一个简单的回调（例子）

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);
    }
}

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一个简单的回调（例子）

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