import java.io.BufferedReader; import java.io.File; import java.io.FileNotFoundException; import java.io.FileReader; import java.io.FileWriter; import java.io.IOException; import java.io.PrintWriter; import jakarta.servlet.ServletException; import jakarta.servlet.annotation.WebServlet; import jakarta.servlet.http.HttpServlet; import jakarta.servlet.http.HttpServletRequest; import jakarta.servlet.http.HttpServletResponse; @WebServlet("/Counter") public class Counter extends HttpServlet { @Override protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html; charset=UTF-8"); PrintWriter out = response.getWriter(); out.println(""); int i; File f = new File(getServletContext() .getRealPath("/WEB-INF/counter.txt")); BufferedReader fin = null; try { fin = new BufferedReader(new FileReader(f)); i = Integer.parseInt(fin.readLine()); } catch (FileNotFoundException // ファイルがなければ | NullPointerException // ファイルが空なら | NumberFormatException e) { // 数でないならば i = 0; // 0 に } finally { if (fin != null) { fin.close(); // closeを忘れない } } PrintWriter fout = new PrintWriter(new FileWriter(f)); fout.println(++i); fout.close(); // closeを忘れない out.printf("あなたは %d番目の来訪者です。%n", i); out.println(""); out.close(); // closeを忘れない } }