Dirty Flag pattern #560

dirty-flag/src/main/java/com/iluwatar/dirtyflag/DataFetcher.java

@@ -0,0 +1,71 @@
+package com.iluwatar.dirtyflag;
+
+import java.io.BufferedReader;
+import java.io.File;
+import java.io.FileReader;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * A mock database manager -- Fetches data from a raw file.
+ * 
+ * @author swaisuan
+ *
+ */
+public class DataFetcher {
+
+  private static DataFetcher df;
+  private final String filename = "world.txt";
+  private long lastFetched = -1;
+
+  private DataFetcher() {
+  }
+
+  /**
+   * Init.
+   * 
+   * @return DataFetcher instance
+   */
+  public static DataFetcher getInstance() {
+    if (df == null) {
+      df = new DataFetcher();
+    }
+    return df;
+  }
+
+  private boolean isDirty(long fileLastModified) {
+    if (lastFetched != fileLastModified) {
+      lastFetched = fileLastModified;
+      return true;
+    }
+    return false;
+  }
+
+  /**
+   * Fetches data/content from raw file.
+   * 
+   * @return List of strings
+   */
+  public List<String> fetch() {
+    ClassLoader classLoader = getClass().getClassLoader();
+    File file = new File(classLoader.getResource(filename).getFile());
+
+    if (isDirty(file.lastModified())) {
+      System.out.println(filename + " is dirty! Re-fetching file content...");
+
+      List<String> data = new ArrayList<String>();
+      try (BufferedReader br = new BufferedReader(new FileReader(file))) {
+        String line;
+        while ((line = br.readLine()) != null) {
+          data.add(line);
+        }
+      } catch (IOException e) {
+        e.printStackTrace();
+      }
+      return data;
+    }
+
+    return null;
+  }
+}