Spring boot's annotation @ServletComponentScan enables scanning of Servlet components. That means Servlet 3.0 annotations: @WebServlet, @WebFilter and @WebListener can be used along with Spring components. This is specially very useful when we are developing a jar project.
@ServletComponentScan imports ServletComponentScanRegistrar which is an implementation of ImportBeanDefinitionRegistrar. This implementation performs package scanning and kicks off the servlet components registration process. By default Spring will scan the package of the class where this annotation is used. The scanning package can be altered by using one of the elements: value, backPackages or basePackageClasses of this annotation.
@ServletComponentScan will only be used when the application needs to run in embedded container. When deployed in an external container, this annotation has no effect, as Servlet container's built-in scanning mechanism (per Servlet specifications) takes care of discovering servlet components.
Example
Spring boot main class with @ServletComponentScan
@ServletComponentScan
@SpringBootApplication
public class Main {
public static void main (String[] args) {
SpringApplication sa = new SpringApplication(Main.class);
sa.setLogStartupInfo(false);
sa.setBannerMode(Banner.Mode.OFF);
sa.run(args);
}
}
A Servlet component
@WebServlet(urlPatterns = "/path2/*")
public class MyServlet extends HttpServlet {
@Override
protected void doGet (HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
PrintWriter writer = resp.getWriter();
writer.println("response from servlet ");
}
}
A Filter component
@WebFilter(urlPatterns = "/*")
public class MyFilter implements Filter{
@Override
public void init (FilterConfig filterConfig) throws ServletException {
}
@Override
public void doFilter (ServletRequest request,
ServletResponse response, FilterChain chain)
throws IOException, ServletException {
String url = request instanceof HttpServletRequest ?
((HttpServletRequest) request).getRequestURL().toString() : "N/A";
System.out.println("from filter, processing url: "+url);
chain.doFilter(request, response);
}
@Override
public void destroy () {
}
}
A ServletContentListener
@WebListener
public class MyServletListener implements ServletContextListener{
@Override
public void contextInitialized (ServletContextEvent sce) {
System.out.println("from ServletContextListener: " +
" context initialized");
}
@Override
public void contextDestroyed (ServletContextEvent sce) {
}
}
A Spring Controller
@Controller
public class MyController {
@RequestMapping("/*")
@ResponseBody
public String handler () {
return "response form spring controller method";
}
}
Running application
mvn spring-boot:run
Output
During startup:
2017-01-31 01:50:03.791 INFO 7440 --- [ main] ationConfigEmbeddedWebApplicationContext : Refreshing org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@70e8f8e: startup date [Tue Jan 31 01:50:03 CST 2017]; root of context hierarchy
2017-01-31 01:50:05.172 INFO 7440 --- [ main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat initialized with port(s): 8080 (http)
2017-01-31 01:50:05.182 INFO 7440 --- [ main] o.apache.catalina.core.StandardService : Starting service Tomcat
2017-01-31 01:50:05.184 INFO 7440 --- [ main] org.apache.catalina.core.StandardEngine : Starting Servlet Engine: Apache Tomcat/8.5.11
2017-01-31 01:50:05.264 INFO 7440 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext
2017-01-31 01:50:05.265 INFO 7440 --- [ost-startStop-1] o.s.web.context.ContextLoader : Root WebApplicationContext: initialization completed in 1477 ms
2017-01-31 01:50:05.423 INFO 7440 --- [ost-startStop-1] o.s.b.w.servlet.ServletRegistrationBean : Mapping servlet: 'dispatcherServlet' to [/path1/*]
2017-01-31 01:50:05.424 INFO 7440 --- [ost-startStop-1] o.s.b.w.servlet.ServletRegistrationBean : Mapping servlet: 'com.logicbig.example.MyServlet' to [/path2/*]
2017-01-31 01:50:05.426 INFO 7440 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: 'characterEncodingFilter' to: [/*]
2017-01-31 01:50:05.427 INFO 7440 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: 'hiddenHttpMethodFilter' to: [/*]
2017-01-31 01:50:05.427 INFO 7440 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: 'httpPutFormContentFilter' to: [/*]
2017-01-31 01:50:05.427 INFO 7440 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: 'requestContextFilter' to: [/*]
2017-01-31 01:50:05.427 INFO 7440 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: 'com.logicbig.example.MyFilter' to urls: [/*]
from ServletContextListener: context initialized
2017-01-31 01:50:05.705 INFO 7440 --- [ main] s.w.s.m.m.a.RequestMappingHandlerAdapter : Looking for @ControllerAdvice: org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@70e8f8e: startup date [Tue Jan 31 01:50:03 CST 2017]; root of context hierarchy
2017-01-31 01:50:05.765 INFO 7440 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/*]}" onto public java.lang.String com.logicbig.example.MyController.handler()
2017-01-31 01:50:05.769 INFO 7440 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/error]}" onto public org.springframework.http.ResponseEntity<java.util.Map<java.lang.String, java.lang.Object>> org.springframework.boot.autoconfigure.web.BasicErrorController.error(javax.servlet.http.HttpServletRequest)
2017-01-31 01:50:05.769 INFO 7440 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/error],produces=[text/html]}" onto public org.springframework.web.servlet.ModelAndView org.springframework.boot.autoconfigure.web.BasicErrorController.errorHtml(javax.servlet.http.HttpServletRequest,javax.servlet.http.HttpServletResponse)
2017-01-31 01:50:05.797 INFO 7440 --- [ main] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path [/webjars/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2017-01-31 01:50:05.797 INFO 7440 --- [ main] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path [/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2017-01-31 01:50:05.834 INFO 7440 --- [ main] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path [/**/favicon.ico] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2017-01-31 01:50:05.956 INFO 7440 --- [ main] o.s.j.e.a.AnnotationMBeanExporter : Registering beans for JMX exposure on startup
2017-01-31 01:50:06.010 INFO 7440 --- [ main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat started on port(s): 8080 (http)
/path1
from filter, processing url: http://localhost:8080/path1
/path2
from filter, processing url: http://localhost:8080/path2
Example Project
Dependencies and Technologies Used: - Spring Boot 1.4.4.RELEASE
Corresponding Spring Version 4.3.6.RELEASE - spring-boot-starter-web : Starter for building web, including RESTful, applications using Spring
MVC. Uses Tomcat as the default embedded container.
- JDK 1.8
- Maven 3.3.9
|
