Java Webアプリのユーティリティロジックのメモ

package xxxx.service;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.security.MessageDigest;

public class Util {

	/**
	 * 文字列が空かどうか判定
	 * 
	 */
	public static boolean isEmpty(String buff) {
		boolean flg = false;
		if (buff == null || buff == "") {
			flg = true;
		}
		return flg;
	}

	/**
	 * テキストファイルの文字コード変換
	 * 
	 */
	public static void convertFile(
			String fromFilePath,
			String fromCharSet,
			String toFilePath,
			String toCharSet
	){
		try{
			FileInputStream inStream = new FileInputStream(fromFilePath);
			FileOutputStream otStream = new FileOutputStream(toFilePath);
			InputStreamReader inReader = new InputStreamReader(inStream,fromCharSet);
			OutputStreamWriter otWriter = new OutputStreamWriter(otStream,toCharSet);
			
			int contents;
			while((contents = inReader.read()) != -1){
				otWriter.write(contents);
			}
			inReader.close();
			otWriter.close();
		}
		catch(Exception e){
			e.printStackTrace();
		}
	}

	/**
	 * MD5変換
	 * 
	 */
	public static String hexString(String value) throws Exception{
		MessageDigest md5 = MessageDigest.getInstance("MD5");
		md5.update(value.getBytes());
		byte[] hash = md5.digest();
		byte[] bin = hash;
		String s = "";
		int size = bin.length;
		for (int i = 0; i < size; i++) {
			int n = bin[i];
			if (n < 0) {
				n += 256;
			}
			String hex = Integer.toHexString(n);
			if (hex.length() == 1) {
				hex = "0" + hex;
			}
			s += hex;
		}
		return s;
	}
}