过滤器的作用：用于过滤请求，在请求发出前后，做一些检查或操作，配置及使用步骤如下:
1.要配置Filter，首先建立一个Java类，实现Filter接口，代码如下
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;
public class CommonFilter implements Filter{
private String name;
@Override
public void destroy() {
// TODO Auto-generated method stub
}
@Override
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
// TODO Auto-generated method stub
System.out.println("name=="+name);
chain.doFilter(request, response);
}
@Override
public void init(FilterConfig FConfig) throws ServletException {
// TODO Auto-generated method stub
//获取web.xml文件中的初始化参数
name = FConfig.getInitParameter("name");
System.out.println("caonima="+name);
}
2.在web.xml中注册该过滤器
<!-- 过滤器配置 -->
<filter>
<display-name>通用过滤器</display-name>
<filter-name>CommonFilter</filter-name>
<filter-class>com.haiyan.filter.CommonFilter</filter-class>
<init-param>
<param-name>name</param-name>
<param-value>张三</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>CommonFilter</filter-name>
<url-pattern>*</url-pattern>
</filter-mapping>
3.测试使用：
启动项目，打印出结果：（因为在web.xml中我将请求路径设置为*，表示任何请求都过滤，所以项目启动，访问首页的时候，过滤器发挥了作用）
}