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.java

package 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.java

package 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.java

package 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.java

package 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

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
<TextView
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:text="@string/filename"
    />

    <EditText
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="022.jpg"
        android:id="@+id/filename"
        />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/button"
        android:id="@+id/button"
        />
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="暂停"
        android:id="@+id/stop"
        />
    <ProgressBar
            android:layout_width="fill_parent"
            android:layout_height="20px"
            style="?android:attr/progressBarStyleHorizontal"
            android:id="@+id/uploadbar"
            />
    <TextView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:id="@+id/result"
        />
</LinearLayout>

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.android.upload"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk android:minSdkVersion="8" />

    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name" >
        <activity
            android:name=".UploadActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>
    <!-- 访问网络的权限 -->
    <uses-permission android:name="android.permission.INTERNET"/>
    <!-- 在SDCard中创建与删除文件权限 -->
    <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>
    <!-- 往SDCard写入数据权限 -->
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
</manifest>

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<Long, FileLog> datas = new HashMap<Long, FileLog>();// 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: