The importance of Servlet in Java
When java language was first introduced, there were mainly desktop applications with AWT and later on SWT libraries. After some time, the small applets (as far as i know) have been introduced and people were able to write java games for mobile phones, not smart phones. After a while, internet became widely available and people started writing web applications with java. Maybe you have heard about the terms EJB or JavaEE. But maybe and probably you haven't heard about the small term called Servlet. You might be trying to develop Spring Framework applications without knowing what servlet means. In this post, i will be explaining why the usually unknown concept of Servlet is a bit of important.
A little bit of background
There is a vast world of libraries of java since it is opensource and suitable for development. For example, we have pdfbox and itextpdf for writing and reading pdf files. Also we have Weka and other libraries for machine learning. There are different libraries that are doing the similar things. Then we have a problem here. Which one should we use and learn? Because there is no standard among them. Because java is is not a monopolized world like .net framework.
I will come back to this matter of standard later. Now we have another subject called OSI layers. A network request is travelling through these semantic layers between 2 devices, just like shown in the simple image below. A web request is constructed in the application layer and then transmitted to ports and sockets via TCP layer. After this point, the web drivers of the operating system is taking care of the rest. The data is transmitted with the data layer and physical layer, well, physically.
At this point, you may already know that we can develop web applications with languages other than java at the application layer. But our topic is now java. Therefore we need a technology to fill the TCP layer. We call them java application servers. For example, Tomcat, Glassfish, Jboss, Payara and Jetty are first ones that come to my mind. We said that there are different libraries doing similar things in the java world since there is no actual standard. Here we have different alternatives to serve hava applications on the web. We can ask the same question in this case. Which one to learn and use?
Standardization
Right now, we are greeted with the concept of JSR, Java Specification Requests. If we didn't have standards to develop web applications with java, we would have to write different java codes for all the servers i have mentioned above. If you look at the page i have linked, you can see there are some standardizations for some concepts in java. For example, you can search for "enterprise javabeans" and see how it is implemented and developed over the years as a standard for web development in java. But there is more. For example the latest servlet specification version 4.0 is the number 369. The image below summarizes the standards that you might use while developing java web applications. Even though it is a bit old, it serves our purpose. There is a JAX-RS there, i wonder what it does?
Alongside these standardizations, we need some intermiediary forms to let java applications and the java application servers talk. Otherwise, the servers would end up outside of java specs and no one would use them. For example let's take Tomcat server. If you take a look at the definition at the website, it says it is an implementation of some specifications. It doesn't say i am a java server. Because when you implement those specifications, you automatically become an application server and can run java web apps. I recommend you to go a little bit deeper and understand what this means, after reading this post.
Now we see Jakarta Servlet (which can be considered as Java servlet) inside that definition. If you ask me, servlet is the most important part there. Because just like we have a main method for the java applications as entrance point, we have servlets as entrance points for web applications. Java web applications greet and route the requests that come to application layer, via servlets. Doesn't matter which java technology or which java server. In other words, you are using servlets to get and redirect the requests in the Spring Framework or Spring Boot applications in the background. Here is a drawing of this adventure.
When you look at the past of the java web applications, you can see HTTPservlet is being extended and doGet and doPost methods are overridden in the old JSP applications. I have given a very simple example down below. You don't have to manually define and override an http servlet these days. This is mainly because we have CDI (context and dependency injection) these days. This is also a deep story but let me summarize it like this: We are defining the routings of the servlet through the frameworks like Jakarta or Spring. Back in the day, there were not frameworks and we had xml files or classes like below.
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
<servlet>
<servlet-name>jerseySerlvet</servlet-name>
<servlet-class>org.glassfish.jersey.servlet.ServletContainer</servlet-class>
<init-param>
<param-name>contextConfigLocation</param-name>
<param-value>/WEB-INF/spring/jerseySerlvet/rest-context.xml</param-value>
</init-param>
<init-param>
<param-name>com.sun.jersey.config.property.packages</param-name>
<!-- package names with comma -->
<param-value>com.example.rest</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>jerseySerlvet</servlet-name>
<url-pattern>/rest/*</url-pattern>
</servlet-mapping>
</web-app>
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@WebServlet("/processForm")
public class MyServlet extends HttpServlet
{
public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException
{
response.getWriter().println("Hello");
}
}
Now if you are telling yourself "i have never used or seen these but i have developed web application", this post is exactly for you :) There is a small possibility that you are developing Jakarta web applications. There is a great chance that you are developing Spring Framework or Boot applications. I can easily prove that servlets are being used in the background in all those 3 technologies.
Proof
First let me present you another picture. This picture explains how an http request is going through the web applications and how a response is produced. You can see the most inner part is possible servlet implementations. Servlet is a standard interface which is implemented by application servers.
First, let me give you an example of a jakarta app. You can develop JaraktaEE applications, which are actually java enterprise edition applications, without the need of old xml configuration files. You can find an example restful service implementation here. You can see restful service endpoints in the BookController class. If you get an exception in one of these methods, you can get an exception stacktrace like below.
javax.servlet.ServletException: javax.ws.rs.InternalServerErrorException
at org.glassfish.jersey.servlet.WebComponent.serviceImpl(WebComponent.java:410)
at org.glassfish.jersey.servlet.WebComponent.service(WebComponent.java:346)
at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:365)
at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:318)
at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:205)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.glassfish.tyrus.servlet.TyrusServletFilter.doFilter(TyrusServletFilter.java:299)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:373)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1589)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:748)
You can see glassfish servlet in the stacktrace.
Similarly, you can take a look at this applications, which is developed with Spring Framework. You can find a web xml file inside this project since it is not a spring boot project. You can see org.springframework.web.servlet.DispatcherServlet in this file. You have seen dispatcherservlet in the image above. This class is the servlet implementation of the spring framework. That means we can take the standard and extend it. You can take a look at the BookController class in this project and get an exception. The stacktrace will look something like this and you will be able to see the servlet (dispactherservlet) there.
java.lang.ArithmeticException: / by zero
at com.example.springjdbcrest.controller.BookController.index(BookController.java:80)
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
at java.base/java.lang.reflect.Method.invoke(Method.java:580)
at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:262)
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:190)
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:118)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:917)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:829)
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1089)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:979)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1014)
at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:903)
at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:564)
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:885)
at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:658)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:205)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:174)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149)
at org.springframework.web.filter.CompositeFilter$VirtualFilterChain.doFilter(CompositeFilter.java:108)
at org.springframework.security.web.FilterChainProxy.lambda$doFilterInternal$3(FilterChainProxy.java:231)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:365)
at org.springframework.security.web.access.intercept.AuthorizationFilter.doFilter(AuthorizationFilter.java:100)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:374)
at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:126)
at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:120)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:374)
at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:131)
at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:85)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:374)
at org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:100)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:374)
at org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:179)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:374)
at org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:63)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:374)
at com.example.springjdbcrest.config.JWTAuthorizationFilter.doFilterInternal(JWTAuthorizationFilter.java:61)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:374)
at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:227)
at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:221)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:374)
at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:107)
at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:93)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:374)
at org.springframework.web.filter.CorsFilter.doFilterInternal(CorsFilter.java:91)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:374)
at org.springframework.security.web.header.HeaderWriterFilter.doHeadersAfter(HeaderWriterFilter.java:90)
at org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:75)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:374)
at org.springframework.security.web.context.SecurityContextHolderFilter.doFilter(SecurityContextHolderFilter.java:82)
at org.springframework.security.web.context.SecurityContextHolderFilter.doFilter(SecurityContextHolderFilter.java:69)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:374)
at org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:62)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:374)
at org.springframework.security.web.session.DisableEncodeUrlFilter.doFilterInternal(DisableEncodeUrlFilter.java:42)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:374)
at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:233)
at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:191)
at org.springframework.web.filter.CompositeFilter$VirtualFilterChain.doFilter(CompositeFilter.java:113)
at org.springframework.web.servlet.handler.HandlerMappingIntrospector.lambda$createCacheFilter$3(HandlerMappingIntrospector.java:195)
at org.springframework.web.filter.CompositeFilter$VirtualFilterChain.doFilter(CompositeFilter.java:113)
at org.springframework.web.filter.CompositeFilter.doFilter(CompositeFilter.java:74)
at org.springframework.security.config.annotation.web.configuration.WebMvcSecurityConfiguration$CompositeFilterChainProxy.doFilter(WebMvcSecurityConfiguration.java:225)
at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:352)
at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:268)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:174)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:167)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:90)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:482)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:115)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:93)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:673)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:340)
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:391)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:63)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:896)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1744)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:52)
at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191)
at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.base/java.lang.Thread.run(Thread.java:1583)
Lastly spring boot. In spring boot applications, you almost do no configurations for web applications. It handles a lot of things for you. Nevertheless, they have to use servlets here too. Take a look at this project and get an exception inside the BookController. You get a similar stacktrace as spring framework but a little bit longer i guess. You can also see dispatcherservlet in the stacktrace.
java.lang.ArithmeticException: / by zero
at com.example.SpringbootJDBCRest.controller.BookController.index(BookController.java:84) ~[classes/:na]
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103) ~[na:na]
at java.base/java.lang.reflect.Method.invoke(Method.java:580) ~[na:na]
at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:254) ~[spring-web-6.1.1.jar:6.1.1]
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:182) ~[spring-web-6.1.1.jar:6.1.1]
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:118) ~[spring-webmvc-6.1.1.jar:6.1.1]
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:917) ~[spring-webmvc-6.1.1.jar:6.1.1]
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:829) ~[spring-webmvc-6.1.1.jar:6.1.1]
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-6.1.1.jar:6.1.1]
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1089) ~[spring-webmvc-6.1.1.jar:6.1.1]
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:979) ~[spring-webmvc-6.1.1.jar:6.1.1]
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1014) ~[spring-webmvc-6.1.1.jar:6.1.1]
at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:903) ~[spring-webmvc-6.1.1.jar:6.1.1]
at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:564) ~[tomcat-embed-core-10.1.16.jar:6.0]
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:885) ~[spring-webmvc-6.1.1.jar:6.1.1]
at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:658) ~[tomcat-embed-core-10.1.16.jar:6.0]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:205) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51) ~[tomcat-embed-websocket-10.1.16.jar:10.1.16]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:174) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
at org.springframework.security.web.FilterChainProxy.lambda$doFilterInternal$3(FilterChainProxy.java:231) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:365) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.security.web.access.intercept.AuthorizationFilter.doFilter(AuthorizationFilter.java:100) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:374) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:126) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:120) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:374) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:131) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:85) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:374) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:100) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:374) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:179) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:374) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:63) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:374) ~[spring-security-web-6.2.0.jar:6.2.0]
at com.example.SpringbootJDBCRest.config.JWTAuthorizationFilter.doFilterInternal(JWTAuthorizationFilter.java:61) ~[classes/:na]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116) ~[spring-web-6.1.1.jar:6.1.1]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:374) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:227) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:221) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:374) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:107) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:93) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:374) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.web.filter.CorsFilter.doFilterInternal(CorsFilter.java:91) ~[spring-web-6.1.1.jar:6.1.1]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116) ~[spring-web-6.1.1.jar:6.1.1]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:374) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.security.web.header.HeaderWriterFilter.doHeadersAfter(HeaderWriterFilter.java:90) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:75) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116) ~[spring-web-6.1.1.jar:6.1.1]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:374) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.security.web.context.SecurityContextHolderFilter.doFilter(SecurityContextHolderFilter.java:82) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.security.web.context.SecurityContextHolderFilter.doFilter(SecurityContextHolderFilter.java:69) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:374) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:62) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116) ~[spring-web-6.1.1.jar:6.1.1]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:374) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.security.web.session.DisableEncodeUrlFilter.doFilterInternal(DisableEncodeUrlFilter.java:42) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116) ~[spring-web-6.1.1.jar:6.1.1]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:374) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:233) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:191) ~[spring-security-web-6.2.0.jar:6.2.0]
at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:352) ~[spring-web-6.1.1.jar:6.1.1]
at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:268) ~[spring-web-6.1.1.jar:6.1.1]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:174) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-6.1.1.jar:6.1.1]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116) ~[spring-web-6.1.1.jar:6.1.1]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:174) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-6.1.1.jar:6.1.1]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116) ~[spring-web-6.1.1.jar:6.1.1]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:174) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-6.1.1.jar:6.1.1]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116) ~[spring-web-6.1.1.jar:6.1.1]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:174) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:167) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:90) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:482) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:115) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:93) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:340) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:391) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:63) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:896) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1744) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:52) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
at java.base/java.lang.Thread.run(Thread.java:1583) ~[na:na]
I have given you only 3 examples. You can see similar stacktraces if you run a web application on Payara or Jboss too. For example, Jersey is a restful service implementation and it has its own servlet too. Or resteasy is another restful service library with its own servlet. You can investigate and prove all these by getting an exception.
Is servlet too important?
These days, we usually don't much use servlet structure manually in the web apps. But it is bringing the java app and the server together as a standard and being used in the background even if we don't see it. And since i am able to write a post this long about servlet, which is a summary believe me, i think servlet is important. Because otherwise, our web applications will feel like they are running in the air. I don't think it is the best way to jump into spring framework while moving from JavaSE to JavaEE. I think the concepts in this post must be understood first. I hope this helps. See you at the next post :)
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