Spring StreamUtilsで「InputStream」→「String」変換している箇所

StreamUtils

package org.springframework.util;

public abstract class StreamUtils {

	/**
	 * The default buffer size used when copying bytes.
	 */
	public static final int BUFFER_SIZE = 4096;

	private static final byte[] EMPTY_CONTENT = new byte[0];

※抜粋

	/**
	 * Copy the contents of the given InputStream into a String.
	 * <p>Leaves the stream open when done.
	 * @param in the InputStream to copy from (may be {@code null} or empty)
	 * @param charset the {@link Charset} to use to decode the bytes
	 * @return the String that has been copied to (possibly empty)
	 * @throws IOException in case of I/O errors
	 */
	public static String copyToString(@Nullable InputStream in, Charset charset) throws IOException {
		if (in == null) {
			return "";
		}

		StringBuilder out = new StringBuilder();
		InputStreamReader reader = new InputStreamReader(in, charset);
		char[] buffer = new char[BUFFER_SIZE];
		int bytesRead = -1;
		while ((bytesRead = reader.read(buffer)) != -1) {
			out.append(buffer, 0, bytesRead);
		}
		return out.toString();
	}