Java Web 三大利器主要有：
- 1.过滤器。
- 2.拦截器。
- 3.监听器。
过滤器是JavaWeb的三大组件之一。
过滤器它是 JavaEE 的规范，可以在浏览器以及目标资源之间起到一个过滤的作用，它的作用是：拦截请求，过滤响应。
Web中的过滤器：当访问服务器的资源时，过滤器可以将请求拦截下来，完成一些特殊的功能。
2.过滤器的应用场景有哪些？- (1)登录验证。
- (2)权限检查。
- (3)事务管理。
- (4)统一编码处理。
- (5)敏感字符处理。
- (1)服务器启动，首先执行构造方法和init方法（这两个方法只执行一次）
- (2)当有匹配过滤条件的请求时执行doFilter方法（该方法可以执行多次）
- (3)服务器正常关闭的时候，或者该Filter类重新加载的时候会执行destroy方法（该方法只执行一次）
@Component
public class FilterPerm implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
System.out.println("init......");
}
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
HttpServletRequest request = (HttpServletRequest) servletRequest;
HttpServletResponse response = (HttpServletResponse) servletResponse;
System.out.println("FilterPerm," + request.getRequestURI());
RespVO vo = new RespVO();
PrintWriter out = null;
response.setCharacterEncoding("UTF-8");
response.setContentType("application/json; charset=utf-8");
try {
String token = request.getParameter("token") == null ? null : request.getParameter("token");
if (token == null || token == "") {
vo.setCode(400);
vo.setMsg("未携带Token");
}
if (token != null && "abcdef".equals(token)) {
filterChain.doFilter(servletRequest, servletResponse);
System.out.println("通过");
}
if (token != null && !"abcdef".equals(token)) {
vo.setCode(403);
vo.setMsg("访问未授权");
}
} catch (Exception e) {
e.printStackTrace();
vo.setCode(500);
vo.setMsg("Server Error");
}
out = response.getWriter();
String json = JSONUtil.toJsonPrettyStr(vo);
// 返回json信息给前端
out.append(json);
out.flush();
}
@Override
public void destroy() {
System.out.println("destroy......");
}
}
二、拦截器
1.什么是拦截器？
Java里的拦截器是动态拦截Action调用的对象，它提供了一种机制可以使开发者在一个Action执行的前后执行一段代码，也可以在一个Action执行前阻止其执行，同时也提供了一种可以提取Action中可重用部分代码的方式。
2.拦截器的应用场景有哪些？- (1)权限控制。
- (2)日志打印。
- (3)参数校验。
核心代码：
AuthInterceptor.java
@Component
public class AuthInterceptor implements HandlerInterceptor {
private String urls[] = {
"/xxnet/token"
};
@Override
public boolean preHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o) throws Exception {
String url = httpServletRequest.getRequestURI();
String username = httpServletRequest.getHeader("username");
String password = httpServletRequest.getHeader("password");
// 遍历需要忽略拦截的路径
for (String item : this.urls) {
if (item.equals(url)) {
return true;
}
}
if (username == null || password == null) {
httpServletResponse.setCharacterEncoding("UTF-8");
httpServletResponse.setContentType("application/json; charset=utf-8");
PrintWriter out = null;
ResultBody res = new ResultBody(ResultCode.TOKEN_ERROR.getCode(), ResultCode.TOKEN_ERROR.getMsg());
res.setMsg("用户名或密码不能为空");
res.setCode("400");
String json = JSONUtil.toJsonPrettyStr(res);
httpServletResponse.setContentType("application/json");
out = httpServletResponse.getWriter();
// 返回json信息给前端
out.append(json);
out.flush();
return false;
}
if (username != null && password != null) {
httpServletResponse.setCharacterEncoding("UTF-8");
httpServletResponse.setContentType("application/json; charset=utf-8");
PrintWriter out = null;
try {
//获取用户名和密码
Props props = new Props("auth.properties");
String userName = props.get(CommonConstant.USERNAME).toString();
String pwd = props.get(CommonConstant.USERNAME).toString();
if (userName.equals(userName) && pwd.equals(password)) {
return true;
} else if (!userName.equals(userName) || !pwd.equals(password)) {
ResultBody res = new ResultBody();
res.setMsg("用户名或密码错误");
res.setCode("500");
String json = JSONUtil.toJsonPrettyStr(res);
httpServletResponse.setContentType("application/json");
out = httpServletResponse.getWriter();
// 返回json信息给前端
out.append(json);
out.flush();
return false;
} else {
ResultBody res = new ResultBody();
res.setMsg("未登录，暂无权限");
res.setCode("500");
String json = JSONUtil.toJsonPrettyStr(res);
httpServletResponse.setContentType("application/json");
out = httpServletResponse.getWriter();
// 返回json信息给前端
out.append(json);
out.flush();
return false;
}
} catch (Exception e) {
e.printStackTrace();
httpServletResponse.sendError(500);
return false;
}
}
return true;
}
@Override
public void afterCompletion(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, Exception e) throws Exception {
// System.out.println("视图渲染之后的操作");
}
}
WebConfig.java
@Configuration
public class WebConfig implements WebMvcConfigurer {
@Autowired
private AuthInterceptor authInterceptor;
@Override
public void addInterceptors(InterceptorRegistry registry) {
registry.addInterceptor(authInterceptor)
.addPathPatterns("
@Component
public class UserHttpSessionListener implements HttpSessionListener {
private static final Logger logger = LoggerFactory.getLogger(UserHttpSessionListener.class);
public Integer count = 0;
@Override
public synchronized void sessionCreated(HttpSessionEvent httpSessionEvent) {
logger.info("新用户上线了");
count++;
httpSessionEvent.getSession().getServletContext().setAttribute("count", count);
}
@Override
public synchronized void sessionDestroyed(HttpSessionEvent httpSessionEvent) {
logger.info("用户下线了");
count--;
httpSessionEvent.getSession().getServletContext().setAttribute("count", count);
}
}
TestController.java
@RestController
@RequestMapping("/listener")
public class TestController {
GetMapping("/total")
public String getTotalUser(HttpServletRequest request, HttpServletResponse response) {
Cookie cookie;
try {
// 把sessionId记录在浏览器中
cookie = new Cookie("JSESSIONID", URLEncoder.encode(request.getSession().getId(), "utf-8"));
cookie.setPath("/");
//设置cookie有效期为2天，设置长一点
cookie.setMaxAge( 48*60 * 60);
response.addCookie(cookie);
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
Integer count = (Integer) request.getSession().getServletContext().getAttribute("count");
return "当前在线人数：" + count;
}
}
