1.聲明一個回調Interface：
public interface CallBack { /** * 執行回調方法 * @param objects 將處理后的結果作為參數返回給回調方法 */ public void execute(Object... objects ); }
2.回調的地方繼承回調，實現回調的方法：
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.回調自己：
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); // 打開和URL之間的連接 URLConnection connection = realUrl.openConnection(); // 設置通用的請求屬性 // connection.setRequestProperty("accept", "*/*"); // connection.setRequestProperty("connection", "Keep-Alive"); // connection.setRequestProperty("user-agent", // "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1;SV1)"); // 建立實際的連接 connection.connect(); // 獲取所有響應頭字段 /* * Map<String, List<String>> map = connection.getHeaderFields(); // * 遍歷所有的響應頭字段 for (String key : map.keySet()) { * System.out.println(key + "--->" + map.get(key)); } */ // 定義 BufferedReader輸入流來讀取URL的響應 in = new BufferedReader(new InputStreamReader( connection.getInputStream())); String line; while ((line = in.readLine()) != null) { result += line; } } catch (Exception e) { System.out.println("發送GET請求出現異常！" + e); e.printStackTrace(); } // 使用finally塊來關閉輸入流 finally { try { if (in != null) { in.close(); } } catch (Exception e2) { e2.printStackTrace(); } } callBack.execute(result); } }