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@Overridepublic 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);}@Overridepublic 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 {@Overrideprotected 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 {@Overridepublic void init(FilterConfig filterConfig) throws ServletException {ServletContext servletContext = filterConfig.getServletContext();}@Overridepublic 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}@Overridepublic 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 {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {process(req, resp);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {process(req, resp);}@SneakyThrowsprivate void process(HttpServletRequest request, HttpServletResponse response) {DispatchUtil.dispatch(request,response,this);}@SneakyThrowsprivate 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 {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {process(req, resp);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {process(req, resp);}@SneakyThrowsprivate void process(HttpServletRequest request, HttpServletResponse response) {DispatchUtil.dispatch(request, response, this);}@SneakyThrowsprivate 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");}}@SneakyThrowsprivate void logout(HttpServletRequest request, HttpServletResponse response){HttpSession session = request.getSession();session.invalidate();response.getWriter().println("注销用户");}@SneakyThrowsprivate 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 {@Overridepublic 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);}@Overridepublic void contextDestroyed(ServletContextEvent sce) {}
}

• filter目录下

@WebFilter("/*")
public class CharacterEncodingFilter implements Filter {List<String> whiteList = null;@SneakyThrows@Overridepublic 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");}@Overridepublic 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");
//        }}@Overridepublic 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 - contextPathString uriSuffix = null;// eg: /demo3/user/nameString requestURI = request.getRequestURI();// eg: /demo3String 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