servlet 文件下载

package com.hkrt.demo;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/download.do")
public class Download extends HttpServlet {

	
	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		String passwd = req.getParameter( "passwd" );
//		resp.sendError(HttpServletResponse.SC_NOT_FOUND , "笔记文件");
//		if("123456".equals(passwd)){
			resp.setContentType( "application/pdf" );
			InputStream in = getServletContext().getResourceAsStream("/WEB-INF/ibatis.pdf");
			OutputStream out = resp.getOutputStream();
			writeBytes(in ,out );
//		}
	}
	
	private void writeBytes(InputStream in , OutputStream out) throws IOException{
		byte [] buffer = new byte[ 1024 ];
		int length = -1 ;
		while((length = in.read(buffer))!= -1){
			System.out.println( "lenth == > : " + length );
			out.write(buffer,0,length);
		}
		in.close();
		out.close();
	}

	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		doPost( req , resp );
	}
	
}