title: IOException when using GCM
body: <p>I'm trying to send push notification to Android devices, but getting an error in following situation.</p>
  
  <pre><code>String msg = "push message";
  String to1 = "123456";
  String from1 = "098776655";
  </code></pre>
  
  <p>This works fine:</p>
  
  <pre><code>Message message = new Message.Builder()
      .collapseKey("1")
      .addData("message", msg)
      .addData("to1", to1)
      .addData("to2", to1)
      .build();
  </code></pre>
  
  <p>But getting error when using the following:</p>
  
  <pre><code>Message message = new Message.Builder()
      .collapseKey("1")
      .addData("message", msg)
      .addData("to", to1)
      .addData("from", from1)
      .build();
  </code></pre>
  
  <p>I have even used other variables in place of <code>from1</code> as well, but still getting error:</p>
  
  <pre><code>java.io.IOException: Server returned HTTP response code: 400 for URL: https://android.googleapis.com/gcm/send
  </code></pre>
  
  <p>StackTrace:</p>
  
  <pre><code>java.io.IOException: Server returned HTTP response code: 400 for URL: https://android.googleapis.com/gcm/send
    [run]     at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    [run]     at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
    [run]     at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
    [run]     at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
    [run]     at sun.net.www.protocol.http.HttpURLConnection$6.run(HttpURLConnection.java:1298)
    [run]     at java.security.AccessController.doPrivileged(Native Method)
    [run]     at sun.net.www.protocol.http.HttpURLConnection.getChainedException(HttpURLConnection.java:1292)
    [run]     at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:948)
    [run]     at sun.net.www.protocol.https.HttpsURLConnectionImpl.getInputStream(HttpsURLConnectionImpl.java:234)
    [run]     at com.google.android.gcm.server.Sender.sendNoRetry(Sender.java:363)
    [run]     at com.google.android.gcm.server.Sender.send(Sender.java:261)
    [run]     at example.HelloServlet.sendToSingleDevice(HelloServlet.java:173)
    [run]     at example.HelloServlet.doGet(HelloServlet.java:36)
    [run]     at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
    [run]     at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    [run]     at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    [run]     at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    [run]     at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    [run]     at java.lang.reflect.Method.invoke(Method.java:597)
    [run]     at org.apache.catalina.security.SecurityUtil$1.run(SecurityUtil.java:270)
    [run]     at org.apache.catalina.security.SecurityUtil$1.run(SecurityUtil.java:269)
    [run]     at java.security.AccessController.doPrivileged(Native Method)
    [run]     at javax.security.auth.Subject.doAsPrivileged(Subject.java:517)
    [run]     at org.apache.catalina.security.SecurityUtil.execute(SecurityUtil.java:302)
    [run]     at org.apache.catalina.security.SecurityUtil.doAsPrivilege(SecurityUtil.java:163)
    [run]     at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:283)
    [run]     at org.apache.catalina.core.ApplicationFilterChain.access$000(ApplicationFilterChain.java:56)
    [run]     at org.apache.catalina.core.ApplicationFilterChain$1.run(ApplicationFilterChain.java:189)
    [run]     at java.security.AccessController.doPrivileged(Native Method)
    [run]     at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:185)
    [run]     at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
    [run]     at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
    [run]     at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
    [run]     at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
    [run]     at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    [run]     at net.stax.appserver.webapp.RequestMonitorValve.invoke(RequestMonitorValve.java:35)
    [run]     at net.stax.appserver.webapp.RequestSetupValve.invoke(RequestSetupValve.java:31)
    [run]     at org.apache.catalina.valves.RemoteIpValve.invoke(RemoteIpValve.java:647)
    [run]     at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
    [run]     at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859)
    [run]     at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:602)
    [run]     at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
    [run]     at java.lang.Thread.run(Thread.java:619)
    [run] Caused by: java.io.IOException: Server returned HTTP response code: 400 for URL: https://android.googleapis.com/gcm/send
    [run]     at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1245)
    [run]     at java.net.HttpURLConnection.getResponseCode(HttpURLConnection.java:373)
    [run]     at sun.net.www.protocol.https.HttpsURLConnectionImpl.getResponseCode(HttpsURLConnectionImpl.java:318)
    [run]     at com.google.android.gcm.server.Sender.sendNoRetry(Sender.java:362)
    [run]     ... 33 more
    [run] Exception Message : Server returned HTTP response code: 400 for URL: https://android.googleapis.com/gcm/send
  </code></pre>