servlet过滤器 servlet过滤器(Filter)详解（九）
柳暗花明睡一觉 人气:0想了解servlet过滤器(Filter)详解（九）的相关内容吗，柳暗花明睡一觉在本文为您仔细讲解servlet过滤器的相关知识和一些Code实例，欢迎阅读和指正，我们先划重点：servlet,过滤器,Filter，下面大家一起来学习吧。
1.servlet过滤器产生背景
项目中我们会遇到这样一类的需求，对访问服务器的用户ip实施过滤，只有在允许名单中的ip才能访问服务，为了实现需求，每当有客户端请求时，我们都会写校验ip的代码，客户端能够访问到的servlet我们都需要这样做，很明显这样做有一个缺点，就是代码冗余，维护不方便，如果验证规则改变，修改起来也特别麻烦。
为了解决以上问题，Filter 技术应运而生。
2.servlet过滤器是什么？
servlet过滤器是在java servlet 2.3 中定义的。它能够对servlet容器传给servlet组件的ServletRequest 对象和 ServletResponse对象进行检查和修改。
3.案例
所有servlet过滤器都要实现javax.servlet.Filter接口。
NoteFilter
package com.learn;
import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
/**
* Created by Administrator on 2017/09/29.
*/
public class NoteFilter implements Filter {
private FilterConfig config = null;
private String ipTable = null; //ip名单
@Override
public void init(FilterConfig filterConfig) throws ServletException {
System.out.println("note filter initial");
this.config = filterConfig;
this.ipTable = config.getInitParameter("ipTable");
}
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
System.out.println("do filter starting");
//校验ip地址
if(!veryfyIP(request,response))
return;
long befor = System.currentTimeMillis();
config.getServletContext().log("before call note Filter");
chain.doFilter(request,response);
config.getServletContext().log("after call note Filter");
long after = System.currentTimeMillis();
String name ="";
if(request instanceof HttpServletRequest){
name = ((HttpServletRequest) request).getRequestURI();
}
config.getServletContext().log("Note Filter : name:"+name +" time :"+(after -befor)+"ms");
}
@Override
public void destroy() {
}
private boolean veryfyIP(ServletRequest request, ServletResponse response){
String ip = request.getRemoteAddr();
System.out.println("请求ip:"+ip);
System.out.println("ipTable 黑名单:"+ipTable);
if(ip.indexOf(ipTable) == -1){
System.out.println("校验不通过");
response.setContentType("text/html");
PrintWriter out = null;
try {
out = response.getWriter();
out.print("<h1>对不起，你的ip不能访问服务器</h1>");
out.flush();
out.close();
} catch (IOException e) {
e.printStackTrace();
}
return false;
} else {
return true;
}
}
}
NoteServlet
package com.learn;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
/**
* Created by Administrator on 2017/09/29.
*/
public class NoteServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
System.out.println("已经通过了过滤器");
}
}
web.xml配置
<filter> <filter-name>ip</filter-name> <filter-class>com.learn.NoteFilter</filter-class> <init-param> <param-name>ipTable</param-name> <param-value>127.0.0.1</param-value> </init-param> </filter> <filter-mapping> <filter-name>ip</filter-name> <url-pattern>/note</url-pattern> </filter-mapping>
<servlet> <servlet-name>note</servlet-name> <servlet-class>com.learn.NoteServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>note</servlet-name> <url-pattern>/note</url-pattern> </servlet-mapping>
结果如下：
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