Java Servlet: PrintWriter strange behaviour with variable
Question
I'm learning how to program servlet by following these 1 2 official tutorials. I cannot find a solution to a simple question about the strange behaviour of PrintWriter class with variables. The code is the following:
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class ServletExample extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException, ServletException
{
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("<html>");
out.println("<head>");
out.println("<title>First example</title>");
out.println("</head>");
out.println("<h2>System information</h2>");
out.println("Host name: " + request.getRemoteHost() + "<br>");
out.println("Remote address: " + request.getRemoteAddr() + "<br>");
out.println("Port: " + request.getServerPort() + "<br>");
out.println("Encoding: " + request.getCharacterEncoding() + "<br>");
out.println("Method: " + request.getMethod() + "<br>");
out.println("Protocol: " + request.getProtocol() + "<br>");
out.println("Address: " + request.getRequestURI() + "<br>");
out.println("Path: " + request.getPathInfo() + "<br>");
out.println("</body>");
out.println("</html>");
out.close();
}
}
The output of the servlet on servlet container is displayed up to
out.println("<h2>System information</h2>");
I cannot figure out why, but I discovered that by splitting the following line into these lines works:
out.println("Host name: ");
out.println(request.getRemoteHost())
out.println("<br>");
I searched a lot on the Web, but I cannot find and answer.
I'm under ubuntu mate 16.04 LTS with apache tomcat 8 installed from repository.
Edit I further investigate about such behaviour by trying different tomcat 7 under ubuntu mate 16.04 LTS and different OS windows 10 with xampp and tomcat 7. The result is the same.
So I took the Request Info official example present into examples folder installed together with tomcat. The code of the example is this:
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class RequestInfo extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException, ServletException
{
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("<html>");
out.println("<head>");
out.println("<title>Request Information Example</title>");
out.println("</head>");
out.println("<body>");
out.println("<h3>Request Information Example</h3>");
out.println("Method: " + request.getMethod());
out.println("Request URI: " + request.getRequestURI());
out.println("Protocol: " + request.getProtocol());
out.println("PathInfo: " + request.getPathInfo());
out.println("Remote Address: " + request.getRemoteAddr());
out.println("</body>");
out.println("</html>");
}
/**
* We are going to perform the same operations for POST requests
* as for GET methods, so this method just sends the request to
* the doGet method.
*/
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws IOException, ServletException
{
doGet(request, response);
}
}
As expected it does not work and its behaviour it is the same of the previous code. However, if I open prebuilt version inside the example folder it works.
Finally, by splitting each line into several lines it works as described before. It is really strange behaviour.
2 answers
solution1
0 2018-04-08 19:39:23
I would recommend that you use a StringBuilder object to generate the result, then. You can, if desired, calculate the content length, which is useful in some situations.
StringBuilder sbText = new StringBuilder();
sbText.append("<html>")
.append("<head>")
.append(etc...);
String text = sbText.toString();
// Option A:
response.getWriter().print(text);
// Option B:
byte[] bytes = text.getBytes();
response.setContentLength(bytes.length);
response.getOutputStream().write(bytes);
solution2
0 2018-05-26 16:06:37
I found the solution at my strange problem. I tried also with latest tomcat v9.0.8 that uses jvm v1.8.0_171-b11 while I compiled my code with javac 1.9. By using javac v1.8 it works.
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