BAEL-9454 How to Reset Inputstream and Read File Again

core-java-modules/core-java-io-8/src/test/java/com/baeldung/resetinputstream/ResetInputStreamUnitTests.java

@@ -0,0 +1,116 @@
+package com.baeldung.resetinputstream;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.io.BufferedInputStream;
+import java.io.ByteArrayInputStream;
+import java.io.FileInputStream;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.io.RandomAccessFile;
+
+import org.junit.jupiter.api.Test;
+
+public class ResetInputStreamUnitTests {
+
+    final int readLimit = 500;
+    final String fileName = "src/test/resources/InputStreamData.txt";
+
+    @Test
+    void givenByteArrayInputStream_whenMarkSupported_thenTrue() {
+        byte[] buffer = { 1, 2, 3, 4, 5 };
+        ByteArrayInputStream bis = new ByteArrayInputStream(buffer);
+        boolean isMarkSupported = bis.markSupported();
+        assertEquals(isMarkSupported, true);
+    }
+
+    @Test
+    void givenByteArrayInputStream_whenMarkAndReset_thenReadMarkedPosition() {
+        final int EXPECTED_NUMBER = 3;
+        byte[] buffer = { 1, 2, 3, 4, 5 };
+        ByteArrayInputStream bis = new ByteArrayInputStream(buffer);
+        int number = bis.read();    //get 1
+        number = bis.read();        //get 2
+        bis.mark(readLimit);
+        number = bis.read();        //get 3
+        number = bis.read();        //get 4
+
+        bis.reset();
+
+        number = bis.read();        //should get 3
+        assertEquals(number, EXPECTED_NUMBER);
+    }
+
+    @Test
+    void givenFileInputStream_whenReset_thenIOException() {
+        assertThrows(IOException.class, () -> {
+            FileInputStream fis = new FileInputStream(fileName);
+            fis.read();
+            fis.mark(readLimit);
+            fis.read();
+            fis.reset();
+        });
+    }
+
+    @Test
+    void givenBufferedInputStream_whenMarkSupported_thenTrue() throws IOException {
+        BufferedInputStream bis = new BufferedInputStream(new FileInputStream(fileName));
+        boolean isMarkSupported = bis.markSupported();
+        assertEquals(isMarkSupported, true);
+    }
+
+    @Test
+    void givenBufferedInputStream_whenMarkAndReset_thenReadMarkedPosition() throws IOException {
+        final char EXPECTED_CHAR = 'w';
+        FileInputStream fis = new FileInputStream(fileName);
+        //content:
+        //All work and no play makes Jack a dull boy
+
+        BufferedInputStream bis = new BufferedInputStream(fis);
+        bis.read();    // A
+        bis.read();    // l
+        bis.read();    // l
+        bis.read();    // space
+        bis.mark(readLimit); // at w
+        bis.read();
+        bis.read();
+
+        bis.reset();
+
+        char test = (char) bis.read();
+        assertEquals(test, EXPECTED_CHAR);
+    }
+
+    @Test
+    void givenFileInputStream_whenMarkSupported_thenFalse() throws FileNotFoundException {
+        FileInputStream fis = new FileInputStream(fileName);
+        boolean isMarkSupported = fis.markSupported();
+        assertEquals(isMarkSupported, false);
+    }
+
+    @Test
+    void givenRandomAccessFile_whenSeek_thenMoveToIndicatedPosition() throws IOException {
+        final char EXPECTED_CHAR = 'w';
+        RandomAccessFile raf = new RandomAccessFile(fileName, "r");
+        //content:
+        //All work and no play makes Jack a dull boy
+
+        raf.read();  // A
+        raf.read();  // l
+        raf.read();  // l
+        raf.read();  // space
+
+        long filePointer = raf.getFilePointer(); //at w
+
+        raf.read();
+        raf.read();
+        raf.read();
+        raf.read();
+
+        raf.seek(filePointer);
+
+        int test = raf.read();
+        assertEquals(test, EXPECTED_CHAR);
+    }
+}

core-java-modules/core-java-io-8/src/test/resources/InputStreamData.txt

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+All work and no play makes Jack a dull boy