Spring Boot is well suited for web application development.
You can create a self-contained HTTP server by using embedded Tomcat, Jetty, Undertow, or Netty.
Most web applications use the spring-boot-starter-web
module to get up and running quickly.
You can also choose to build reactive web applications by using the spring-boot-starter-webflux
module.
If you have not yet developed a Spring Boot web application, you can follow the "Hello World!" example in the Getting started section.
The Spring Web MVC framework (often referred to as simply “Spring MVC”) is a rich “model view controller” web framework.
Spring MVC lets you create special @Controller
or @RestController
beans to handle incoming HTTP requests.
Methods in your controller are mapped to HTTP by using @RequestMapping
annotations.
The following code shows a typical @RestController
that serves JSON data:
@RestController @RequestMapping(value="/users") public class MyRestController { @RequestMapping(value="/\{user}", method=RequestMethod.GET) public User getUser(@PathVariable Long user) { // ... } @RequestMapping(value="/\{user}/customers", method=RequestMethod.GET) List<Customer> getUserCustomers(@PathVariable Long user) { // ... } @RequestMapping(value="/\{user}", method=RequestMethod.DELETE) public User deleteUser(@PathVariable Long user) { // ... } }
Spring MVC is part of the core Spring Framework, and detailed information is available in the reference documentation. There are also several guides that cover Spring MVC available at spring.io/guides.
Spring Boot provides auto-configuration for Spring MVC that works well with most applications.
The auto-configuration adds the following features on top of Spring’s defaults:
ContentNegotiatingViewResolver
and BeanNameViewResolver
beans.Converter
, GenericConverter
, and Formatter
beans.HttpMessageConverters
(covered later in this document).MessageCodesResolver
(covered later in this document).index.html
support.Favicon
support (covered later in this document).ConfigurableWebBindingInitializer
bean (covered later in this document).If you want to keep Spring Boot MVC features and you want to add additional MVC configuration (interceptors, formatters, view controllers, and other features), you can add your own @Configuration
class of type WebMvcConfigurer
but without @EnableWebMvc
.
If you wish to provide custom instances of RequestMappingHandlerMapping
, RequestMappingHandlerAdapter
, or ExceptionHandlerExceptionResolver
, you can declare a WebMvcRegistrationsAdapter
instance to provide such components.
If you want to take complete control of Spring MVC, you can add your own @Configuration
annotated with @EnableWebMvc
.
Spring MVC uses the HttpMessageConverter
interface to convert HTTP requests and responses.
Sensible defaults are included out of the box. For example, objects can be automatically converted to JSON (by using the Jackson library) or XML (by using the Jackson XML extension, if available, or by using JAXB if the Jackson XML extension is not available).
By default, strings are encoded in UTF-8
.
If you need to add or customize converters, you can use Spring Boot’s HttpMessageConverters
class, as shown in the following listing:
import org.springframework.boot.autoconfigure.http.HttpMessageConverters; import org.springframework.context.annotation.*; import org.springframework.http.converter.*; @Configuration public class MyConfiguration { @Bean public HttpMessageConverters customConverters() { HttpMessageConverter<?> additional = ... HttpMessageConverter<?> another = ... return new HttpMessageConverters(additional, another); } }
Any HttpMessageConverter
bean that is present in the context is added to the list of converters.
You can also override default converters in the same way.
If you use Jackson to serialize and deserialize JSON data, you might want to write your own JsonSerializer
and JsonDeserializer
classes.
Custom serializers are usually registered with Jackson through a module, but Spring Boot provides an alternative @JsonComponent
annotation that makes it easier to directly register Spring Beans.
You can use the @JsonComponent
annotation directly on JsonSerializer
or JsonDeserializer
implementations.
You can also use it on classes that contain serializers/deserializers as inner classes, as shown in the following example:
import java.io.*; import com.fasterxml.jackson.core.*; import com.fasterxml.jackson.databind.*; import org.springframework.boot.jackson.*; @JsonComponent public class Example { public static class Serializer extends JsonSerializer<SomeObject> { // ... } public static class Deserializer extends JsonDeserializer<SomeObject> { // ... } }
All @JsonComponent
beans in the ApplicationContext
are automatically registered with Jackson.
Because @JsonComponent
is meta-annotated with @Component
, the usual component-scanning rules apply.
Spring Boot also provides JsonObjectSerializer
and JsonObjectDeserializer
base classes that provide useful alternatives to the standard Jackson versions when serializing objects.
See JsonObjectSerializer
and JsonObjectDeserializer
in the Javadoc for details.
Spring MVC has a strategy for generating error codes for rendering error messages from binding errors: MessageCodesResolver
.
If you set the spring.mvc.message-codes-resolver.format
property PREFIX_ERROR_CODE
or POSTFIX_ERROR_CODE
, Spring Boot creates one for you (see the enumeration in DefaultMessageCodesResolver.Format
).
By default, Spring Boot serves static content from a directory called /static
(or /public
or /resources
or /META-INF/resources
) in the classpath or from the root of the ServletContext
.
It uses the ResourceHttpRequestHandler
from Spring MVC so that you can modify that behavior by adding your own WebMvcConfigurer
and overriding the addResourceHandlers
method.
In a stand-alone web application, the default servlet from the container is also enabled and acts as a fallback, serving content from the root of the ServletContext
if Spring decides not to handle it.
Most of the time, this does not happen (unless you modify the default MVC configuration), because Spring can always handle requests through the DispatcherServlet
.
By default, resources are mapped on /**
, but you can tune that with the spring.mvc.static-path-pattern
property.
For instance, relocating all resources to /resources/**
can be achieved as follows:
spring.mvc.static-path-pattern=/resources/**
You can also customize the static resource locations by using the spring.resources.static-locations
property (replacing the default values with a list of directory locations).
The root Servlet context path, "/"
, is automatically added as a location as well.
In addition to the “standard” static resource locations mentioned earlier, a special case is made for Webjars content.
Any resources with a path in /webjars/**
are served from jar files if they are packaged in the Webjars format.
![]() | Tip |
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Do not use the |
Spring Boot also supports the advanced resource handling features provided by Spring MVC, allowing use cases such as cache-busting static resources or using version agnostic URLs for Webjars.
To use version agnostic URLs for Webjars, add the webjars-locator-core
dependency.
Then declare your Webjar. Using jQuery as an example, adding "/webjars/jquery/jquery.min.js"
results in "/webjars/jquery/x.y.z/jquery.min.js"
where x.y.z
is the Webjar version.
![]() | Note |
---|---|
If you use JBoss, you need to declare the |
To use cache busting, the following configuration configures a cache busting solution for all static resources, effectively adding a content hash, such as <link href="/css/spring-2a2d595e6ed9a0b24f027f2b63b134d6.css"/>
, in URLs:
spring.resources.chain.strategy.content.enabled=true spring.resources.chain.strategy.content.paths=/**
![]() | Note |
---|---|
Links to resources are rewritten in templates at runtime, thanks to a |
When loading resources dynamically with, for example, a JavaScript module loader, renaming files is not an option. That is why other strategies are also supported and can be combined. A "fixed" strategy adds a static version string in the URL without changing the file name, as shown in the following example:
spring.resources.chain.strategy.content.enabled=true spring.resources.chain.strategy.content.paths=/** spring.resources.chain.strategy.fixed.enabled=true spring.resources.chain.strategy.fixed.paths=/js/lib/ spring.resources.chain.strategy.fixed.version=v12
With this configuration, JavaScript modules located under "/js/lib/"
use a fixed versioning strategy ("/v12/js/lib/mymodule.js"
), while other resources still use the content one (<link href="/css/spring-2a2d595e6ed9a0b24f027f2b63b134d6.css"/>
).
See ResourceProperties
for more supported options.
![]() | Tip |
---|---|
This feature has been thoroughly described in a dedicated blog post and in Spring Framework’s reference documentation. |
Spring Boot supports both static and templated welcome pages. It first looks for an index.html
file in the configured static content locations.
If one is not found, it then looks for an index
template.
If either is found, it is automatically used as the welcome page of the application.
Spring Boot looks for a favicon.ico
in the configured static content locations and the root of the classpath (in that order).
If such a file is present, it is automatically used as the favicon of the application.
Spring MVC can map incoming HTTP requests to handlers by looking at the request path and matching it to the mappings defined in your application (for example, @GetMapping
annotations on Controller methods).
Spring Boot chooses to disable suffix pattern matching by default, which means that requests like "GET /projects/spring-boot.json"
won’t be matched to @GetMapping("/projects/spring-boot")
mappings.
This is considered as a best practice for Spring MVC applications.
This feature was mainly useful in the past for HTTP clients which did not send proper "Accept" request headers; we needed to make sure to send the correct Content Type to the client.
Nowadays, Content Negotiation is much more reliable.
There are other ways to deal with HTTP clients that don’t consistently send proper "Accept" request headers.
Instead of using suffix matching, we can use a query parameter to ensure that requests like "GET /projects/spring-boot?format=json"
will be mapped to @GetMapping("/projects/spring-boot")
:
spring.mvc.contentnegotiation.favor-parameter=true # We can change the parameter name, which is "format" by default: # spring.mvc.contentnegotiation.parameter-name=myparam # We can also register additional file extensions/media types with: spring.mvc.contentnegotiation.media-types.markdown=text/markdown
If you understand the caveats and would still like your application to use suffix pattern matching, the following configuration is required:
spring.mvc.contentnegotiation.favor-path-extension=true spring.mvc.pathmatch.use-suffix-pattern=true
Alternatively, rather than open all suffix patterns, it’s more secure to just support registered suffix patterns:
spring.mvc.contentnegotiation.favor-path-extension=true spring.mvc.pathmatch.use-registered-suffix-pattern=true # You can also register additional file extensions/media types with: # spring.mvc.contentnegotiation.media-types.adoc=text/asciidoc
Spring MVC uses a WebBindingInitializer
to initialize a WebDataBinder
for a particular request.
If you create your own ConfigurableWebBindingInitializer
@Bean
, Spring Boot automatically configures Spring MVC to use it.
As well as REST web services, you can also use Spring MVC to serve dynamic HTML content. Spring MVC supports a variety of templating technologies, including Thymeleaf, FreeMarker, and JSPs. Also, many other templating engines include their own Spring MVC integrations.
Spring Boot includes auto-configuration support for the following templating engines:
![]() | Tip |
---|---|
If possible, JSPs should be avoided. There are several known limitations when using them with embedded servlet containers. |
When you use one of these templating engines with the default configuration, your templates are picked up automatically from src/main/resources/templates
.
![]() | Tip |
---|---|
Depending on how you run your application, IntelliJ IDEA orders the classpath differently.
Running your application in the IDE from its main method results in a different ordering than when you run your application by using Maven or Gradle or from its packaged jar.
This can cause Spring Boot to fail to find the templates on the classpath.
If you have this problem, you can reorder the classpath in the IDE to place the module’s classes and resources first.
Alternatively, you can configure the template prefix to search every |
By default, Spring Boot provides an /error
mapping that handles all errors in a sensible way, and it is registered as a “global” error page in the servlet container.
For machine clients, it produces a JSON response with details of the error, the HTTP status, and the exception message.
For browser clients, there is a “whitelabel” error view that renders the same data in HTML format (to customize it, add a View
that resolves to error
).
To replace the default behavior completely, you can implement ErrorController
and register a bean definition of that type or add a bean of type ErrorAttributes
to use the existing mechanism but replace the contents.
![]() | Tip |
---|---|
The |
You can also define a class annotated with @ControllerAdvice
to customize the JSON document to return for a particular controller and/or exception type, as shown in the following example:
@ControllerAdvice(basePackageClasses = AcmeController.class) public class AcmeControllerAdvice extends ResponseEntityExceptionHandler { @ExceptionHandler(YourException.class) @ResponseBody ResponseEntity<?> handleControllerException(HttpServletRequest request, Throwable ex) { HttpStatus status = getStatus(request); return new ResponseEntity<>(new CustomErrorType(status.value(), ex.getMessage()), status); } private HttpStatus getStatus(HttpServletRequest request) { Integer statusCode = (Integer) request.getAttribute("javax.servlet.error.status_code"); if (statusCode == null) { return HttpStatus.INTERNAL_SERVER_ERROR; } return HttpStatus.valueOf(statusCode); } }
In the preceding example, if YourException
is thrown by a controller defined in the same package as AcmeController
, a JSON representation of the CustomErrorType
POJO is used instead of the ErrorAttributes
representation.
If you want to display a custom HTML error page for a given status code, you can add a file to an /error
folder.
Error pages can either be static HTML (that is, added under any of the static resource folders) or be built by using templates.
The name of the file should be the exact status code or a series mask.
For example, to map 404
to a static HTML file, your folder structure would be as follows:
src/ +- main/ +- java/ | + <source code> +- resources/ +- public/ +- error/ | +- 404.html +- <other public assets>
To map all 5xx
errors by using a FreeMarker template, your folder structure would be as follows:
src/ +- main/ +- java/ | + <source code> +- resources/ +- templates/ +- error/ | +- 5xx.ftl +- <other templates>
For more complex mappings, you can also add beans that implement the ErrorViewResolver
interface, as shown in the following example:
public class MyErrorViewResolver implements ErrorViewResolver { @Override public ModelAndView resolveErrorView(HttpServletRequest request, HttpStatus status, Map<String, Object> model) { // Use the request or status to optionally return a ModelAndView return ... } }
You can also use regular Spring MVC features such as @ExceptionHandler
methods and @ControllerAdvice
.
The ErrorController
then picks up any unhandled exceptions.
For applications that do not use Spring MVC, you can use the ErrorPageRegistrar
interface to directly register ErrorPages
.
This abstraction works directly with the underlying embedded servlet container and works even if you do not have a Spring MVC DispatcherServlet
.
@Bean public ErrorPageRegistrar errorPageRegistrar(){ return new MyErrorPageRegistrar(); } // ... private static class MyErrorPageRegistrar implements ErrorPageRegistrar { @Override public void registerErrorPages(ErrorPageRegistry registry) { registry.addErrorPages(new ErrorPage(HttpStatus.BAD_REQUEST, "/400")); } }
![]() | Note |
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If you register an |
@Bean public FilterRegistrationBean myFilter() { FilterRegistrationBean registration = new FilterRegistrationBean(); registration.setFilter(new MyFilter()); ... registration.setDispatcherTypes(EnumSet.allOf(DispatcherType.class)); return registration; }
Note that the default FilterRegistrationBean
does not include the ERROR
dispatcher type.
CAUTION:When deployed to a servlet container, Spring Boot uses its error page filter to forward a request with an error status to the appropriate error page.
The request can only be forwarded to the correct error page if the response has not already been committed.
By default, WebSphere Application Server 8.0 and later commits the response upon successful completion of a servlet’s service method.
You should disable this behavior by setting com.ibm.ws.webcontainer.invokeFlushAfterService
to false
.
If you develop a RESTful API that makes use of hypermedia, Spring Boot provides auto-configuration for Spring HATEOAS that works well with most applications.
The auto-configuration replaces the need to use @EnableHypermediaSupport
and registers a number of beans to ease building hypermedia-based applications, including a LinkDiscoverers
(for client side support) and an ObjectMapper
configured to correctly marshal responses into the desired representation.
The ObjectMapper
is customized by setting the various spring.jackson.*
properties or, if one exists, by a Jackson2ObjectMapperBuilder
bean.
You can take control of Spring HATEOAS’s configuration by using @EnableHypermediaSupport
.
Note that doing so disables the ObjectMapper
customization described earlier.
Cross-origin resource sharing (CORS) is a W3C specification implemented by most browsers that lets you specify in a flexible way what kind of cross-domain requests are authorized., instead of using some less secure and less powerful approaches such as IFRAME or JSONP.
As of version 4.2, Spring MVC supports CORS.
Using controller method CORS configuration with @CrossOrigin
annotations in your Spring Boot application does not require any specific configuration.
Global CORS configuration can be defined by registering a WebMvcConfigurer
bean with a customized addCorsMappings(CorsRegistry)
method, as shown in the following example:
@Configuration public class MyConfiguration { @Bean public WebMvcConfigurer corsConfigurer() { return new WebMvcConfigurer() { @Override public void addCorsMappings(CorsRegistry registry) { registry.addMapping("/api/**"); } }; } }
Spring WebFlux is the new reactive web framework introduced in Spring Framework 5.0. Unlike Spring MVC, it does not require the Servlet API, is fully asynchronous and non-blocking, and implements the Reactive Streams specification through the Reactor project.
Spring WebFlux comes in two flavors: functional and annotation-based. The annotation-based one is quite close to the Spring MVC model, as shown in the following example:
@RestController @RequestMapping("/users") public class MyRestController { @GetMapping("/\{user}") public Mono<User> getUser(@PathVariable Long user) { // ... } @GetMapping("/\{user}/customers") public Flux<Customer> getUserCustomers(@PathVariable Long user) { // ... } @DeleteMapping("/\{user}") public Mono<User> deleteUser(@PathVariable Long user) { // ... } }
“WebFlux.fn”, the functional variant, separates the routing configuration from the actual handling of the requests, as shown in the following example:
@Configuration public class RoutingConfiguration { @Bean public RouterFunction<ServerResponse> monoRouterFunction(UserHandler userHandler) { return route(GET("/\{user}").and(accept(APPLICATION_JSON)), userHandler::getUser) .andRoute(GET("/\{user}/customers").and(accept(APPLICATION_JSON)), userHandler::getUserCustomers) .andRoute(DELETE("/\{user}").and(accept(APPLICATION_JSON)), userHandler::deleteUser); } } @Component public class UserHandler { public Mono<ServerResponse> getUser(ServerRequest request) { // ... } public Mono<ServerResponse> getUserCustomers(ServerRequest request) { // ... } public Mono<ServerResponse> deleteUser(ServerRequest request) { // ... } }
WebFlux is part of the Spring Framework and detailed information is available in its reference documentation.
![]() | Tip |
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You can define as many |
To get started, add the spring-boot-starter-webflux
module to your application.
![]() | Note |
---|---|
Adding both |
Spring Boot provides auto-configuration for Spring WebFlux that works well with most applications.
The auto-configuration adds the following features on top of Spring’s defaults:
HttpMessageReader
and HttpMessageWriter
instances (described later in this document).If you want to keep Spring Boot WebFlux features and you want to add additional WebFlux configuration, you can add your own @Configuration
class of type WebFluxConfigurer
but without @EnableWebFlux
.
If you want to take complete control of Spring WebFlux, you can add your own @Configuration
annotated with @EnableWebFlux
.
Spring WebFlux uses the HttpMessageReader
and HttpMessageWriter
interfaces to convert HTTP requests and responses.
They are configured with CodecConfigurer
to have sensible defaults by looking at the libraries available in your classpath.
Spring Boot applies further customization by using CodecCustomizer
instances.
For example, spring.jackson.*
configuration keys are applied to the Jackson codec.
If you need to add or customize codecs, you can create a custom CodecCustomizer
component, as shown in the following example:
import org.springframework.boot.web.codec.CodecCustomizer; @Configuration public class MyConfiguration { @Bean public CodecCustomizer myCodecCustomizer() { return codecConfigurer -> { // ... } } }
You can also leverage Boot’s custom JSON serializers and deserializers.
By default, Spring Boot serves static content from a directory called /static
(or /public
or /resources
or /META-INF/resources
) in the classpath.
It uses the ResourceWebHandler
from Spring WebFlux so that you can modify that behavior by adding your own WebFluxConfigurer
and overriding the addResourceHandlers
method.
By default, resources are mapped on /**
, but you can tune that by setting the spring.webflux.static-path-pattern
property.
For instance, relocating all resources to /resources/**
can be achieved as follows:
spring.webflux.static-path-pattern=/resources/**
You can also customize the static resource locations by using spring.resources.static-locations
.
Doing so replaces the default values with a list of directory locations. If you do so, the default welcome page detection switches to your custom locations.
So, if there is an index.html
in any of your locations on startup, it is the home page of the application.
In addition to the “standard” static resource locations listed earlier, a special case is made for Webjars content.
Any resources with a path in /webjars/**
are served from jar files if they are packaged in the Webjars format.
![]() | Tip |
---|---|
Spring WebFlux applications do not strictly depend on the Servlet API, so they cannot be deployed as war files and do not use the |
As well as REST web services, you can also use Spring WebFlux to serve dynamic HTML content. Spring WebFlux supports a variety of templating technologies, including Thymeleaf, FreeMarker, and Mustache.
Spring Boot includes auto-configuration support for the following templating engines:
When you use one of these templating engines with the default configuration, your templates are picked up automatically from src/main/resources/templates
.
Spring Boot provides a WebExceptionHandler
that handles all errors in a sensible way.
Its position in the processing order is immediately before the handlers provided by WebFlux, which are considered last.
For machine clients, it produces a JSON response with details of the error, the HTTP status, and the exception message.
For browser clients, there is a “whitelabel” error handler that renders the same data in HTML format.
You can also provide your own HTML templates to display errors (see the next section).
The first step to customizing this feature often involves using the existing mechanism but replacing or augmenting the error contents. For that, you can add a bean of type`ErrorAttributes`.
To change the error handling behavior, you can implement ErrorWebExceptionHandler
and register a bean definition of that type.
Because a WebExceptionHandler
is quite low-level, Spring Boot also provides a convenient AbstractErrorWebExceptionHandler
to let you handle errors in a WebFlux functional way, as shown in the following example:
public class CustomErrorWebExceptionHandler extends AbstractErrorWebExceptionHandler { // Define constructor here @Override protected RouterFunction<ServerResponse> getRoutingFunction(ErrorAttributes errorAttributes) { return RouterFunctions .route(aPredicate, aHandler) .andRoute(anotherPredicate, anotherHandler); } }
For a more complete picture, you can also subclass DefaultErrorWebExceptionHandler
directly and override specific methods.
If you want to display a custom HTML error page for a given status code, you can add a file to an /error
folder.
Error pages can either be static HTML (that is, added under any of the static resource folders) or built with templates.
The name of the file should be the exact status code or a series mask.
For example, to map 404
to a static HTML file, your folder structure would be as follows:
src/ +- main/ +- java/ | + <source code> +- resources/ +- public/ +- error/ | +- 404.html +- <other public assets>
To map all 5xx
errors by using a Mustache template, your folder structure would be as follows:
src/ +- main/ +- java/ | + <source code> +- resources/ +- templates/ +- error/ | +- 5xx.mustache +- <other templates>
Spring WebFlux provides a WebFilter
interface that can be implemented to filter HTTP request-response exchanges.
WebFilter
beans found in the application context will be automatically used to filter each exchange.
Where the order of the filters is important they can implement Ordered
or be annotated with @Order
.
Spring Boot auto-configuration may configure web filters for you.
When it does so, the orders shown in the following table will be used:
Web Filter | Order |
---|---|
|
|
|
|
|
|
If you prefer the JAX-RS programming model for REST endpoints, you can use one of the available implementations instead of Spring MVC.
Jersey and Apache CXF work quite well out of the box.
CXF requires you to register its Servlet
or Filter
as a @Bean
in your application context.
Jersey has some native Spring support, so we also provide auto-configuration support for it in Spring Boot, together with a starter.
To get started with Jersey, include the spring-boot-starter-jersey
as a dependency and then you need one @Bean
of type ResourceConfig
in which you register all the endpoints, as shown in the following example:
@Component public class JerseyConfig extends ResourceConfig { public JerseyConfig() { register(Endpoint.class); } }
![]() | Warning |
---|---|
Jersey’s support for scanning executable archives is rather limited.
For example, it cannot scan for endpoints in a package found in a fully executable jar file or in |
For more advanced customizations, you can also register an arbitrary number of beans that implement ResourceConfigCustomizer
.
All the registered endpoints should be @Components
with HTTP resource annotations (@GET
and others), as shown in the following example:
@Component @Path("/hello") public class Endpoint { @GET public String message() { return "Hello"; } }
Since the Endpoint
is a Spring @Component
, its lifecycle is managed by Spring and you can use the @Autowired
annotation to inject dependencies and use the @Value
annotation to inject external configuration.
By default, the Jersey servlet is registered and mapped to /*
. You can change the mapping by adding @ApplicationPath
to your ResourceConfig
.
By default, Jersey is set up as a Servlet in a @Bean
of type ServletRegistrationBean
named jerseyServletRegistration
.
By default, the servlet is initialized lazily, but you can customize that behavior by setting spring.jersey.servlet.load-on-startup
.
You can disable or override that bean by creating one of your own with the same name.
You can also use a filter instead of a servlet by setting spring.jersey.type=filter
(in which case, the @Bean
to replace or override is jerseyFilterRegistration
).
The filter has an @Order
, which you can set with spring.jersey.filter.order
.
Both the servlet and the filter registrations can be given init parameters by using spring.jersey.init.*
to specify a map of properties.
There is a Jersey sample so that you can see how to set things up.
Spring Boot includes support for embedded Tomcat, Jetty, and Undertow servers.
Most developers use the appropriate “Starter” to obtain a fully configured instance.
By default, the embedded server listens for HTTP requests on port 8080
.
When using an embedded servlet container, you can register servlets, filters, and all the listeners (such as HttpSessionListener
) from the Servlet spec, either by using Spring beans or by scanning for Servlet components.
Any Servlet
, Filter
, or servlet *Listener
instance that is a Spring bean is registered with the embedded container.
This can be particularly convenient if you want to refer to a value from your application.properties
during configuration.
By default, if the context contains only a single Servlet, it is mapped to /
.
In the case of multiple servlet beans, the bean name is used as a path prefix.
Filters map to /*
.
If convention-based mapping is not flexible enough, you can use the ServletRegistrationBean
, FilterRegistrationBean
, and ServletListenerRegistrationBean
classes for complete control.
Spring Boot ships with many auto-configurations that may define Filter beans. Here are a few examples of Filters and their respective order (lower order value means higher precedence):
Servlet Filter | Order |
---|---|
|
|
|
|
|
|
|
|
It is usually safe to leave Filter beans unordered.
If a specific order is required, you should avoid configuring a Filter that reads the request body at Ordered.HIGHEST_PRECEDENCE
, since it might go against the character encoding configuration of your application.
If a Servlet filter wraps the request, it should be configured with an order that is less than or equal to OrderedFilter.REQUEST_WRAPPER_FILTER_MAX_ORDER
.
![]() | Warning |
---|---|
Take care when registering |
Embedded servlet containers do not directly execute the Servlet 3.0+ javax.servlet.ServletContainerInitializer
interface or Spring’s org.springframework.web.WebApplicationInitializer
interface.
This is an intentional design decision intended to reduce the risk that third party libraries designed to run inside a war may break Spring Boot applications.
If you need to perform servlet context initialization in a Spring Boot application, you should register a bean that implements the org.springframework.boot.web.servlet.ServletContextInitializer
interface.
The single onStartup
method provides access to the ServletContext
and, if necessary, can easily be used as an adapter to an existing WebApplicationInitializer
.
When using an embedded container, automatic registration of classes annotated with @WebServlet
, @WebFilter
, and @WebListener
can be enabled by using @ServletComponentScan
.
![]() | Tip |
---|---|
|
Under the hood, Spring Boot uses a different type of ApplicationContext
for embedded servlet container support.
The ServletWebServerApplicationContext
is a special type of WebApplicationContext
that bootstraps itself by searching for a single ServletWebServerFactory
bean.
Usually a TomcatServletWebServerFactory
, JettyServletWebServerFactory
, or UndertowServletWebServerFactory
has been auto-configured.
![]() | Note |
---|---|
You usually do not need to be aware of these implementation classes.
Most applications are auto-configured, and the appropriate |
Common servlet container settings can be configured by using Spring Environment
properties.
Usually, you would define the properties in your application.properties
file.
Common server settings include:
server.port
), interface address to bind to server.address
, and so on.server.servlet.session.persistent
), session timeout (server.servlet.session.timeout
), location of session data (server.servlet.session.store-dir
), and session-cookie configuration (server.servlet.session.cookie.*
).server.error.path
) and so on.Spring Boot tries as much as possible to expose common settings, but this is not always possible.
For those cases, dedicated namespaces offer server-specific customizations (see server.tomcat
and server.undertow
).
For instance, access logs can be configured with specific features of the embedded servlet container.
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See the |
If you need to programmatically configure your embedded servlet container, you can register a Spring bean that implements the WebServerFactoryCustomizer
interface.
WebServerFactoryCustomizer
provides access to the ConfigurableServletWebServerFactory
, which includes numerous customization setter methods.
The following example shows programmatically setting the port:
import org.springframework.boot.web.server.WebServerFactoryCustomizer; import org.springframework.boot.web.servlet.server.ConfigurableServletWebServerFactory; import org.springframework.stereotype.Component; @Component public class CustomizationBean implements WebServerFactoryCustomizer<ConfigurableServletWebServerFactory> { @Override public void customize(ConfigurableServletWebServerFactory server) { server.setPort(9000); } }
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If the preceding customization techniques are too limited, you can register the TomcatServletWebServerFactory
, JettyServletWebServerFactory
, or UndertowServletWebServerFactory
bean yourself.
@Bean public ConfigurableServletWebServerFactory webServerFactory() { TomcatServletWebServerFactory factory = new TomcatServletWebServerFactory(); factory.setPort(9000); factory.setSessionTimeout(10, TimeUnit.MINUTES); factory.addErrorPages(new ErrorPage(HttpStatus.NOT_FOUND, "/notfound.html")); return factory; }
Setters are provided for many configuration options. Several protected method “hooks” are also provided should you need to do something more exotic. See the source code documentation for details.
When running a Spring Boot application that uses an embedded servlet container (and is packaged as an executable archive), there are some limitations in the JSP support.
java -jar
, and will also be deployable to any standard container.
JSPs are not supported when using an executable jar.error.jsp
page does not override the default view for error handling.
Custom error pages should be used instead.There is a JSP sample so that you can see how to set things up.
Spring Boot includes support for the following embedded reactive web servers: Reactor Netty, Tomcat, Jetty, and Undertow. Most developers use the appropriate “Starter” to obtain a fully configured instance. By default, the embedded server listens for HTTP requests on port 8080.
When auto-configuring a Reactor Netty or Jetty server, Spring Boot will create specific beans that will provide HTTP resources to the server instance: ReactorResourceFactory
or JettyResourceFactory
.
By default, those resources will be also shared with the Reactor Netty and Jetty clients for optimal performances, given:
WebClient.Builder
bean auto-configured by Spring BootDevelopers can override the resource configuration for Jetty and Reactor Netty by providing a custom ReactorResourceFactory
or JettyResourceFactory
bean - this will be applied to both clients and servers.
You can learn more about the resource configuration on the client side in the WebClient Runtime section.