修复验证码位数的bug，优化代码

src/main/java/com/wf/captcha/Captcha.java

@@ -5,100 +5,114 @@ import java.awt.Font;
 import java.io.OutputStream;
 
 /**
- * <p>
- * 验证码抽象类,暂时不支持中文
- * </p>
- * 
- * @author: wuhongjun
- * @version:1.0
+ * 验证码抽象类
+ * Created by 王帆 on 2018-07-27 上午 10:08.
  */
 public abstract class Captcha extends Randoms {
-	protected Font font = new Font("Verdana", Font.ITALIC | Font.BOLD, 28); // 字体
-	protected int len = 5; // 验证码随机字符长度
-	protected int width = 150; // 验证码显示跨度
-	protected int height = 40; // 验证码显示高度
-	private String chars = null; // 随机字符串
+    protected Font font = new Font("Verdana", Font.ITALIC | Font.BOLD, 28); // 字体
+    protected int len = 5; // 验证码随机字符长度
+    protected int width = 150; // 验证码显示宽度
+    protected int height = 40; // 验证码显示高度
+    private String chars = null; // 当前验证码
 
-	/**
-	 * 生成随机字符数组
-	 * 
-	 * @return 字符数组
-	 */
-	protected char[] alphas() {
-		char[] cs = new char[len];
-		for (int i = 0; i < len; i++) {
-			cs[i] = alpha();
-		}
-		chars = new String(cs);
-		return cs;
-	}
+    /**
+     * 生成随机验证码
+     *
+     * @return 验证码字符数组
+     */
+    protected char[] alphas() {
+        char[] cs = new char[len];
+        for (int i = 0; i < len; i++) {
+            cs[i] = alpha();
+        }
+        chars = new String(cs);
+        return cs;
+    }
 
-	public Font getFont() {
-		return font;
-	}
+    /**
+     * 给定范围获得随机颜色
+     *
+     * @param fc 0-255
+     * @param bc 0-255
+     * @return 随机颜色
+     */
+    protected Color color(int fc, int bc) {
+        if (fc > 255)
+            fc = 255;
+        if (bc > 255)
+            bc = 255;
+        int r = fc + num(bc - fc);
+        int g = fc + num(bc - fc);
+        int b = fc + num(bc - fc);
+        return new Color(r, g, b);
+    }
 
-	public void setFont(Font font) {
-		this.font = font;
-	}
+    /**
+     * 验证码输出,抽象方法，由子类实现
+     *
+     * @param os 输出流
+     * @return 是否成功
+     */
+    public abstract boolean out(OutputStream os);
 
-	public int getLen() {
-		return len;
-	}
+    /**
+     * 获取当前的验证码
+     *
+     * @return 字符串
+     */
+    public String text() {
+        checkAlpha();
+        return chars;
+    }
 
-	public void setLen(int len) {
-		this.len = len;
-	}
+    /**
+     * 获取当前验证码的字符数组
+     *
+     * @return 字符数组
+     */
+    public char[] textChar() {
+        checkAlpha();
+        return chars.toCharArray();
+    }
 
-	public int getWidth() {
-		return width;
-	}
+    /**
+     * 检查验证码是否生成，没有这立即生成
+     */
+    public void checkAlpha() {
+        if (chars == null) {
+            alphas(); // 生成验证码
+        }
+    }
 
-	public void setWidth(int width) {
-		this.width = width;
-	}
+    public Font getFont() {
+        return font;
+    }
 
-	public int getHeight() {
-		return height;
-	}
+    public void setFont(Font font) {
+        this.font = font;
+    }
 
-	public void setHeight(int height) {
-		this.height = height;
-	}
+    public int getLen() {
+        return len;
+    }
 
-	/**
-	 * 给定范围获得随机颜色
-	 * 
-	 * @return Color 随机颜色
-	 */
-	protected Color color(int fc, int bc) {
-		if (fc > 255)
-			fc = 255;
-		if (bc > 255)
-			bc = 255;
-		int r = fc + num(bc - fc);
-		int g = fc + num(bc - fc);
-		int b = fc + num(bc - fc);
-		return new Color(r, g, b);
-	}
+    public void setLen(int len) {
+        this.len = len;
+    }
 
-	/**
-	 * 验证码输出,抽象方法，由子类实现
-	 * 
-	 * @param os
-	 *            输出流
-	 */
-	public abstract void out(OutputStream os);
+    public int getWidth() {
+        return width;
+    }
 
-	/**
-	 * 获取随机字符串
-	 * 
-	 * @return string
-	 */
-	public String text() {
-		return chars;
-	}
-	
-	public char[] textChar() {
-		return chars.toCharArray();
-	}
+    public void setWidth(int width) {
+        this.width = width;
+    }
+
+    public int getHeight() {
+        return height;
+    }
+
+    public void setHeight(int height) {
+        this.height = height;
+    }
 }