[RandomJava-101] add a Utility class to process file

fishercoder1534 · fishercoder1534 · commit 5d53c4cbbbd8 · 2024-09-09T15:18:50.000-07:00
diff --git a/src/main/java/IO_example/ExtractFieldsFromFile.java b/src/main/java/IO_example/ExtractFieldsFromFile.java
@@ -0,0 +1,93 @@
+package IO_example;
+
+import java.io.*;
+import java.util.HashSet;
+import java.util.Scanner;
+import java.util.Set;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class ExtractFieldsFromFile {
+    private static final String BASE_FILE = "/Users/Downloads/base_file";
+    private static final String UPDATE_FILE = "/Users/Downloads/update_file";
+
+    public static void main(String... args) throws IOException {
+        System.out.println("Program started.");
+        readAllFieldNames("");
+        Set<String> baseSet = readAllFieldNames(BASE_FILE);
+        Set<String> updateFileSet = readAllFieldNames(UPDATE_FILE);
+        Set<String> baseSetCopy = new HashSet<>(baseSet);
+        baseSetCopy.removeAll(updateFileSet);
+        System.out.println("baseSetCopy size after removing updateFileSet is: " + baseSetCopy.size());
+
+        Set<String> linesOnlyExistInBaseSet = readLinesMatchingSet(BASE_FILE, baseSetCopy);
+//        linesOnlyExistInBaseSet.forEach(System.out::println);
+        System.out.println("Found a total of " + linesOnlyExistInBaseSet.size() + " matches.");
+
+        appendLinesToFile(UPDATE_FILE, linesOnlyExistInBaseSet);
+
+        System.out.println("Program finished.");
+    }
+
+    private static void appendLinesToFile(String updateFile, Set<String> linesToBeAppended) throws IOException {
+        BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(updateFile, true));
+        bufferedWriter.append("\n\n\n");
+        bufferedWriter.append("#Added below fields from base file ---------\n");
+        for (String str : linesToBeAppended) {
+            bufferedWriter.append(str);
+            bufferedWriter.append("\n");
+        }
+        bufferedWriter.close();
+    }
+
+    private static Set<String> readLinesMatchingSet(String filePath, Set<String> set) throws FileNotFoundException {
+        if (filePath.isEmpty()) {
+            System.out.println("No file to read, exit.");
+            return null;
+        }
+        Scanner scanner = new Scanner(new File(filePath));
+        scanner.useDelimiter("\n");
+        Set<String> lines = new HashSet<>();
+        int i = 0;
+        while (scanner.hasNext()) {
+            String line = scanner.next();
+            i++;
+            if (!line.isEmpty() && Character.isAlphabetic(line.charAt(0))) {
+                String[] parts = line.split("=");
+                if (set.contains(parts[0])) {
+                    lines.add(line);
+                }
+            }
+        }
+        scanner.close();
+        System.out.println("A total of " + i + " lines were gone through, and found a total of " + lines.size() + " matches.");
+        return lines;
+    }
+
+    public static Set<String> readAllFieldNames(String filePath) throws IOException {
+        if (filePath.isEmpty()) {
+            System.out.println("No file to read, exit.");
+            return null;
+        }
+        Scanner scanner = new Scanner(new File(filePath));
+        scanner.useDelimiter("\n");
+
+        assertTrue(scanner.hasNext());
+        int i = 0;
+        int nonEmptyLines = 0;
+        Set<String> fields = new HashSet<>();
+        while (scanner.hasNext()) {
+            String line = scanner.next();
+            i++;
+            if (!line.isEmpty() && Character.isAlphabetic(line.charAt(0))) {
+                String[] parts = line.split("=");
+                fields.add(parts[0]);
+                nonEmptyLines++;
+            }
+        }
+        System.out.println("For this file: " + filePath + ": A total of " + i + " lines, in which " + nonEmptyLines + " are non empty.");
+
+        scanner.close();
+        return fields;
+    }
+}
