Web组件

• JavaEE的Web组件（三大Web组件）：
  1. Servlet → 处理请求对应的业务
  2. Listener → 监听器
  3. Filter → 过滤器

---

Listener监听器

• 监听器在监听到主体做了XX事情，就会触发对应的事件
• 监听的东西与命名有关系
• 要加上注解@WebListener

ServletContextListener

监听的主体就是ServletContext，当发现ServletContext做了事情，Listener（监听器）就会执行该事件特定的方法。

• ServletContext如果初始化，则会执行监听器的初始化方法contextInitialized
  • ServletContext应用程序启动的时候初始化，就意味着应用程序启动
• ServletContext如果销毁，则会执行监听器的销毁方法contextDestroy
  • ServletContext应用程序关闭的时候销毁，意味着应用程序关闭
• 应用程序启动的时候会执行ServletContextListener的contextInitialized方法；应用程序关闭的时候会执行contextDestroy

执行过程

当应用程序启动的过程中，逐步加载Web组件

• 首先会加载ServletContext和Listener组件
  • ServletContext伴随着应用程序初始化，它开始初始化，然后ServletContextListener监听到ServletContext初始化，会执行Listener的Initialized方法
• 然后初始化loadOnStartup为正数的Servlet

eg：

@WebListener
public class PropertyInitServletContextListener implements ServletContextListener {
    @SneakyThrows
    @Override
    public void contextInitialized(ServletContextEvent servletContextEvent) {
        ServletContext servletContext = servletContextEvent.getServletContext();

        InputStream inputStream = PropertyInitServletContextListener.class.getClassLoader()
        .getResourceAsStream("parameter.properties");
        Properties properties = new Properties();
        properties.load(inputStream);
        String picPath = properties.getProperty("pic.path");

        servletContext.setAttribute("picPath", picPath);
    }

    @Override
    public void contextDestroyed(ServletContextEvent servletContextEvent) {
        System.out.println("应用程序关闭，可以做一些资源的释放");
    }
}

/**
 * localhost:8080/demo1/picture/fetch?name=1.jpg
 */
@WebServlet("/picture/fetch")
public class PictureAccessServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // InputStream inputStream = PictureAccessServlet.class.getClassLoader()
        //         .getResourceAsStream("parameter.properties");
        // Properties properties = new Properties();
        // properties.load(inputStream);
        // String path = properties.getProperty("pic.path");
        String path = (String) getServletContext().getAttribute("picPath");

        File file = new File(path,request.getParameter("name"));
        FileInputStream fileInputStream = new FileInputStream(file);

        ServletOutputStream outputStream = response.getOutputStream();
        int length = 0;
        byte[] bytes = new byte[1024];
        while((length = fileInputStream.read(bytes)) != -1) {
            outputStream.write(bytes,0,length);
        }
        fileInputStream.close();
        outputStream.close();
    }
}

---

Filter过滤器

• Filter是一个执行过滤任务的一个对象
  • 它既可以作用于Request对象，也可以作用于Response对象，或者两者均作用
• 就是Servlet中获取请求之前，Servlet响应之后

Filter与Servlet的执行

• URL-Pattern和Servlet之间存在着映射关系，URL-Pattern和Filter之间也存在着映射关系
  • 1个URL-Pattern只能对应一个Servlet，但是可以对应多个Filter
  • Servlet和URL-Pattern之间是一对多的关系，但是URL-Pattern和Servlet之间是一对一
• 其实，一个URL-Pattern对应的请求
  • 对应1个Servlet
  • 对应多个Filter

eg：

@WebFilter("/user/*")
public class CharacterEncodingFilter implements Filter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        ServletContext servletContext = filterConfig.getServletContext();
    }

    @Override
    public void doFilter(ServletRequest servletRequest
            , ServletResponse servletResponse, FilterChain filterChain)
            throws IOException, ServletException {
        // 做过滤，里面写的就是通用的业务
        // 前半部分
        
        // 这部分是解决中文乱码问题
        HttpServletResponse response = (HttpServletResponse) servletResponse;
        HttpServletRequest request = (HttpServletRequest) servletRequest;
        request.setCharacterEncoding("utf-8");
        response.setContentType("text/html;charset=utf-8");

        filterChain.doFilter(servletRequest, servletResponse); // 执行下一个过滤器或者Servlet

        // 后半部分
        // 但是一般业务代码都写在前半部分

    }

    @Override
    public void destroy() {

    }
}

---

案例（登录案例）

• 需求
  • /user/login
  • /user/logout
  • /user/info
  • /order/list
  • 增加web组件中的filter功能
  • 增加web组件中的listener功能
  • 增加白名单功能

• bean目录下

@Data
public class Order {
    private Integer id;
    private String name;
    private Double price;
    private Integer userId;
}

@Data
public class User {
    private Integer id;

    private String username;

    private String password;

    private Integer age;

    private Date birthday;

    private Date createdate;

    private String mobile;

}

• mapper目录下

public interface OrderMapper {
    List<Order> selectByUserId(Integer id);
}

public interface UserMapper {
    List<User> selectByUserNameAndPassword
            (@Param("username") String username, @Param("password") String password);

    User selectByPrimaryKey(Integer id);
}

• servlet目录下

@WebServlet("/order/*")
public class OrderServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        process(req, resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        process(req, resp);
    }

    @SneakyThrows
    private void process(HttpServletRequest request, HttpServletResponse response) {
        DispatchUtil.dispatch(request,response,this);
    }

    @SneakyThrows
    private void list(HttpServletRequest request, HttpServletResponse response){
        // 先判断是否是登录状态
        // 如果没有登录，则跳转到登录页面
        // 这里filter帮我们完成了

        // 如果已经登录，则查询orderlist信息
        OrderMapper orderMapper = MybatisUtil.getSqlSession().getMapper(OrderMapper.class);
        HttpSession session = request.getSession();
        User user = (User) session.getAttribute("user");
        List<Order> orders = orderMapper.selectByUserId(user.getId());
        response.getWriter().println(orders);
    }
}

@WebServlet("/user/*")
public class UserServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        process(req, resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        process(req, resp);
    }

    @SneakyThrows
    private void process(HttpServletRequest request, HttpServletResponse response) {
        DispatchUtil.dispatch(request, response, this);
    }

    @SneakyThrows
    private void login(HttpServletRequest request, HttpServletResponse response){
        // 获取username和password，查询user记录
        String username = request.getParameter("username");
        String password = request.getParameter("password");

        UserMapper userMapper = MybatisUtil.getSqlSession().getMapper(UserMapper.class);
        List<User> users = userMapper.selectByUserNameAndPassword(username, password);

        // 有可能用户名和密码相同，则取第一条数据
        if (users != null && users.size() > 0) {
            User user = users.get(0);
            HttpSession session = request.getSession();
            session.setAttribute("user",user);
            response.getWriter().println("登录成功");
        } else {
            response.getWriter().println("用户名或密码错误，即将跳转到登录页面...");
            response.setHeader("refresh","2;url=/demo3/login.html");
        }
    }

    @SneakyThrows
    private void logout(HttpServletRequest request, HttpServletResponse response){
        HttpSession session = request.getSession();
        session.invalidate();
        response.getWriter().println("注销用户");
    }

    @SneakyThrows
    private void info(HttpServletRequest request, HttpServletResponse response){
        // 先判断是否是登录状态
        // 如果没有登录，则跳转到登录页面
        // 这里filter帮我们做了

        // 如果已经登录，可以从session中获取信息 -> 响应信息
        HttpSession session = request.getSession();
        User user = (User) session.getAttribute("user");
        response.getWriter().println(user);
    }
}

• listener目录下

@WebListener
public class PropertyServletContextListener implements ServletContextListener {
    @Override
    public void contextInitialized(ServletContextEvent servletContextEvent) {
        ServletContext servletContext = servletContextEvent.getServletContext();

        Properties properties = new Properties();

        InputStream inputStream = PropertyServletContextListener.class.getClassLoader()
                .getResourceAsStream("application.properties");

        try {
            properties.load(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }

        String whiteList = properties.getProperty("whiteList");

        String[] whiteListStr = whiteList.split(",");

        List<String> list = Arrays.asList(whiteListStr);

        servletContext.setAttribute("whiteList", list);
    }

    @Override
    public void contextDestroyed(ServletContextEvent sce) {

    }
}

• filter目录下

@WebFilter("/*")
public class CharacterEncodingFilter implements Filter {
    List<String> whiteList = null;

    @SneakyThrows
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        // 方法1：
//        Properties properties = new Properties();
//        InputStream inputStream = CharacterEncodingFilter.class.getClassLoader()
//                .getResourceAsStream("application.properties");
//        properties.load(inputStream);
//        String whiteListStr = properties.getProperty("whiteList");
//        String[] whiteArray = whiteListStr.split(",");
//        whiteList = Arrays.asList(whiteArray);

        // 方法2：
        // 可以先把配置文件在Listener的时候放入
        whiteList = (List<String>) filterConfig.getServletContext().getAttribute("whiteList");
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse
            , FilterChain filterChain)
            throws IOException, ServletException {
        // List<String> list = Arrays.asList("/user/login", "/user/logout", "/login.html");

        // 强转
        HttpServletRequest request = (HttpServletRequest) servletRequest;
        HttpServletResponse response = (HttpServletResponse) servletResponse;

        String uriSuffix = UriUtil.getUriSuffix(request);
        if (whiteList.contains(uriSuffix)) {
            if (!uriSuffix.endsWith("html")) {
                // 1. 解决字符集
                request.setCharacterEncoding("utf-8");
                // 响应的字符集问题
                response.setContentType("text/html;charset=utf-8");
            }
            filterChain.doFilter(request, response);
        }

        // 1. 解决字符集
        request.setCharacterEncoding("utf-8");
        // 响应的字符集问题
        response.setContentType("text/html;charset=utf-8");

        // 2. 解决登录状态的判断
        HttpSession session = request.getSession();
        Object user = session.getAttribute("user");

        // 2.1 如果已经登录（或者登录/注销请求）就放行
        if (user != null) {
            filterChain.doFilter(request, response);
        } else {
            // 2.2 如果没有登录就提示，跳转到登录页面
            response.getWriter().println("没有登录，请先登录，即将跳转到登录页面...");
            response.setHeader("refresh", "2;url=/demo3/login.html");
        }


//        String requestURI = request.getRequestURI();


//        if (requestURI.endsWith("html")) {
//            filterChain.doFilter(request, response);
//        }

        // 2.1 如果已经登录（或者登录/注销请求）就放行
//        if (user != null || requestURI.endsWith("login")
//                || requestURI.endsWith("logout")){
//            filterChain.doFilter(request, response);
//        } else {
//            // 2.2 如果没有登录就提示，跳转到登录页面
//            response.getWriter().println("没有登录，请先登录，即将跳转到登录页面...");
//            response.setHeader("refresh","2;url=/demo3/login.html");
//        }
    }

    @Override
    public void destroy() {

    }
}

• util目录下

public class DispatchUtil {
    public static void dispatch(String operation, HttpServletRequest request, HttpServletResponse response, HttpServlet instance)
            throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
        Method method = instance.getClass().getDeclaredMethod(operation, HttpServletRequest.class, HttpServletResponse.class);
        method.setAccessible(true);
        method.invoke(instance, new Object[]{request, response});
    }

    public static void dispatch(HttpServletRequest request, HttpServletResponse response, HttpServlet userServlet)
            throws NoSuchMethodException, IllegalAccessException, InvocationTargetException {
        String requestURI = request.getRequestURI();
        String operation = requestURI.substring(requestURI.lastIndexOf("/") + 1);
        dispatch(operation, request, response, userServlet);
    }
}

public class MybatisUtil {
    private static SqlSession sqlSession;

    static{
        try {
            sqlSession = new SqlSessionFactoryBuilder()
                    .build(Resources.getResourceAsStream("mybatis.xml")).openSession(true);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static SqlSession getSqlSession() {
        return sqlSession;
    }
}

public class UriUtil {

    // Suffix的意思是后缀
    public static String getUriSuffix(HttpServletRequest request) {
        // uri - contextPath
        String uriSuffix = null;
        // eg: /demo3/user/name
        String requestURI = request.getRequestURI();
        // eg: /demo3
        String contextPath = request.getContextPath();
        if (contextPath == null || contextPath.length() == 0) {
            // 这是一个root应用
            uriSuffix = requestURI;
        } else {
            uriSuffix = requestURI.replaceAll(contextPath, "");
            // 或者：uriSuffix = requestURI.substring();
        }
        return uriSuffix;
    }
}

• UserMapper的xml目录

<mapper namespace="com.coo1heisenberg.demo3.mapper.OrderMapper">

    <select id="selectByUserId" resultType="com.coo1heisenberg.demo3.bean.Order">
        select id, name, price, user_id as userId from test_product
        <where>
            user_id = #{user_id}
        </where>
    </select>
</mapper>

<mapper namespace="com.coo1heisenberg.demo3.mapper.UserMapper">

    <select id="selectByUserNameAndPassword" resultType="com.coo1heisenberg.demo3.bean.User">
        select id, username, password, age, birthday, createDate, mobile from test_user
        <where>
            username = #{username} and password = #{password}
        </where>
    </select>

    <select id="selectByPrimaryKey" resultType="com.coo1heisenberg.demo3.bean.User">
        select id, username, password, age, birthday, createDate, mobile from test_user
        <where>
            id = #{id}
        </where>
    </select>
</mapper>

---

小结

Web组件

• 核心是Servlet，处理核心业务
• Listener，用来做资源的初始化
• Filter，在Servlet处理前后增加通用的处理