BAEL-325: Added UML sources. Applied some small improvements.

patterns/src/main/java/com/baeldung/patterns/filters/AuthenticationFilter.java

@@ -3,22 +3,23 @@ package com.baeldung.patterns.filters;
 import com.baeldung.patterns.commands.FrontCommand;
 import com.baeldung.patterns.commands.LoginCommand;
 
-import javax.servlet.FilterChain;
+import javax.servlet.*;
-import javax.servlet.ServletException;
-import javax.servlet.ServletRequest;
-import javax.servlet.ServletResponse;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 import javax.servlet.http.HttpSession;
 import java.io.IOException;
 
-public class AuthenticationFilter extends BaseFilter {
+public class AuthenticationFilter implements Filter {
     private OnIntercept callback;
 
     public AuthenticationFilter(OnIntercept callback) {
         this.callback = callback;
     }
 
+    @Override
+    public void init(FilterConfig filterConfig) throws ServletException {
+    }
+
     @Override
     public void doFilter(
       ServletRequest request,
@@ -37,4 +38,8 @@ public class AuthenticationFilter extends BaseFilter {
             chain.doFilter(request, response);
         }
     }
+
+    @Override
+    public void destroy() {
+    }
 }

patterns/src/main/java/com/baeldung/patterns/filters/EncodingFilter.java

@@ -2,9 +2,13 @@ package com.baeldung.patterns.filters;
 
 import javax.servlet.*;
 import javax.servlet.annotation.WebFilter;
+import javax.servlet.annotation.WebInitParam;
 import java.io.IOException;
 
-@WebFilter(servletNames = "front-controller")
+@WebFilter(
+  servletNames = {"front-controller"},
+  initParams = {@WebInitParam(name = "encoding", value = "UTF-8")}
+)
 public class EncodingFilter extends BaseFilter {
     private String encoding;
 

patterns/src/main/java/com/baeldung/patterns/filters/FilterChainImpl.java

@@ -1,14 +1,11 @@
 package com.baeldung.patterns.filters;
 
-import javax.servlet.Filter;
+import javax.servlet.*;
-import javax.servlet.ServletException;
-import javax.servlet.ServletRequest;
-import javax.servlet.ServletResponse;
 import java.io.IOException;
 import java.util.Arrays;
 import java.util.Iterator;
 
-public class FilterChainImpl implements javax.servlet.FilterChain {
+public class FilterChainImpl implements FilterChain {
     private Iterator<Filter> filters;
 
     public FilterChainImpl(Filter... filters) {

patterns/src/main/java/com/baeldung/patterns/filters/TemplateFilter.java

@@ -0,0 +1,35 @@
+package com.baeldung.patterns.filters;
+
+import javax.servlet.FilterChain;
+import javax.servlet.ServletException;
+import javax.servlet.ServletRequest;
+import javax.servlet.ServletResponse;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+import java.io.IOException;
+
+public abstract class TemplateFilter extends BaseFilter {
+
+    protected abstract void preFilter(
+      HttpServletRequest request,
+      HttpServletResponse response
+    ) throws IOException, ServletException;
+
+    protected abstract void postFilter(
+      HttpServletRequest request,
+      HttpServletResponse response
+    ) throws IOException, ServletException;
+
+    @Override
+    public void doFilter(
+      ServletRequest request,
+      ServletResponse response,
+      FilterChain chain
+    ) throws IOException, ServletException {
+        HttpServletRequest httpServletRequest = (HttpServletRequest) request;
+        HttpServletResponse httpServletResponse = (HttpServletResponse) response;
+        preFilter(httpServletRequest, httpServletResponse);
+        chain.doFilter(request, response);
+        postFilter(httpServletRequest, httpServletResponse);
+    }
+}

patterns/src/main/java/com/baeldung/patterns/filters/VisitorCounterFilter.java

@@ -1,18 +1,19 @@
 package com.baeldung.patterns.filters;
 
-import javax.servlet.FilterChain;
+import javax.servlet.*;
-import javax.servlet.ServletException;
-import javax.servlet.ServletRequest;
-import javax.servlet.ServletResponse;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpSession;
 import java.io.IOException;
 import java.util.HashSet;
 import java.util.Set;
 
-public class VisitorCounterFilter extends BaseFilter {
+public class VisitorCounterFilter implements Filter {
     private static Set<String> users = new HashSet<>();
 
+    @Override
+    public void init(FilterConfig filterConfig) throws ServletException {
+    }
+
     @Override
     public void doFilter(
       ServletRequest request,
@@ -21,10 +22,12 @@ public class VisitorCounterFilter extends BaseFilter {
     ) throws IOException, ServletException {
         HttpSession session = ((HttpServletRequest) request).getSession(false);
         String username = (String) session.getAttribute("username");
-        if (!users.contains(username)) {
         users.add(username);
-        }
         request.setAttribute("counter", users.size());
         chain.doFilter(request, response);
     }
+
+    @Override
+    public void destroy() {
+    }
 }

patterns/src/main/resources/intercepting_filter.puml

@@ -0,0 +1,17 @@
+@startuml
+scale 1.5
+
+class Client
+class FilterManager
+interface FilterChain
+interface "Filter 1"
+interface "Filter 2"
+interface "Filter 3"
+
+Client .right.-- FilterManager
+FilterManager .right.-- Target
+FilterManager -- FilterChain
+FilterChain .right.-- "Filter 3"
+FilterChain .right.-- "Filter 2"
+FilterChain .right.-- "Filter 1"
+@enduml