Analysis of detailed steps for generating verification code in java

This article mainly introduces in detail the steps to generate verification code in Java. Friends who need it can refer to

1, serialVersionUID

    private static final long serialVersionUID = -8501285780349046114L;

Java The serialization mechanism verifies version consistency by judging the serialVersionUID of the class at runtime.

Equivalent to the Java ID card. Mainly used for version control.

2. BufferedImage class

——BufferedImage subclass describes an Image with an accessible image data buffer.

TYPE_INT_RGB

Represents an image that has 8-bit RGB color components synthesized into integer pixels.

——getGraphics()

This method returns Graphics2D, but this is for backward compatibility reasons.

3. request.getParameter()

The data passed by the request.getParameter() method will be passed from the Web client to the Web server, representing HTTP request data.

The request.getParameter() method returns String type data.

4. String... excludeProperty represents variable parameters, that is, multiple String objects can be passed in when calling this method (variable parameters: suitable for uncertain number of parameters) , when the type is determined, java treats the variable parameters as an array

Note: The variable parameters must be located in the last item eg: private String drawRandomNum(Graphics2D g,String... createTypeFlag))

5. Graphics class

The Graphics class is the abstract base class for all graphics contexts, allowing applications to perform operations on components (already implemented on various devices) and off-screen images. draw.

[Steps]:

1. Create a picture in the memory;

  BufferedImage bi = new BufferedImage(WIDTH,HEIGHT,BufferedImage.TYPE_INT_RGB);

——BufferedImage subclass describes an Image with an accessible image data buffer.​ ​ ​​

——getGraphics()

This method returns Graphics2D, but this is for backward compatibility reasons.

2. Get the picture;

        Graphics g = bi.getGraphics();

3. Set the background color of the picture;

        setBackGround(g);

4. Set the background color of the picture Border;

        setBorder(g);

5. Draw interference lines on the picture;

        drawRandomLine(g);

6. Write random numbers on the picture;

        String random = drawRandomNum((Graphics2D) g,createTypeFlag);//根据客户端传递的createTypeFlag

7. Store random numbers in the session;

        request.getSession().setAttribute("checkcode",random);

8. Set the response header to notify the browser to open it as a picture;

        response.setContentType("image/jpeg");//等同于res[onse.setHeader("Content-Type","image/jpeg");

9. Set the response header to control browsing Do not cache the server;

  response.setDateHeader("expries",-1);
  response.setHeader("Cache-Control","no-cache");
  response.setHeader("Pragma","no-cache");

——setDateHeader

    public void setDateHeader(java.lang.String name,long date)

Parameters:

name - the name of the header to set

date - the assigned date value

——setHeader

            public void setHeader(java.lang.String name, java.lang.String value)

Parameters:

name - the name of the header

                    value - the header value If it contains octet string, it should be encoded according to RFC 2047 (http://www.ietf.org/rfc/rfc2047.txt)

10. Write the image to the browser;

        ImageIO.write(bi,"jpg",response.getOutputStream());

——Parameters:

im - the RenderedImage to be written.

                                                                                                                                          formatName - A String containing the informal name of the format.

# Output -OutputStream will be written into the data.

throwing:

# illegalargumentexception -If any parameter is NULL.

            IOException - if an error occurs during writing. ​

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