java - 如何重写方法中获取消息的循环

Question

我有一个蓝牙服务器，它从客户端(手机)接收数据。我正在使用的代码如下

@Override
public void run() {
    try {
        this.localDevice = LocalDevice.getLocalDevice();
        this.localDevice.setDiscoverable(DiscoveryAgent.GIAC);

        this.server = (StreamConnectionNotifier) Connector.open(URL);

        while(true) {
            if(this.connection == null) {
                this.connection = this.server.acceptAndOpen();

                System.out.println("INFO: Bluetooth client connected");

                BufferedReader reader = new BufferedReader(new InputStreamReader(connection.openInputStream()));
                this.writer = new BufferedWriter(new OutputStreamWriter(connection.openOutputStream()));

                String line;
                while((line = reader.readLine()) != null) {
                    if(line.equals("--#do:disconnect")) {
                        break;
                    }

                    System.out.println("INFO: Received from Bluetooth: " + line);
                }

                System.out.println("INFO: Client disconnected");
            }
        }
    } catch(BluetoothStateException ex) {
        ex.printStackTrace();
    } catch(IOException ex) {
        ex.printStackTrace();
    }
}

如您所见，我有一个不定式循环来接收消息，直到被告知停止为止。目前，循环接收到所有消息。这是有问题的。使用代码的类是MVC中的模型类。在课堂上，我还有一个名为getContacts()的方法。它用于通过蓝牙从电话接收联系人。当服务器发送--#do:getcontacts时，电话被告知要发送联系人。

我需要做的是在getContacts()方法的ArrayList中获取联系人并将其作为方法的返回值返回，以便控制器可以处理联系人。

public ArrayList<Contact> getContacts() {
    ArrayList<Contact> contacts = new ArrayList<>();

    // How do I get the contacts in the ArrayList?

    return contacts;
}

Answer 1

我会给你一些建议。我的示例不是有效的代码，只是适合您的工作基础。

首先，我强烈建议您在服务器中使用线程。每次客户端连接到服务器时，您都会创建一个新线程，其参数包含启动它所需的所有数据:

boolean running = true;    //this class variable will allow you to shut down the server correctly

public void stopServer(){    //this method will shut down the server
    this.running = false;
}

public void run() {
    ...

    while(running) {
        // if(this.connection == null) {  // I removed this line since it's unnecessary, or even harmful!
        StreamConnection connection = this.server.acceptAndOpen();  //This line will block until a connection is made...
        System.out.println("INFO: Bluetooth client connected");
        Thread thread = new ServerThread(connection);
        thread.start()              //don't forget exception handling...
    } 
}

并且在ServerThread类中，您实现了以下这些处理客户端的行(未编译的代码，没有异常处理!):

Class ServerThread extends Thread {
    StreamConnection connection;

    public ServerThread(StreamConnection connection){
        this.connection = connection;
    }

    public void run() {
        ...

        connection.close();     //closing the connection...don't forget exception handling!
        System.out.println("INFO: Client disconnected");
    }
}

此代码的优点是什么？现在，您的服务器可以同时处理一千个客户端。您已经进行了并行化，这就是服务器通常的工作方式!没有线程的服务器就像没有鞋子的袜子...

其次，如果您有Java客户端和Java服务器，则可以使用一种更简单的方法将对象发送到服务器:ObjectOutputStream / ObjectInputStream。您只需将包含联系人的数组(通常将使用ArraList)发送到服务器，然后读取该数组。这是服务器的代码(同样未编译且没有任何异常处理):

Class ServerThread extends Thread {
    StreamConnection connection;

    public ServerThread(StreamConnection connection){
        this.connection = connection;
    }

    public void run() {

        BufferedInputStream bis = new BufferedInputStream(this.connection.openInputStream());
        ObjectInputStream ois = new ObjectInputStream(bis);

        ArrayList contacts = (ArrayList) ois.readObject();  //this is a cast: don't forget exception handling!
        //You could also try the method ois.readUTF(); especially if you wanna use other non-Java clients

        System.out.println("INFO: Received from Bluetooth: " + contacts);
        this.connection.close();    //closing the connection...don't forget exception handling!
        //ois.close();      //do this instead of "this.connection.close()" if you want the connection to be open...i.e. to receive more data

        System.out.println("INFO: Client disconnected");

        //here you do whatever you wanna do with the contacts array, maybe add to your other contacts?
    }
}

在Java中，每个类都是一个对象，包括ArrayList。而且由于对象的末尾将被视为断开连接，因此您无需执行其他任何操作。

第三:您不仅将上述服务器用于蓝牙连接，而且还将WLAN连接用于aso。然后，您可以轻松地启动不同的线程，例如伪代码if(connection.isBluetooth()){//create a thread from BluetoothThread} else if(connection.isWLAN()){//create a thread from WLANsThread}。我不知道您的应用程序是关于什么的，但是也许有一天您想将其扩展到台式机，所以使用WLAN是正确的选择。另外，由于无论如何是蓝牙还是WLAN，无论如何，您都需要在客户端中建立一个验证(“哪些联系人将被发送到哪个服务器？”)，因为蓝牙的范围很小，无法为您提供任何安全性。 ;)

第四，最后是关于您的问题:要获得某些东西，您需要具有数据源和/或类变量。这是一个简短的示例，其中包含一个存储联系人的文件(但也可以是数据库...本地或其他地方!):

public class MyApp(){
    ArrayList contacts;
    ...

    public void run(){                  //this happens when we start our app
        this.contacts = new ArrayList();
        FileReader fr = new FileReader ("C:\WhereverYourFileIs\Contacts.file");
        BufferedReader br = new BufferedReader(fr);
        //here you use a loop to read the contacts via "br" from the file and fill them into your array...I can't provide you more code, since the exact data structure is up to you.
    }

    //now we want to send our contacts array to the already connected server:
    public sendArrayToServer() {
        BufferedOutputStream bos = new BufferedOutputStream (this.connection.openOutputStream());
        ObjectOutputStream oos = new ObjectOutputStream(bos);
        oos.writeObject(this.contacts);
         //If you use readUTF() in the server, you need to call here something like oos.writeUTF(this.contacts.toString()); or even need to use another parser method which exactly creates the string you want.
        this.connection.close();    //closing the connection...don't forget exception handling!
        //oos.close();      //do this instead of "this.connection.close()" if you want the connection to stay open...
    }
}

现在，在服务器中，您已经如上所述读出了联系人数组。您对这些联系人的处理方式仍由您决定。

希望这可以帮助您了解问题并找到解决方案。编程是关于反复试验和改进代码的。

编辑:

在讨论之后，我终于找到了您需要的东西:您需要一个名为BluetoothManager的单线程服务器，该服务器与另一个名为GUIController的线程进行交互。现在，无论如何我都在脑海中实现了该实现，因此可以将其连同一些说明一起发布给您。请注意，在这种情况下，您不需要初始化服务器中的另一个线程，因为BluetoothManager已经是一个线程，并且无论如何您只需要同时连接一个(问题仍然存在，如果那是一个“服务器” ，我宁愿称其为“接收者”):

Public class BluetoothManager extends Thread{
    boolean running = true;    //this class variable will allow you to shut down the server correctly
    GUIController controller;

    public BluetoothManager(GUIController controller){
        this.controller = controller;  //this registers the GUIController in the BluetoothManager
    }

    public void stop(){    //this method will shut down the "server"
        this.running = false;
    }

    public void run() {
        this.localDevice = LocalDevice.getLocalDevice();
        this.localDevice.setDiscoverable(DiscoveryAgent.GIAC);
        this.server = (StreamConnectionNotifier) Connector.open(URL);
        while(running){
            StreamConnection connection = this.server.acceptAndOpen();  //This line will block until a connection is made...or running==false!
            System.out.println("INFO: Bluetooth client connected");
            BufferedInputStream bis = new BufferedInputStream(this.connection.openInputStream());
            ObjectInputStream ois = new ObjectInputStream(bis);
            ArrayList contacts = (ArrayList) ois.readObject();  //this is a cast: don't forget exception handling!
            System.out.println("INFO: Received from Bluetooth: " + contacts);
            this.connection.close();    //closing the connection...don't forget exception handling!
            System.out.println("INFO: Client disconnected");
            this.controller.refreshContacts(contacts);
        }
    } 
}

public class GUIController extends Thread implements Runnable {
    ArrayList contacts;   //also a HashMap may be appropriate
    BluetoothManager manager;

    public void run(){
        this.contacts = new ArrayList();
        FileReader fr = new FileReader ("C:\WhereverYourFileIs\Contacts.file");
        BufferedReader br = new BufferedReader(fr);
        //here you use a loop to read the contacts via "br" from the file and fill them into your array...I can't provide you more code, since the exact data structure is up to you.
    }

    public void startBluetoothManager(){    //starting the BluetoothManager
        this.manager = new BluetoothManager(this);
        this.manager.start();
    }

    public void abortBluetoothManager(){  //call this when clicking on the "Abort" button
        this.manager.stop();
        //now the next 2 lines you normally don't need...still may use it if you've problems shutting down the thread:
        // try{ this.manager.interrupt(); }   //we want to be 100% sure to shut down our thread!
        // catch(Exception e){}
        this.manager = null; //now the garbage collector can clean everything...byebye
    }

    public void refreshContacts(ArrayList contacts) {
        // synchronize(this.contactArray){  //no synchronisation needed if you have a GUI pop-up with an "Abort"-button!
        Iterator i = this.contacts.iterator();
        while(i.hasNext()){
            this.contacts.add(i.next());
        }
        //At the end you need remove the "Receiving message" pop-up together with the "Abort Receiving"-button, these are all class variables!
        // important note: If you have unique entries, you may need to replace them! In this case I suggest storing all contact objects better in a HashMap contacts, and use the unique ID as a key to find the element. And then you may prompt the user, if there are identical entries, to overwrite each entry or not. These things remain all up to you.
    }
}
//As always: This is no compiled code!!

GUIController首先使用startBluetoothManager()运行BluetoothManager，除显示通知“正在接收联系人”和“中止接收”按钮外，什么也不做。当BluetoothManager完成时，他只需调用refreshContacts(...)将新联系人添加到GUIController内部现有的contacts-array中。如果按下“中止接收”按钮，则立即调用abortBluetoothManager()方法，该方法在BluetoothManager中设置running=false以结束服务器并完成线程。

该解决方案解决的主要问题是:两个线程不可能直接相互通信!调用thread.start()后，每个线程都是独立的。这就是为什么BluetoothManager线程无法告诉GUIController线程“我已经完成!”的原因。这些线程唯一能做的就是共享相同的资源，并通过该资源进行通信。在我们的例子中，它是GUIController中的contacts -ArrayList，我首先认为它需要同步，并且可以由两个线程进行更新(但不能同时进行)。而且-有趣的是-还有第二个共享资源，实际上是BluetoothManager类中的running标志可以将其关闭(但永远不需要running的任何同步，此变量只能由GUIController更改)。

现在，关于同步:我更加思考了这个问题，并且理解了，您也可以解决问题，而无需任何“synchronized(...)”调用。因此，如果您不想同步ArrayList，则必须执行以下操作:服务器运行时，仅显示“正在接收联系人”弹出窗口和“中止接收”按钮。发生这种情况时，您永远不会访问GUIController中的contact-ArrayList。这就是某种“本征同步”，不需要真正的Java同步。仍然可以实现同步，只是要100％确保以后再扩展应用程序时什么都不会发生。