Java FileWriter Example

Java FileWriter

• Java FileWriter class is a part of java.io package.
• FileWriter is a sub class of java.io.OutputStreamWriter class.
• FileWriter is meant for writing streams of characters.
• FileWriter is used to write to character files. Its write() methods allow you to write character(s) or strings to a file.
• FileWriters are usually wrapped by higher-level Writer objects, such as BufferedWriter or PrintWriter, which provide better performance and higher-level, more flexible methods to write data.

FileWriter Constructors

1. FileWriter(File file): Creates a FileWriter object using specified File object. It throws an IOException if the file exists but is a directory rather than a regular file or does not exist but cannot be created, or cannot be opened for any other reason.
2. FileWriter(File file, boolean append): Creates a FileWriter object using specified File object. If the second argument is true, then bytes will be written to the end of the file rather than the beginning. It throws an IOException if the file exists but is a directory rather than a regular file or does not exist but cannot be created, or cannot be opened for any other reason.
3. FileWriter(FileDescriptor fd): Creates a FileWriter object associated with specified file descriptor.
4. FileWriter(String fileName): Creates a FileWriter object using specified fileName. It throws an IOException if the named file exists but is a directory rather than a regular file or does not exist but cannot be created, or cannot be opened for any other reason.
5. FileWriter(String fileName, boolean append): Creates a FileWriter object using specified fileName with a boolean indicating whether or not to append the data written. If the second argument is true, then the data will be written to the end of the file rather than the beginning. It throws an IOException if the named file exists but is a directory rather than a regular file or does not exist but cannot be created, or cannot be opened for any other reason.

Java FileWriter Example

FileWriter inherits the method of java.io.OutputStreamWriter and java.io.Writer classes. Let’s have a look at the below methods with examples.

write(int c)

This method writes a single character specified by int c.

package com.journaldev.io.filewriter;

import java.io.FileWriter;
import java.io.IOException;

/**
 * Java write file using FileWriter write method
 * 
 * @author pankaj
 *
 */
public class FileWriterWriteIntExample {

	public static void main(String[] args) {
		FileWriter fileWriter = null;
		try {
			fileWriter = new FileWriter("D:/data/file.txt");
			//inherited method from java.io.OutputStreamWriter 
			fileWriter.write(65);
			fileWriter.write(66);
			fileWriter.write(67);
		} catch (Exception e) {
			e.printStackTrace();
		}finally {
			try {
				if (fileWriter != null) {
					fileWriter.flush();
					fileWriter.close();					
				}
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
	}
}

FileWriter implements AutoCloseable interface, hence we can use try with resources while using FileWriter class.

package com.journaldev.io.filewriter;

import java.io.FileWriter;

/**
 * Java write file using FileWriter write method using try with resource
 * 
 * @author pankaj
 *
 */
public class FileWriterWriteIntTryWithResource {

	public static void main(String[] args) {
		try(FileWriter fileWriter = new FileWriter("D:/data/file.txt")) {
			//inherited method from java.io.OutputStreamWriter 
			fileWriter.write(65);
			fileWriter.write(66);
			fileWriter.write(67);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

Note: In the above program fileWriter.write(65) will write A into file because the 65 is the decimal value for the character A, hence integer 65 will be converted into character A and same for the other.

write(String str, int off, int len)

This method writes a portion of String str from int off to int len.

• str: String to be written
• off: Offset from which to start reading characters
• len: Number of characters to be written

If the value of the len parameter is negative then no characters are written.

package com.journaldev.io.filewriter;

import java.io.FileWriter;

/**
 * Java write file using FileWriter write(String  s,  int  off,  int  len) method
 * 
 * @author pankaj
 *
 */
public class FileWriterWriteStringExample {

	public static void main(String[] args) {
		String data = "This is FileWriter Example.";
		try(FileWriter fileWriter = new FileWriter("D:/data/file.txt")) {
			//inherited method from java.io.OutputStreamWriter 
			fileWriter.write(data, 8, 10);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

write(char[] cbuf, int off, int len)

This method writes a portion of an array of characters specified by char[] cbuf from int off to int len.

• cbuf: A character array
• off: Offset from which to start reading characters
• len : Number of characters to write

package com.journaldev.io.filewriter;

import java.io.FileWriter;

/**
 * Java write file using FileWriter write(char[] cbuf,  int  off,  int  len) method
 * 
 * @author pankaj
 *
 */
public class FileWriterWriteCharArray {

	public static void main(String[] args) {
		char[] data = "This is FileWriter Example.".toCharArray();
		try(FileWriter fileWriter = new FileWriter("D:/data/file.txt")) {
			//inherited method from java.io.OutputStreamWriter 
			fileWriter.write(data, 8, 10);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

write(char[] cbuf)

This method writes the array of character specified by cbuf.

package com.journaldev.io.filewriter;

import java.io.FileWriter;

/**
 * Java write file using FileWriter write(char[] cbuf) method
 * 
 * @author pankaj
 *
 */
public class FileWriterWriteCharArrayExample {

	public static void main(String[] args) {
		char[] data = "This is FileWriter Example.".toCharArray();
		try(FileWriter fileWriter = new FileWriter("D:/data/file.txt")) {
			//inherited method from java.io.Writer 
			fileWriter.write(data);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

write(String str)

This method writes a string value into file specified by str.

package com.journaldev.io.filewriter;

import java.io.FileWriter;

/**
 * Java write file using FileWriter write(String  str) method
 * 
 * @author pankaj
 *
 */
public class FileWriterWriteString {

	public static void main(String[] args) {
		try(FileWriter fileWriter = new FileWriter("D:/data/file.txt")) {
			//inherited method from java.io.Writer 
			fileWriter.write("JournalDev");
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

append(char c)

This method appends the specified character to this writer where c is the 16-bit character to append.

package com.journaldev.io.filewriter;

import java.io.FileWriter;

/**
 * Java write file using FileWriter append(char c) method
 * 
 * @author pankaj
 *
 */
public class FileWriterAppendCharacter {

	public static void main(String[] args) {
		try(FileWriter fileWriter = new FileWriter("D:/data/file.txt")) {
			//inherited method from java.io.Writer 
			fileWriter.write("JournalDev");
			fileWriter.append('C');
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

flush()

This method flushes the stream. When flush() method is called it immediately writes the data to the output file.

package com.journaldev.io.filewriter;

import java.io.FileWriter;

/**
 * Java write file with FileWriter flush() method
 * 
 * @author pankaj
 *
 */
public class FileWriterFlushExample {

	public static void main(String[] args) {
		try(FileWriter fileWriter = new FileWriter("D:/data/file.txt")) {
			//inherited method from java.io.Writer 
			fileWriter.write("JournalDev");
			//inherited method from java.io.OutputStreamWriter
			fileWriter.flush();
			
			fileWriter.write(" Tutorials");
			fileWriter.flush();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

close()

This method flush the stream before close it. Once the stream has been closed, invocation of write() or flush() method will cause an IOException to be thrown. Closing a previously closed stream has no effect.

package com.journaldev.io.filewriter;

import java.io.FileWriter;

/**
 * Java write file with FileWriter close() method
 * 
 * @author pankaj
 *
 */
public class FileWriterCloseExample {

	public static void main(String[] args) {
		try(FileWriter fileWriter = new FileWriter("D:/data/file.txt")) {
			//inherited method from java.io.Writer 
			fileWriter.write("JournalDev");
			//inherited method from java.io.OutputStreamWriter
			fileWriter.close();;
			
			fileWriter.write(" Tutorials");
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

Output:

java.io.IOException: Stream closed
	at sun.nio.cs.StreamEncoder.ensureOpen(Unknown Source)
	at sun.nio.cs.StreamEncoder.write(Unknown Source)
	at sun.nio.cs.StreamEncoder.write(Unknown Source)
	at java.io.OutputStreamWriter.write(Unknown Source)
	at java.io.Writer.write(Unknown Source)
	at com.journaldev.examples.FileWriterCloseExample.main(FileWriterCloseExample.java:20)

FileWriter vs FileOutputStream

• FileWriter is meant for writing streams of characters while FileOutputStream is used for writing streams of raw bytes.
• FileWriter deal with 16-bit characters while FileOutputStream deals with 8-bit bytes.
• FileWriter can handle Unicode strings while FileOutputStream writes bytes to a file and do not accepts characters or strings hence it needs to wrapped up by OutputStreamWriter to accept strings.

Also check java write file for more about how to write file in java. That’s all for Java FileWriter, I hope nothing important got missed here.

You can download all the examples code from our GitHub Repository.

Reference: API Doc