Java - OutputStreamWriter Class

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Introduction

The Java OutputStreamWriter class is a bridge from character streams to byte streams. Characters written to it are encoded into bytes using a specified charset.

Class declaration

Following is the declaration for Java.io.OutputStreamWriter class −

public class OutputStreamWriter
   extends Writer

Field

Following are the fields for Java.io.OutputStreamWriter class −

• protected Object lock − This is the object used to synchronize operations on this stream.

Class constructors

Class methods

Methods inherited

This class inherits methods from the following classes −

• Java.io.Writer
• Java.io.Object

Example - Using close() to release file resources

The following example shows the usage of ObjectStreamWriter close() method.

OutputStreamWriterDemo.java

package com.tutorialspoint;

import java.io.FileOutputStream;
import java.io.OutputStreamWriter;
import java.io.IOException;

public class OutputStreamWriterDemo {
   public static void main(String[] args) {
      try {
         FileOutputStream fos = new FileOutputStream("output_writer1.txt");
         OutputStreamWriter writer = new OutputStreamWriter(fos);

         writer.write("This is written using OutputStreamWriter.");

         // Close the writer to flush and release resources
         writer.close();

         System.out.println("Data written and stream closed.");
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output

Let us compile and run the above program, this will produce the following result−

Data written and stream closed.

Explanation

• close() flushes any buffered characters and closes the stream.

• It's essential to prevent data loss and free system resources.

• If close() is not called, some characters may remain in the buffer and not be written to the file.

Example - Using flush() to force data write before closing

The following example shows the usage of ObjectStreamWriter flush() method.

OutputStreamWriterDemo.java

package com.tutorialspoint;

import java.io.FileOutputStream;
import java.io.OutputStreamWriter;
import java.io.IOException;

public class OutputStreamWriterDemo {
   public static void main(String[] args) {
      try {
         FileOutputStream fos = new FileOutputStream("flush_output1.txt");
         OutputStreamWriter writer = new OutputStreamWriter(fos);

         writer.write("Flush ensures data is written immediately.");
         writer.flush();  // Forces characters to be written to file

         // Writer is still open here, more data could be written
         System.out.println("Data flushed to file.");
         writer.close();  // Finally close the stream
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output

Let us compile and run the above program, this will produce the following result−

Data flushed to file.

Explanation

• write() writes to an internal buffer.

• flush() pushes that buffered data to the underlying FileOutputStream immediately, without closing the stream.

• Useful when you want to make sure data is written while keeping the stream open for more output later.

Example - Getting default encoding used by OutputStreamWriter

The following example shows the usage of ObjectStreamWriter getEncoding() method.

OutputStreamWriterDemo.java

package com.tutorialspoint;

import java.io.FileOutputStream;
import java.io.OutputStreamWriter;
import java.io.IOException;

public class OutputStreamWriterDemo {
   public static void main(String[] args) {
      try {
         OutputStreamWriter writer = new OutputStreamWriter(new FileOutputStream("encoding1.txt"));

         System.out.println("Encoding used: " + writer.getEncoding());

         writer.write("Sample text.");
         writer.close();
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output

Let us compile and run the above program, this will produce the following result−

Encoding used: UTF8

Explanation

• When you don't specify an encoding, OutputStreamWriter uses the default character encoding of the JVM (e.g., UTF-8, platform dependent).

• getEncoding() returns the actual encoding used by the writer.

• Useful for debugging or ensuring correct text file formats.