fixed README file

changed filter to match url pattern

javax-servlets-3/Dockerfile

@@ -1,2 +1,2 @@
 FROM tomcat
-ADD ./target/javax-servlets-3-1.0-SNAPSHOT.war /usr/local/tomcat/webapps/
+ADD ./target/uppercasing-app.war /usr/local/tomcat/webapps/

javax-servlets-3/README.md

@@ -3,7 +3,8 @@ mvn package
 
 ## Run with Tomcat on Docker container:
 docker build --tag my-tomcat .
+
 docker run -it --rm -p 8080:8080 my-tomcat
 
-### Relevant Articles:
+## Relevant Articles:
 - [Java Web Application Without Web.xml]

javax-servlets-3/pom.xml

@@ -31,6 +31,7 @@
         <spring.version>5.1.3.RELEASE</spring.version>
     </properties>
     <build>
+        <finalName>uppercasing-app</finalName>
         <plugins>
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>

javax-servlets-3/src/main/java/com/baeldung/servlets3/web/filters/EmptyParamFilter.java

@@ -8,9 +8,8 @@ import javax.servlet.ServletRequest;
 import javax.servlet.ServletResponse;
 import javax.servlet.annotation.WebFilter;
 import java.io.IOException;
-import java.io.PrintWriter;
 
-@WebFilter(servletNames = { "uppercaseServlet" }, filterName = "emptyParamFilter")
+@WebFilter(servletNames = { "uppercaseServlet" }, urlPatterns = "/uppercase")
 public class EmptyParamFilter implements Filter {
 
     @Override
@@ -22,21 +21,13 @@ public class EmptyParamFilter implements Filter {
         FilterChain filterChain) throws IOException, ServletException {
         String inputString = servletRequest.getParameter("input");
 
-        if (inputString == null || inputString.isEmpty()) {
-            response(servletResponse);
-        } else {
+        if (inputString != null && inputString.matches("[A-Za-z0-9]+")) {
             filterChain.doFilter(servletRequest, servletResponse);
+        } else {
+            servletResponse.getWriter().println("Missing input parameter");
         }
     }
 
-    private void response(ServletResponse response) throws IOException {
-        response.setContentType("text/html");
-
-        PrintWriter out = response.getWriter();
-
-        out.println("Missing input parameter");
-    }
-
     @Override
     public void destroy() {
     }