Java append to file
last modified January 27, 2024
Java append to file tutorial shows how to append to a file in Java. We use
FileWriter, FileOutputStream, Files,
RandomAccessFile, Google Guava, and Apache Commons IO.
Appending to a file is often used in logging.
In the examples, we append text to the files.
Bratislava Moldava Košice Trenčín Prešov
We use this text file. It is located in src/main/resources directory.
Java append to file with FileWriter
FileWriter class is used for writing streams of characters.
FileWriter takes an optional second parameter: append.
If set to true, then the data will be written to the end of the file.
package com.zetcode;
import java.io.FileWriter;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
public class JavaAppendFileFileWriter {
public static void main(String[] args) throws IOException {
String fileName = "src/main/resources/towns.txt";
try (var fw = new FileWriter(fileName, StandardCharsets.UTF_8, true)) {
fw.append("Žilina\n");
}
}
}
This example appends data to a file with FileWriter.
try (var fw = new FileWriter(fileName, StandardCharsets.UTF_8, true)) {
fw.append("Žilina\n");
}
We define the FileWriter and use its append method.
Java append to file with FileOutputStream
FileOutputStream is an output stream for writing data to a
File or to a FileDescriptor. It takes an optional
second parameter, which determines whether the data is appended to the file.
package com.zetcode;
import java.io.FileOutputStream;
import java.io.IOException;
public class JavaAppendFileFileOutputStream {
public static void main(String[] args) throws IOException {
String fileName = "src/main/resources/towns.txt";
byte[] tb = "Žilina\n".getBytes();
try (var fos = new FileOutputStream(fileName, true)) {
fos.write(tb);
}
}
}
This example appends data to a file with FileOutputStream.
try (var fos = new FileOutputStream(fileName, true)) {
fos.write(tb);
}
We create an instance of the FileOutputStream with append
parameter set to true and use its write method.
Java append to file with Files
The java.nio.file.Files class is a convenient class to easily
append data to a file.
package com.zetcode;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;
public class JavaAppendFileFiles {
public static void main(String[] args) throws IOException {
String fileName = "src/main/resources/towns.txt";
String town = "Žilina\n";
Files.writeString(Paths.get(fileName), town, StandardCharsets.UTF_8,
StandardOpenOption.APPEND);
}
}
This example appends data with Files.
Files.writeString(Paths.get(fileName), town, StandardCharsets.UTF_8,
StandardOpenOption.APPEND);
The fourth parameter of Files.writeString tells how the file was
opened for writing. With the StandardOpenOption.APPEND, the file
was opened for appending.
Java append to file with RandomAccessFile
RandomAccessFile is used for reading and writing
to a random access file.
package com.zetcode;
import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
public class JavaAppendFileRandomAccessFile {
public static void main(String[] args) throws IOException {
String fileName = "src/main/resources/towns.txt";
var file = new File(fileName);
var town = "Žilina\n";
try (var raf = new RandomAccessFile(file, "rw")) {
long length = raf.length();
raf.setLength(length + 1);
raf.seek(raf.length());
raf.write(town.getBytes());
}
}
}
In this example we append data with RandomAccessFile.
long length = raf.length(); raf.setLength(length + 1); raf.seek(raf.length()); raf.write(town.getBytes());
We determine the length of the file, locate to the end of the file, and write the bytes.
Java append to file with Guava
We can use Guava library for appending to a file.
implementation 'com.google.guava:guava:31.1-jre'
We need a Guava dependency.
package com.zetcode;
import com.google.common.base.Charsets;
import com.google.common.io.CharSink;
import com.google.common.io.FileWriteMode;
import com.google.common.io.Files;
import java.io.File;
import java.io.IOException;
public class JavaAppendFileGuava {
public static void main(String[] args) throws IOException {
String fileName = "src/main/resources/towns.txt";
File file = new File(fileName);
CharSink chs = Files.asCharSink(file, Charsets.UTF_8, FileWriteMode.APPEND);
chs.write("Žilina\n");
}
}
In the example, we append to a file with with Guava's CharSink class.
CharSink chs = Files.asCharSink(file, Charsets.UTF_8, FileWriteMode.APPEND);
The third parameter of Files.asCharSink specifies the file writing
mode; with FileWriteMode.APPEND option the file is opened for writing.
Java append to file with Apache Commons IO
In the final example, we use Apache Commons IO to append to a file.
implementation 'commons-io:commons-io:2.11.0'
We need this dependency.
package com.zetcode;
import java.io.File;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import org.apache.commons.io.FileUtils;
public class JavaAppendFileApacheCommons {
public static void main(String[] args) throws IOException {
String fileName = "src/main/resources/towns.txt";
File file = new File(fileName);
FileUtils.writeStringToFile(file, "Žilina\n", StandardCharsets.UTF_8, true);
}
}
We append to the file with the FileUtils.writeStringToFile method.
The last append parameter determines whether to append to a file.
Source
In this article we have shown how to append to a file in Java with built-in tools and third-party libraries.
Author
List all Java tutorials.
