需求：通过udp传输方式，快速找到同局域网内某设备
思路：需要某设备发送，手机接收。或者手机发送，设备接收，两个设备需在同一局域网内
1、建立udpsocket服务
2、提供数据，并将数据封装到数据包中
3、通过socket服务的发送功能，将数据包发送出去。
4、关闭资源。
DatagramSocket：此类表示用来发送和接收数据报包的套接字。在 DatagramSocket 上总是启用 UDP 广播发送。
DatagramPacket：此类表示数据报包。数据报包用来实现无连接包投递服务。每条报文仅根据该包中包含的信息从一台机器路由到另一台机器。从一台机器发送到另一台机器的多个包可能选择不同的路由，也可能按不同的顺序到达。不对包投递做出保证。

先看个图：

UDP发送数据

UDP接收数据

具体代码如下：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".ui.activity.TestActivity">

    <Button
        android:id="@+id/btn_send"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="发送" />

    <Button
        android:id="@+id/btn_wait"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="开始等待接收" />

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


        <TextView
            android:id="@+id/tv_data"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="-------------" />
    </ScrollView>
</LinearLayout>

package com.fzm.coldwallet.ui.activity;

import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import com.fzm.coldwallet.R;
import com.fzm.coldwallet.ui.base.BaseActivity;
import com.fzm.coldwallet.utils.ToastUtils;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.SocketException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Timer;
import java.util.TimerTask;

import butterknife.BindView;
import butterknife.ButterKnife;
import butterknife.OnClick;

public class TestActivity extends BaseActivity {

    @BindView(R.id.btn_send)
    Button btnSend;
    @BindView(R.id.btn_wait)
    Button btnWait;
    @BindView(R.id.tv_data)
    TextView tvData;
    private MainHandle mMainHandle;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_test);
        ButterKnife.bind(this);
        mMainHandle = new MainHandle();

    }

    @OnClick({R.id.btn_send, R.id.btn_wait})
    public void onViewClicked(View view) {
        switch (view.getId()) {
            case R.id.btn_send:
                sendMsg();
                break;
            case R.id.btn_wait:
                new Thread(new Runnable() {
                    @Override
                    public void run() {
                        waitMsg();
                    }
                }).start();
                break;
        }
    }

    private String sLog = "";

    private void sendMsg() {
        try {
            final DatagramSocket hostSocket = new DatagramSocket();
            // 设置接收超时时间
            hostSocket.setSoTimeout(1500);
            final String sendData = "my name is zzz";
            InetAddress broadIP = InetAddress.getByName("255.255.255.255");
            final DatagramPacket sendPack = new DatagramPacket(sendData.getBytes(), sendData.length(), broadIP, 9901);

            new Timer().schedule(new TimerTask() {
                @Override
                public void run() {
                    String log = sendData + new SimpleDateFormat("yyyy-MM-dd HH：mm：ss").format(new Date()) + "\n";
                    Log.v("tag", Thread.currentThread() + log);
                    if (sLog.split("\n").length > 10) {
                        sLog = "";
                    }
                    try {
                        hostSocket.send(sendPack);
                        sLog += log;
                        runOnUiThread(new Runnable() {
                            @Override
                            public void run() {
                                tvData.setText(sLog);
                            }
                        });
                    } catch (Exception e) {
                        e.printStackTrace();
                    }

                }
            }, 0, 1000);


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

    }


    private String rLog = "";

    private void waitMsg() {
        byte[] buffer = new byte[1024];
        /*在这里同样使用约定好的端口*/
        int port = 9901;
        DatagramSocket server = null;
        try {
            server = new DatagramSocket(port);
            final DatagramPacket packet = new DatagramPacket(buffer, buffer.length);
            while (true) {
                // 等待主机的搜索
                try {
                    server.receive(packet);
                    final String s = new String(packet.getData(), 0, packet.getLength(), "UTF-8");
                    String log = packet.getAddress() + ",port:" + packet.getPort() + "," + s + "\n";
                    Log.v("tag", log);
                    rLog += log;
                    if (rLog.split("\n").length > 10) {
                        rLog = "";
                    }
                    mMainHandle.sendEmptyMessage(1);

                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        } catch (SocketException e) {
            e.printStackTrace();
        } finally {
            if (server != null)
                server.close();
        }
    }

    class MainHandle extends Handler {
        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            tvData.setText(rLog);
        }
    }
}

最后别忘了网络权限：

    <uses-permission android:name="android.permission.INTERNET" />