Merge pull request eugenp#6158 from RajeshBhojwani/master

BAEL-2525 - Clear a text file without deleting in Java

Author: eric-martin

core-java-io/src/test/java/com/baeldung/file/FilesClearDataUnitTest.java

@@ -0,0 +1,96 @@
+package com.baeldung.file;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.io.BufferedWriter;
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.FileWriter;
+import java.io.IOException;
+import java.io.PrintWriter;
+import java.nio.channels.FileChannel;
+import java.nio.charset.Charset;
+import java.nio.file.Files;
+import java.nio.file.Paths;
+import java.nio.file.StandardOpenOption;
+
+import org.apache.commons.io.FileUtils;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+import com.baeldung.util.StreamUtils;
+
+public class FilesClearDataUnitTest {
+	
+    public static final String FILE_PATH = "src/test/resources/fileexample.txt";
+
+    @Before
+    @After
+    public void setup() throws IOException {
+        PrintWriter writer = new PrintWriter(FILE_PATH);
+        writer.print("This example shows how we can delete the file contents without deleting the file");
+        writer.close();
+    }
+    
+    @Test
+    public void givenExistingFile_whenDeleteContentUsingPrintWritter_thenEmptyFile() throws IOException {
+        PrintWriter writer = new PrintWriter(FILE_PATH);
+        writer.print("");
+        writer.close();
+        assertEquals(0, StreamUtils.getStringFromInputStream(new FileInputStream(FILE_PATH)).length());
+    }    
+
+    @Test
+    public void givenExistingFile_whenDeleteContentUsingPrintWritterWithougObject_thenEmptyFile() throws IOException {
+        new PrintWriter(FILE_PATH).close();
+        assertEquals(0, StreamUtils.getStringFromInputStream(new FileInputStream(FILE_PATH)).length());
+    }    
+       
+    @Test
+    public void givenExistingFile_whenDeleteContentUsingFileWriter_thenEmptyFile() throws IOException {
+        new FileWriter(FILE_PATH, false).close();
+ 
+        assertEquals(0, StreamUtils.getStringFromInputStream(new FileInputStream(FILE_PATH)).length());
+    }
+    
+    @Test
+    public void givenExistingFile_whenDeleteContentUsingFileOutputStream_thenEmptyFile() throws IOException {
+        new FileOutputStream(FILE_PATH).close();
+
+        assertEquals(0, StreamUtils.getStringFromInputStream(new FileInputStream(FILE_PATH)).length());
+    }    
+
+    @Test
+    public void givenExistingFile_whenDeleteContentUsingFileUtils_thenEmptyFile() throws IOException {
+        FileUtils.write(new File(FILE_PATH), "", Charset.defaultCharset());
+
+        assertEquals(0, StreamUtils.getStringFromInputStream(new FileInputStream(FILE_PATH)).length());
+    }    
+
+    @Test
+    public void givenExistingFile_whenDeleteContentUsingNIOFiles_thenEmptyFile() throws IOException {
+        BufferedWriter writer = Files.newBufferedWriter(Paths.get(FILE_PATH));
+        writer.write("");
+        writer.flush();
+ 
+        assertEquals(0, StreamUtils.getStringFromInputStream(new FileInputStream(FILE_PATH)).length());
+    }    
+    
+    @Test
+    public void givenExistingFile_whenDeleteContentUsingNIOFileChannel_thenEmptyFile() throws IOException {
+        FileChannel.open(Paths.get(FILE_PATH), StandardOpenOption.WRITE).truncate(0).close();
+ 
+        assertEquals(0, StreamUtils.getStringFromInputStream(new FileInputStream(FILE_PATH)).length());
+    }   
+    
+    @Test
+    public void givenExistingFile_whenDeleteContentUsingGuava_thenEmptyFile() throws IOException {
+        File file = new File(FILE_PATH);
+        byte[] empty = new byte[0];
+        com.google.common.io.Files.write(empty, file);
+        
+        assertEquals(0, StreamUtils.getStringFromInputStream(new FileInputStream(FILE_PATH)).length());
+    }    
+}

core-java-io/src/test/resources/fileexample.txt

@@ -0,0 +1 @@
+This example shows how we can delete the file contents without deleting the file