java-file-class demo code

core-java-modules/core-java-io-2/src/test/java/com/baeldung/file/FileClassDemoUnitTest.java

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+package com.baeldung.file;
+
+import org.junit.Test;
+
+import java.io.*;
+import java.util.Arrays;
+import java.util.List;
+
+import static org.junit.Assert.*;
+
+public class FileClassDemoUnitTest {
+
+    @Test
+    public void givenDirectoryCreated_whenMkdirIsInvoked_thenDirectoryIsDeleted() {
+        File directory = new File("testDirectory");
+        if (!directory.isDirectory() || !directory.exists()) {
+            directory.mkdir();
+        }
+
+        assertTrue(directory.delete());
+    }
+
+    @Test
+    public void givenFileCreated_whenCreateNewFileIsInvoked_thenFileIsDeleted() throws IOException {
+        File file = new File("testFile.txt");
+        if (!file.isFile() || !file.exists()) {
+            file.createNewFile();
+        }
+
+        assertTrue(file.delete());
+    }
+
+
+    @Test
+    public void givenFileCreated_whenCreateNewFileInvoked_thenMetadataIsAsExpected() throws IOException {
+
+        // different Operating systems have different separator characters
+        String separatorCharacter = System.getProperty("file.separator");
+
+        File parentDirectory = makeDirectory("filesDirectory");
+
+        File childFile = new File(parentDirectory, "file1.txt");
+        childFile.createNewFile();
+
+        assertTrue(childFile.getName().equals("file1.txt"));
+        assertTrue(childFile.getParentFile().getName().equals(parentDirectory.getName()));
+        assertTrue(childFile.getPath().equals(parentDirectory.getPath() + separatorCharacter + "file1.txt"));
+
+        removeDirectory(parentDirectory);
+    }
+
+
+    @Test(expected = FileNotFoundException.class)
+    public void givenReadOnlyFileCreated_whenCreateNewFileInvoked_thenFileCannotBeWrittenTo() throws IOException {
+        File parentDirectory = makeDirectory("filesDirectory");
+
+        File childFile = new File(parentDirectory, "file1.txt");
+        childFile.createNewFile();
+
+        childFile.setWritable(false);
+
+        FileOutputStream fos = new FileOutputStream(childFile);
+        fos.write("Hello World".getBytes()); // write operation
+        fos.flush();
+        fos.close();
+
+        removeDirectory(parentDirectory);
+    }
+
+    @Test(expected = FileNotFoundException.class)
+    public void givenWriteOnlyFileCreated_whenCreateNewFileInvoked_thenFileCannotBeReadFrom() throws IOException {
+        File parentDirectory = makeDirectory("filesDirectory");
+
+        File childFile = new File(parentDirectory, "file1.txt");
+        childFile.createNewFile();
+
+        childFile.setReadable(false);
+
+        FileInputStream fis = new FileInputStream(childFile);
+        fis.read(); // read operation
+        fis.close();
+
+        removeDirectory(parentDirectory);
+    }
+
+    @Test
+    public void givenFilesCreatedInDirectory_whenCreateNewFileInvoked_thenTheyCanBeListedAsExpected() throws IOException {
+        File directory = makeDirectory("filtersDirectory");
+
+        File csvFile = new File(directory, "csvFile.csv");
+        csvFile.createNewFile();
+
+        File txtFile = new File(directory, "txtFile.txt");
+        txtFile.createNewFile();
+
+        //normal listing
+        assertEquals(2, directory.list().length);
+
+        //filtered listing
+        FilenameFilter csvFilter = (dir, ext) -> ext.endsWith(".csv");
+        assertEquals(1, directory.list(csvFilter).length);
+
+        removeDirectory(directory);
+    }
+
+    @Test
+    public void givenDirectoryIsCreated_whenMkdirInvoked_thenDirectoryCanBeRenamed() {
+
+        File source = makeDirectory("source");
+        File destination = makeDirectory("destination");
+        source.renameTo(destination);
+
+        assertFalse(source.isDirectory());
+        assertTrue(destination.isDirectory());
+
+        removeDirectory(destination);
+    }
+
+    @Test
+    public void givenDataIsWrittenToFile_whenWriteIsInvoked_thenFreeSpaceOnSystemDecreases() throws IOException {
+
+        String name = System.getProperty("user.home") + System.getProperty("file.separator") + "test";
+        File testDir = makeDirectory(name);
+        File sample = new File(testDir, "sample.txt");
+
+        long freeSpaceBeforeWrite = testDir.getFreeSpace();
+        writeSampleDataToFile(sample);
+
+        long freeSpaceAfterWrite = testDir.getFreeSpace();
+        assertTrue(freeSpaceAfterWrite < freeSpaceBeforeWrite);
+
+        removeDirectory(testDir);
+    }
+
+    private static File makeDirectory(String directoryName) {
+        File directory = new File(directoryName);
+        directory.mkdir();
+        if (directory.isDirectory()) {
+            return directory;
+        }
+        throw new RuntimeException("Directory not created for " + directoryName);
+    }
+
+    private static void removeDirectory(File directory) {
+        // make sure you don't delete your home directory here
+        if (directory.getPath().equals(System.getProperty("user.home"))) {
+            return;
+        }
+
+        // remove directory and its files from system
+        if (directory != null && directory.exists()) {
+            // delete all files inside the directory
+            File[] filesInDirectory = directory.listFiles();
+            if (filesInDirectory != null) {
+                List<File> files = Arrays.asList(filesInDirectory);
+                files.forEach(f -> deleteFile(f));
+            }
+
+            // finally delete the directory itself
+            deleteFile(directory);
+        }
+    }
+
+    private static void deleteFile(File fileToDelete) {
+        if (fileToDelete != null && fileToDelete.exists()) {
+            fileToDelete.delete();
+        }
+    }
+
+    private static void writeSampleDataToFile(File sample) throws IOException {
+        //write sample text to file
+        try (FileOutputStream out = new FileOutputStream(sample)) {
+            for (int i = 1; i <= 100000; i++) {
+                String sampleText = "Sample line number " + i + "\n";
+                out.write(sampleText.getBytes());
+            }
+        }
+    }
+}