basic saving command

.gitignore

@@ -4,6 +4,8 @@ target/
 !**/src/test/**/target/
 .kotlin
 
+*.output.json
+
 ### IntelliJ IDEA ###
 .idea/
 

pom.xml

@@ -18,5 +18,11 @@
             <artifactId>jsoup</artifactId>
             <version>1.22.2</version>
         </dependency>
+        <dependency>
+            <groupId>com.google.code.gson</groupId>
+            <artifactId>gson</artifactId>
+            <version>2.14.0</version>
+            <scope>compile</scope>
+        </dependency>
     </dependencies>
 </project>

src/main/java/internal/hw/crawler/Main.java

@@ -1,9 +1,6 @@
 package internal.hw.crawler;
 
-import internal.hw.crawler.commands.CrawlCommand;
+import internal.hw.crawler.commands.*;
-import internal.hw.crawler.commands.ExitCommand;
-import internal.hw.crawler.commands.HelpCommand;
-import internal.hw.crawler.commands.ListCommand;
 import internal.hw.crawler.repositories.ArticleRepository;
 import internal.hw.crawler.views.ConsoleView;
 
@@ -16,6 +13,7 @@ public class Main {
         controller.registerCommand(new ExitCommand());
         controller.registerCommand(new CrawlCommand(repository, view));
         controller.registerCommand(new ListCommand(repository, view));
+        controller.registerCommand(new SaveCommand(repository, view));
         controller.registerCommand(new HelpCommand(controller.getCommands(), view));
 
         view.printSuccess("Welcome to crawler. Type `help` for a list of available commands.");

src/main/java/internal/hw/crawler/commands/SaveCommand.java

@@ -0,0 +1,61 @@
+package internal.hw.crawler.commands;
+
+import com.google.gson.Gson;
+import internal.hw.crawler.models.Article;
+import internal.hw.crawler.repositories.ArticleRepository;
+import internal.hw.crawler.views.CommandOutput;
+
+import java.io.*;
+import java.util.*;
+import java.util.stream.Collectors;
+
+public class SaveCommand implements Command {
+    Gson gson = new Gson();
+    private final ArticleRepository articleRepository;
+    private final CommandOutput out;
+
+    public SaveCommand(ArticleRepository articleRepository, CommandOutput out) {
+        this.articleRepository = articleRepository;
+        this.out = out;
+    }
+
+    @Override
+    public String getName() {
+        return "save";
+    }
+
+    @Override
+    public void execute(String[] args) {
+        String filename = "articles.output.json";
+
+        List<Article> articles = getExistingArticles(filename);
+        Map<String, Article> articleMap = articles.stream().collect(Collectors.toMap(this::articleMapId, it -> it));
+
+        // Update existing articles with new articles
+        for (Article article : articleRepository.getAll()) {
+            articleMap.put(articleMapId(article), article);
+        }
+
+        Article[] articlesToSave = articleMap.values().toArray(new Article[0]);
+
+        try (BufferedWriter writer = new BufferedWriter(new FileWriter(filename));) {
+            writer.write(gson.toJson(articlesToSave));
+            out.success(String.format("Wrote %d articles to %s", articlesToSave.length, filename));
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    private String articleMapId(Article article) {
+        return String.format("%s-%s", article.getSource(), article.getId());
+    }
+
+    private List<Article> getExistingArticles(String filename) {
+        try (BufferedReader reader = new BufferedReader(new FileReader(filename))) {
+            Article[] articles = gson.fromJson(reader, Article[].class);
+            return Arrays.asList(articles);
+        } catch (IOException e) {
+            return List.of();
+        }
+    }
+}

src/main/java/internal/hw/crawler/models/Article.java

@@ -5,6 +5,7 @@ import java.util.Set;
 
 public class Article {
     private String id;
+    private String source;
     private URL url;
     private String title;
     private Set<String> authors;
@@ -18,6 +19,14 @@ public class Article {
         this.id = id;
     }
 
+    public String getSource() {
+        return source;
+    }
+
+    public void setSource(String source) {
+        this.source = source;
+    }
+
     public URL getUrl() {
         return url;
     }

src/main/java/internal/hw/crawler/strategies/crawl/IthomeCrawlStrategy.java

@@ -39,6 +39,7 @@ public class IthomeCrawlStrategy implements CrawlStrategy {
 
         Article article = new Article();
         article.setId(id);
+        article.setSource("ithome");
         article.setUrl(url);
         article.setTitle(title);
         article.setAuthors(authors);