1.写的一个简单的例子

package forword;import java.io.IOException;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;import javax.servlet.http.HttpServletResponse;import org.apache.commons.io.IOUtils;import org.apache.commons.lang.StringUtils;@WebFilter("/*")public class ProxyFilter implements Filter {    public ProxyFilter() {    }    public void destroy() {    }    public void doFilter(ServletRequest request1, ServletResponse response1, FilterChain chain1) throws IOException, ServletException {        HttpServletRequest request = (HttpServletRequest) request1;        HttpServletResponse response = (HttpServletResponse) response1;        request.setCharacterEncoding("UTF-8");        response.setCharacterEncoding("UTF-8");        String basePath = request.getScheme() + "://" + "127.0.0.1:9080";        String locationUrl = basePath + request.getRequestURI();        String queryValue = request.getQueryString();        if (StringUtils.isNotBlank(queryValue)) {            locationUrl += "?" + queryValue;        }        IOUtils.write(HttpUtils.sendGet(locationUrl, request), response.getOutputStream());    }    public void init(FilterConfig fConfig) throws ServletException {    }    @SuppressWarnings("unused")    private String solveUrl(HttpServletRequest request) {        return request.getRequestURI().replaceAll(request.getContextPath(), "");    }    public static void main(String[] args) {    }}

思路如下:

1.首先所以的请求都必须要经过代理服务器,有代理服务器根据相应的规则(自定义),选择合适的目标服务器进行转发,

2.转发的实现,我们可以自己去创建HttpURLConnection 连接到目标服务器获取数据,也可以采用成熟的httpclient 去请求数据

3.将数据响应回去.

实现难点: 苦难的地方主要是在对http协议的解析,在这里我使用了httpclient 来屏蔽这些底层的实现,但是我们自己应该懂得如何解析http请求

解析请求的例子:

public class ParseUtils {    public static byte[] readLine(InputStream in) throws IOException {        ByteAppender appender = new ByteAppender();        int _data = -1;        while(true) {            int data = in.read();            if(data == -1) break;            if(_data == '\r') {                if(data == '\n') break;                else {                    appender.append((byte)_data);                    appender.append((byte)data);                }            }            if(data != '\r') {                appender.append((byte) data);            }            _data = data;        }        return appender.getDatas();    }}

//解析传递过来的报文 private void parse_(Socket socket) throws IOException {        InputStream in = socket.getInputStream();        byte[] firstLine = ParseUtils.readLine(in);        if(firstLine.length == 0) {            throw new HttpException("heart-beaten test from client side");        }         messageHeader = new String(firstLine);        parseHeaders(in);        bodyInput = in;        InetAddress address = socket.getInetAddress();        setClientHost(address.getHostAddress());    }