Here is an example of using the TaggedWriter class from the org.apache.commons.io package in Java to write to a Writer with a tag that can be used to identify the source of the data:

import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import org.apache.commons.io.output.TaggedWriter;

public class TaggedWriterExample {
    public static void main(String[] args) throws IOException {
        // File to write to
        File outputFile = new File("example.txt");
        // Create a FileWriter for the file
        FileWriter fw = new FileWriter(outputFile);
        // Create a TaggedWriter with a tag
        TaggedWriter tw = new TaggedWriter(fw, "ExampleTag");

        // Write to the TaggedWriter
        tw.write("Hello World!");
        // Close the TaggedWriter
        tw.close();
    }
}

In this example, a FileWriter is created for a file named "example.txt" and a TaggedWriter is created to wrap it and take a tag "ExampleTag". The TaggedWriter is then used to write the string "Hello World!" to the file.

This class is useful when you need to add a tag to an existing Writer, for example, to identify the source of the data or to distinguish between different data sources. The TaggedWriter class allows you to add this tag by wrapping an existing Writer.

It can also be used when you want to add a prefix to the data written to the writer, which can then be used to identify the source of the data.