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什么是Socket?     

     所谓Socket通常也称作“套接字”，用于描述IP地址和端口，是一个通信连的句柄，应用程序通常通过“套接字”向网络发送请求或者应答网络请求，它就是网络通信过程中端点的抽象表示。它主要包括以下两个协议：

      TCP (Transmission Control Protocol 传输控制协议)：传输控制协议,提供的是面向连接、可靠的字节流服务。当客户和服务器彼此交换数据前，必须先在双方之间建立一个TCP连接，之后才能传输数据。TCP提供超时重发，丢弃重复数据，检验数据，流量控制等功能，保证数据能从一端传到另一端。

      UDP (User Datagram Protocl 用户数据报协议)：用户数据报协议，是一个简单的面向数据报的运输层协议。UDP不提供可靠性，它只是把应用程序传给IP层的数据报发送出去，但是并不能保证它们能到达目的地。由于UDP在传输数据报前不用在客户和服务器之间建立一个连接，且没有超时重发等机制，故而传输速度很快。

详细解说如下:

      TCP传输和UDP不一样，TCP传输是流式的，必须先建立连接，然后数据流沿已连接的线路(虚电路)传输。因此TCP的数据流不会像UDP数据报一样，每个数据报都要包含目标地址和端口，因为每个数据报要单独路由。TCP传输则只需要在建立连接时指定目标地址和端口就可以了。

　　形象的讲，TCP就像打电话，UDP就像发电报。宏观上来看UDP是不分客户端和服务端的。通信双方是平等的。微观上来讲只相对一个报文，发送端是客户端，监听端是服务端。发送端把数据报发给路由器就像把电报发给了邮局，后面的事情就是发送者无法控制，也无从知晓的了。所以说是不可靠的，可能会出现报文丢失而无从知晓。就像每张电报都要有收件人一样，每个数据报都要有目的地址和端口。

　　而TCP每次连接都是分客户端和服务端的。连接的发起者(相当与拨号打电话的人)是客户端，监听者(相当于在电话边等着接电话的人)是服务端。发起者指定要连接的服务器地址和端口(相当于拨号)，监听者通过和发起者三次握手建立连接(相当于听到电话响去接电话)。建立连接后双方可以互相发送和接受数据(打电话)。

Java如何操作Socket?

       值得一提的是，Java分别为TCP和UDP提供了相应的类,TCP是java.net中提供了两个类Socket和ServerSocket，分别用来表示双向连接的客户端和服务端。这是两个封装得非常好的类，使用起来很方便！UDP是java.net.DatagramSocket.

       127.0.0.1是回路地址,用于测试,相当于localhost本机地址,没有网卡,不设DNS都可以访问,端口地址在0~65535之间,其中0~1023之间的端口是用于一些知名的网络服务和应用,用户的普通网络应用程序应该使用1024以上的端口.

Socket通信模型如下：

如果大家对Java Socket编程还有模糊的地方抓紧温习(),本文不在此赘述,下面我们以最常用的TCP协议举例:

服务器，使用ServerSocket监听指定的端口，端口可以随意指定（由于1024以下的端口通常属于保留端口，在一些操作系统中不可以随意使用，所以建议使用大于1024的端口），等待客户连接请求，客户连接后，会话产生；在完成会话后，关闭连接。

客户端，使用Java socket通信对网络上某一个服务器的某一个端口发出连接请求，一旦连接成功，打开会话；会话完成后，关闭Socket。客户端不需要指定打开的端口，通常临时的、动态的分配一个1024以上的端口。

TCP网络连接模型：

 

Android客户端程序代分析:

UploadActivity.javapackage com.android.upload;import java.io.File;  import java.io.OutputStream;  import java.io.PushbackInputStream;  import java.io.RandomAccessFile;  import java.net.Socket;    import android.app.Activity;  import android.os.Bundle;  import android.os.Environment;  import android.os.Handler;  import android.os.Message;  import android.view.View;  import android.view.View.OnClickListener;import android.widget.Button;  import android.widget.EditText;  import android.widget.ProgressBar;  import android.widget.TextView;  import android.widget.Toast;    import com.android.service.UploadLogService;  import com.android.socket.utils.StreamTool;  public class UploadActivity extends Activity {      private EditText filenameText;      private TextView resulView;      private ProgressBar uploadbar;      private UploadLogService logService;      private boolean start=true;    private Handler handler = new Handler(){          @Override          public void handleMessage(Message msg) {              int length = msg.getData().getInt("size");              uploadbar.setProgress(length);              float num = (float)uploadbar.getProgress()/(float)uploadbar.getMax();              int result = (int)(num * 100);              resulView.setText(result+ "%");              if(uploadbar.getProgress()==uploadbar.getMax()){                  Toast.makeText(UploadActivity.this, R.string.success, 1).show();              }          }      };            @Override      public void onCreate(Bundle savedInstanceState) {          super.onCreate(savedInstanceState);          setContentView(R.layout.main);                    logService = new UploadLogService(this);          filenameText = (EditText)this.findViewById(R.id.filename);          uploadbar = (ProgressBar) this.findViewById(R.id.uploadbar);          resulView = (TextView)this.findViewById(R.id.result);          Button button =(Button)this.findViewById(R.id.button);          Button button1 =(Button)this.findViewById(R.id.stop);         button1 .setOnClickListener(new OnClickListener() {						@Override			public void onClick(View v) {				start=false;							}		});        button.setOnClickListener(new View.OnClickListener() {              @Override              public void onClick(View v) {              	start=true;                String filename = filenameText.getText().toString();                  if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){                      File uploadFile = new File(Environment.getExternalStorageDirectory(), filename);                      if(uploadFile.exists()){                          uploadFile(uploadFile);                      }else{                          Toast.makeText(UploadActivity.this, R.string.filenotexsit, 1).show();                      }                  }else{                      Toast.makeText(UploadActivity.this, R.string.sdcarderror, 1).show();                  }              }          });      }      /**      * 上传文件      * @param uploadFile      */      private void uploadFile(final File uploadFile) {          new Thread(new Runnable() {                       @Override              public void run() {                  try {                      uploadbar.setMax((int)uploadFile.length());                      String souceid = logService.getBindId(uploadFile);                      String head = "Content-Length="+ uploadFile.length() + ";filename="+ uploadFile.getName() + ";sourceid="+                          (souceid==null? "" : souceid)+"\r\n";                      Socket socket = new Socket("192.168.1.78",7878);                      OutputStream outStream = socket.getOutputStream();                      outStream.write(head.getBytes());                                            PushbackInputStream inStream = new PushbackInputStream(socket.getInputStream());                          String response = StreamTool.readLine(inStream);                      String[] items = response.split(";");                      String responseid = items[0].substring(items[0].indexOf("=")+1);                      String position = items[1].substring(items[1].indexOf("=")+1);                      if(souceid==null){//代表原来没有上传过此文件，往数据库添加一条绑定记录                          logService.save(responseid, uploadFile);                      }                      RandomAccessFile fileOutStream = new RandomAccessFile(uploadFile, "r");                      fileOutStream.seek(Integer.valueOf(position));                      byte[] buffer = new byte[1024];                      int len = -1;                      int length = Integer.valueOf(position);                      while(start&&(len = fileOutStream.read(buffer)) != -1){                          outStream.write(buffer, 0, len);                          length += len;                          Message msg = new Message();                          msg.getData().putInt("size", length);                          handler.sendMessage(msg);                      }                      fileOutStream.close();                      outStream.close();                      inStream.close();                      socket.close();                      if(length==uploadFile.length()) logService.delete(uploadFile);                  } catch (Exception e) {                      e.printStackTrace();                  }              }          }).start();      }  }  StreamTool.javapackage com.android.socket.utils;import java.io.ByteArrayOutputStream;import java.io.File;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStream;import java.io.PushbackInputStream;public class StreamTool {	 	 public static void save(File file, byte[] data) throws Exception {		 FileOutputStream outStream = new FileOutputStream(file);		 outStream.write(data);		 outStream.close();	 }	 	 public static String readLine(PushbackInputStream in) throws IOException {			char buf[] = new char[128];			int room = buf.length;			int offset = 0;			int c;loop:		while (true) {				switch (c = in.read()) {					case -1:					case '\n':						break loop;					case '\r':						int c2 = in.read();						if ((c2 != '\n') && (c2 != -1)) in.unread(c2);						break loop;					default:						if (--room < 0) {							char[] lineBuffer = buf;							buf = new char[offset + 128];						    room = buf.length - offset - 1;						    System.arraycopy(lineBuffer, 0, buf, 0, offset);						   						}						buf[offset++] = (char) c;						break;				}			}			if ((c == -1) && (offset == 0)) return null;			return String.copyValueOf(buf, 0, offset);	}	 	/**	* 读取流	* @param inStream	* @return 字节数组	* @throws Exception	*/	public static byte[] readStream(InputStream inStream) throws Exception{			ByteArrayOutputStream outSteam = new ByteArrayOutputStream();			byte[] buffer = new byte[1024];			int len = -1;			while( (len=inStream.read(buffer)) != -1){				outSteam.write(buffer, 0, len);			}			outSteam.close();			inStream.close();			return outSteam.toByteArray();	}}UploadLogService.javapackage com.android.service;import java.io.File;import android.content.Context;import android.database.Cursor;import android.database.sqlite.SQLiteDatabase;public class UploadLogService {	private DBOpenHelper dbOpenHelper;		public UploadLogService(Context context){		this.dbOpenHelper = new DBOpenHelper(context);	}		public void save(String sourceid, File uploadFile){		SQLiteDatabase db = dbOpenHelper.getWritableDatabase();		db.execSQL("insert into uploadlog(uploadfilepath, sourceid) values(?,?)",				new Object[]{uploadFile.getAbsolutePath(),sourceid});	}		public void delete(File uploadFile){		SQLiteDatabase db = dbOpenHelper.getWritableDatabase();		db.execSQL("delete from uploadlog where uploadfilepath=?", new Object[]{uploadFile.getAbsolutePath()});	}		public String getBindId(File uploadFile){		SQLiteDatabase db = dbOpenHelper.getReadableDatabase();		Cursor cursor = db.rawQuery("select sourceid from uploadlog where uploadfilepath=?", 				new String[]{uploadFile.getAbsolutePath()});		if(cursor.moveToFirst()){			return cursor.getString(0);		}		return null;	}}DBOpenHelper.javapackage com.android.service;import android.content.Context;import android.database.sqlite.SQLiteDatabase;import android.database.sqlite.SQLiteOpenHelper;public class DBOpenHelper extends SQLiteOpenHelper {	public DBOpenHelper(Context context) {		super(context, "upload.db", null, 1);	}	@Override	public void onCreate(SQLiteDatabase db) {		db.execSQL("CREATE TABLE uploadlog (_id integer primary key autoincrement, uploadfilepath varchar(100), sourceid varchar(10))");	}	@Override	public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {		db.execSQL("DROP TABLE IF EXISTS uploadlog");		onCreate(db);			}}main.xml
   
   
            
    	        
        
    	
     	
    	
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Java服务端:

SocketServer.javapackage com.android.socket.server;import java.io.File;import java.io.FileInputStream;import java.io.FileOutputStream;import java.io.IOException;import java.io.OutputStream;import java.io.PushbackInputStream;import java.io.RandomAccessFile;import java.net.ServerSocket;import java.net.Socket;import java.text.SimpleDateFormat;import java.util.Date;import java.util.HashMap;import java.util.Map;import java.util.Properties;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import com.android.socket.utils.StreamTool;public class SocketServer {	private String uploadPath="D:/uploadFile/";	private ExecutorService executorService;// 线程池	private ServerSocket ss = null;	private int port;// 监听端口	private boolean quit;// 是否退出	private Map
   
     datas = new HashMap
    
     ();// 存放断点数据，最好改为数据库存放	public SocketServer(int port) {		this.port = port;		// 初始化线程池		executorService = Executors.newFixedThreadPool(Runtime.getRuntime()				.availableProcessors() * 50);	}	// 启动服务	public void start() throws Exception {		ss = new ServerSocket(port);		while (!quit) {			Socket socket = ss.accept();// 接受客户端的请求			// 为支持多用户并发访问，采用线程池管理每一个用户的连接请求			executorService.execute(new SocketTask(socket));// 启动一个线程来处理请求		}	}	// 退出	public void quit() {		this.quit = true;		try {			ss.close();		} catch (IOException e) {			e.printStackTrace();		}	}	public static void main(String[] args) throws Exception {		SocketServer server = new SocketServer(7878);		server.start();	}	private class SocketTask implements Runnable {		private Socket socket;		public SocketTask(Socket socket) {			this.socket = socket;		}		@Override		public void run() {			try {				System.out.println("accepted connenction from "						+ socket.getInetAddress() + " @ " + socket.getPort());				PushbackInputStream inStream = new PushbackInputStream(						socket.getInputStream());				// 得到客户端发来的第一行协议数据：Content-Length=143253434;filename=xxx.3gp;sourceid=				// 如果用户初次上传文件，sourceid的值为空。				String head = StreamTool.readLine(inStream);				System.out.println(head);				if (head != null) {					// 下面从协议数据中读取各种参数值					String[] items = head.split(";");					String filelength = items[0].substring(items[0].indexOf("=") + 1);					String filename = items[1].substring(items[1].indexOf("=") + 1);					String sourceid = items[2].substring(items[2].indexOf("=") + 1);					Long id = System.currentTimeMillis();					FileLog log = null;					if (null != sourceid && !"".equals(sourceid)) {						id = Long.valueOf(sourceid);						log = find(id);//查找上传的文件是否存在上传记录					}					File file = null;					int position = 0;					if(log==null){//如果上传的文件不存在上传记录,为文件添加跟踪记录						String path = new SimpleDateFormat("yyyy/MM/dd/HH/mm").format(new Date());						File dir = new File(uploadPath+ path);						if(!dir.exists()) dir.mkdirs();						file = new File(dir, filename);						if(file.exists()){//如果上传的文件发生重名，然后进行改名							filename = filename.substring(0, filename.indexOf(".")-1)+ dir.listFiles().length+ filename.substring(filename.indexOf("."));							file = new File(dir, filename);						}						save(id, file);					}else{// 如果上传的文件存在上传记录,读取上次的断点位置						file = new File(log.getPath());//从上传记录中得到文件的路径						if(file.exists()){							File logFile = new File(file.getParentFile(), file.getName()+".log");							if(logFile.exists()){								Properties properties = new Properties();								properties.load(new FileInputStream(logFile));								position = Integer.valueOf(properties.getProperty("length"));//读取断点位置							}						}					}										OutputStream outStream = socket.getOutputStream();					String response = "sourceid="+ id+ ";position="+ position+ "\r\n";					//服务器收到客户端的请求信息后，给客户端返回响应信息：sourceid=1274773833264;position=0					//sourceid由服务生成，唯一标识上传的文件，position指示客户端从文件的什么位置开始上传					outStream.write(response.getBytes());										RandomAccessFile fileOutStream = new RandomAccessFile(file, "rwd");					if(position==0) fileOutStream.setLength(Integer.valueOf(filelength));//设置文件长度					fileOutStream.seek(position);//移动文件指定的位置开始写入数据					byte[] buffer = new byte[1024];					int len = -1;					int length = position;					while( (len=inStream.read(buffer)) != -1){//从输入流中读取数据写入到文件中						fileOutStream.write(buffer, 0, len);						length += len;						Properties properties = new Properties();						properties.put("length", String.valueOf(length));						FileOutputStream logFile = new FileOutputStream(new File(file.getParentFile(), file.getName()+".log"));						properties.store(logFile, null);//实时记录文件的最后保存位置						logFile.close();					}					if(length==fileOutStream.length()) delete(id);					fileOutStream.close();										inStream.close();					outStream.close();					file = null;				}			} catch (Exception e) {				e.printStackTrace();			} finally {				try {	                if(socket != null && !socket.isClosed()) socket.close();	            } catch (IOException e) {}			}		}	}	public FileLog find(Long sourceid) {		return datas.get(sourceid);	}	// 保存上传记录	public void save(Long id, File saveFile) {		// 日后可以改成通过数据库存放		datas.put(id, new FileLog(id, saveFile.getAbsolutePath()));	}	// 当文件上传完毕，删除记录	public void delete(long sourceid) {		if (datas.containsKey(sourceid))			datas.remove(sourceid);	}	private class FileLog {		private Long id;		private String path;				public FileLog(Long id, String path) {			super();			this.id = id;			this.path = path;		}		public Long getId() {			return id;		}		public void setId(Long id) {			this.id = id;		}		public String getPath() {			return path;		}		public void setPath(String path) {			this.path = path;		}	}}ServerWindow.javapackage com.android.socket.server;import java.awt.BorderLayout;import java.awt.Frame;import java.awt.Label;import java.awt.event.WindowEvent;import java.awt.event.WindowListener;public class ServerWindow extends Frame{	private SocketServer server;	private Label label;		public ServerWindow(String title){		super(title);		server = new SocketServer(7878);		label = new Label();		add(label, BorderLayout.PAGE_START);		label.setText("服务器已经启动");		this.addWindowListener(new WindowListener() {			@Override			public void windowOpened(WindowEvent e) {				new Thread(new Runnable() {								@Override					public void run() {						try {							server.start();						} catch (Exception e) {							e.printStackTrace();						}					}				}).start();			}						@Override			public void windowIconified(WindowEvent e) {			}						@Override			public void windowDeiconified(WindowEvent e) {			}						@Override			public void windowDeactivated(WindowEvent e) {			}						@Override			public void windowClosing(WindowEvent e) {				 server.quit();				 System.exit(0);			}						@Override			public void windowClosed(WindowEvent e) {			}						@Override			public void windowActivated(WindowEvent e) {			}		});	}	/**	 * @param args	 */	public static void main(String[] args) {		ServerWindow window = new ServerWindow("文件上传服务端"); 		window.setSize(300, 300); 		window.setVisible(true);	}}StreamTool.javapackage com.android.socket.utils;import java.io.ByteArrayOutputStream;import java.io.File;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStream;import java.io.PushbackInputStream;public class StreamTool {	 	 public static void save(File file, byte[] data) throws Exception {		 FileOutputStream outStream = new FileOutputStream(file);		 outStream.write(data);		 outStream.close();	 }	 	 public static String readLine(PushbackInputStream in) throws IOException {			char buf[] = new char[128];			int room = buf.length;			int offset = 0;			int c;loop:		while (true) {				switch (c = in.read()) {					case -1:					case '\n':						break loop;					case '\r':						int c2 = in.read();						if ((c2 != '\n') && (c2 != -1)) in.unread(c2);						break loop;					default:						if (--room < 0) {							char[] lineBuffer = buf;							buf = new char[offset + 128];						    room = buf.length - offset - 1;						    System.arraycopy(lineBuffer, 0, buf, 0, offset);						   						}						buf[offset++] = (char) c;						break;				}			}			if ((c == -1) && (offset == 0)) return null;			return String.copyValueOf(buf, 0, offset);	}	 	/**	* 读取流	* @param inStream	* @return 字节数组	* @throws Exception	*/	public static byte[] readStream(InputStream inStream) throws Exception{			ByteArrayOutputStream outSteam = new ByteArrayOutputStream();			byte[] buffer = new byte[1024];			int len = -1;			while( (len=inStream.read(buffer)) != -1){				outSteam.write(buffer, 0, len);			}			outSteam.close();			inStream.close();			return outSteam.toByteArray();	}}
    
   

运行效果如下:

Android前端控制:

后台监控日志:

下载后的文件路径:

 

 

 

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