在一些比较特殊的情况,不允许把内网端口映射到外网,可以是用此方法。通过流的方式把数据通过ServletResponse响应给客户端

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.OutputStream;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;

/**filter转发内网图片*/
@WebFilter(displayName="imgFilter" ,urlPatterns=ImgFilter.FILTERPATH+"*")
public class ImgFilter implements Filter {

	protected final static String FILTERPATH = "/img/";
	
	@Override
	public void destroy() {
	}

	@Override
	public void doFilter(ServletRequest req, ServletResponse response, FilterChain filterChain)
			throws IOException, ServletException {
		HttpServletRequest  request = (HttpServletRequest )req;
		String fileName = getName(request.getServletPath());
		if (verif(fileName)) {//验证图片格式
			/*
			 * 转发思路,从数据源获取到流,通过ServletResponse转发给客户端
			 * 1.在一些比较特殊的情况,不允许把内网端口映射到外网,可以是用此方法
			 * 如果可以映射到外网使用nginx是个不错的选择
			 * 测试模拟使用Flle 读取本地文件
			 */
			File file = new File("D:\\img\\"+fileName);
			if (!file.exists()) {
				write(response, "404".getBytes());
				return;
			}
	        FileInputStream fis;
	        fis = new FileInputStream(file);
	        long size = file.length();
	        byte[] temp = new byte[(int) size];
	        fis.read(temp, 0, (int) size);
	        fis.close();
	        write(response, temp);
		}else{
			filterChain.doFilter(req, response);	
		}
	}

	@Override
	public void init(FilterConfig arg0) throws ServletException {
	}

	/**获取文件名*/
	private  String getName(String address){
		String name = "";
		if (FILTERPATH.length() < address.length()) {
			name = address.substring(FILTERPATH.length(),address.length());
		}
		return name;
	}
	
	/**验证文件后缀*/
	private  boolean verif(String name){
		int index = name.lastIndexOf(".");
		if (index > 0) {
			String[] strings = new String[]{"jpg","png"};
			for (String string : strings) {
				if (string.equals(name.substring(index+1))) {
					return true;
				}
			}
		}
		return false;
	}

	/**输出消息*/
	public void write(ServletResponse response,byte[] data) throws IOException{
		OutputStream out = response.getOutputStream();
	    response.setContentType("image/jpeg");
	    out.write(data);
	    out.flush();
	    out.close();
	}
	
}