firstfilter.java

JavaWeb高级特性书中源代码

package org.it315.filters;

import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import java.util.Enumeration;
import javax.servlet.http.HttpServletRequest;
import java.io.PrintWriter;

public class FirstFilter implements Filter
{
	private FilterConfig filterConfig = null;
	String paramValue = null;
	public void init(FilterConfig filterConfig) throws ServletException
	{
		this.filterConfig = filterConfig;
		paramValue = filterConfig.getInitParameter("encoding");
	}
	
	public void doFilter(ServletRequest request,
		ServletResponse response,FilterChain chain)
			throws IOException, ServletException
	{
		/*下面这段代码在命令行窗口中打印出所有的请求头信息，
		以便确认Filter是否起作用和帮助分析问题*/		
		System.out.println("begin headers---------------");
		Enumeration headerNames = 
				((HttpServletRequest)request).getHeaderNames();
		while(headerNames.hasMoreElements())
		{
			String headerName = (String)headerNames.nextElement();
			System.out.println(headerName + " : " + 
				((HttpServletRequest)request).getHeader(headerName));
		}
		System.out.println("---------------end headers");
		
		//在调用目标Servlet前写入响应内容
		response.setContentType("text/html;charset=gb2312");
		PrintWriter out = response.getWriter();
		out.println("您的IP地址为：" + request.getRemoteHost() + "<br>");
		
		chain.doFilter(request, response);

		//在目标Servlet返回后写入响应内容
		out.println("<br>名称为encoding的初始化参数的值为：" + paramValue);
		out.println("<br>当前WEB程序的真实路径为：" + 
				filterConfig.getServletContext().getRealPath("/"));
	}

	public void destroy()
	{
		this.filterConfig = null;
	}
}