1.声明一个回调Interface：
public interface CallBack {
/**
* 执行回调方法
* @param objects 将处理后的结果作为参数返回给回调方法
*/
public void execute(Object... objects );
}
2.回调的地方继承回调，实现回调的方法：
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.io.UnsupportedEncodingException;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLConnection;import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.xml.ws.spi.http.HttpContext;public class testServlet extends HttpServlet implements CallBack{
NetTool netTool;
HttpServletResponse globalResponse;
String netResult;
/**
* Constructor of the object.
*/
public testServlet() {
super();
}/**
* Destruction of the servlet. <br>
*/
public void destroy() {
super.destroy(); // Just puts "destroy" string in log
// Put your code here
}/**
* The doGet method of the servlet. <br>
*
* This method is called when a form has its tag value method equals to get.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {globalResponse = response;
netTool = new NetTool();netTool.sendGet("", this);
}public void outPut(HttpServletResponse response){
response.setContentType("text/html");
response.setHeader("content-type", "text/html;charset=UTF-8");
PrintWriter out;
try {
out = response.getWriter();
out.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
out.println("<HTML>");
out.println(" <HEAD><TITLE>A Servlet</TITLE></HEAD>");
out.println(" <BODY>");
out.print(" ");
out.print(this.getClass()+" : \n");
out.print(netResult);
out.println(" </BODY>");
out.println("</HTML>");
out.flush();
out.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}}
/**
* The doPost method of the servlet. <br>
*
* This method is called when a form has its tag value method equals to post.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
out.println("<HTML>");
out.println(" <HEAD><TITLE>A Servlet</TITLE></HEAD>");
out.println(" <BODY>");
out.print(" This is ");
out.print(this.getClass());
out.println(", using the POST method");
out.println(" </BODY>");
out.println("</HTML>");
out.flush();
out.close();
}@Override
public void execute(Object... objects) {
// TODO Auto-generated method stub
try {
String result = (String)objects[0];
netResult = new String(result.getBytes(), "UTF-8");
} catch (UnsupportedEncodingException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
outPut(globalResponse);
}}
3.回调自己：
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.URL;
import java.net.URLConnection;public class NetTool {
public NetTool(){
super();
}public void sendGet(String url, CallBack callBack) {
String result = "";
BufferedReader in = null;
try {
String urlNameString = "http://m.weather.com.cn/data/101010100.html";
URL realUrl = new URL(urlNameString);
// 打开和URL之间的连接
URLConnection connection = realUrl.openConnection();
// 设置通用的请求属性
// connection.setRequestProperty("accept", "*/*");
// connection.setRequestProperty("connection", "Keep-Alive");
// connection.setRequestProperty("user-agent",
// "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1;SV1)");
// 建立实际的连接
connection.connect();
// 获取所有响应头字段
/*
* Map<String, List<String>> map = connection.getHeaderFields(); //
* 遍历所有的响应头字段 for (String key : map.keySet()) {
* System.out.println(key + "--->" + map.get(key)); }
*/
// 定义 BufferedReader输入流来读取URL的响应
in = new BufferedReader(new InputStreamReader(
connection.getInputStream()));
String line;
while ((line = in.readLine()) != null) {
result += line;
}
} catch (Exception e) {
System.out.println("发送GET请求出现异常！" + e);
e.printStackTrace();
}
// 使用finally块来关闭输入流
finally {
try {
if (in != null) {
in.close();
}
} catch (Exception e2) {
e2.printStackTrace();
}
}
callBack.execute(result);
}
}