Gottox Socket.IO-java-客户端“握手时出错”空指针异常

Question

我正在尝试使用socket.io连接到Geoloqi托管的流媒体服务器

我直接从github获取了Gottox socket.io-java-client代码，除了更改url之外，没有做任何修改，但它给了我一条“握手时出错”的消息。url应该和我从Geoloqi的制造者那里得到的一样：https://community.geoloqi.com/discussion/19/data-streaming#Item_11 (见第一个回复)。

下面是来自BasicExample.java的代码

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 + "'");
    }
}

以下是错误消息：

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

代码出了什么问题？

Answer 1

查看异常来自的source code (IOConnection.java:302，来自内部NullPointerException)，下面是这段代码：

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

显然，connection必须是非空的，否则它将无法通过instanceof测试。因此，sslContext必须为空。由于该文件中引用sslContext的其他位置仅在setSslContext()和getSslContext()中，因此唯一合乎逻辑的结论是，您必须在建立连接之前调用 SSL 。SocketIO.setDefaultSSLSocketFactory()也会调用IOConnection.setSslContext()，所以你也可以直接调用它。

试试这个：

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

Answer 2

当我使用https://github.com/Gottox/socket.io-java-client创建我的Java客户端时，我得到了同样的错误。看起来我的服务器是基于1.X的，而且它只支持1.0 (https://github.com/Gottox/socket.io-java-client/issues/101)。通过使用https://github.com/socketio/socket.io-client-java解决。