输入输出流的效率问题

用servlet返回图片，
浏览器访问单张图片很快，但是同时访问6张却很慢，
容器是tomcat8，

下面是同时访问时耗时

下面是单个访问耗时

我得代码是这么写的

package com.bigzhi.servlet;

import com.bigzhi.Common;
import com.google.common.net.HttpHeaders;
import com.google.common.net.MediaType;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.OutputStream;

@WebServlet("/img")
public class ImageServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String id = req.getParameter("id");
        resp.setContentType(MediaType.ANY_IMAGE_TYPE.type());

        if (req.getHeader(HttpHeaders.IF_NONE_MATCH) != null) {
            resp.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
            return;
        }

        if (id == null) {
            resp.setStatus(HttpServletResponse.SC_NOT_FOUND);
            return;
        }

        resp.setHeader(HttpHeaders.ETAG, id);
        FileInputStream fileInputStream = new FileInputStream(Common.IMAGE_DIR.concat(id));

        OutputStream out = resp.getOutputStream();

        byte[] bufferByte = new byte[fileInputStream.available()];
        while (fileInputStream.read(bufferByte) != -1) {
            out.write(bufferByte);
        }

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

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图片是静态资源，应该是动静分离吧

图片是放到静态服务器或是ＣＤＮ，通过一个ＵＲＬ来访问，而不是通应用服务器来返回数据。