我正在尝试将MQTT eclipse paho库用于我的Android应用程序。我首先在java中编写代码并在Eclipse中进行测试。它完美地运作。但是，相同的库和函数在Android中无法正常工作。我已将我的jar添加到应用程序的libs文件夹中。我还在应用程序的gradle中添加了编译文件（'libs / org.eclipse.paho.client.mqttv3-1.0.2.jar'）。该应用程序正确编译，但抛出异常。 这是我的代码：
package com.example.ankur.mqtt;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.TextView;
import org.eclipse.paho.client.mqttv3.MqttClient;
import org.eclipse.paho.client.mqttv3.MqttConnectOptions;
import org.eclipse.paho.client.mqttv3.MqttException;
public class MainActivity extends ActionBarActivity {
private TextView isConnected;
private boolean isMQTT;
private boolean connectionState;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
MQTTconnection mqtTconnection = new MQTTconnection();
mqtTconnection.execute("Execute");
isConnected = (TextView) findViewById(R.id.isConnected);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
private class MQTTconnection extends AsyncTask<String, Void, String>{
@Override
protected String doInBackground(String... params){
boolean connectionState;
connectionState = connectMQTT("tcp://iot.eclipse.org:1883","ankur145");
System.out.println(connectionState);
if (connectionState == true){
isMQTT = "True";
return "TRUE";
}
isMQTT = "False";
return "False";
}
@Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
Log.d("DownloadClass", "Result was " + result);
}
protected boolean connectMQTT(String URL, String clientId){
boolean connectionState;
try {
MqttClient mqClient = new MqttClient(URL, clientId);
MqttConnectOptions connOpts = new MqttConnectOptions();
connOpts.setCleanSession(true);
mqClient.connect(connOpts);
connectionState = mqClient.isConnected();
Log.d("Connection", String.valueOf(connectionState));
//mqClient.setCallback(this);
} catch (MqttException me) {
// TODO Auto-generated catch block
System.out.println("reason "+me.getReasonCode());
System.out.println("msg "+me.getMessage());
System.out.println("loc "+me.getLocalizedMessage());
System.out.println("cause "+me.getCause());
System.out.println("excep " + me);
me.printStackTrace();
return false;
}
Log.d("ConnectionState","in ConnectionC");
return connectionState;
}
}
}
这是我得到的例外：
12-12 12:44:35.466 2038-2038/com.example.ankur.mqtt I/System.out: msg MqttException
12-12 12:44:35.466 2038-2038/com.example.ankur.mqtt I/System.out: loc MqttException
12-12 12:44:35.466 2038-2038/com.example.ankur.mqtt I/System.out: cause null
12-12 12:44:35.466 2038-2038/com.example.ankur.mqtt I/System.out: excep MqttException (0)
2-11 17:57:41.981 30284-30312/com.example.ankur.mqtt W/System.err: MqttException (0)
12-11 17:57:41.982 30284-30312/com.example.ankur.mqtt W/System.err: at org.eclipse.paho.client.mqttv3.persist.MqttDefaultFilePersistence.open(MqttDefaultFilePersistence.java:80)
12-11 17:57:41.982 30284-30312/com.example.ankur.mqtt W/System.err: at org.eclipse.paho.client.mqttv3.MqttAsyncClient.<init>(MqttAsyncClient.java:286)
12-11 17:57:41.982 30284-30312/com.example.ankur.mqtt W/System.err: at org.eclipse.paho.client.mqttv3.MqttAsyncClient.<init>(MqttAsyncClient.java:167)
12-11 17:57:41.982 30284-30312/com.example.ankur.mqtt W/System.err: at org.eclipse.paho.client.mqttv3.MqttClient.<init>(MqttClient.java:224)
12-11 17:57:41.982 30284-30312/com.example.ankur.mqtt W/System.err: at org.eclipse.paho.client.mqttv3.MqttClient.<init>(MqttClient.java:136)
12-11 17:57:41.982 30284-30312/com.example.ankur.mqtt W/System.err: at com.example.ankur.mqtt.MainActivity$MQTTconnection.connectMQTT(MainActivity.java:96)
12-11 17:57:41.982 30284-30312/com.example.ankur.mqtt W/System.err: at com.example.ankur.mqtt.MainActivity$MQTTconnection.doInBackground(MainActivity.java:75)
12-11 17:57:41.982 30284-30312/com.example.ankur.mqtt W/System.err: at com.example.ankur.mqtt.MainActivity$MQTTconnection.doInBackground(MainActivity.java:71)
12-11 17:57:41.982 30284-30312/com.example.ankur.mqtt W/System.err: at android.os.AsyncTask$2.call(AsyncTask.java:292)
12-11 17:57:41.982 30284-30312/com.example.ankur.mqtt W/System.err: at java.util.concurrent.FutureTask.run(FutureTask.java:237)
12-11 17:57:41.982 30284-30312/com.example.ankur.mqtt W/System.err: at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
12-11 17:57:41.982 30284-30312/com.example.ankur.mqtt W/System.err: at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
12-11 17:57:41.982 30284-30312/com.example.ankur.mqtt W/System.err: at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
12-11 17:57:41.982 30284-30312/com.example.ankur.mqtt W/System.err: at java.lang.Thread.run(Thread.java:818)
清单文件的权限：
uses-permission android:name="android.permission.INTERNET"
答案 0 :(得分：1)
问题是因为您使用默认构造函数来创建MqttClient对象。这实例化了一个MqttDefaultFilePersistence对象，用于在传递消息时将消息写入（QOS 1或2）。即使使用写入权限，您也无法访问默认目录。
您需要使用此版本的constructor
并传递一个MqttDefaultFilePersistence对象，该对象指向您可以写入的目录或传递MemoryPersistence对象