Java FileWriter Tutorial with Examples
1. FileWriter
No ADS
FileWriter is a subclass of OutputStreamWriter, used to write text files.
FileWriter has no other methods but the ones inherited from OutputStreamWriter. You can actually use OutputStreamWriter to write characters to any target. However, FileWriter is specifically designed to write characters to the system file.
FileWriter constructors
FileWriter(File file)
FileWriter(FileDescriptor fd)
FileWriter(File file, boolean append)
FileWriter(File file, Charset charset)
FileWriter(File file, Charset charset, boolean append)
FileWriter(String fileName)
FileWriter(String fileName, boolean append)
FileWriter(String fileName, Charset charset)
FileWriter(String fileName, Charset charset, boolean append)
Note: Constructors with the Charset parameter have been added to FileWriter since Java 11. Therefore, if you are using previous Java version and want to write a file with specified encoding, use the OutputStreamWriter class for replacement.
2. Examples
No ADS
FileWriterEx1.java
package org.o7planning.filewriter.ex;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
public class FileWriterEx1 {
public static void main(String[] args) throws IOException {
// Windows: C:/SomeFolder/out-file.txt
File outFile = new File("/Volumes/Data/test/out-file.txt");
outFile.getParentFile().mkdirs();
FileWriter fileWriter = new FileWriter(outFile);
System.out.println("Writer file: " + outFile.getAbsolutePath());
System.out.println("With encoding: " + fileWriter.getEncoding());
fileWriter.write("Line 1");
fileWriter.write("\n");
fileWriter.write("Line 2");
fileWriter.write("\n");
fileWriter.write("Line 3");
fileWriter.close();
}
}
Output:
out-file.txt
Line 1
Line 2
Line 3
FileWriter also allows you to append data to an existing file, if the file does not exist it will be created.
FileWriterEx2.java
package org.o7planning.filewriter.ex;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
public class FileWriterEx2 {
public static void main(String[] args) throws IOException {
// Windows: C:/SomeFolder/out-file.txt
File outFile = new File("/Volumes/Data/test/out-file.txt");
outFile.getParentFile().mkdirs();
// FileWriter(File outFile, boolean append)
FileWriter fileWriter = new FileWriter(outFile, true);
System.out.println("Writer file: " + outFile.getAbsolutePath());
System.out.println("With encoding: " + fileWriter.getEncoding());
fileWriter.write("Line 4");
fileWriter.write("\n");
fileWriter.append("Line 5").append("\n");
fileWriter.close();
}
}
For example, use FileWriter to write a file with UTF-16 encoding, then read the file with FileInputStream to view the bytes on the file.
FileWriter_UTF16_Ex1.java
package org.o7planning.filewriter.ex;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
public class FileWriter_UTF16_Ex1 {
// Windows: C:/SomeFolder/out-utf16-file.txt
private static final String filePath = "/Volumes/Data/test/out-utf16-file.txt";
public static void main(String[] args) throws IOException {
System.out.println("--- Write UTF-16 File ---");
write_UTF16_File();
System.out.println("--- Read File as Binary Stream ---");
readAsInputStream();
}
private static void write_UTF16_File() throws IOException {
File outFile = new File(filePath);
outFile.getParentFile().mkdirs();
// FileWriter(File outFile, boolean append)
FileWriter fileWriter = new FileWriter(outFile, StandardCharsets.UTF_16);
fileWriter.write("JP日本-八洲");
fileWriter.close();
}
private static void readAsInputStream() throws IOException {
File file = new File(filePath);
FileInputStream fis = new FileInputStream(file);
int byteCode;
while ((byteCode = fis.read()) != -1) {
System.out.println((char) byteCode + " " + byteCode);
}
fis.close();
}
}
Output:
--- Write UTF-16 File ---
--- Read File as Binary Stream ---
þ 254
ÿ 255
0
J 74
0
P 80
e 101
å 229
g 103
, 44
0
- 45
Q 81
k 107
m 109
2 50
Below is an illustration of the bytes on the FileWriter and the bytes in the file just written by FileWriter:
The first two bytes (254,255) in the UTF-16 file are used to mark that it starts an UTF-16 encoded data.
Check out my articles about InputStreamReader and OutputStreamWriter to learn more details about how Java reads and writes UTF-16 and UTF-8 encodings.
No ADS
Java IO Tutorials
- Java CharArrayWriter Tutorial with Examples
- Java FilterReader Tutorial with Examples
- Java FilterWriter Tutorial with Examples
- Java PrintStream Tutorial with Examples
- Java BufferedReader Tutorial with Examples
- Java BufferedWriter Tutorial with Examples
- Java StringReader Tutorial with Examples
- Java StringWriter Tutorial with Examples
- Java PipedReader Tutorial with Examples
- Java LineNumberReader Tutorial with Examples
- Java PrintWriter Tutorial with Examples
- Java IO Binary Streams Tutorial with Examples
- Java IO Character Streams Tutorial with Examples
- Java BufferedOutputStream Tutorial with Examples
- Java ByteArrayOutputStream Tutorial with Examples
- Java DataOutputStream Tutorial with Examples
- Java PipedInputStream Tutorial with Examples
- Java OutputStream Tutorial with Examples
- Java ObjectOutputStream Tutorial with Examples
- Java PushbackInputStream Tutorial with Examples
- Java SequenceInputStream Tutorial with Examples
- Java BufferedInputStream Tutorial with Examples
- Java Reader Tutorial with Examples
- Java Writer Tutorial with Examples
- Java FileReader Tutorial with Examples
- Java FileWriter Tutorial with Examples
- Java CharArrayReader Tutorial with Examples
- Java ByteArrayInputStream Tutorial with Examples
- Java DataInputStream Tutorial with Examples
- Java ObjectInputStream Tutorial with Examples
- Java InputStreamReader Tutorial with Examples
- Java OutputStreamWriter Tutorial with Examples
- Java InputStream Tutorial with Examples
- Java FileInputStream Tutorial with Examples
Show More