Road to a more functional Java with vavr.io - example refactoring

src/main/java/com/softwaremill/java_fp_example/contest/hexmind/ExtractionOptions.java

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+package com.softwaremill.java_fp_example.contest.hexmind;
+
+import lombok.Builder;
+import lombok.Getter;
+import lombok.NonNull;
+
+/**
+ * The Open Graph protocol enables any web page to become a rich object in a social graph. For instance, this is used on
+ * Facebook to allow any web page to have the same functionality as any other object on Facebook.
+ *
+ * @link http://ogp.me
+ */
+@Getter
+@Builder
+public class ExtractionOptions {
+
+    @NonNull
+    private final String pageUrl;
+
+    @NonNull
+    private final Integer timeoutMs;
+
+    @NonNull
+    private final String metaProperty;
+
+    @NonNull
+    private final String fallbackContent;
+
+}

src/main/java/com/softwaremill/java_fp_example/contest/hexmind/FacebookImage.java

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+package com.softwaremill.java_fp_example.contest.hexmind;
+
+import com.softwaremill.java_fp_example.DefaultImage;
+
+public class FacebookImage {
+
+    private static final int TIMEOUT_MS = 10_000;
+    private static final String META_PROPERTY = "og:image";
+
+    private final OpenGraphPage page;
+
+    public FacebookImage(ExtractionOptions options) {
+        this.page = new OpenGraphPage(options);
+    }
+
+    public static FacebookImage fromPage(String pageUrl) {
+        return new FacebookImage(setupForPage(pageUrl));
+    }
+
+    public String extractUrl() {
+        return page.extractMetaContent();
+    }
+
+    private static ExtractionOptions setupForPage(String pageUrl) {
+        return ExtractionOptions.builder()
+            .pageUrl(pageUrl)
+            .timeoutMs(TIMEOUT_MS)
+            .metaProperty(META_PROPERTY)
+            .fallbackContent(DefaultImage.DEFAULT_IMAGE)
+            .build();
+    }
+
+}

src/main/java/com/softwaremill/java_fp_example/contest/hexmind/LICENSE

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+MIT License
+
+Copyright (c) 2017 Hexmind
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

src/main/java/com/softwaremill/java_fp_example/contest/hexmind/OpenGraphExtractor.java

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+package com.softwaremill.java_fp_example.contest.hexmind;
+
+import java.io.IOException;
+import java.net.URL;
+
+import org.jsoup.Jsoup;
+import org.jsoup.nodes.Document;
+import org.jsoup.nodes.Element;
+import org.jsoup.select.Elements;
+
+import javaslang.collection.List;
+import javaslang.control.Try;
+
+public class OpenGraphExtractor {
+
+    private final ExtractionOptions options;
+
+    public OpenGraphExtractor(ExtractionOptions options) {
+        this.options = options;
+    }
+
+    public Try<String> extractContent() {
+        return Try.of(this::loadWebPage)
+            .map(this::getMetaElements)
+            .flatMap(this::findContent);
+    }
+
+    private Document loadWebPage() throws IOException {
+        URL url = new URL(options.getPageUrl());
+        return Jsoup.parse(url, options.getTimeoutMs());
+    }
+
+    private Elements getMetaElements(Document document) {
+        return document.head().getElementsByTag("meta");
+    }
+
+    private Try<String> findContent(Elements elements) {
+        return List.ofAll(elements)
+            .filter(this::hasMetaProperty)
+            .map(element -> element.attr("content"))
+            .toTry();
+    }
+
+    private boolean hasMetaProperty(Element element) {
+        return options.getMetaProperty().equals(element.attr("property"));
+    }
+}

src/main/java/com/softwaremill/java_fp_example/contest/hexmind/OpenGraphPage.java

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+package com.softwaremill.java_fp_example.contest.hexmind;
+
+import java.net.MalformedURLException;
+import java.net.UnknownHostException;
+
+import lombok.extern.slf4j.Slf4j;
+
+@Slf4j
+public class OpenGraphPage {
+
+    private final ExtractionOptions options;
+
+    public OpenGraphPage(ExtractionOptions options) {
+        this.options = options;
+    }
+
+    public String extractMetaContent() {
+        return new OpenGraphExtractor(options)
+            .extractContent()
+            .onFailure(this::onFailure)
+            .getOrElse(options::getFallbackContent);
+    }
+
+    private void onFailure(Throwable error) {
+        if (error instanceof MalformedURLException) {
+            log.error("Invalid URL {}. Problem: {}", options.getPageUrl(), error.getMessage());
+        } else if (error instanceof UnknownHostException) {
+            log.error("Unable to extract content from URL {}. Problem: {}", options.getPageUrl(), error.getMessage());
+        } else {
+            log.warn("No {} found for page {}", options.getMetaProperty(), options.getPageUrl());
+        }
+    }
+
+}

src/main/java/com/softwaremill/java_fp_example/contest/hexmind/README.md

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+# Road to a more functional Java
+## Example refactoring
+
+### Prologue
+
+> The Open Graph protocol enables any web page to become a rich object in a social graph.
+> og:image - An image URL which should represent your object within the graph.
+> 
+> http://ogp.me/
+
+
+## Who is who?
+
+### [FacebookImage](FacebookImage.java)
+
+client-specific *OpenGraphPage* image
+
+```
+String img = FacebookImage.fromPage(postUrl).extractUrl()
+```
+
+### [OpenGraphPage](OpenGraphPage.java) 
+
+non-functional OG node: errors handling and *OpenGraphExtractor* as internal implementation
+
+```
+public String extractMetaContent() {
+    return new OpenGraphExtractor(options)
+        .extractContent()
+        .onFailure(this::onFailure)
+        .getOrElse(options::getFallbackContent);
+}
+```
+
+### [OpenGraphExtractor](OpenGraphExtractor.java) 
+
+functional OG node metadata: extraction without side effects
+
+```
+Try<String> extractContent() {
+    return Try.of(this::loadWebPage)
+        .map(this::getMetaElements)
+        .flatMap(this::findContent);
+}
+```

src/test/groovy/com/softwaremill/java_fp_example/contest/hexmind/FacebookImageSpec.groovy

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+package com.softwaremill.java_fp_example.contest.hexmind
+
+import spock.lang.Specification
+import spock.lang.Unroll
+
+import static com.softwaremill.java_fp_example.DefaultImage.DEFAULT_IMAGE
+
+@Unroll
+class FacebookImageSpec extends Specification {
+
+    def "should test Hexmind version with address #postAddress"() {
+        when:
+        FacebookImage facebookImage = FacebookImage.fromPage(postAddress)
+
+        then:
+        facebookImage.extractUrl() == expectedImageUrl
+
+        where:
+        postAddress                                                || expectedImageUrl
+        "https://softwaremill.com/the-wrong-abstraction-recap/"    || "https://softwaremill.com/images/uploads/2017/02/street-shoe-chewing-gum.0526d557.jpg"
+        "https://softwaremill.com/using-kafka-as-a-message-queue/" || "https://softwaremill.com/images/uploads/2017/02/kmq.93f842cf.png"
+        "https://twitter.com/softwaremill"                         || DEFAULT_IMAGE
+        "http://i-do-not-exist.pl"                                 || DEFAULT_IMAGE
+        "i-am-not-a-url"                                           || DEFAULT_IMAGE
+    }
+
+}