Android 面试Socket与WebSocket

Android 面试Socket与WebSocket

Socket

什么是Socket

• 网络上的两个程序通过以一个双向通讯的链接来实现数据交换，这是一个双端链路，可以实现android的**跨进程通信，**Socket通常用来实现客户端和服务端的连接，一个Socket由一个IP地址和一个端口号唯一确定。
• 支持TCP/UDP协议栈，是长链接，一旦建立起连接将不会主动断掉，除非网络挂掉
• Socket是一种编程接口，不是协议**，Socket是应用层与TCP/IP协议族通信的中间软件抽象层，**它把复杂的TCP/IP协议族隐藏在Socket接口后面，对用户来说，一组简单的接口就是全部，让Socket去组织数据，以符合指定的协议。
• 

Socket通讯的过程

• 基于TCP：服务器端先初始化Socket，然后与端口绑定(bind)，对端口进行监听(listen)，调用accept阻塞，等待客户端连接。在这时如果有个客户端初始化一个Socket，然后连接服务器(connect)，如果连接成功，这时客户端与服务器端的连接就建立了。客户端发送数据请求，服务器端接收请求并处理请求，然后把回应数据发送给客户端，客户端读取数据，最后关闭连接，一次交互结束。
• 基于UDP：UDP 协议是用户数据报协议的简称，也用于网络数据的传输。虽然 UDP 协议是一种不太可靠的协议，但有时在需要较快地接收数据并且可以忍受较小错误的情况下，UDP 就会表现出更大的优势。我客户端只需要发送，服务端能不能接收的到我不管

TCP协议Socket代码示例

1·服务端：

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.ServerSocket;
import java.net.Socket;

//TCP协议Socket使用BIO进行通行：服务端
public class BIOServer {
    // 在main线程中执行下面这些代码
    public static void main(String[] args) {
        //1单线程服务
        ServerSocket server = null;
        Socket socket = null;
        InputStream in = null;
        OutputStream out = null;
        try {
            server = new ServerSocket(8000);
            System.out.println("服务端启动成功，监听端口为8000，等待客户端连接...");
            while (true){
                socket = server.accept(); //等待客户端连接
                System.out.println("客户连接成功，客户信息为：" + socket.getRemoteSocketAddress());
                in = socket.getInputStream();
                byte[] buffer = new byte[1024];
                int len = 0;
                //读取客户端的数据
                while ((len = in.read(buffer)) > 0) {
                    System.out.println(new String(buffer, 0, len));
                }
                //向客户端写数据
                out = socket.getOutputStream();
                out.write("hello!".getBytes());
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

2·客户端

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

//TCP协议Socket：客户端
public class Client01 {
    public static void main(String[] args) throws IOException {
        //创建套接字对象socket并封装ip与port
        Socket socket = new Socket("127.0.0.1", 8000);
        //根据创建的socket对象获得一个输出流
        OutputStream outputStream = socket.getOutputStream();
        //控制台输入以IO的形式发送到服务器
        System.out.println("TCP连接成功 \n请输入：");
        while(true){
            byte[] car = new Scanner(System.in).nextLine().getBytes();
            outputStream.write(car);
            System.out.println("TCP协议的Socket发送成功");
            //刷新缓冲区
            outputStream.flush();
        }
    }
}

先运行服务端，在运行客户端。测试结果发送成功：

UDP协议Socket代码示例

1·服务器

//UDP协议Socket：服务端
public class Server1 {
    public static void main(String[] args) {
        try {
            //DatagramSocket代表声明一个UDP协议的Socket
            DatagramSocket socket = new DatagramSocket(8888);
            //byte数组用于数据存储。
            byte[] car = new byte[1024];
            //DatagramPacket 类用来表示数据报包DatagramPacket
            DatagramPacket packet = new DatagramPacket(car, car.length);
            // //创建DatagramPacket的receive()方法来进行数据的接收,等待接收一个socket请求后才执行后续操作；
            System.out.println("等待UDP协议传输数据");
            socket.receive(packet);
            //packet.getLength返回将要发送或者接收的数据的长度。
            int length = packet.getLength();
            System.out.println("啥东西来了：" + new String(car, 0, length));
            socket.close();
            System.out.println("UDP协议Socket接受成功");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

2·客户端

//UDP协议Socket：客户端
public class Client1 {
    public static void main(String[] args) {
        try {
            //DatagramSocket代表声明一个UDP协议的Socket
            DatagramSocket socket = new DatagramSocket(2468);
            //字符串存储人Byte数组
            byte[] car = "UDP协议的Socket请求，有可能失败哟".getBytes();
            //InetSocketAddress类主要作用是封装端口
            InetSocketAddress address = new InetSocketAddress("127.0.0.1", 8888);
            //DatagramPacket 类用来表示数据报包DatagramPacket
            DatagramPacket packet = new DatagramPacket(car, car.length, address);
            //send() 方法发送数据包。
            socket.send(packet);
            System.out.println("UDP协议的Socket发送成功");
            socket.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Socket实现Android跨进程通信

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    package="com.example.socketdemo">

    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <application
        android:allowBackup="true"
        android:dataExtractionRules="@xml/data_extraction_rules"
        android:fullBackupContent="@xml/backup_rules"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.SocketDemo"
        tools:targetApi="31">
        <activity
            android:name=".TCPClientActivity"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <service android:name=".TCPServerService"
            android:process=":remote" />
    </application>

</manifest>

package com.example.socketdemo;

import android.app.ActivityManager;
import android.app.ActivityManager.RunningAppProcessInfo;
import android.content.Context;

import java.io.Closeable;
import java.io.IOException;
import java.util.List;

public class MyUtils {

    public static String getProcessName(Context cxt, int pid) {
        ActivityManager am = (ActivityManager) cxt
                .getSystemService(Context.ACTIVITY_SERVICE);
        List<RunningAppProcessInfo> runningApps = am.getRunningAppProcesses();
        if (runningApps == null) {
            return null;
        }
        for (RunningAppProcessInfo procInfo : runningApps) {
            if (procInfo.pid == pid) {
                return procInfo.processName;
            }
        }
        return null;
    }

    public static void close(Closeable closeable) {
        try {
            if (closeable != null) {
                closeable.close();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static void executeInThread(Runnable runnable) {
        new Thread(runnable).start();
    }

}

package com.example.socketdemo;

import android.annotation.SuppressLint;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.os.SystemClock;
import android.text.TextUtils;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.Socket;
import java.sql.Date;
import java.text.SimpleDateFormat;

public class TCPClientActivity extends Activity implements OnClickListener {

    private static final int MESSAGE_RECEIVE_NEW_MSG = 1;
    private static final int MESSAGE_SOCKET_CONNECTED = 2;

    private Button mSendButton;
    private TextView mMessageTextView;
    private EditText mMessageEditText;

    private PrintWriter mPrintWriter;
    private Socket mClientSocket;

    @SuppressLint("HandlerLeak")
    private Handler mHandler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
            case MESSAGE_RECEIVE_NEW_MSG: {
                mMessageTextView.setText(mMessageTextView.getText()
                        + (String) msg.obj);
                break;
            }
            case MESSAGE_SOCKET_CONNECTED: {
                mSendButton.setEnabled(true);
                break;
            }
            default:
                break;
            }
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_tcpclient);
        mMessageTextView = (TextView) findViewById(R.id.msg_container);
        mSendButton = (Button) findViewById(R.id.send);
        mSendButton.setOnClickListener(this);
        mMessageEditText = (EditText) findViewById(R.id.msg);
        Intent service = new Intent(this, TCPServerService.class);
        startService(service);
        new Thread() {
            @Override
            public void run() {
                connectTCPServer();
            }
        }.start();
    }

    @Override
    protected void onDestroy() {
        if (mClientSocket != null) {
            try {
                mClientSocket.shutdownInput();
                mClientSocket.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        super.onDestroy();
    }

    @Override
    public void onClick(View v) {
        if (v == mSendButton) {
            final String msg = mMessageEditText.getText().toString();
            if (!TextUtils.isEmpty(msg) && mPrintWriter != null) {
                new Thread(new Runnable() {
                    @Override
                    public void run() {
                        mPrintWriter.println(msg);
                    }
                }).start();
                mMessageEditText.setText("");
                String time = formatDateTime(System.currentTimeMillis());
                final String showedMsg = "self " + time + ":" + msg + "\n";
                mMessageTextView.setText(mMessageTextView.getText() + showedMsg);
            }
        }
    }

    @SuppressLint("SimpleDateFormat")
    private String formatDateTime(long time) {
        return new SimpleDateFormat("(HH:mm:ss)").format(new Date(time));
    }

    private void connectTCPServer() {
        Socket socket = null;
        while (socket == null) {
            try {
                socket = new Socket("localhost", 8688);
                mClientSocket = socket;
                mPrintWriter = new PrintWriter(new BufferedWriter(
                        new OutputStreamWriter(socket.getOutputStream())), true);
                mHandler.sendEmptyMessage(MESSAGE_SOCKET_CONNECTED);
                System.out.println("connect server success");
            } catch (IOException e) {
                SystemClock.sleep(1000);
                System.out.println("connect tcp server failed, retry...");
            }
        }

        try {
            // 接收服务器端的消息
            BufferedReader br = new BufferedReader(new InputStreamReader(
                    socket.getInputStream()));
            while (!TCPClientActivity.this.isFinishing()) {
                String msg = br.readLine();
                System.out.println("receive :" + msg);
                if (msg != null) {
                    String time = formatDateTime(System.currentTimeMillis());
                    final String showedMsg = "server " + time + ":" + msg
                            + "\n";
                    mHandler.obtainMessage(MESSAGE_RECEIVE_NEW_MSG, showedMsg)
                            .sendToTarget();
                }
            }
            System.out.println("quit...");
            MyUtils.close(mPrintWriter);
            MyUtils.close(br);
            socket.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#ffffff"
    android:orientation="vertical"
    android:padding="5dp"
    tools:context="${relativePackage}.${activityClass}" >

    <ScrollView
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1" >

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="vertical" >

            <TextView
                android:id="@+id/msg_container"
                android:layout_width="match_parent"
                android:layout_height="wrap_content" />
        </LinearLayout>
    </ScrollView>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content" >

        <EditText
            android:id="@+id/msg"
            android:layout_width="0dp"
            android:layout_height="35dp"
            android:layout_weight="1"
            android:background="@drawable/edit"
            android:ems="10"
            android:padding="5dp" />

        <Button
            android:id="@+id/send"
            android:layout_width="wrap_content"
            android:layout_height="35dp"
            android:enabled="false"
            android:text="发送" />
    </LinearLayout>

</LinearLayout>

package com.example.socketdemo;

import android.app.Service;
import android.content.Intent;
import android.os.IBinder;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.Random;

public class TCPServerService extends Service {

    private boolean mIsServiceDestoryed = false;
    private String[] mDefinedMessages = new String[] {
            "你好啊，哈哈",
            "请问你叫什么名字呀？",
            "今天北京天气不错啊，shy",
            "你知道吗？我可是可以和多个人同时聊天的哦",
            "给你讲个笑话吧：据说爱笑的人运气不会太差，不知道真假。"
    };

    @Override
    public void onCreate() {
        new Thread(new TcpServer()).start();
        super.onCreate();
    }

    @Override
    public IBinder onBind(Intent intent) {
        return null;
    }

    @Override
    public void onDestroy() {
        mIsServiceDestoryed = true;
        super.onDestroy();
    }

    private class TcpServer implements Runnable {

        @SuppressWarnings("resource")
        @Override
        public void run() {
            ServerSocket serverSocket = null;
            try {
                serverSocket = new ServerSocket(8688);
            } catch (IOException e) {
                System.err.println("establish tcp server failed, port:8688");
                e.printStackTrace();
                return;
            }

            while (!mIsServiceDestoryed) {
                try {
                    // 接受客户端请求
                    final Socket client = serverSocket.accept();
                    System.out.println("accept");
                    new Thread() {
                        @Override
                        public void run() {
                            try {
                                responseClient(client);
                            } catch (IOException e) {
                                e.printStackTrace();
                            }
                        };
                    }.start();

                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    private void responseClient(Socket client) throws IOException {
        // 用于接收客户端消息
        BufferedReader in = new BufferedReader(new InputStreamReader(
                client.getInputStream()));
        // 用于向客户端发送消息
        PrintWriter out = new PrintWriter(new BufferedWriter(
                new OutputStreamWriter(client.getOutputStream())), true);
        out.println("欢迎来到聊天室！");
        while (!mIsServiceDestoryed) {
            String str = in.readLine();
            System.out.println("msg from client:" + str);
            if (str == null) {
                break;
            }
            int i = new Random().nextInt(mDefinedMessages.length);
            String msg = mDefinedMessages[i];
            out.println(msg);
            System.out.println("send :" + msg);
        }
        System.out.println("client quit.");
        // 关闭流
        MyUtils.close(out);
        MyUtils.close(in);
        client.close();
    }

}

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android" >

    <item>
        <shape android:shape="rectangle" >
            <solid android:color="#0ac39e" />
        </shape>
    </item>

    <item android:bottom="6dp">
        <shape android:shape="rectangle" >
            <solid android:color="#ffffff" />
        </shape>
    </item>

    <item
        android:bottom="1dp"
        android:left="1dp"
        android:right="1dp">
        <shape android:shape="rectangle" >
            <solid android:color="#ffffff" />
        </shape>
    </item>

</layer-list>

WebSocket

什么是websocket

• websocket是一种在单个TCP连接上进行的全双工通信息，websocket使得客户端和服务器之间的数据交换变得更加简单，允许服务端主动向客户端推送数据
• 浏览器和服务器只需要完成一次握手，两者之间就直接可以创建持久性的连接，并且进行双向数据传输
• websocket是一种计算机应用层协议，弥补了http协议在通信持久能力上的不足。
• 它的最大特点就是，服务器可以主动向客户端推送信息，客户端也可以主动向服务器发送信息，是真正的双向平等对话，属于服务器推送技术的一种。
• 与 HTTP 协议有着良好的兼容性。默认端口也是80和443，并且握手阶段采用 HTTP 协议，因此握手时不容易屏蔽，能通过各种 HTTP 代理服务器。
• 数据格式比较轻量，，性能开销小，通信高效。可以发送文本，也可以发送二进制数据。
• 没有同源限制，客户端可以与任意服务器通信。
• 协议标识符是ws（如果加密，则为wss），服务器网址就是 URL。

ws://example.com:80/some/path

推荐阅读：一文吃透 WebSocket 原理 刚面试完，趁热赶紧整理