Patchca简单而功能强大
Jar包下载：lecode/files/patchca-0.5.0.zip
源代码：lecode/svn/trunk/
一：定义一个servlet生成图片（先引入jar包）
（1）：配置xml
<servlet>
        <servlet-name>patchca</servlet-name>
        <servlet-class>com.ssh.servlet.CaptchaServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>patchca</servlet-name>
        <url-pattern>/patchca.png</url-pattern>
</servlet-mapping>
session下载（2）：servlet（自定义CaptchaService）
public class CaptchaServlet extends HttpServlet {
    private static final long serialVersionUID = 4968328161261528097L;
    private static MyCaptchaService cs = null;
    @Override
public void init() throws ServletException {
        super.init();
        //可直接使用ConfigurableCaptchaService，然后修改配置
        cs = new MyCaptchaService();
    }
@Override
    public void destroy() {
        cs = null;
        super.destroy();
    }
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("image/png");
        response.setHeader("cache", "no-cache");
        HttpSession session = Session(true);
        OutputStream os = OutputStream();
        String patchca= EncoderHelper.getChallangeAndWriteImage(cs, "png", os);
        session.setAttribute("PATCHCA", patchca);
        os.flush();
        os.close();
    }
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        this.doGet(request, response);
    }
    private class MyCaptchaService extends AbstractCaptchaService {
        public MyCaptchaService() {
            //文本内容
            wordFactory = new MyWordFactory();
            //字体
            fontFactory = new RandomFontFactory();
            //效果
            textRenderer = new BestFitTextRenderer();
            //背景
            backgroundFactory = new SingleColorBackgroundFactory();
            //字体颜
            colorFactory = new SingleColorFactory(new Color(25, 60, 170));
            //样式(曲线波纹加干扰线)
            filterFactory = new CurvesRippleFilterFactory(colorFactory);
//图片长宽
            width = 150;
            height = 50;
        }
    }
    private class MyWordFactory extends RandomWordFactory {
        public MyWordFactory() {
//文本范围和长度
            characters = "absdekmnowx23456789";
            minLength = 5;
            maxLength = 4;
        }
    }
}
（3）包中提供的配置：
一：ConfigurableCaptchaService：
FontFactory 字体
    默认：RandomFontFactory（Verdana，Tahoma，minSize、maxSize=45）
WordFactory 单词范围和长度
    默认：RandomWordFactory 单词6-6
    其他：AdaptiveRandomWordFactory 自适应(mw字母宽度加长)
ColorFactory
    默认：SingleColorFactory 黑
BackgroundFactory
    默认：SingleColorBackgroundFactory 白
TextRenderer 文本渲染
    默认：BestFitTextRenderer
FilterFactory 样式
    默认：CurvesRippleFilterFactory（曲线波纹带干扰线，干扰线颜为当前colorFactory）
width/height 图片长宽（默认160*70）
使用：
public class CaptchaServlet extends HttpServlet {
private static final long serialVersionUID = 4968328161261528097L;
private static ConfigurableCaptchaService cs = null;
private static ColorFactory cf = null;
private static RandomWordFactory wf = null;
private static Random r = new Random();
private static CurvesRippleFilterFactory crff = null;
private static MarbleRippleFilterFactory mrff = null;
private static DoubleRippleFilterFactory drff = null;
private static WobbleRippleFilterFactory wrff = null;
private static DiffuseRippleFilterFactory dirff = null;
@Override
public void init() throws ServletException {
    super.init();
    cs = new ConfigurableCaptchaService();
    cf = new SingleColorFactory(new Color(25, 60, 170));
    wf = new RandomWordFactory();
    crff = new ColorFactory());
    drff = new DoubleRippleFilterFactory();
    wrff = new WobbleRippleFilterFactory();
    dirff = new DiffuseRippleFilterFactory();
    mrff = new MarbleRippleFilterFactory();
    cs.setWordFactory(wf);
    cs.setColorFactory(cf);
    cs.setWidth(120);
    cs.setHeight(50);
}
@Override
public void destroy() {
    wf = null;
    cf = null;
    cs = null;
    super.destroy();
}
public void doGet(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
    response.setContentType("image/png");
    response.setHeader("cache", "no-cache");
    wf.setMaxLength(5);
    wf.setMinLength(3);
    HttpSession session = Session(true);
    OutputStream os = OutputStream();
//随机产生5种效果（filter）
    switch (r.nextInt(5)) {
    case 0:
        cs.setFilterFactory(crff);
        break;
    case 1:
        cs.setFilterFactory(mrff);
        break;
    case 2:
        cs.setFilterFactory(drff);
        break;
    case 3:
        cs.setFilterFactory(wrff);
        break;
    case 4:
        cs.setFilterFactory(dirff);
        break;
    }
    String patchca= EncoderHelper.getChallangeAndWriteImage(cs, "png", os);
    session.setAttribute("PATCHCA", patchca);

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