Servlet javoblarini shakllantirish

3.1 HttpServletResponse klassi

Servletingni service() usulini chaqirgandan so'ng, web-konteyner HttpServletResponse obyektiga asoslanib mijozga javobni shakllantiradi. Shunday ekan, agar javobga qandaydir ta'sir o'tkazmoqchi bo'lsang, ushbu obyektni o'zgartirishingiz kerak.

Server javobi uch qismdan iborat:

• Status qatori (masalan: 200 OK)
• Headers (zagolovkalar)
• Javobning tanasi (response body)

Va HttpServletResponse klassining usullari ham 3 guruhga bo'linadimi? Hamma ham o'ylagandek emas:

Usullar juda oson. Lekin ba'zi narsalarni tushuntirib beraman.

Buffer. Servlet javobi bufferga yoziladi va bu foydalanuvchiga to'g'ridan-to'g'ri yuborilmaydi. Shunday ekan, biror sabab bilan (masalan, xato bo'lsa), bufferda yozilgan hamma narsani bekor qilishingiz mumkin. Hattoki reset() usulini chaqirib, buffer tarkibini va javob kodlarini ham o'chirishingiz mumkin.

3.2 redirect()

Ikkinchi muhim jihat — bu redirect. Agar servletingiz mijozni boshqa URL'ga yo'naltirishga qaror qilsa, qandaydir tarzda URL'ni mijozga yuborishingiz kerak bo'ladi. Buni sendRedirect usuli yordamida amalga oshirishingiz mumkin.

Lekin muhim bir jihat bor. URI response body'da ruxsat berilganidan ko'ra ko'proq belgilarni o'z ichiga olishi mumkin. Shuning uchun URL'ni sendRedirect() usulini chaqirishdan oldin ruxsat etilgan belgilar to'plamiga kodlash kerak. Buning uchun maxsus encodeRedirectURL(String url) usuli mavjud. Shu usuldan foydalaning.

Redirect misoli:

public class RedirectServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws Exception {
        String newUrl = "http://google.com?q=O'rganishni davom ettir!";
        String redirectUrl = response.encodeRedirectURL(newUrl);
        response.sendRedirect(redirectUrl);
    }
}

3.3 getWriter() usuli

Endi bizning matnni javobning tanasi sifatida yozishni o'rganamiz. Buning uchun HttpServletResponse klassida getWriter() deb ataladigan maxsus usul mavjud bo'lib, u PrintStream obyektini qaytaradi. Agar kimdir unutgan bo'lsa, bu System.out ismli maydon turidagi obyekt.

Servlet javobi sifatida matn yozish uchun:

• PrintStream obyektini response.getWriter() usulini chaqirish orqali oling.
• PrintStream obyektiga kerakli narsalarni yozing (barcha ma'lumotlar bufferga yoziladi).
• Bufferni foydalanuvchiga yuboring, PrintStream'da close() usulini chaqirish orqali.

Ikki son a va b ni qo'shib foydalanuvchiga natijani qaytaradigan servlet yozamiz:

public class CalculatorServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws Exception {
         // So'rovdan “a” va “b” parametrlarini olish
        String a = request.getParameter("a");
        String b = request.getParameter("b");
 
        try {
            // Matnni raqamlarga aylantirib yig'indini hisoblash
            int sum = Integer.parseInt(a) + Integer.parseInt(b);
 
            // HTML-ni brauzer uchun javob sifatida chiqarish
            response.setContentType("text/html;charset=UTF-8");
            PrintWriter out = response.getWriter();
 
            out.println("<html>");
            out.println("<head> <title> CalculatorServlet </title> </head>");
            out.println("<body>");
            out.println("<h1> Sum == " + sum + "</h1>");
            out.println("</body>");
            out.println("</html>");
        } finally {
            out.close();
        }
    }
}