Java - FilterWriter write(String str, int off, int len) method

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Description

The Java FilterWriter write(String str, int off, int len) method writes a portion of a string to the output stream. It allows you to specify where to start (off) and how many characters to write (len). off is the starting index in the string. len is the number of characters to write from off. Throws IndexOutOfBoundsException if off + len exceeds the string length.

Declaration

Following is the declaration for java.io.FilterWriter.write(String str, int off, int len) method −

public void write(String str, int off, int len)

Parameters

• str − Source string to be written to Filter Writer.

• off − Offset from which to start reading characters.

• len − Number of characters to be written.

Return Value

The method does not return any value.

Exception

IOException − If an I/O error occurs.

Example - Usage of FilterWriter write(String str, int off, int len) method

The following example shows the usage of Java FilterWriter write(String str, int off, int len) method.

FilterWriterDemo.java

package com.tutorialspoint;

import java.io.FilterWriter;
import java.io.StringWriter;
import java.io.Writer;

public class FilterWriterDemo {
   public static void main(String[] args) throws Exception {
      FilterWriter fw = null;
      Writer w = null;
      String str = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
      String s = null;
      
      try {
         // create new reader
         w = new StringWriter(6);
          
         // filter writer
         fw = new FilterWriter(w) {
         };
         
         // write to filter writer
         fw.write(str, 5, 7);
         
         // get the string
         s = w.toString();
         
         // print
         System.out.print("String: "+s);
         
      } catch(Exception e) {
         // if any I/O error occurs
         e.printStackTrace();
      } finally {
         // releases system resources associated with this stream
         if(w!=null)
            w.close();
         if(fw!=null)
            fw.close();
      }
   }
}

Output

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

String: FGHIJKL

Example - Writing a Substring Using a Custom FilterWriter

The following example shows the usage of Java FilterWriter write(String str, int off, int len) method.

FilterWriterDemo.java

package com.tutorialspoint;

import java.io.FilterWriter;
import java.io.FileWriter;
import java.io.IOException;
import java.io.Writer;

// Custom FilterWriter implementation
class CustomFilterWriter extends FilterWriter {
   protected CustomFilterWriter(Writer out) {
      super(out);
   }
}

public class FilterWriterDemo {
   public static void main(String[] args) {
      try (FilterWriter fw = new CustomFilterWriter(new FileWriter("output.txt"))) {
         String text = "Hello, FilterWriter Example!";

         // Write only "FilterWriter" (starting from index 7, length 12)
         fw.write(text, 7, 12);

         System.out.println("Substring written successfully to output.txt.");
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output(if example.txt contains "Hello")

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

Substring written successfully to output.txt.

Explanation

• Creates a custom CustomFilterWriter, as FilterWriter is abstract.

• Uses write(text, 7, 12) to write only "FilterWriter" from the string.

• The first 7 characters ("Hello, ") are skipped.

Example - Writing a Portion of a Sentence Using BufferedWriter

The following example shows the usage of Java FilterWriter write(String str, int off, int len) method.

FilterWriterDemo.java

package com.tutorialspoint;

import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.FilterWriter;
import java.io.IOException;
import java.io.Writer;

// Custom FilterWriter implementation
class CustomBufferedFilterWriter extends FilterWriter {
   protected CustomBufferedFilterWriter(Writer out) {
      super(out);
   }
}

public class FilterWriterDemo {
   public static void main(String[] args) {
      try (FilterWriter fw = new CustomBufferedFilterWriter(new BufferedWriter(new FileWriter("data.txt")))) {
         String sentence = "Microservices architecture is powerful!";

         // Write "architecture is" (from index 13, length 15)
         fw.write(sentence, 13, 15);

         System.out.println("Substring written successfully to data.txt.");
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output

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

Substring written successfully to data.txt.

Explanation

• Uses CustomBufferedFilterWriter, which extends FilterWriter with BufferedWriter.

• Calls write(sentence, 13, 15), writing only "architecture is".

• Skips the first 13 characters ("Microservices ").