Gottox socket.io-java-client“握手時出錯”空指針異常

Question

我正在嘗試使用socket.io連接到Geoloqi托管的流媒體服務器

我直接從github抓取了Gottox socket.io-java-client代碼並且沒有做任何修改，除了更改網址，但它給了我“握手時出錯”的消息。 網址應該是我從Geoloqi的制造商那里得到的： https ：//community.geoloqi.com/discussion/19/data-streaming#Item_11（參見第一回復）。

這是來自BasicExample.java的代碼

package basic;
/*
 * socket.io-java-client Test.java
 *
 * Copyright (c) 2012, Enno Boland
 * socket.io-java-client is a implementation of the socket.io protocol in Java.
 * 
 * See LICENSE file for more information
 */
import io.socket.IOAcknowledge;
import io.socket.IOCallback;
import io.socket.SocketIO;
import io.socket.SocketIOException;

import org.json.JSONException;
import org.json.JSONObject;

public class BasicExample implements IOCallback {
    private SocketIO socket;

    /**
     * @param args
     */
    public static void main(String[] args) {
        try {
            new BasicExample();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public BasicExample() throws Exception {
        socket = new SocketIO();
//      socket.connect("http://localhost:8080/", this);
        socket.connect("https://subscribe.geoloqi.com:443", this);

        // Sends a string to the server.
        socket.send("Hello Server");

        // Sends a JSON object to the server.
        socket.send(new JSONObject().put("key", "value").put("key2",
                "another value"));

        // Emits an event to the server.
        socket.emit("event", "argument1", "argument2", 13.37);
    }

    @Override
    public void onMessage(JSONObject json, IOAcknowledge ack) {
        try {
            System.out.println("Server said:" + json.toString(2));
        } catch (JSONException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void onMessage(String data, IOAcknowledge ack) {
        System.out.println("Server said: " + data);
    }

    @Override
    public void onError(SocketIOException socketIOException) {
        System.out.println("an Error occured");
        socketIOException.printStackTrace();
    }

    @Override
    public void onDisconnect() {
        System.out.println("Connection terminated.");
    }

    @Override
    public void onConnect() {
        System.out.println("Connection established");
    }

    @Override
    public void on(String event, IOAcknowledge ack, Object... args) {
        System.out.println("Server triggered event '" + event + "'");
    }
}

這是錯誤消息：

an Error occured
io.socket.SocketIOException: Error while handshaking
    at io.socket.IOConnection.handshake(IOConnection.java:322)
    at io.socket.IOConnection.access$7(IOConnection.java:292)
    at io.socket.IOConnection$ConnectThread.run(IOConnection.java:199)
Caused by: java.lang.NullPointerException
    at io.socket.IOConnection.handshake(IOConnection.java:302)
    ... 2 more
May 1, 2013 10:02:49 PM io.socket.IOConnection cleanup
INFO: Cleanup

代碼出了什么問題？

Answer 1

查看異常來源的源代碼 （ IOConnection.java:302 ，來自內部NullPointerException ），有以下代碼塊：

if (connection instanceof HttpsURLConnection) {
    ((HttpsURLConnection) connection)
        .setSSLSocketFactory(sslContext.getSocketFactory());
}

顯然connection必須是非null，否則它不會通過instanceof測試。 因此， sslContext必須為null。 由於該文件中sslContext引用sslContext其他位置在setSslContext()和getSslContext() ，唯一合乎邏輯的結論是您必須在建立SSL連接之前調用setSslContext() 。 SocketIO.setDefaultSSLSocketFactory()也調用IOConnection.setSslContext() ，所以你也可以調用它。

嘗試這個：

SocketIO.setDefaultSSLSocketFactory(SSLContext.getDefault());
socket = new SocketIO();
socket.connect("https://subscribe.geoloqi.com:443", this);
...

Answer 2

當我使用https://github.com/Gottox/socket.io-java-client創建我的Java客戶端時，我得到了同樣的錯誤。 好像我的服務器基於1.X，這只支持1.0（ https://github.com/Gottox/socket.io-java-client/issues/101 ）。 通過使用https://github.com/socketio/socket.io-client-java解決。