Day59 过滤器补充、监听器

1.思维导图

2.代码部分

过滤器：屏蔽敏感词

@WebFilter(
        filterName = "SensitiveWordsFilter" ,
        urlPatterns = "/*",
        initParams = {
                @WebInitParam(name = "word1",value = "山寨"),
                @WebInitParam(name = "word2" ,value = "水货"),
                @WebInitParam(name = "word3" ,value = "盗版"),
                @WebInitParam(name = "word4",value = "刻录")
        })
public class SensitiveWordsFilter implements Filter {

    //敏感词
    List<String> sensitiveWords = new ArrayList<>();

    public void init(FilterConfig config) throws ServletException {
        Enumeration<String> parameterNames = config.getInitParameterNames();
        while (parameterNames.hasMoreElements()) {
            String sensitiveWord = config.getInitParameter(parameterNames.nextElement());
            sensitiveWords.add(sensitiveWord);
        }
    }

    public void destroy() {
    }

    public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws ServletException, IOException {
        System.out.println("SensitiveWordsFilter doFilter");
        HttpServletRequest request = (HttpServletRequest) req;
        //增强request下的getParameter方法
        HttpServletRequest requestPrxoy = (HttpServletRequest) Proxy.newProxyInstance(
                request.getClass().getClassLoader(),
                request.getClass().getInterfaces(),
                new InvocationHandler() {
                    @Override
                    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                        //增强getParameter方法
                        Object returnValue = null;
                        String methodName = method.getName();
                        if ("getParameter".equals(methodName)) {
                            //returnValue就是getParameter方法的返回值,可能会存在敏感词
                            String returnValue1 = (String)method.invoke(request, args);
                            //开始处理敏感词
                            for (String sensitiveWord : sensitiveWords) {
                                if (returnValue1.contains(sensitiveWord)) {
                                    //getParameter方法的返回值包含敏感词
                                    returnValue1 = returnValue1.replace(sensitiveWord,"***");
                                }
                            }
                            return returnValue1;
                        } else {
                            returnValue = method.invoke(request, args);
                        }
                        return returnValue;
                    }
                });
        chain.doFilter(requestPrxoy, resp);
    }
}

一类监听器

• 监听器

public class MyListener01 implements ServletContextListener {

    @Override
    public void contextInitialized(ServletContextEvent sce) {
        //监听ServletContext域的初始化,随着服务器的启动
        System.out.println("ServletContext初始化");
    }

    @Override
    public void contextDestroyed(ServletContextEvent sce) {
        //监听ServletContext域的销毁，随着服务器的关闭
        System.out.println("ServletContext销毁");
    }
}

• web.xml

<listener>
    <listener-class>com.qfedu.listener.MyListener01</listener-class>
</listener>

二类监听器

• 监听器

public class MyServletContextAttributeListener implements ServletContextAttributeListener {

    @Override
    public void attributeAdded(ServletContextAttributeEvent scae) {
        //监听ServletContext域对象中属性添加
        System.out.println("ServletContext added");
    }

    @Override
    public void attributeReplaced(ServletContextAttributeEvent scae) {
        //监听ServletContext域对象中属性值被替换
        System.out.println("ServletContext replaced");

    }

    @Override
    public void attributeRemoved(ServletContextAttributeEvent scae) {
        //监听ServletContext域对象中属性值移除
        System.out.println("ServletContext removed");

    }
}

• web.xml

<listener>
    <listener-class>com.qfedu.listener.MyServletContextAttributeListener</listener-class>
</listener>

三类监听器

public class User implements HttpSessionBindingListener {


    @Override
    public void valueBound(HttpSessionBindingEvent event) {
        System.out.println("User绑定");
    }

    @Override
    public void valueUnbound(HttpSessionBindingEvent event) {
        System.out.println("User解绑");
    }
       
}

• 注：HttpSessionBindingListener 不需要配置web.xml