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Merge pull request #6571 from anuraggoyal1/master 

[BAEL-1951] Guide to FileChannel
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ashleyfrieze 2019-04-17 22:12:55 +01:00 committed by GitHub
parent 53d4e269f3 fece0dc4b8
commit d37e7e3d8f
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core-java-io/src/test/java/com/baeldung/filechannel/FileChannelUnitTest.java Normal file
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package com.baeldung.filechannel;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertNotNull;
import java.io.ByteArrayOutputStream;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.FileLock;
import java.nio.charset.StandardCharsets;
import org.junit.Test;
public class FileChannelUnitTest {
@Test
public void givenFile_whenReadWithFileChannelUsingRandomAccessFile_thenCorrect() throws IOException {
try (RandomAccessFile reader = new RandomAccessFile("src/test/resources/test_read.in", "r");
FileChannel channel = reader.getChannel();
ByteArrayOutputStream out = new ByteArrayOutputStream();) {
int bufferSize = 1024;
if (bufferSize > channel.size()) {
bufferSize = (int) channel.size();
}
ByteBuffer buff = ByteBuffer.allocate(bufferSize);
while (channel.read(buff) > 0) {
out.write(buff.array(), 0, buff.position());
buff.clear();
}
String fileContent = new String(out.toByteArray(), StandardCharsets.UTF_8);
assertEquals("Hello world", fileContent);
}
}
@Test
public void givenFile_whenReadWithFileChannelUsingFileInputStream_thenCorrect() throws IOException {
try (ByteArrayOutputStream out = new ByteArrayOutputStream();
FileInputStream fin = new FileInputStream("src/test/resources/test_read.in");
FileChannel channel = fin.getChannel();) {
int bufferSize = 1024;
if (bufferSize > channel.size()) {
bufferSize = (int) channel.size();
}
ByteBuffer buff = ByteBuffer.allocate(bufferSize);
while (channel.read(buff) > 0) {
out.write(buff.array(), 0, buff.position());
buff.clear();
}
String fileContent = new String(out.toByteArray(), StandardCharsets.UTF_8);
assertEquals("Hello world", fileContent);
}
}
@Test
public void givenFile_whenReadAFileSectionIntoMemoryWithFileChannel_thenCorrect() throws IOException {
try (RandomAccessFile reader = new RandomAccessFile("src/test/resources/test_read.in", "r");
FileChannel channel = reader.getChannel();
ByteArrayOutputStream out = new ByteArrayOutputStream();) {
MappedByteBuffer buff = channel.map(FileChannel.MapMode.READ_ONLY, 6, 5);
if (buff.hasRemaining()) {
byte[] data = new byte[buff.remaining()];
buff.get(data);
assertEquals("world", new String(data, StandardCharsets.UTF_8));
}
}
}
@Test
public void whenWriteWithFileChannelUsingRandomAccessFile_thenCorrect() throws IOException {
String file = "src/test/resources/test_write_using_filechannel.txt";
try (RandomAccessFile writer = new RandomAccessFile(file, "rw");
FileChannel channel = writer.getChannel();) {
ByteBuffer buff = ByteBuffer.wrap("Hello world".getBytes(StandardCharsets.UTF_8));
channel.write(buff);
// now we verify whether the file was written correctly
RandomAccessFile reader = new RandomAccessFile(file, "r");
assertEquals("Hello world", reader.readLine());
reader.close();
}
}
@Test
public void givenFile_whenWriteAFileUsingLockAFileSectionWithFileChannel_thenCorrect() throws IOException {
try (RandomAccessFile reader = new RandomAccessFile("src/test/resources/test_read.in", "rw");
FileChannel channel = reader.getChannel();
FileLock fileLock = channel.tryLock(6, 5, Boolean.FALSE);) {
assertNotNull(fileLock);
}
}
@Test
public void givenFile_whenReadWithFileChannelGetPosition_thenCorrect() throws IOException {
try (ByteArrayOutputStream out = new ByteArrayOutputStream();
RandomAccessFile reader = new RandomAccessFile("src/test/resources/test_read.in", "r");
FileChannel channel = reader.getChannel();) {
int bufferSize = 1024;
if (bufferSize > channel.size()) {
bufferSize = (int) channel.size();
}
ByteBuffer buff = ByteBuffer.allocate(bufferSize);
while (channel.read(buff) > 0) {
out.write(buff.array(), 0, buff.position());
buff.clear();
}
// the original file is 11 bytes long, so that's where the position pointer should be
assertEquals(11, channel.position());
channel.position(4);
assertEquals(4, channel.position());
}
}
@Test
public void whenGetFileSize_thenCorrect() throws IOException {
try (RandomAccessFile reader = new RandomAccessFile("src/test/resources/test_read.in", "r");
FileChannel channel = reader.getChannel();) {
// the original file is 11 bytes long, so that's where the position pointer should be
assertEquals(11, channel.size());
}
}
@Test
public void whenTruncateFile_thenCorrect() throws IOException {
String input = "this is a test input";
FileOutputStream fout = new FileOutputStream("src/test/resources/test_truncate.txt");
FileChannel channel = fout.getChannel();
ByteBuffer buff = ByteBuffer.wrap(input.getBytes());
channel.write(buff);
buff.flip();
channel = channel.truncate(5);
assertEquals(5, channel.size());
fout.close();
channel.close();
}
}

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core-java-io/src/test/resources/test_truncate.txt Normal file
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this

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core-java-io/src/test/resources/test_write_using_filechannel.txt Normal file
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Hello world