JavaServlet过滤器与监听器

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1、过滤器：

1）简介：过滤无效请求，避免非正常逻辑进入相关页面。

2）实现：

新建过滤器类，实现Filter接口，如下：

package com.demo.filter;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;

public class LoginFilter implements Filter {

public void destroy() {
// TODO Auto-generated method stub

}

public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain)
throws IOException, ServletException {
HttpServletRequest request = (HttpServletRequest) servletRequest;
HttpSession session = request.getSession();
Object object = session.getAttribute("currentUser");
String path = request.getServletPath();
if (object == null && path.indexOf("login")<0) {
request.getRequestDispatcher("login.jsp").forward(servletRequest, servletResponse);
}else {

//继续执行，不进行重定向。
filterChain.doFilter(servletRequest,servletResponse);
}

}

public void init(FilterConfig arg0) throws ServletException {
// TODO Auto-generated method stub

}

}

过滤器在web.xml注册：

<filter>
<filter-name>loginFilter</filter-name>
<filter-class>com.demo.filter.LoginFilter</filter-class>
</filter>

<filter-mapping>
<filter-name>loginFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>

这样就可以实现过滤，*表示所有的请求都经过监听器
2，监听器：

1）简介：

监听web 事件；如application,session,request值得增加，删除，与变化。

2）实现：

新建类监听，三个监听分别如下：

package com.demo.listener;

import javax.servlet.ServletContextAttributeEvent;
import javax.servlet.ServletContextAttributeListener;

public class ApplicationAttributeListener implements ServletContextAttributeListener{

public void attributeAdded(ServletContextAttributeEvent servletContextAttributeEvent) {
System.out.println("Application添加的属性："+ servletContextAttributeEvent.getName()+",属性值：" + servletContextAttributeEvent.getValue());
}

public void attributeRemoved(ServletContextAttributeEvent servletContextAttributeEvent) {
System.out.println("Application删除的属性："+ servletContextAttributeEvent.getName()+",属性值：" + servletContextAttributeEvent.getValue());
}

public void attributeReplaced(ServletContextAttributeEvent servletContextAttributeEvent) {
System.out.println("Application修改的属性："+ servletContextAttributeEvent.getName()+",属性值：" + servletContextAttributeEvent.getValue());
}

}
package com.demo.listener;

import javax.servlet.ServletRequestAttributeEvent;
import javax.servlet.ServletRequestAttributeListener;

public class RequesterAttributeLitener implements ServletRequestAttributeListener{

public void attributeAdded(ServletRequestAttributeEvent servletRequestAttributeEvent) {
System.out.println("Requeste添加的属性："+ servletRequestAttributeEvent.getName()+",属性值：" + servletRequestAttributeEvent.getValue());

}

public void attributeRemoved(ServletRequestAttributeEvent servletRequestAttributeEvent) {
System.out.println("Requeste删除的属性："+ servletRequestAttributeEvent.getName()+",属性值：" + servletRequestAttributeEvent.getValue());

}

public void attributeReplaced(ServletRequestAttributeEvent servletRequestAttributeEvent) {
System.out.println("Requeste修改的属性："+ servletRequestAttributeEvent.getName()+",属性值：" + servletRequestAttributeEvent.getValue());
}

}
package com.demo.listener;

import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;

public class SessionAttributeListener implements HttpSessionAttributeListener {

public void attributeAdded(HttpSessionBindingEvent httpSessionBindingEvent) {

System.out.println("Session添加的属性："+ httpSessionBindingEvent.getName()+",属性值：" + httpSessionBindingEvent.getValue());

}

public void attributeRemoved(HttpSessionBindingEvent httpSessionBindingEvent) {

System.out.println("Session删除的属性："+ httpSessionBindingEvent.getName()+",属性值：" + httpSessionBindingEvent.getValue());

}

public void attributeReplaced(HttpSessionBindingEvent httpSessionBindingEvent) {

System.out.println("Session修改的属性："+ httpSessionBindingEvent.getName()+",属性值：" + httpSessionBindingEvent.getValue());

}

}

web.xml注册如下：
<listener>
<listener-class>
com.demo.listener.SessionAttributeListener
</listener-class>
</listener>

<listener>
<listener-class>
com.demo.listener.ApplicationAttributeListener
</listener-class>
</listener>

<listener>
<listener-class>
com.demo.listener.RequesterAttributeLitener
</listener-class>
</listener>

实现的servlet如下：
package com.demo.web;

import java.io.IOException;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

public class ListenerServlet extends HttpServlet {

/**
*
*/
private static final long serialVersionUID = 1L;

@Override
protected void doGet(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse) throws ServletException, IOException {
this.doPost(httpServletRequest, httpServletResponse);
}

@Override
protected void doPost(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse) throws ServletException, IOException {
httpServletResponse.setCharacterEncoding("utf-8");
HttpSession session = httpServletRequest.getSession();
ServletContext application = httpServletRequest.getServletContext();
httpServletRequest.setAttribute("request", "request值1");
session.setAttribute("session", "session值1");
application.setAttribute("application", "application值1");

httpServletRequest.setAttribute("request", "request值2");
session.setAttribute("session", "session值2");
application.setAttribute("application", "application值2");

httpServletRequest.removeAttribute("request");
session.removeAttribute("session");
application.removeAttribute("application");

httpServletResponse.getWriter().print("操作完成");

}

}

servlet注册如下：
<servlet>
<servlet-name>ListenerServlet</servlet-name>
<servlet-class>com.demo.web.ListenerServlet</servlet-class>
</servlet>

<servlet-mapping>
<servlet-name>ListenerServlet</servlet-name>
<url-pattern>/listener</url-pattern>
</servlet-mapping>

访问的效果如下：
访问效果如下：



打印日志如下：



过滤器及监听器介绍到此。