add a new handler for dealing download mp3 from remote server.

app/src/main/java/weian/cheng/mediaplayerwitexoplayer/MainActivity.kt

@@ -37,6 +37,10 @@ class MainActivity:AppCompatActivity() {
         onPlayerStateChanged = { state ->
             Log.i("MainActivity", "onPlayerStateChanged: $state")
         }
+
+        onDownloadTrack = { isSuccess ->
+            Log.i("MainActivity", "onDownloadTrack: $isSuccess")
+        }
     }
 
     override fun onCreate(savedInstanceState:Bundle?) {
@@ -51,6 +55,12 @@ class MainActivity:AppCompatActivity() {
         val play = findViewById<Button>(R.id.btn_play) as Button
         play.setOnClickListener { view ->
             player.play(url)
+            if (player.writeToFile(url, local)) {
+                Log.i("Weian", "play button, url is valid")
+            } else {
+                Log.i("Weian", "play button, url is not valid")
+            }
+            player.seekTo(220)
         }
 
         val stop = findViewById<Button>(R.id.btn_stop) as Button

mediaplayerwithexoplayer2/src/main/AndroidManifest.xml

@@ -1,2 +1,5 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
-          package="weian.cheng.mediaplayerwithexoplayer"/>
+          package="weian.cheng.mediaplayerwithexoplayer">
+    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
+    <uses-permission android:name="android.permission.ACCESS_WIFI_STATE"/>
+</manifest>

mediaplayerwithexoplayer2/src/main/java/weian/cheng/mediaplayerwithexoplayer/DownloadHandler.kt

@@ -0,0 +1,99 @@
+package weian.cheng.mediaplayerwithexoplayer
+
+import android.util.Log
+import java.io.BufferedInputStream
+import java.io.File
+import java.io.FileOutputStream
+import java.net.HttpURLConnection
+import java.net.URL
+
+class DownloadHandler(private val url: String, filePath: String, private val eventListener: ExoPlayerEventListener.PlayerEventListener? = null) : Thread() {
+    private val tag = "DownloadHandler"
+    private val bufferSize = 2048
+    private val tempTrackPath = "/storage/emulated/0/Download/temp_track.mp3"
+    private var totalSize: Int = -1
+    private var path: String = ""
+    private var file: File? = null
+    private var listener: ExoPlayerEventListener.PlayerEventListener? = null
+
+    init {
+        when (filePath.isEmpty()) {
+            true -> path = tempTrackPath
+            false -> path = filePath
+        }
+        listener = eventListener
+    }
+
+    override fun run() {
+        super.run()
+        Runnable {
+            if (!isRemoteAvailable()) {
+                listener?.onDownloadTrack(false)
+                Thread.currentThread().interrupt()
+            }
+
+            if (!createFile()) {
+                listener?.onDownloadTrack(false)
+                Thread.currentThread().interrupt()
+            }
+
+            if (!downloadFile()) {
+                listener?.onDownloadTrack(false)
+                Thread.currentThread().interrupt()
+            } else {
+                listener?.onDownloadTrack(true)
+            }
+
+        }.run()
+    }
+
+    private fun isRemoteAvailable(): Boolean {
+        var result = false
+        Log.i(tag, "url is $url")
+        val httpURLConnection = URL(url).openConnection() as HttpURLConnection
+        HttpURLConnection.setFollowRedirects(false)
+        httpURLConnection.connect()
+        httpURLConnection.requestMethod = "GET"
+        if (httpURLConnection.responseCode == HttpURLConnection.HTTP_OK)
+            result = true
+
+        totalSize = httpURLConnection.contentLength
+        httpURLConnection.disconnect()
+        return result
+    }
+
+    private fun createFile(): Boolean {
+        file = File(path)
+        file?.takeIf { it.exists() }.let {
+            it?.createNewFile()
+        }
+
+        return true
+    }
+
+    private fun downloadFile(): Boolean {
+        val fileOutputStream = FileOutputStream(file)
+        val inputStream = BufferedInputStream(URL(url).openStream())
+
+        var downloadSize = 0
+
+        val buffer = ByteArray(bufferSize)
+        var bufferLength: Int
+        while (true) {
+            bufferLength = inputStream.read(buffer)
+            if (bufferLength <= 0)
+                break
+            fileOutputStream.write(buffer, 0, bufferLength)
+            downloadSize += bufferLength
+        }
+
+        fileOutputStream.flush()
+        fileOutputStream.close()
+        inputStream.close()
+        if (downloadSize != totalSize) {
+            Log.e(tag, "file was not complete")
+            return false
+        }
+        return true
+    }
+}

mediaplayerwithexoplayer2/src/main/java/weian/cheng/mediaplayerwithexoplayer/ExoPlayerEventListener.kt

@@ -12,13 +12,15 @@ class ExoPlayerEventListener {
         fun onBufferPercentage(percent: Int)
         fun onCurrentTime(second: Int)
         fun onPlayerStateChanged(state: MusicPlayerState)
+        fun onDownloadTrack(isSuccess: Boolean)
     }
 
     class PlayerEventListenerFunc {
         var onDurationChanged: ((duration: Int) -> Unit)? = null
         var onBufferPercentage: ((percent: Int) -> Unit)? = null
         var onCurrentTime: ((second: Int) -> Unit)? = null
         var onPlayerStateChanged: ((state: MusicPlayerState) -> Unit)? = null
+        var onDownloadTrack: ((isSuccess: Boolean) -> Int)? = null
     }
 
     class PlayerEventListener(func: PlayerEventListenerFunc.() -> Unit): IEventListener {
@@ -40,5 +42,9 @@ class ExoPlayerEventListener {
         override fun onPlayerStateChanged(state: MusicPlayerState) {
             func.onPlayerStateChanged?.invoke(state)
         }
+
+        override fun onDownloadTrack(isSuccess: Boolean) {
+            func.onDownloadTrack?.invoke(isSuccess)
+        }
     }
 }

mediaplayerwithexoplayer2/src/main/java/weian/cheng/mediaplayerwithexoplayer/ExoPlayerWrapper.kt

@@ -1,6 +1,7 @@
 package weian.cheng.mediaplayerwithexoplayer
 
 import android.content.Context
+import android.net.ConnectivityManager
 import android.net.Uri
 import android.util.Log
 import com.google.android.exoplayer2.ExoPlaybackException
@@ -40,7 +41,10 @@ class ExoPlayerWrapper(private val context: Context): IMusicPlayer {
 
     private var listener: PlayerEventListener ?= null
 
-    override fun play(uri: String) {
+    override fun play(uri: String): Boolean {
+        if (!isNetworkAvailable())
+            return false
+
         if (playerState == Play) {
             // TODO: find out a appropriate exception or make one.
             throw Exception("now is playing")
@@ -49,9 +53,10 @@ class ExoPlayerWrapper(private val context: Context): IMusicPlayer {
         initExoPlayer(uri)
         exoPlayer.playWhenReady = true
         setPlayerState(Play)
+        return true
     }
 
-    override fun play() {
+    override fun play(): Boolean {
         when (isPlaying) {
             true -> {
                 timer.pause()
@@ -72,6 +77,7 @@ class ExoPlayerWrapper(private val context: Context): IMusicPlayer {
             setPlayerState(Play)
         }
         exoPlayer.playWhenReady = !isPlaying
+        return true
     }
 
     override fun stop() {
@@ -106,7 +112,9 @@ class ExoPlayerWrapper(private val context: Context): IMusicPlayer {
 
     override fun getPlayerState() = playerState
 
-    override fun writeToFile(uri: String): Boolean {
+    override fun writeToFile(url: String, filePath: String): Boolean {
+        val downloadThread = DownloadHandler(url, filePath, listener)
+        downloadThread.start()
         return true
     }
 
@@ -121,6 +129,14 @@ class ExoPlayerWrapper(private val context: Context): IMusicPlayer {
         }
     }
 
+    private fun isNetworkAvailable(): Boolean {
+        val connectivityManager = context.getSystemService(Context.CONNECTIVITY_SERVICE) as ConnectivityManager
+        if (connectivityManager.activeNetworkInfo == null) {
+            return false
+        }
+        return true
+    }
+
     private fun initExoPlayer(url: String) {
         Log.i(tag, "initExoPlayer")
         val meter = DefaultBandwidthMeter()

mediaplayerwithexoplayer2/src/main/java/weian/cheng/mediaplayerwithexoplayer/IMusicPlayer.kt

@@ -10,15 +10,17 @@ interface IMusicPlayer {
     /**
      * Start playing a music.
      * This function will play the music which is specified with an URI.
+     * If playing is failed, the function returns false.
      */
-    fun play(uri: String)
+    fun play(uri: String): Boolean
 
     /**
      * This function is also about play the music, but when the music is playing,
      * executing this function will pause the music.
      * If the music is pausing, executing this function will resume the music.
+     * If playing is failed, the function returns false.
      */
-    fun play()
+    fun play(): Boolean
 
     /**
      * stop playing the music.
@@ -58,7 +60,7 @@ interface IMusicPlayer {
      * Return true is that writing file successful.
      * Return false is that writing file unsuccessful.
      */
-    fun writeToFile(uri: String): Boolean
+    fun writeToFile(url: String, filePath: String): Boolean
 
     /**
      * The function is used to set up an event listener which monitor the activity of music player.