发送java&；来自servlet lang.NullPointerException的未捕获异常

我在appengine.google.com上发现了这个错误。事实上，邮件不是 在我的应用程序上收到错误显示为警告& 取消。所以请给我这个问题的解决方案。谢谢

messenger.server

import java.io.IOException;

import java.util.logging.Level;
import java.util.logging.Logger;

import javax.persistence.EntityManager;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import e.gochat.messenger.model.Contact;
import e.gochat.messenger.model.EMFService;

import com.google.android.gcm.server.Message;
import com.google.android.gcm.server.Result;
import com.google.android.gcm.server.Sender;

@SuppressWarnings("serial")
public class SendServlet extends HttpServlet {

    private static final Logger logger = Logger.getLogger(SendServlet.class.getCanonicalName());

    public void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
        resp.setContentType("text/plain");
        resp.getWriter().println("Sends a message to the GCM server.");     
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String msg = req.getParameter(Constants.MSG);
        String from = req.getParameter(Constants.FROM);
        String to = req.getParameter(Constants.TO);

        Contact contact = null;
        EntityManager em = EMFService.get().createEntityManager();
        try {
            contact = Contact.find(to, em);
            if (contact == null) return;
        } finally {
            em.close();
        }

        String regId = contact.getRegId();
        Sender sender = new Sender(Constants.API_KEY);
        Message message = new Message.Builder()
//          .delayWhileIdle(true)
            .addData(Constants.TO, to).addData(Constants.FROM, from).addData(Constants.MSG, msg)
            .build();

        try {
            Result result = sender.send(message, regId, 5);
/*          List<String> regIds = new ArrayList<String>();
            regIds.add(regId);
            MulticastResult result = sender.send(message, regIds, 5);*/

            logger.log(Level.WARNING, "Result: " + result.toString());
        } catch (IOException e) {
            logger.log(Level.SEVERE, e.getMessage());
        }
    }

}

取消错误

    >Uncaught exception from servlet
java.lang.NullPointerException
    at java.net.URLEncoder.encode(URLEncoder.java:205)
    at com.google.android.gcm.server.Sender.sendNoRetry(Sender.java:166)
    at com.google.android.gcm.server.Sender.send(Sender.java:121)
    at e.gochat.messenger.server.SendServlet.doPost(SendServlet.java:53)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1166)
    at com.google.apphosting.utils.servlet.ParseBlobUploadFilter.doFilter(ParseBlobUploadFilter.java:125)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.apphosting.runtime.jetty.SaveSessionFilter.doFilter(SaveSessionFilter.java:35)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.apphosting.utils.servlet.JdbcMySqlConnectionCleanupFilter.doFilter(JdbcMySqlConnectionCleanupFilter.java:60)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:43)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388)
    at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
    at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
    at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
    at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:418)
    at com.google.apphosting.runtime.jetty.AppVersionHandlerMap.handle(AppVersionHandlerMap.java:266)
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
    at org.mortbay.jetty.Server.handle(Server.java:326)
    at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
    at org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:923)
    at com.google.apphosting.runtime.jetty.RpcRequestParser.parseAvailable(RpcRequestParser.java:76)
    at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
    at com.google.apphosting.runtime.jetty.JettyServletEngineAdapter.serviceRequest(JettyServletEngineAdapter.java:146)
    at com.google.apphosting.runtime.JavaRuntime$RequestRunnable.run(JavaRuntime.java:446)
    at com.google.tracing.TraceContext$TraceContextRunnable.runInContext(TraceContext.java:435)
    at com.google.tracing.TraceContext$TraceContextRunnable$1.run(TraceContext.java:442)
    at com.google.tracing.CurrentContext.runInContext(CurrentContext.java:186)
    at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContextNoUnref(TraceContext.java:306)
    at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContext(TraceContext.java:298)
    at com.google.tracing.TraceContext$TraceContextRunnable.run(TraceContext.java:439)
    at com.google.apphosting.runtime.ThreadGroupPool$PoolEntry.run(ThreadGroupPool.java:251)
    at java.lang.Thread.run(Thread.java:724)

---

当有效负载数据为空时会发生这种情况。看

我碰巧遇到了这种情况，原因是有效负载的一个字段为空

---

解决方案是在发送GCM消息之前检查任何有效负载字段是否为空。

代码在哪里？有人不看代码怎么回答？很抱歉，我认为messenger服务器上的问题这并不能提供问题的答案。若要评论或要求作者澄清，请在其帖子下方留下评论-您可以随时对自己的帖子发表评论，一旦您有足够的评论，您就可以发表评论。出现此问题的一个可能原因是有效负载中的字段为空。既然最初的海报要求解决问题，从技术上讲，你是对的。我将按照这些思路更新我的答案。

    >Uncaught exception from servlet
java.lang.NullPointerException
    at java.net.URLEncoder.encode(URLEncoder.java:205)
    at com.google.android.gcm.server.Sender.sendNoRetry(Sender.java:166)
    at com.google.android.gcm.server.Sender.send(Sender.java:121)
    at e.gochat.messenger.server.SendServlet.doPost(SendServlet.java:53)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1166)
    at com.google.apphosting.utils.servlet.ParseBlobUploadFilter.doFilter(ParseBlobUploadFilter.java:125)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.apphosting.runtime.jetty.SaveSessionFilter.doFilter(SaveSessionFilter.java:35)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.apphosting.utils.servlet.JdbcMySqlConnectionCleanupFilter.doFilter(JdbcMySqlConnectionCleanupFilter.java:60)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:43)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388)
    at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
    at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
    at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
    at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:418)
    at com.google.apphosting.runtime.jetty.AppVersionHandlerMap.handle(AppVersionHandlerMap.java:266)
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
    at org.mortbay.jetty.Server.handle(Server.java:326)
    at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
    at org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:923)
    at com.google.apphosting.runtime.jetty.RpcRequestParser.parseAvailable(RpcRequestParser.java:76)
    at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
    at com.google.apphosting.runtime.jetty.JettyServletEngineAdapter.serviceRequest(JettyServletEngineAdapter.java:146)
    at com.google.apphosting.runtime.JavaRuntime$RequestRunnable.run(JavaRuntime.java:446)
    at com.google.tracing.TraceContext$TraceContextRunnable.runInContext(TraceContext.java:435)
    at com.google.tracing.TraceContext$TraceContextRunnable$1.run(TraceContext.java:442)
    at com.google.tracing.CurrentContext.runInContext(CurrentContext.java:186)
    at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContextNoUnref(TraceContext.java:306)
    at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContext(TraceContext.java:298)
    at com.google.tracing.TraceContext$TraceContextRunnable.run(TraceContext.java:439)
    at com.google.apphosting.runtime.ThreadGroupPool$PoolEntry.run(ThreadGroupPool.java:251)
    at java.lang.Thread.run(Thread.java:724)