Merge pull request #1539 from Dkafetzis/UNDERTOW-2335

[UNDERTOW-2335] Add an example of the PredicatesHandler and specifically the predicate handler parser

examples/src/main/java/io/undertow/examples/predicates/PredicateParser.java

@@ -0,0 +1,56 @@
+/*
+* JBoss, Home of Professional Open Source.
+* Copyright 2023 Red Hat, Inc., and individual contributors
+* as indicated by the @author tags.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*     http://www.apache.org/licenses/LICENSE-2.0
+*
+*  Unless required by applicable law or agreed to in writing, software
+*  distributed under the License is distributed on an "AS IS" BASIS,
+*  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+*  See the License for the specific language governing permissions and
+*  limitations under the License.
+*/
+package io.undertow.examples.predicates;
+
+import io.undertow.Undertow;
+import io.undertow.examples.UndertowExample;
+import io.undertow.predicate.PredicatesHandler;
+import io.undertow.server.handlers.builder.PredicatedHandler;
+import io.undertow.server.handlers.builder.PredicatedHandlersParser;
+import io.undertow.util.Headers;
+
+import java.util.List;
+
+@UndertowExample("Predicate Parser")
+public class PredicateParser {
+
+    /**
+     * @author Dimitris Kafetzis
+     */
+    public static void main(final String[] args) {
+
+        //The predicate parser accepts either a File, Path, InputStream or String containing the rules in order to generate the handlers and predicates.
+        //In this case a redirect is executed when the path of the request starts with bar, which is then redirected to path foo
+        List<PredicatedHandler> predicatedHandlers = PredicatedHandlersParser.parse("path-prefix('/bar') -> redirect(/foo);", io.undertow.examples.predicates.PredicateParser.class.getClassLoader());
+
+        //A predicatesHandler is required along with a handler to be called in after all other handlers are done
+        PredicatesHandler predicatesHandler = new PredicatesHandler(exchange -> {
+            exchange.getResponseHeaders().put(Headers.CONTENT_TYPE, "text/plain");
+            exchange.getResponseSender().send("Hello World from path: " + exchange.getRequestPath());
+        });
+
+        for (PredicatedHandler handler : predicatedHandlers) {
+            predicatesHandler.addPredicatedHandler(handler);
+        }
+        Undertow server = Undertow.builder()
+                .addHttpListener(8080, "localhost")
+                .setHandler(predicatesHandler)
+                .build();
+        server.start();
+    }
+}