1、概念简介
JavaWeb三大组件：Servlet，Listener，Filter。监听器就是指在应用程序中监听相关对象状态变化的组件。
2、事件源对象
指被监听对象。
ServletContext
ServletContextListener生命周期监听，它有两个方法，出生时调用contextInitialized()，销毁时调用contextDestroyed();
ServletContextAttributeListener属性监听，它有三个方法，添加属性attributeAdded()，替换属性attributeReplaced()，移除属性时attributeRemoved()。
HttpSession
HttpSessionListener生命周期监听：它有两个方法，出生时调用sessionCreated()，销毁时调用sessionDestroyed()；
HttpSessioniAttributeListener属性监听：它有三个方法，添加属性attributeAdded()，替换属性attributeReplaced()，移除属性attributeRemoved()。
ServletRequest
ServletRequestListener生命周期监听：它有两个方法，出生时调用requestInitialized()，销毁时调用requestDestroyed()；
ServletRequestAttributeListener属性监听：它有三个方法，添加属性attributeAdded()，替换属性attributeReplaced()，移除属性attributeRemoved()。
3、编码案例
相关监听器
TheContextListener
public class TheContextListener implements ServletContextListener {
@Override
public void contextInitialized(ServletContextEvent servletContextEvent) {
System.out.println("初始化：TheContextListener");
ServletContext servletContext = servletContextEvent.getServletContext() ;
servletContext.setAttribute("author","cicada");
}
@Override
public void contextDestroyed(ServletContextEvent servletContextEvent) {
System.out.println("销毁：TheContextListener");
}
}
TheRequestListener
public class TheRequestListener implements ServletRequestListener {
@Override
public void requestDestroyed(ServletRequestEvent servletRequestEvent) {
System.out.println("初始化：TheRequestListener");
}
@Override
public void requestInitialized(ServletRequestEvent servletRequestEvent) {
System.out.println("销毁：TheRequestListener");
}
}
TheSessionListener
public class TheSessionListener implements HttpSessionListener {
@Override
public void sessionCreated(HttpSessionEvent httpSessionEvent) {
System.out.println("初始化：TheSessionListener");
}
@Override
public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {
System.out.println("销毁：TheSessionListener");
}
}
RequestAttributeListener
public class RequestAttributeListener implements ServletRequestAttributeListener {
@Override
public void attributeAdded(ServletRequestAttributeEvent evt) {
System.out.println("Request添加属性："+evt.getName()+";"+evt.getValue());
}
@Override
public void attributeRemoved(ServletRequestAttributeEvent evt) {
System.out.println("Request移除属性："+evt.getName()+";"+evt.getValue());
}
@Override
public void attributeReplaced(ServletRequestAttributeEvent evt) {
System.out.println("Request替换属性："+evt.getName()+";"+evt.getValue());
}
}
web.xml配置文件
<!-- 监听器相关配置 -->
<listener>
<listener-class>com.node05.servlet.listener.TheContextListener</listener-class>
</listener>
<listener>
<listener-class>com.node05.servlet.listener.TheSessionListener</listener-class>
</listener>
<listener>
<listener-class>com.node05.servlet.listener.TheRequestListener</listener-class>
</listener>
<listener>
<listener-class>com.node05.servlet.listener.RequestAttributeListener</listener-class>
</listener>
<session-config>
<!-- 设置session失效时间为1分钟 -->
<session-timeout>1</session-timeout>
</session-config>
测试接口
public class ListenerServletImpl extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=utf-8");
// 1、获取TheContextListener初始化数据
ServletContext servletContext = this.getServletContext() ;
String author = String.valueOf(servletContext.getAttribute("author")) ;
System.out.println("TheContextListener Author:"+author);
// 2、Request属性设置
request.setAttribute("mood","smile");
request.setAttribute("mood","agitated");
// 3、Session创建，1分钟失效，调用销毁
HttpSession session = request.getSession(true) ;
session.setAttribute("casually","casually");
response.getWriter().print("Hello:Listener");
}
}
二、Filter过滤器
1、过滤器简介
客户端请求Servlet时，先执行相关Filter，如果Filter通过，则继承执行请求的Servlet；如果Filter不通过，则不会执行用户请求的Servlet。过滤器可以动态地拦截请求和响应。
2、Filter接口
Filter接口定义了三个核心方法。
init()
应用程序启动时，服务器实例化Filter对象，并调用其init方法，读取web.xml配置，完成对象的初始化加载。
doFilter()
实际的过滤操作，请求达到服务器时，Servlet容器将先调用过滤器的doFilter方法。
destroy()
容器在销毁过滤器前调用该方法，释放过滤器占用的资源。
3、编码案例
编写过滤器
public class ThePrintLogFilter implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
String myName = filterConfig.getInitParameter("myName") ;
System.out.println("myName："+myName);
}
@Override
public void doFilter(ServletRequest servletRequest,
ServletResponse servletResponse,
FilterChain chain) throws IOException, ServletException {
HttpServletRequest request = (HttpServletRequest)servletRequest ;
HttpServletResponse response = (HttpServletResponse)servletResponse ;
String name = request.getParameter("name") ;
if (!name.equals("cicada")){
response.getWriter().print("User Error !");
return ;
}
chain.doFilter(servletRequest,servletResponse);
}
@Override
public void destroy() {
System.out.println("ThePrintLogFilter destroy()");
}
}
web.xml配置文件
<!-- 过滤器相关配置 -->
<filter>
<filter-name>thePrintLogFilter</filter-name>
<filter-class>com.node05.servlet.filter.ThePrintLogFilter</filter-class>
<init-param>
<param-name>myName</param-name>
<param-value>cicada</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>thePrintLogFilter</filter-name>
<url-pattern>/filterServletImpl</url-pattern>
</filter-mapping>
测试接口
public class FilterServletImpl extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=utf-8");
response.getWriter().print("Hello:Filter");
}
}
三、Interceptor拦截器
Spring框架中的拦截器Interceptor类似于Servlet中的过滤器Filter，主要用于拦截用户请求并作相应的处理。例如通过拦截器可以进行权限验证、记录请求信息的日志、判断用户是否登录等。请求转发不执行拦截、过滤；重定向执行拦截和过滤。
四、源代码地址
GitHub·地址
https://github.com/cicadasmile/java-base-parent
GitEE·地址
https://gitee.com/cicadasmile/java-base-parent
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来源：oschina
链接：https://my.oschina.net/u/4403897/blog/4183013