android端实现验证码随机生成功能

package com.nobeg.util; 
import java.util.Random; 
import android.graphics.Bitmap; 
import android.graphics.Canvas; 
import android.graphics.Color; 
import android.graphics.Paint; 
import android.graphics.Bitmap.Config; 
public class Code { 
private static final char[] CHARS = { 
'2', '3', '4', '5', '6', '7', '8', '9', 
'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'j', 'k', 'l', 'm', 
'n', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', 
'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 
'N', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z' 
}; 
private static Code bmpCode; 
public static Code getInstance() { 
if(bmpCode == null) 
bmpCode = new Code(); 
return bmpCode; 
} 
//default settings 
private static final int DEFAULT_CODE_LENGTH = 3; 
private static final int DEFAULT_FONT_SIZE = 25; 
private static final int DEFAULT_LINE_NUMBER = 2; 
private static final int BASE_PADDING_LEFT = 5, RANGE_PADDING_LEFT = 15, BASE_PADDING_TOP = 15, RANGE_PADDING_TOP = 20; 
private static final int DEFAULT_WIDTH = 60, DEFAULT_HEIGHT = 40; 
//settings decided by the layout xml 
//canvas width and height 
private int width = DEFAULT_WIDTH, height = DEFAULT_HEIGHT; 
//random word space and pading_top 
private int base_padding_left = BASE_PADDING_LEFT, range_padding_left = RANGE_PADDING_LEFT, 
base_padding_top = BASE_PADDING_TOP, range_padding_top = RANGE_PADDING_TOP; 
//number of chars, lines; font size 
private int codeLength = DEFAULT_CODE_LENGTH, line_number = DEFAULT_LINE_NUMBER, font_size = DEFAULT_FONT_SIZE; 
//variables 
private String code; 
private int padding_left, padding_top; 
private Random random = new Random(); 
//验证码图片 
public Bitmap createBitmap() { 
padding_left = 0; 
Bitmap bp = Bitmap.createBitmap(width, height, Config.ARGB_8888); 
Canvas c = new Canvas(bp); 
code = createCode(); 
c.drawColor(Color.WHITE); 
Paint paint = new Paint(); 
paint.setTextSize(font_size); 
for (int i = 0; i < code.length(); i++) { 
randomTextStyle(paint); 
randomPadding(); 
c.drawText(code.charAt(i) + "", padding_left, padding_top, paint); 
} 
for (int i = 0; i < line_number; i++) { 
drawLine(c, paint); 
} 
c.save( Canvas.ALL_SAVE_FLAG );//保存 
c.restore();// 
return bp; 
} 
public String getCode() { 
return code; 
} 
//验证码 
private String createCode() { 
StringBuilder buffer = new StringBuilder(); 
for (int i = 0; i < codeLength; i++) { 
buffer.append(CHARS[random.nextInt(CHARS.length)]); 
} 
return buffer.toString(); 
} 
private void drawLine(Canvas canvas, Paint paint) { 
int color = randomColor(); 
int startX = random.nextInt(width); 
int startY = random.nextInt(height); 
int stopX = random.nextInt(width); 
int stopY = random.nextInt(height); 
paint.setStrokeWidth(1); 
paint.setColor(color); 
canvas.drawLine(startX, startY, stopX, stopY, paint); 
} 
private int randomColor() { 
return randomColor(1); 
} 
private int randomColor(int rate) { 
int red = random.nextInt(256) / rate; 
int green = random.nextInt(256) / rate; 
int blue = random.nextInt(256) / rate; 
return Color.rgb(red, green, blue); 
} 
private void randomTextStyle(Paint paint) { 
int color = randomColor(); 
paint.setColor(color); 
paint.setFakeBoldText(random.nextBoolean()); //true为粗体，false为非粗体 
float skewX = random.nextInt(11) / 10; 
skewX = random.nextBoolean() ? skewX : -skewX; 
paint.setTextSkewX(skewX); //float类型参数，负数表示右斜，整数左斜 
//  paint.setUnderlineText(true); //true为下划线，false为非下划线 
//  paint.setStrikeThruText(true); //true为删除线，false为非删除线 
} 
private void randomPadding() { 
padding_left += base_padding_left + random.nextInt(range_padding_left); 
padding_top = base_padding_top + random.nextInt(range_padding_top); 
} 
} 

yanzhengma_img = (ImageView) findViewById(R.id.yanzhengma_img); 
yanzhengma_huan = (Button) findViewById(R.id.yanzhengma_huan); 
yanzhengma_val = (EditText) findViewById(R.id.yanzhengma_val); 
yanzhengma_img.setImageBitmap(code.getInstance().createBitmap()); 
System.out.println("验证码："+code.getInstance().getCode()); 
yanzhengma_huan.setOnClickListener(new View.OnClickListener() { 
public void onClick(View v) { 
yanzhengma_img.setImageBitmap(code.getInstance().createBitmap()); 
System.out.println("验证码："+code.getInstance().getCode()); 
} 
});