JavaEE基础(05):过滤器、监听器、拦截器,应用详解
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一、Listener监听器
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
com.node05.servlet.listener.TheContextListener
com.node05.servlet.listener.TheSessionListener
com.node05.servlet.listener.TheRequestListener
com.node05.servlet.listener.RequestAttributeListener
1
- 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
thePrintLogFilter
com.node05.servlet.filter.ThePrintLogFilter
myName
cicada
thePrintLogFilter
/filterServletImpl
- 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
本文题目:JavaEE基础(05):过滤器、监听器、拦截器,应用详解
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