Here is an example of using the ChunkedOutputStream class from the Apache Commons IO library in Java to write a large file to disk in small chunks:

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import org.apache.commons.io.output.ChunkedOutputStream;

public class ChunkedOutputStreamExample {
    public static void main(String[] args) {
        // specify the file to write to
        File file = new File("/path/to/large_file.txt");
        
        // specify the chunk size
        int chunkSize = 8192;
        
        try (FileOutputStream fos = new FileOutputStream(file);
             ChunkedOutputStream out = new ChunkedOutputStream(fos, chunkSize)) {
            // write data to the stream in chunks
            for (int i = 0; i < 1000000; i++) {
                out.write("This is some text to be written to the file.\n".getBytes());
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

In this example, the ChunkedOutputStream class is used to write data to a large file in small chunks, using the write() method. The ChunkedOutputStream is created by passing a FileOutputStream object and a chunk size as arguments. In this example, the FileOutputStream writes to a file and the chunk size is set to 8192 bytes, but you can use any other output stream and chunk size as you need.

The ChunkedOutputStream class provides the ability to write large files in small chunks without the need to store the entire file in memory. This can be useful when working with large files that may not fit in the available memory, and can also be useful for sending large files over a network in small chunks.