Android4.0 以后不允许在主线程进行网络连接

Android4.0 以后不允许在主线程进行网络连接，否则会出现 android.os.NetworkOnMainThreadException。因此，必须另起一个线程进行网络连接方面的操作。

 package com.lujinhong.irmcdc.dao;

 import java.io.IOException;
 import java.net.Socket;
 import java.net.UnknownHostException;
 import java.util.Scanner;

 public class ResourceDao {

     String returnLine = "hi";

     public String getAllContentByName() {
         Runnable r = new NetWorkHandler();
         Thread thread = new Thread(r);
         thread.start();

         try {
             Thread.sleep(15000);
         } catch (InterruptedException e) {
             e.printStackTrace();
         }
         return returnLine;
     }

     private class NetWorkHandler implements Runnable {

         String line = "line";
         Socket socket = null;
         Scanner scanner = null;
         @Override
         public void run() {
             try {
                 socket = new Socket("time-A.timefreq.bldrdoc.gov", 13);
                 scanner = new Scanner(socket.getInputStream());
                 while (scanner.hasNextLine()) {
                     line = scanner.nextLine();
                     returnLine += line;
                 }

             } catch (UnknownHostException e) {
                 e.printStackTrace();
             } catch (IOException e) {
                 e.printStackTrace();
             } finally {
                 scanner.close();
                 try {
                     socket.close();
                 } catch (IOException e) {
                     e.printStackTrace();
                 }
             }
         }
     }
 }

1、由于网络连接需要一定时间，为了在主界面上进行网络信息的展现，暂时用sleep()方法简单实现，使主线程等待网络信息读取完成。

 Thread.sleep(5000);

修改以下 问题，使用wai()及nofifyAll处理。

 package com.ljh.irmcdc.dao;

 import java.io.IOException;
 import java.net.Socket;
 import java.net.UnknownHostException;
 import java.util.Scanner;

 public class ResourceDao {

     String returnLine = "";

     public String getAllContentByName() {
         Runnable r = new NetWorkHandler();
         Thread thread = new Thread(r);
         thread.start();

         synchronized (this) {
             try {
                 wait(20000);
             } catch (InterruptedException e) {
                 e.printStackTrace();
             }
         }
         return returnLine;
     }

     private class NetWorkHandler implements Runnable {

         String line = "line";
         Socket socket = null;
         Scanner scanner = null;

         @Override
         public void run() {
             try {
                 // socket = new Socket("time-A.timefreq.bldrdoc.gov", 13);
                 socket = new Socket("192.168.136.44", 8179);
                 scanner = new Scanner(socket.getInputStream());
                 returnLine = "";
                 while (scanner.hasNextLine()) {
                     line = scanner.nextLine();
                     returnLine += line;
                 }
 <span style="white-space:pre">              </span>//不要直接使用this，否则nofity的对象不是上面wait所锁定的对象。
                 synchronized (ResourceDao.this) {
                     ResourceDao.this.notifyAll();
                 }
             } catch (UnknownHostException e) {
                 e.printStackTrace();
             } catch (IOException e) {
                 e.printStackTrace();
             } finally {
                 scanner.close();
                 try {
                     socket.close();
                 } catch (IOException e) {
                     e.printStackTrace();
                 }
             }
         }
     }
 }

注意：

1、在内部类中引用外部类对象的方法：

 ResourceDao.this.notifyAll();

2、wai()及nofity()必须放在synchronized块里面。

尤其注意在内部类中notify()外部类对象时，不要使用this，而应该是上述所表。