Hi Ankit,
Maybe, I can help you.
I write below the code than I use to do Captcha check.
In the form panel:
#########
FormPanel form = new FormPanel();
....
VerticalPanel vp = new VerticalPanel();
HorizontalPanel hp = new HorizontalPanel();
hp.setSpacing(10);
codeCheck = new TextField<String>();
codeCheck.setFieldLabel("Controllo");
codeCheck.setAllowBlank(false);
verifyImage = new Image("verify.png");
hp.add(verifyImage);
hp.setCellHorizontalAlignment(verifyImage,
HasAlignment.ALIGN_RIGHT);
hp.setCellWidth(verifyImage, "170px");
final Button clickImage = new Button("New image");
clickImage.addSelectionListener(new
SelectionListener<ButtonEvent>()
{
@Override
public void componentSelected(ButtonEvent ce) {
codeCheck.setValue("");
int rand = Random.nextInt();
String url = "verify.png?rand=" + rand;
verifyImage.setUrl(url);
}
});
hp.add(clickImage);
vp.add(hp);
HTML info = new HTML("Write in the check field the sequence of
characters in the image.");
info.setStyleName("x-label");
vp.add(info);
panel.add(vp);
panel.add(codeCheck);
errorCaptcha = new HTML("");
errorCaptcha.setStyleName("x-label");
errorCaptcha.addStyleName("x-label-red");
vp.add(errorCaptcha);
Button btn = new Button("Check");
btn.addSelectionListener(new SelectionListener<ButtonEvent>() {
@Override
public void componentSelected(ButtonEvent ce) {
if (!panel.isValid() ||
codeCheck.getValue()==null) {
return;
}
service.checkCode(codeCheck.getValue(), new
AsyncCallback<String>() {
public void onFailure(Throwable caught)
{
MessageBox.alert("error",caught.getMessage(),null);
}
public void onSuccess(String result) {
if
(((String)result).equals("Sorry please enter correct code for
verification.")){
errorCaptcha.setHTML(result);
return;
} else {
errorCaptcha.setHTML("");
}
}
});
// panel.submit(); // this is your form submit
}
});
panel.addButton(btn);
##############
Now, the GWT RPC servlet code (it's very simple):
##############
public String checkCode(String entercode)
{
session = getThreadLocalRequest().getSession();
String code = (String)session.getAttribute("verification.code");
String attempt = entercode;
String msg = "";
if (code!=null && code.equals(attempt)){
msg = "Correct verification code";
} else {
msg = "Sorry please enter correct code for
verification.";
}
return msg;
}
##############
In the reality the url "verify.png" for the image is a servlet, and
you must define this into web.xml:
##############
<servlet>
<servlet-name>VerificationServlet</servlet-name>
<servlet-class>com.yourpackage.server.VerificationServlet</servlet-
class>
</servlet>
<servlet-mapping>
<servlet-name>VerificationServlet</servlet-name>
<url-pattern>/verify.png</url-pattern>
</servlet-mapping>
##############
Now the code about VerificationServlet:
##############
package com.yourpackage.server;
import java.io.*;
import javax.servlet.ServletContext;
import javax.servlet.*;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
public class VerificationServlet extends HttpServlet
{
private static final long serialVersionUID = 1L;
HttpSession session;
ServletContext context = null;
public void init(ServletConfig config) throws ServletException
{
super.init(config);
context = config.getServletContext();
}
@Override
protected void doGet(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException
{
session = request.getSession(true);
response.setHeader("Pragma", "public");
response.setHeader("cache-control", "max-age=0,no-cache, no-
store,must-revalidate, proxy-revalidate, s-maxage=0");
response.setDateHeader("Expires", 0);
response.setContentType("image/png");
ImageVerification verification = new
ImageVerification(response.getOutputStream());
String code = verification.getVerificationValue();
session.setAttribute("verification.code", code);
response.flushBuffer();
}
}
##############
And the last is the code about ImageVerification:
##############
package com.yourpackage.server;
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics2D;
import java.awt.geom.AffineTransform;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.io.OutputStream;
import java.util.Random;
import java.util.UUID;
import javax.imageio.ImageIO;
/**
* ImageVerification is a simple utility class for
* creating an image verification PNG file that will
* allow you to make sure that only a human can read
* the alphanumeric values and enter them into a text
* field during verification. <P>
*
*/
public class ImageVerification
{
private String value;
public ImageVerification (OutputStream out) throws IOException
{
this(50,120,out);
}
public ImageVerification (int height, int width, OutputStream out)
throws IOException
{
BufferedImage bimage = new BufferedImage(width, height,
BufferedImage.TYPE_INT_RGB);
Random rand=new Random(System.currentTimeMillis());
Graphics2D g = bimage.createGraphics();
// create a random color
Color color = new Color(rand.nextInt(255), rand.nextInt(255),
rand.nextInt(255));
// the the background to the random color to fill the
// background and make it darker
g.setColor(color.darker());
g.fillRect(0, 0, width, height);
// set the font
g.setFont(new Font("arial",Font.BOLD,36));
// generate a random value
this.value =
UUID.randomUUID().toString().replace("-","").substring(0,5);
int w = (g.getFontMetrics()).stringWidth(value);
int d = (g.getFontMetrics()).getDescent();
int a = (g.getFontMetrics()).getMaxAscent();
int x = 0, y =0;
// randomly set the color and draw some straight lines through
it
for (int i = 0; i < height; i += 5)
{
g.setColor(new Color(rand.nextInt(255), rand.nextInt(255),
rand.nextInt(255)));
g.drawLine(x, y + i, width, y+i);
}
// reset x and y
x=0;
y=0;
// randomly set the color of the lines and just draw think at
an angle
for (int i = 0; i < height; i += 5)
{
g.setColor(new Color(rand.nextInt(255), rand.nextInt(255),
rand.nextInt(255)));
g.drawLine(x, y + d - i, width + w, height + d - i);
}
// randomly set the color and make it really bright for more
readability
g.setColor(new Color(rand.nextInt(255), rand.nextInt(255),
rand.nextInt(255)).brighter().brighter());
// we need to position the text in the center of the box
x = width/2 - w/2;
y = height/2 + a/2 - 2;
// affine transform is used to rock the text a bit
AffineTransform fontAT = new AffineTransform();
int xp = x-2;
// walk through each character and rotate it randomly
for (int c=0;c<value.length();c++)
{
// apply a random radian either left or right (left is
half since it's too far back)
int rotate = rand.nextInt(20);
fontAT.rotate(rand.nextBoolean() ?
Math.toRadians(rotate) : -Math.toRadians(rotate/2));
Font fx = new Font("arial", Font.BOLD,
36).deriveFont(fontAT);
g.setFont(fx);
String ch = String.valueOf(value.charAt(c));
int ht = rand.nextInt(3);
// draw the string and move the y either up or down
slightly
g.drawString(ch, xp, y + (rand.nextBoolean()?-ht:ht));
// move our pointer
xp+=g.getFontMetrics().stringWidth(ch) + 2;
}
// write out the PNG file
ImageIO.write(bimage, "png", out);
//System.out.println("DONE WRITYING NEW IMAGHE");
// make sure your clean up the graphics object
g.dispose();
}
/**
* return the value to check for when the user enters it in. Make
sure you
* store this off in the session or something like a database and
NOT in the
* form of the webpage since the whole point of this exercise is
to ensure that
* only humans and not machines are entering the data.
*
* @return
*/
public String getVerificationValue ()
{
return this.value;
}
}
################
Ok, this is all.
I hope this could help you.
Hi
Carlo
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