Realization of graphics verification code with JSP

js| Graphics | Verification Code

Import java.io.*;
Import java.util.*;
Import com.sun.image.codec.jpeg.*;
Import javax.servlet.*;
Import javax.servlet.http.*;
Import java.awt.*;
Import java.awt.image.*;

public class Validatecode extends HttpServlet {

Private font mfont=new font ("Arial", font.plain,12);//Set Font
Process Post
public void DoPost (httpservletrequest request,httpservletresponse response)
Throws Servletexception,ioexception {

Doget (Request,response);
}
public void doget (httpservletrequest request,httpservletresponse response)
Throws Servletexception,ioexception {
Get a random number of 1000-9999
String s= "";

int intcount=0;

Intcount= (New Random ()). Nextint (9999);

if (intcount<1000) intcount+=1000;

S=intcount+ "";

Save in session for comparison with user input.
Note that the session is cleared after the comparison is complete.

HttpSession session=request.getsession (TRUE);

Session.setattribute ("Validatecode", s);

Response.setcontenttype ("Image/gif");

Servletoutputstream Out=response.getoutputstream ();

BufferedImage image=new BufferedImage (35,14,BUFFEREDIMAGE.TYPE_INT_RGB);

Graphics Gra=image.getgraphics ();
Set Background color
Gra.setcolor (Color.yellow);

Gra.fillrect (1,1,33,12);
Set Font Color
Gra.setcolor (Color.Black);

Gra.setfont (Mfont);
Output numbers
char c;

for (int i=0;i<4;i++) {

C=s.charat (i);

Gra.drawstring (c+ "", i*7+4,11); 7 is width, 11 is the top and bottom height position

}

JPEGImageEncoder Encoder=jpegcodec.createjpegencoder (out);

Encoder.encode (image);

Out.close ();

}
}

Java Image processing package requires a graphics environment, and Linux does not start the graphics environment, the graphics environment can not find the server (X11 window server using ': 0.0 ') so will report this error. By java-djava.awt.headless=true This parameter's designation can avoid Java 2d to find graphics environment.

Either try it or you can. At the beginning of the servlet, write a sentence:

System.setproperty ("Java.awt.headless", "true");

The Java Virtual machine for the Web server must be a parameter java.awt.headless=true

Taking Tomcat as an example

You can add in the catalina_opts variable in the. Bash_profile of the user who/etc/profile or starts the Web service:

Catalina_opts= "...-djava.awt.headless=true"

Others can also look at the startup script. Just add this parameter to the problem.