.properties.

Hot swapping

Reload static content

There are several options for hot reloading. Running in an IDE (especially with debugging on) is a good way to do development (all modern IDEs allow reloading of static resources and usually also hot-swapping of Java class changes). The Maven and Gradle plugins also support running from the command line with reloading of static files. You can use that with an external css/js compiler process if you are writing that code with higher level tools.

Reload Thymeleaf templates without restarting the container

If you are using Thymeleaf, then set spring.thymeleaf.cache to false. See {sc-spring-boot-autoconfigure}/thymeleaf/ThymeleafAutoConfiguration.{sc-ext}[ThymeleafAutoConfiguration] for other template customization options.

Reload Java classes without restarting the container

Modern IDEs (Eclipse, IDEA, etc.) all support hot swapping of bytecode, so if you make a change that doesn’t affect class or method signatures it should reload cleanly with no side effects.

Spring Loaded goes a little further in that it can reload class definitions with changes in the method signatures. With some customization it can force an ApplicationContext to refresh itself (but there is no general mechanism to ensure that would be safe for a running application anyway, so it would only ever be a development time trick probably).

Build

Build an executable archive with Ant

To build with Ant you need to grab dependencies, compile and then create a jar or war archive as normal. To make it executable:

  1. Use the appropriate launcher as a Main-Class, e.g. JarLauncher for a jar file, and specify the other properties it needs as manifest entries, principally a Start-Class.

  2. Add the runtime dependencies in a nested "lib" directory (for a jar) and the provided (embedded container) dependencies in a nested lib-provided directory. Remember not to compress the entries in the archive.

  3. Add the spring-boot-loader classes at the root of the archive (so the Main-Class is available).

Example:

<target name="build" depends="compile">
	<copy todir="target/classes/lib">
		<fileset dir="lib/runtime" />
	</copy>
	<jar destfile="target/spring-boot-sample-actuator-${spring-boot.version}.jar" compress="false">
		<fileset dir="target/classes" />
		<fileset dir="src/main/resources" />
		<zipfileset src="lib/loader/spring-boot-loader-jar-${spring-boot.version}.jar" />
		<manifest>
			<attribute name="Main-Class" value="org.springframework.boot.loader.JarLauncher" />
			<attribute name="Start-Class" value="${start-class}" />
		</manifest>
	</jar>
</target>

The Actuator Sample has a build.xml that should work if you run it with

$ ant -lib <path_to>/ivy-2.2.jar

after which you can run the application with

$ java -jar target/*.jar

Traditional deployment

Create a deployable war file

Use the SpringBootServletInitializer base class, which is picked up by Spring’s Servlet 3.0 support on deployment. Add an extension of that to your project and build a war file as normal. For more detail, see the ``Converting a jar Project to a war'' guide on the spring.io website and the sample below.

The war file can also be executable if you use the Spring Boot build tools. In that case the embedded container classes (to launch Tomcat for instance) have to be added to the war in a lib-provided directory. The tools will take care of that as long as the dependencies are marked as "provided" in Maven or Gradle. Here’s a Maven example {github-code}/spring-boot-samples/spring-boot-sample-traditional/pom.xml[in the Boot Samples].

Create a deployable war file for older servlet containers

Older Servlet containers don’t have support for the ServletContextInitializer bootstrap process used in Servlet 3.0. You can still use Spring and Spring Boot in these containers but you are going to need to add a web.xml to your application and configure it to load an ApplicationContext via a DispatcherServlet.

Convert an existing application to Spring Boot

For a non-web application it should be easy (throw away the code that creates your ApplicationContext and replace it with calls to SpringApplication or SpringApplicationBuilder). Spring MVC web applications are generally amenable to first creating a deployable war application, and then migrating it later to an executable war and/or jar. Useful reading is in the Getting Started Guide on Converting a jar to a war.

Create a deployable war by extending SpringBootServletInitializer (e.g. in a class called Application), and add the Spring Boot @EnableAutoConfiguration annotation. Example:

@Configuration
@EnableAutoConfiguration
@ComponentScan
public class Application extends SpringBootServletInitializer {

	@Override
	protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
		return application.sources(Application.class);
	}

}

Remember that whatever you put in the sources is just a Spring ApplicationContext and normally anything that already works should work here. There might be some beans you can remove later and let Spring Boot provide its own defaults for them, but it should be possible to get something working first.

Static resources can be moved to /public (or /static or /resources or /META-INF/resources) in the classpath root. Same for messages.properties (Spring Boot detects this automatically in the root of the classpath).

Vanilla usage of Spring DispatcherServlet and Spring Security should require no further changes. If you have other features in your application, using other servlets or filters for instance, then you may need to add some configuration to your Application context, replacing those elements from the web.xml as follows:

  • A @Bean of type Servlet or ServletRegistrationBean installs that bean in the container as if it was a <servlet/> and <servlet-mapping/> in web.xml.

  • A @Bean of type Filter or FilterRegistrationBean behaves similarly (like a <filter/> and <filter-mapping/>.

  • An ApplicationContext in an XML file can be added to an @Import in your Application. Or simple cases where annotation configuration is heavily used already can be recreated in a few lines as @Bean definitions.

Once the war is working we make it executable by adding a main method to our Application, e.g.

public static void main(String[] args) {
	SpringApplication.run(Application.class, args);
}

Applications can fall into more than one category:

  • Servlet 3.0 applications with no web.xml.

  • Applications with a web.xml.

  • Applications with a context hierarchy.

  • Applications without a context hierarchy.

All of these should be amenable to translation, but each might require slightly different tricks.

Servlet 3.0 applications might translate pretty easily if they already use the Spring Servlet 3.0 initializer support classes. Normally all the code from an existing WebApplicationInitializer can be moved into a SpringBootServletInitializer. If your existing application has more than one ApplicationContext (e.g. if it uses AbstractDispatcherServletInitializer) then you might be able to squash all your context sources into a single SpringApplication. The main complication you might encounter is if that doesn’t work and you need to maintain the context hierarchy. See the entry on building a hierarchy for examples. An existing parent context that contains web-specific features will usually need to be broken up so that all the ServletContextAware components are in the child context.

Applications that are not already Spring applications might be convertible to a Spring Boot application, and the guidance above might help, but your mileage may vary.