获取 XMPPConnection 的 Nullpointer 异常

Posted 2023-02-24

【中文标题】获取 XMPPConnection 的 Nullpointer 异常

【英文标题】：Getting Nullpointer exception for XMPPConnection

【发布时间】：2018-07-17 18:31:17

【问题描述】：

我在 localhost 上运行 openfire 服务器， Smack 版本 4.2.4.GetAllContacts() 方法中出现异常。 下面是我的类 XmppConnection 的代码，它扩展了类 org.jivesoftware.smack.ConnectionListener。

  public class XmppConnection implements ConnectionListener
  private  XMPPTCPConnection mConnection;

  public List<Contact> getAllContacts() throws SmackException.NotLoggedInException, InterruptedException, SmackException.NotConnectedException 

    Log.d(TAG,"getAllContats called()");
    List<Contact> contacts = new ArrayList<>();

    if(XmppConnectService.sConnectionState == ConnectionState.AUTHENTICATED)
        Roster roster = Roster.getInstanceFor(mConnection);  //exception here

            Collection<RosterEntry> entries = roster.getEntries();
            Presence presence;

            for (RosterEntry entry : entries) 
                Contact c = new Contact(entry.getJid().toString());
                presence = roster.getPresence(entry.getJid());

                contacts.add(c);
                       


    return contacts;



public XmppConnection( Context context)


    mApplicationContext = context.getApplicationContext();
    String jid = PreferenceManager.getDefaultSharedPreferences(mApplicationContext)
            .getString("xmpp_jid",null);
    mPassword = PreferenceManager.getDefaultSharedPreferences(mApplicationContext)
            .getString("xmpp_password",null);

    if( jid != null)
    
        mUsername = jid.split("@")[0];
        mServiceName = jid.split("@")[1];
    else
    
        mUsername ="";
        mServiceName="";
    



public void connect() throws IOException,XMPPException,SmackException

    Log.d(TAG, "Connecting to server " + mServiceName);

    InetAddress addr = InetAddress.getByName(OPENFIRE_HOST);

    HostnameVerifier verifier = new HostnameVerifier() 
        @Override
        public boolean verify(String hostname, SSLSession session) 

            return true;
        
    ;


    DomainBareJid serviceName = JidCreate.domainBareFrom(OPENFIRE_HOST);
    conf = XMPPTCPConnectionConfiguration.builder();
            conf.setXmppDomain(serviceName
            .setHostAddress(addr)
            .setUsernameAndPassword(mUsername,mPassword)
            .setPort(5222)
            .setHostnameVerifier(verifier)
                                      .setSecurityMode(ConnectionConfiguration.SecurityMode.required)

            .setSecurityMode(ConnectionConfiguration.SecurityMode.disabled)
            .setCompressionEnabled(true);

    mConnection = new XMPPTCPConnection(conf.build());

    setupUiThreadBroadCastMessageReceiver();

    mConnection.addConnectionListener(this);
    try 

         mConnection.connect();

        mConnection.login(mUsername,mPassword);


     catch (InterruptedException e) 
        e.printStackTrace();

    


    ReconnectionManager reconnectionManager = ReconnectionManager.getInstanceFor(mConnection);
    reconnectionManager.setEnabledPerDefault(true);
    reconnectionManager.enableAutomaticReconnection();

    



@Override
public void connected(XMPPConnection connection) 
    XmppConnectService.sConnectionState = ConnectionState.CONNECTED;
    Log.w(TAG,"Connected Successfully; id:" + XmppConnectService.sConnectionState);



@Override
public void authenticated(XMPPConnection connection, boolean resumed) 
    XmppConnectService.sConnectionState = ConnectionState.AUTHENTICATED;
    Log.w(TAG,"Authenticated Successfully");
    showContactListActivityWhenAuthenticated();
 
    

以上代码在 logcat 中显示此错误：java.lang.NullPointerException: XMPPConnection must not be null

我从另一个类中调用 getAllContacts()

XmppConnection xmpp = new XmppConnection(this);
contacts = xmpp.getAllContacts();

getAllContacts() 方法从另一个活动调用，并在 authenticated() 方法之后调用。 因为它是在 authenticated() 方法之后调用的，所以 mConnection 应该已经初始化了。

【参考方案1】：

正如您的代码所示，您在方法 connect() 中初始化 mConnection 变量。 并且您的方法 authenticated() 不会对方法 connect() 进行任何调用。 您能否确保在调用方法 authenticated() 之前或在方法内调用 connect() 方法

【讨论】：

感谢您的回复。我确信在 connect() 方法之后调用了 authenticated() 方法。 mConnection.connect() 确保先调用 connected()，然后再调用 authenticated()。

【参考方案2】：

为 XmppConnection 类创建一个新对象会将其变量初始化为 null。 将 XMPPTCPConnection 声明为 static 有效：

private static XMPPTCPConnection mConnection;