web.xml中过滤器实现总结

在web开发过程中，往往需要在web.xml中进行过滤配置，对用户的请求以及服务器的响应进行过滤。 
 过滤器的实现总结：
  1、定义一个类实现Filter接口
  2、在init()初始化方法中获取web.xml中配置的参数值
  3、在doFilter方法中实现过滤逻辑
Filter接口提供了三个方法：
init()：初始化，读取web.xml中配置的参数
doFilter()：实现过滤逻辑
destory()：注销该过滤器
public interface Filter {
default void init(FilterConfig filterConfig) throws ServletException {
}

void doFilter(ServletRequest var1, ServletResponse var2, FilterChain var3) throws IOException, ServletException;

default void destroy() {
}
}下面举例说明过滤器的用法：该过滤器禁止某些IP访问应用
定义类实现Filter接口：
package Filter;

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 java.io.IOException;
import java.io.PrintWriter;

public class IpFilter implements Filter {
protected FilterConfig filterConfig ;
protected String ip;
//过滤器初始化的时候调用，在过滤器初始化过程中从web配置文件读取参数的内容
@Override
public void init(FilterConfig filterConfig) throws ServletException {
this.filterConfig = filterConfig;
this.ip = this.filterConfig.getInitParameter("ip");
}
//实现过滤操作
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
String remoteIp = servletRequest.getRemoteAddr();
if (remoteIp.equals(ip)) {
servletResponse.setCharacterEncoding("GBK");
PrintWriter out = servletResponse.getWriter();
out.println("<b>你的IP地址被禁止访问.</b>");
} else {
filterChain.doFilter(servletRequest, servletResponse);
}
}

@Override
public void destroy() {

}
}web.xml中过滤器的配置：
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" version="3.1">
<!--IP过滤的过滤器配置-->
<filter>
<filter-name>IpFilter</filter-name>
<filter-class>Filter.IpFilter</filter-class>
<!--在初始化的时候加载的参数-->
<init-param>
<param-name>ip</param-name>
<param-value>127.0.0.1</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>IpFilter</filter-name>
<url-pattern>/*</url-pa
4000
ttern>
</filter-mapping>
<!--编码过滤器的配置-->
<filter>
<filter-name>SetCharacterEncoding</filter-name>
<filter-class>
Filter.SetCharacterEncodingFilter
</filter-class>
<init-param>
<param-name>encoding</param-name>
<param-value>gb2312</param-value>
</init-param>
<init-param>
<param-name>enable</param-name>
<param-value>true</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>SetCharacterEncoding</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<!--Servlet配置-->
<servlet>
<servlet-name>HelloWorlds</servlet-name>
<servlet-class>HelloWorld.HelloServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>HelloWorlds</servlet-name>
<url-pattern>/HelloWorld</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>AcceptForm</servlet-name>
<servlet-class>servlets.AcceptForm</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>AcceptForm</servlet-name>
<url-pattern>/AcceptForm</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>AcceptLink</servlet-name>
<servlet-class>servlets.AcceptLink</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>AcceptLink</servlet-name>
<url-pattern>/AcceptLink</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>FileReader</servlet-name>
<servlet-class>servlets.FileReader</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>FileReader</servlet-name>
<url-pattern>/FileReader</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>FileWriter</servlet-name>
<servlet-class>servlets.FileWriter</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>FileWriter</servlet-name>
<url-pattern>/FileWriter</url-pattern>
</servlet-mapping>
</web-app>