BAEL-325: Implemented various filter examples.

enterprise-patterns/intercepting-filter-pattern/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <artifactId>intercepting-filter-pattern</artifactId>
+    <packaging>war</packaging>
+
+    <parent>
+        <artifactId>enterprise-patterns-parent</artifactId>
+        <groupId>com.baeldung.enterprise.patterns</groupId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>javax.servlet</groupId>
+            <artifactId>javax.servlet-api</artifactId>
+            <version>3.1.0</version>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.slf4j</groupId>
+            <artifactId>slf4j-api</artifactId>
+            <version>1.7.21</version>
+            <scope>provided</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+            </plugin>
+            <plugin>
+                <groupId>org.eclipse.jetty</groupId>
+                <artifactId>jetty-maven-plugin</artifactId>
+                <version>9.3.11.v20160721</version>
+                <configuration>
+                    <webApp>
+                        <contextPath>/intercepting-filter</contextPath>
+                    </webApp>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+</project>

enterprise-patterns/intercepting-filter-pattern/src/main/java/com/baeldung/enterprise/patterns/front/controller/FrontControllerServlet.java

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+package com.baeldung.enterprise.patterns.front.controller;
+
+import com.baeldung.enterprise.patterns.front.controller.commands.FrontCommand;
+import com.baeldung.enterprise.patterns.front.controller.commands.UnknownCommand;
+
+import javax.servlet.ServletException;
+import javax.servlet.annotation.WebServlet;
+import javax.servlet.http.HttpServlet;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+import java.io.IOException;
+
+@WebServlet(name = "front-controller", urlPatterns = "/")
+public class FrontControllerServlet extends HttpServlet {
+    @Override
+    protected void doGet(
+      HttpServletRequest request,
+      HttpServletResponse response
+    ) throws ServletException, IOException {
+        doCommand(request, response);
+    }
+
+    @Override
+    protected void doPost(
+      HttpServletRequest request,
+      HttpServletResponse response
+    ) throws ServletException, IOException {
+          doCommand(request, response);
+    }
+
+    private void doCommand(
+      HttpServletRequest request,
+      HttpServletResponse response
+    ) throws ServletException, IOException {
+        FrontCommand command = getCommand(request);
+        command.init(request, response);
+        command.process();
+    }
+
+    private FrontCommand getCommand(HttpServletRequest request) {
+        try {
+            Class type = Class.forName(
+              String.format(
+                "com.baeldung.enterprise.patterns.front.controller.commands.%sCommand",
+                request.getParameter("command")
+              )
+            );
+            return (FrontCommand) type
+              .asSubclass(FrontCommand.class)
+              .newInstance();
+        } catch (Exception e) {
+            return new UnknownCommand();
+        }
+    }
+}

enterprise-patterns/intercepting-filter-pattern/src/main/java/com/baeldung/enterprise/patterns/front/controller/commands/FrontCommand.java

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+package com.baeldung.enterprise.patterns.front.controller.commands;
+
+import com.baeldung.enterprise.patterns.front.controller.filters.FilterManager;
+import com.baeldung.enterprise.patterns.front.controller.filters.OnIntercept;
+
+import javax.servlet.RequestDispatcher;
+import javax.servlet.ServletException;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+import java.io.IOException;
+
+public abstract class FrontCommand implements OnIntercept {
+    protected HttpServletRequest request;
+    protected HttpServletResponse response;
+    private boolean intercept;
+
+    public FrontCommand() {
+    }
+
+    public void init(HttpServletRequest request, HttpServletResponse response) {
+        this.request = request;
+        this.response = response;
+    }
+
+    public void process() throws ServletException, IOException {
+        FilterManager.process(request, response, this);
+    }
+
+    public void forward(String target) throws ServletException, IOException {
+        if (intercept) {
+            return;
+        }
+        String path = String.format("/WEB-INF/jsp/%s.jsp", target);
+        RequestDispatcher dispatcher = request.getServletContext()
+          .getRequestDispatcher(path);
+        dispatcher.forward(request, response);
+    }
+
+    @Override
+    public void intercept() {
+        intercept = true;
+    }
+}

enterprise-patterns/intercepting-filter-pattern/src/main/java/com/baeldung/enterprise/patterns/front/controller/commands/LoginCommand.java

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+package com.baeldung.enterprise.patterns.front.controller.commands;
+
+import javax.servlet.ServletException;
+import javax.servlet.http.HttpSession;
+import java.io.IOException;
+
+public class LoginCommand extends FrontCommand {
+    @Override
+    public void process() throws ServletException, IOException {
+        if (request.getMethod().equals("GET")) {
+            request.setAttribute("redirect", request.getRequestURL()
+              .append("?").append(request.getQueryString()).toString());
+            forward("login");
+        } else {
+            HttpSession session = request.getSession(true);
+            session.setAttribute("username", request.getParameter("username"));
+            response.sendRedirect(request.getParameter("redirect"));
+        }
+    }
+}

enterprise-patterns/intercepting-filter-pattern/src/main/java/com/baeldung/enterprise/patterns/front/controller/commands/SearchCommand.java

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+package com.baeldung.enterprise.patterns.front.controller.commands;
+
+import com.baeldung.enterprise.patterns.front.controller.data.Book;
+import com.baeldung.enterprise.patterns.front.controller.data.BookshelfImpl;
+
+import javax.servlet.ServletException;
+import java.io.IOException;
+
+public class SearchCommand extends FrontCommand {
+    @Override
+    public void process() throws ServletException, IOException {
+        super.process();
+        Book book = new BookshelfImpl().getInstance()
+          .findByTitle(request.getParameter("title"));
+        if (book != null) {
+            request.setAttribute("book", book);
+            forward("book-found");
+        } else {
+            forward("book-notfound");
+        }
+    }
+}

enterprise-patterns/intercepting-filter-pattern/src/main/java/com/baeldung/enterprise/patterns/front/controller/commands/UnknownCommand.java

@@ -0,0 +1,11 @@
+package com.baeldung.enterprise.patterns.front.controller.commands;
+
+import javax.servlet.ServletException;
+import java.io.IOException;
+
+public class UnknownCommand extends FrontCommand {
+    @Override
+    public void process() throws ServletException, IOException {
+        forward("unknown");
+    }
+}

enterprise-patterns/intercepting-filter-pattern/src/main/java/com/baeldung/enterprise/patterns/front/controller/data/Book.java

@@ -0,0 +1,15 @@
+package com.baeldung.enterprise.patterns.front.controller.data;
+
+public interface Book {
+    String getAuthor();
+
+    void setAuthor(String author);
+
+    String getTitle();
+
+    void setTitle(String title);
+
+    Double getPrice();
+
+    void setPrice(Double price);
+}

enterprise-patterns/intercepting-filter-pattern/src/main/java/com/baeldung/enterprise/patterns/front/controller/data/BookImpl.java

@@ -0,0 +1,46 @@
+package com.baeldung.enterprise.patterns.front.controller.data;
+
+public class BookImpl implements Book {
+    private String author;
+    private String title;
+    private Double price;
+
+    public BookImpl() {
+    }
+
+    public BookImpl(String author, String title, Double price) {
+        this.author = author;
+        this.title = title;
+        this.price = price;
+    }
+
+    @Override
+    public String getAuthor() {
+        return author;
+    }
+
+    @Override
+    public void setAuthor(String author) {
+        this.author = author;
+    }
+
+    @Override
+    public String getTitle() {
+        return title;
+    }
+
+    @Override
+    public void setTitle(String title) {
+        this.title = title;
+    }
+
+    @Override
+    public Double getPrice() {
+        return price;
+    }
+
+    @Override
+    public void setPrice(Double price) {
+        this.price = price;
+    }
+}

enterprise-patterns/intercepting-filter-pattern/src/main/java/com/baeldung/enterprise/patterns/front/controller/data/Bookshelf.java

@@ -0,0 +1,16 @@
+package com.baeldung.enterprise.patterns.front.controller.data;
+
+public interface Bookshelf {
+
+    default void init() {
+        add(new BookImpl("Wilson, Robert Anton & Shea, Robert", "Illuminati", 9.99));
+        add(new BookImpl("Fowler, Martin", "Patterns of Enterprise Application Architecture", 27.88));
+        add(new BookImpl("Unknown", "Something about German Umlauts (äüö) and ß", 5.49));
+    }
+
+    Bookshelf getInstance();
+
+    <E extends Book> boolean add(E book);
+
+    Book findByTitle(String title);
+}

enterprise-patterns/intercepting-filter-pattern/src/main/java/com/baeldung/enterprise/patterns/front/controller/data/BookshelfImpl.java

@@ -0,0 +1,24 @@
+package com.baeldung.enterprise.patterns.front.controller.data;
+
+import java.util.ArrayList;
+
+public class BookshelfImpl extends ArrayList<Book> implements Bookshelf {
+    private static Bookshelf INSTANCE;
+
+    @Override
+    public Bookshelf getInstance() {
+        if (INSTANCE == null) {
+            INSTANCE = new BookshelfImpl();
+            INSTANCE.init();
+        }
+        return INSTANCE;
+    }
+
+    @Override
+    public Book findByTitle(String title) {
+        return this.stream()
+          .filter(book -> book.getTitle().toLowerCase().contains(title.toLowerCase()))
+          .findFirst()
+          .orElse(null);
+    }
+}

enterprise-patterns/intercepting-filter-pattern/src/main/java/com/baeldung/enterprise/patterns/front/controller/filters/AuditFilter.java

@@ -0,0 +1,25 @@
+package com.baeldung.enterprise.patterns.front.controller.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.HttpSession;
+import java.io.IOException;
+
+public class AuditFilter extends BaseFilter {
+    @Override
+    public void doFilter(
+      ServletRequest request,
+      ServletResponse response,
+      FilterChain chain
+    ) throws IOException, ServletException {
+        HttpServletRequest httpServletRequest = (HttpServletRequest) request;
+        HttpSession session = httpServletRequest.getSession(false);
+        if (session != null && session.getAttribute("username") != null) {
+            request.setAttribute("username", session.getAttribute("username"));
+        }
+        chain.doFilter(request, response);
+    }
+}

enterprise-patterns/intercepting-filter-pattern/src/main/java/com/baeldung/enterprise/patterns/front/controller/filters/AuthenticationFilter.java

@@ -0,0 +1,40 @@
+package com.baeldung.enterprise.patterns.front.controller.filters;
+
+import com.baeldung.enterprise.patterns.front.controller.commands.FrontCommand;
+import com.baeldung.enterprise.patterns.front.controller.commands.LoginCommand;
+
+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 javax.servlet.http.HttpSession;
+import java.io.IOException;
+
+public class AuthenticationFilter extends BaseFilter {
+    private OnIntercept callback;
+
+    public AuthenticationFilter(OnIntercept callback) {
+        this.callback = callback;
+    }
+
+    @Override
+    public void doFilter(
+      ServletRequest request,
+      ServletResponse response,
+      FilterChain chain
+    ) throws IOException, ServletException {
+        HttpServletRequest httpServletRequest = (HttpServletRequest) request;
+        HttpServletResponse httpServletResponse = (HttpServletResponse) response;
+        HttpSession session = httpServletRequest.getSession(false);
+        if (session == null || session.getAttribute("username") == null) {
+            FrontCommand command = new LoginCommand();
+            command.init(httpServletRequest, httpServletResponse);
+            command.process();
+            callback.intercept();
+        } else {
+            chain.doFilter(request, response);
+        }
+    }
+}

enterprise-patterns/intercepting-filter-pattern/src/main/java/com/baeldung/enterprise/patterns/front/controller/filters/BaseFilter.java

@@ -0,0 +1,25 @@
+package com.baeldung.enterprise.patterns.front.controller.filters;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import javax.servlet.Filter;
+import javax.servlet.FilterConfig;
+import javax.servlet.ServletException;
+
+public abstract class BaseFilter implements Filter {
+    private static final Logger log = LoggerFactory.getLogger(BaseFilter.class);
+
+    protected FilterConfig filterConfig;
+
+    @Override
+    public void init(FilterConfig filterConfig) throws ServletException {
+        log.info("Initialize filter: {}", getClass().getSimpleName());
+        this.filterConfig = filterConfig;
+    }
+
+    @Override
+    public void destroy() {
+        log.info("Destroy filter: {}", getClass().getSimpleName());
+    }
+}

enterprise-patterns/intercepting-filter-pattern/src/main/java/com/baeldung/enterprise/patterns/front/controller/filters/EncodingFilter.java

@@ -0,0 +1,30 @@
+package com.baeldung.enterprise.patterns.front.controller.filters;
+
+import javax.servlet.*;
+import javax.servlet.annotation.WebFilter;
+import java.io.IOException;
+
+@WebFilter(servletNames = "front-controller")
+public class EncodingFilter extends BaseFilter {
+    private String encoding;
+
+    @Override
+    public void init(FilterConfig filterConfig) throws ServletException {
+        super.init(filterConfig);
+        this.encoding = filterConfig.getInitParameter("encoding");
+    }
+
+    @Override
+    public void doFilter(
+      ServletRequest request,
+      ServletResponse response,
+      FilterChain chain
+    ) throws IOException, ServletException {
+        String encoding = request.getParameter("encoding");
+        if (encoding == null) {
+            encoding = this.encoding;
+        }
+        response.setCharacterEncoding(encoding);
+        chain.doFilter(request, response);
+    }
+}

enterprise-patterns/intercepting-filter-pattern/src/main/java/com/baeldung/enterprise/patterns/front/controller/filters/FilterChainImpl.java

@@ -0,0 +1,28 @@
+package com.baeldung.enterprise.patterns.front.controller.filters;
+
+import javax.servlet.Filter;
+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 {
+    private Iterator<Filter> filters;
+
+    public FilterChainImpl(Filter... filters) {
+        this.filters = Arrays.asList(filters).iterator();
+    }
+
+    @Override
+    public void doFilter(
+      ServletRequest request,
+      ServletResponse response
+    ) throws IOException, ServletException {
+        if (filters.hasNext()) {
+            Filter filter = filters.next();
+            filter.doFilter(request, response, this);
+        }
+    }
+}

enterprise-patterns/intercepting-filter-pattern/src/main/java/com/baeldung/enterprise/patterns/front/controller/filters/FilterManager.java

@@ -0,0 +1,21 @@
+package com.baeldung.enterprise.patterns.front.controller.filters;
+
+import javax.servlet.FilterChain;
+import javax.servlet.ServletException;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+import java.io.IOException;
+
+public class FilterManager {
+    public static void process(
+      HttpServletRequest request,
+      HttpServletResponse response,
+      OnIntercept callback
+    ) throws ServletException, IOException {
+        FilterChain filterChain = new FilterChainImpl(
+          new AuthenticationFilter(callback),
+          new AuditFilter()
+        );
+        filterChain.doFilter(request, response);
+    }
+}

enterprise-patterns/intercepting-filter-pattern/src/main/java/com/baeldung/enterprise/patterns/front/controller/filters/LoggingFilter.java

@@ -0,0 +1,39 @@
+package com.baeldung.enterprise.patterns.front.controller.filters;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import javax.servlet.FilterChain;
+import javax.servlet.ServletException;
+import javax.servlet.ServletRequest;
+import javax.servlet.ServletResponse;
+import javax.servlet.annotation.WebFilter;
+import javax.servlet.http.HttpServletRequest;
+import java.io.IOException;
+
+@WebFilter(servletNames = "front-controller")
+public class LoggingFilter extends BaseFilter {
+    private static final Logger log = LoggerFactory.getLogger(LoggingFilter.class);
+
+    @Override
+    public void doFilter(
+      ServletRequest request,
+      ServletResponse response,
+      FilterChain chain
+    ) throws IOException, ServletException {
+        chain.doFilter(request, response);
+        HttpServletRequest httpServletRequest = (HttpServletRequest) request;
+        String username = (String) httpServletRequest.getAttribute("username");
+        if (username != null && username.length() > 0) {
+            username = username.concat("@");
+        } else {
+            username = "";
+        }
+        String intro = "Request";
+        if (username.length() > 0) {
+            intro = "Authenticated request";
+        }
+        log.info("{} from '{}{}': {}?{}", intro, username, request.getRemoteAddr(),
+          httpServletRequest.getRequestURI(), request.getParameterMap());
+    }
+}

enterprise-patterns/intercepting-filter-pattern/src/main/java/com/baeldung/enterprise/patterns/front/controller/filters/OnIntercept.java

@@ -0,0 +1,5 @@
+package com.baeldung.enterprise.patterns.front.controller.filters;
+
+public interface OnIntercept {
+    void intercept();
+}

enterprise-patterns/intercepting-filter-pattern/src/main/java/com/baeldung/enterprise/patterns/front/controller/filters/VisitorCounterFilter.java

@@ -0,0 +1,23 @@
+package com.baeldung.enterprise.patterns.front.controller.filters;
+
+import javax.servlet.FilterChain;
+import javax.servlet.ServletException;
+import javax.servlet.ServletRequest;
+import javax.servlet.ServletResponse;
+import javax.servlet.annotation.WebFilter;
+import java.io.IOException;
+
+@WebFilter(servletNames = "front-controller")
+public class VisitorCounterFilter extends BaseFilter {
+    private int counter;
+
+    @Override
+    public void doFilter(
+      ServletRequest request,
+      ServletResponse response,
+      FilterChain chain
+    ) throws IOException, ServletException {
+        request.setAttribute("counter", ++counter);
+        chain.doFilter(request, response);
+    }
+}

enterprise-patterns/intercepting-filter-pattern/src/main/webapp/WEB-INF/jsp/book-found.jsp

@@ -0,0 +1,13 @@
+<!DOCTYPE html>
+<html>
+    <head>
+        <title>Bookshelf: Title found</title>
+    </head>
+    <body>
+        <p>Our Bookshelf contains this title:</p>
+        <h2>${book.getTitle()}</h2>
+        <p>Author: ${book.getAuthor()}</p>
+        <input type="submit" value="Buy it: ${book.getPrice()}$">
+        <%@include file="visitor-counter.jsp"%>
+    </body>
+</html>

enterprise-patterns/intercepting-filter-pattern/src/main/webapp/WEB-INF/jsp/book-notfound.jsp

@@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <title>Bookshelf: Title not found</title>
+</head>
+    <body>
+        <p>Our Bookshelf doesn't contains this title:</p>
+        <h2>${param.get("title")}</h2>
+        <%@include file="visitor-counter.jsp"%>
+    </body>
+</html>

enterprise-patterns/intercepting-filter-pattern/src/main/webapp/WEB-INF/jsp/login.jsp

@@ -0,0 +1,15 @@
+<!DOCTYPE html>
+<html>
+    <head>
+        <title>Bookshelf: Login</title>
+    </head>
+    <body>
+        <p>Please input a username:</p>
+        <h2>Login</h2>
+        <form action="/intercepting-filter/?command=Login" method="POST">
+            <input type="text" name="username" placeholder="Username">
+            <input type="hidden" name="redirect" value="${redirect}">
+            <input type="submit" value="Proceed">
+        </form>
+    </body>
+</html>

enterprise-patterns/intercepting-filter-pattern/src/main/webapp/WEB-INF/jsp/unknown.jsp

@@ -0,0 +1,10 @@
+<!DOCTYPE html>
+<html>
+    <head>
+        <title>Bookshelf: Command unknown</title>
+    </head>
+    <body>
+        <p>Sorry, this command is not known!</p>
+        <%@include file="visitor-counter.jsp"%>
+    </body>
+</html>

enterprise-patterns/intercepting-filter-pattern/src/main/webapp/WEB-INF/jsp/visitor-counter.jsp

@@ -0,0 +1,2 @@
+<hr/>
+<p>You are visitor #${counter}!</p>