过滤器、监听器和拦截器 - pingdongyi/blog-2 GitHub Wiki

过滤器

Servlet中的过滤器Filter是实现了javax.servlet.Filter接口的服务器端程序，主要的用途是过滤字符编码、做一些业务逻辑判断等。其工作原理是，只要你在web.xml文件配置好要拦截的客户端请求，它都会帮你拦截到请求，此时你就可以对请求或响应(Request、Response)统一设置编码，简化操作；同时还可进行逻辑判断，如用户是否已经登陆、有没有权限访问该页面等等工作。它是随你的web应用启动而启动的，只初始化一次，以后就可以拦截相关请求，只有当你的web应用停止或重新部署的时候才销毁

通过实现Filter接口创建过滤器

@Transactional
public class LogFilter implements Filter {

    //可在该config里获取配置的初始化参数等
    private FilterConfig config;

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        this.config = filterConfig;
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) servletRequest;
        HttpServletResponse response = (HttpServletResponse) servletResponse;
        //response.sendError(403,"Forbidden") //可以判断不符合逻辑的请求直接返回错误
        //return;
        System.out.println(request.getRequestURI()+request.getQueryString());
        long begin = System.currentTimeMillis();
        filterChain.doFilter(servletRequest, servletResponse);
        long end = System.currentTimeMillis();
        System.out.println("this is the filter: " + (end - begin));

    }

    @Override
    public void destroy() {
        this.config = null;
    }
}

在web.xml里声明配置过滤器

#web.xml中的配置
<filter>
    <filter-name>logFilter</filter-name>
    <filter-class>com.ibingbo.filter.LogFilter</filter-class>
</filter>
<!--可以配置多个过滤映射-->
<filter-mapping>
    <filter-name>logFilter</filter-name>
    <url-pattern>/aa</url-pattern>
</filter-mapping>
<filter-mapping>
    <filter-name>logFilter</filter-name>
    <url-pattern>/bb</url-pattern>
</filter-mapping>

监听器

监听器主要做一些初始化工作,做一些初始化的内容添加工作、设置一些基本的内容、比如一些参数或者是一些固定的对象等等

可以通过实现ServletContextListener,RequestContextFilter等创建监听器

/**
 * 监听器主要做 一些初始化工作
 * 做一些初始化的内容添加工作、设置一些基本的内容、比如一些参数或者是一些固定的对象等等
 * Created by bing on 2016/12/29.
 */
public class LogListener implements ServletContextListener{
    @Override
    public void contextInitialized(ServletContextEvent servletContextEvent) {
        System.out.println("this is the listener doing....");
    }

    @Override
    public void contextDestroyed(ServletContextEvent servletContextEvent) {
        System.out.println("this is the listener done ...");
    }
}

在web.xml中声明配置监听器

#web.xml中配置
<listener>
		<listener-class>com.ibingbo.listener.LogListener</listener-class>
	</listener>

拦截器

拦截器是在面向切面编程中应用的，就是在你的service或者一个方法前调用一个方法，或者在方法后调用一个方法。是基于JAVA的反射机制。拦截器不是在web.xml，比如struts在struts.xml中配置

通过实现HandlerInterceptor接口创建拦截器

public class LogInterceptor implements HandlerInterceptor{
    @Override
    public boolean preHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o) throws Exception {
        System.out.println("LogInterceptor pre handle ...."+httpServletRequest.getRequestURI()+httpServletRequest.getQueryString());
        //返回false就不往下执行
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, ModelAndView modelAndView) throws Exception {
        System.out.println("LogInterceptor post handle ....");

    }

    @Override
    public void afterCompletion(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, Exception e) throws Exception {
        System.out.println("LogInterceptor after completion ....");

    }
}

通过继承HandlerInterceptorAdapter适配器创建拦截器，可以重写自己需要的方法

public class LogInterceptor2 extends HandlerInterceptorAdapter{
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("LogInterceptor2 pre handle ...."+request.getRequestURI()+request.getQueryString());
        //return super.preHandle(request, response, handler);
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("LogInterceptor2 post handle ....");
        super.postHandle(request, response, handler, modelAndView);
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println("LogInterceptor2 after completion ....");
        super.afterCompletion(request, response, handler, ex);
    }
}

在spring中配置拦截器

#spring-context.xml中的配置
<!--拦截器应用-->
<bean id="logInterceptor" class="com.ibingbo.interceptor.LogInterceptor"/>
<bean id="logInterceptor2" class="com.ibingbo.interceptor.LogInterceptor2"/>
<bean class="org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping">
    <property name="interceptors">
        <list>
            <ref bean="logInterceptor"/>
            <ref bean="logInterceptor2"/>
        </list>
    </property>
</bean>
<mvc:interceptors>
    <mvc:interceptor>
        <mvc:mapping path="/**"/>
        <bean class="com.ibingbo.interceptor.LogInterceptor"/>
    </mvc:interceptor>
    <mvc:interceptor>
        <mvc:mapping path="/**"/>
        <bean class="com.ibingbo.interceptor.LogInterceptor2"/>
    </mvc:interceptor>
</mvc:interceptors>