WxMpDefaultConfigImpl config = new WxMpDefaultConfigImpl();
config.setAppId("..."); // 设置微信公众号的appid
config.setSecret("..."); // 设置微信公众号的app corpSecret
config.setToken("..."); // 设置微信公众号的token
config.setAesKey("..."); // 设置微信公众号的EncodingAESKey

WxMpService wxService = new WxMpServiceImpl();// 实际项目中请注意要保持单例，不要在每次请求时构造实例，具体可以参考demo项目
wxService.setWxMpConfigStorage(config);

// 用户的openid在下面地址获得 
// https://mp.weixin.qq.com/debug/cgi-bin/apiinfo?t=index&type=用户管理&form=获取关注者列表接口%20/user/get 
String openid = "...";
WxMpKefuMessage message = WxMpKefuMessage.TEXT().toUser(openid).content("Hello World").build();
wxService.getKefuService().sendKefuMessage(message);

public class WxMpServlet extends HttpServlet {

  protected WxMpDefaultConfigImpl config;
  protected WxMpService wxMpService;
  protected WxMpMessageRouter wxMpMessageRouter;

  @Override 
public void init() throws ServletException {
    super.init();

    config = new WxMpDefaultConfigImpl();
    config.setAppId("..."); // 设置微信公众号的appid
    config.setSecret("..."); // 设置微信公众号的app corpSecret
    config.setToken("..."); // 设置微信公众号的token
    config.setAesKey("..."); // 设置微信公众号的EncodingAESKey

    wxMpService = new WxMpServiceImpl();
    wxMpService.setWxMpConfigStorage(config);

    WxMpMessageHandler handler = new WxMpMessageHandler() {
      @Override 
public WxMpXmlOutMessage handle(WxMpXmlMessage wxMessage, Map<String, Object> context, WxMpService wxMpService) {
        WxMpXmlOutTextMessage m
            = WxMpXmlOutMessage.TEXT().content("测试加密消息").fromUser(wxMessage.getToUser())
            .toUser(wxMessage.getFromUser()).build();
        return m;
      }
    };

    wxMpMessageRouter = new WxMpMessageRouter(wxMpService);
    wxMpMessageRouter
        .rule()
        .async(false)
        .content("哈哈") // 拦截内容为“哈哈”的消息
        .handler(handler)
        .end();

  }

  @Override protected void service(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {

    response.setContentType("text/html;charset=utf-8");
    response.setStatus(HttpServletResponse.SC_OK);

    String signature = request.getParameter("signature");
    String nonce = request.getParameter("nonce");
    String timestamp = request.getParameter("timestamp");

    if (!wxMpService.checkSignature(timestamp, nonce, signature)) {
      // 消息签名不正确，说明不是公众平台发过来的消息
      response.getWriter().println("非法请求");
      return;
    }

    String echostr = request.getParameter("echostr");
    if (StringUtils.isNotBlank(echostr)) {
      // 说明是一个仅仅用来验证的请求，回显echostr
      response.getWriter().println(echostr);
      return;
    }

    String encryptType = StringUtils.isBlank(request.getParameter("encrypt_type")) ?
        "raw" :
        request.getParameter("encrypt_type");

    if ("raw".equals(encryptType)) {
      // 明文传输的消息
      WxMpXmlMessage inMessage = WxMpXmlMessage.fromXml(request.getInputStream());
      WxMpXmlOutMessage outMessage = wxMpMessageRouter.route(inMessage);
      if(outMessage == null) {
          //为null，说明路由配置有问题，需要注意
          response.getWriter().write("");
      }
      response.getWriter().write(outMessage.toXml());
      return;
    }

    if ("aes".equals(encryptType)) {
      // 是aes加密的消息
      String msgSignature = request.getParameter("msg_signature");
      WxMpXmlMessage inMessage = WxMpXmlMessage.fromEncryptedXml(request.getInputStream(), wxMpConfigStorage, timestamp, nonce, msgSignature);
      WxMpXmlOutMessage outMessage = wxMpMessageRouter.route(inMessage);
      if(outMessage == null) {
          //为null，说明路由配置有问题，需要注意
          response.getWriter().write("");
      }
      response.getWriter().write(outMessage.toEncryptedXml(wxMpConfigStorage));
      return;
    }

    response.getWriter().println("不可识别的加密类型");
    return;
  }

}