文件的显示与下载

package csdn.servlet;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class DemoServlet extends HttpServlet {
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		showImg(request, response);
		// downImg(request, response);
	}
	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		this.doGet(request, response);
	}
	public void showImg(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		
		response.setContentType("image/jpeg ");
		//获取项目绝对路径
		String p = this.getServletContext().getRealPath("/");
		//图片的路径
		File file = new File(p+"./images/3.jpg");
		//创建文件的输入流
		FileInputStream is = new FileInputStream(file);
		//响应的输出流
		ServletOutputStream out = response.getOutputStream();
		//读取缓冲区
		byte buffer[] = new byte[1024];
		int len = 0;//记录读取的长度
		while ((len = is.read(buffer)) != -1) {
			out.write(buffer, 0, len);//写入
		}//释放资源 
		is.close();
		out.flush();
		out.close();
	}
	public void downImg(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		//
		String p = this.getServletContext().getRealPath("/");
		File file = new File(p + "/images/j.jpg");
		FileInputStream is = new FileInputStream(file);
		response.setHeader("Content-Disposition", "attachment;filename="+file.getName());
		ServletOutputStream out = response.getOutputStream();
		byte buffer[] = new byte[1024];
		int len = 0;
		while ((len = is.read(buffer)) != 1) {
			out.write(buffer, 0, len);

		}
		is.close();
		out.flush();
		out.close();
	}	
}