Android/kotlin/http通信のソースを表示

==準備==
AndroidManifext.xmlに以下を追加しておく。
 <uses-permission android:name="android.permission.INTERNET" />

==サンプル==
HttpRequest.kt
<pre>
class HttpRequest {
    private var status = 0;
    private var body = "";
    fun request(requestUrl: String): Boolean {
        if (requestUrl.isEmpty()) {
            Log.w(TAG, "URLが空です。")
            return false
        }
        val url = URL(requestUrl)
        val urlConnection = url.openConnection() as HttpURLConnection
        urlConnection.requestMethod = "GET"
        urlConnection.connect()
        status = urlConnection.responseCode
        val br = BufferedReader(InputStreamReader(urlConnection.inputStream))
        val sb = StringBuilder()
        for (line: String? in br.readLines()) {
            line?.let { sb.append(line) }
        }
        br.close()
        body = sb.toString()
        return true
    }
    fun getBody(): String {
        return body
    }
    fun getStatusCode(): Int {
        return status
    }
    companion object {
        private const val TAG = "HttpRequest"
    }
}
</pre>
参考：https://qiita.com/naoi/items/8df1409ad48ad8f3c632

==AsyncTsnkでアクセス==
直アクセスだとアクセスできないのでAsyncTaskをかます。

起動方法
 var task = HttpAsyncTask();
 task.execute();

HttpAsyncTask.kt
<pre>
import android.os.AsyncTask
class HttpAsyncTask : AsyncTask<Void, Void, Boolean>() {
    override fun onPreExecute() {
        Log.i(TAG, "onPreExecute")
    }
    override fun doInBackground(vararg p: Void?): Boolean {
        var httpRequest = HttpRequest()
        var success: Boolean = httpRequest.request("https://example.com/?hogehoge")
        Log.i(TAG, "body=" + httpRequest.getBody())
        return true
    }
    override fun onPostExecute(flag: Boolean) {
        Log.i(TAG, "onPostExecute flag=" + flag)
        super.onPostExecute(flag)
    }
}
</pre>

===AsyncTsnkでException===
doInBackground内でExceptionは使えない。cancel(true)などを使えば、onCancelledが呼ばれるのでそのようにする。
<pre>
    override fun doInBackground(vararg p: Void?): Boolean {
        throw Exception("error")
        // cancel(true)
        return true
    }
    override fun onCancelled(flag: Boolean) {
        super.onCancelled(flag)
    }
</pre>
<pre>
        try {
            var task = HttpAsyncTask()
            task.execute()
        } catch (e: Exception) {
            Log.e("test", "HttpAsyncTask ${e.message}")
        }
</pre>

==コールチンでアクセス==
AsyncTaskの代わりにkotlin1.3より公式となったコールチンでもアクセスできます。

準備

app/build.gradle
<pre>
dependencies {
    implementation "org.jetbrains.kotlinx:kotlinx-coroutines-core:1.3.2"
    implementation "org.jetbrains.kotlinx:kotlinx-coroutines-android:1.3.2"
}
</pre>


MainActivity.kt
<pre>
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.util.Log
import kotlinx.android.synthetic.main.activity_main.*
import kotlinx.coroutines.CoroutineScope
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.launch
import kotlinx.coroutines.withContext

class MainActivity : AppCompatActivity() {
    val scope = CoroutineScope(Dispatchers.Default)
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        scope.launch {
            httpTask()
        }
    }
    private suspend fun httpTask() {
        try {
            withContext(Dispatchers.Main) {
                Log.i(localClassName, "onPreExecute")
            }
            var httpRequest = HttpRequest()
            //var http = HttpUtil()
            var success: Boolean = httpRequest.request("https://h2ch.com/?hogehoge")
            Log.i(localClassName, "body=" + httpRequest.getBody())
            Log.i(localClassName, "status=" + httpRequest.getStatusCode().toString())

            withContext(Dispatchers.Main) {
                Log.i(localClassName, "onPostExecute")
            }
        } catch (e: Exception) {
            Log.e(localClassName, "onCancelled", e)
        }
    }
}
</pre>

コルーチンから呼び出すメソッドはsuspend修飾子が必要。

===コールチンのExceptionについて===
以下はできるが、
<pre>
private suspend fun httpTask() {
    try {
        throw Exception("damedesu")
    } catch (e: Exception) {
        Log.e(localClassName, "onCancelled", e)
    }
}
</pre>
以下はできない。
<pre>
try {
    scope.launch {
        httpTask()
    }
} catch (e: Exception) {
    Log.e(localClassName, "onCancelled", e)
}
private suspend fun httpTask() {
    throw Exception("damedesu")
}
</pre>