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PONullPointerException Error when using RPC
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copied!<p>I'm now currently extracting out data from my database using rpc, but whenever I click the button it does generates a error and my <code>onFailure</code> command is being triggered always.</p> <p>Below is my Code for the program.</p> <pre><code>public class PleaseWork implements EntryPoint { private TextBox textbox2 = new TextBox(); private Label Hi = new Label("New label"); @SuppressWarnings("deprecation") public void onModuleLoad() { RootPanel rootPanel = RootPanel.get(); Button btnNewButton = new Button("New button"); btnNewButton.addClickListener(new ClickListener() { public void onClick(Widget event) { HelpConnectionAsync Abra =(HelpConnectionAsync) GWT.create(HelpConnection.class); ServiceDefTarget target = (ServiceDefTarget) Abra; String moduleRelativeURL = GWT.getModuleBaseURL() + "MySQLConnection"; target.setServiceEntryPoint(moduleRelativeURL); AsyncCallback callback = new AsyncCallback(){ public void onSuccess (Object result){ textbox2.setText((String)result); Hi.setText("You Pass!"); } public void onFailure(Throwable caught) { caught.printStackTrace(); Hi.setText("You fail!"); } }; Abra.sensors(callback); } }); rootPanel.add(btnNewButton, 23, 30); rootPanel.add(textbox2,23, 70); rootPanel.add(Hi, 23, 130); } </code></pre> <p>}</p> <p>This consist of both my Async and Service program</p> <pre><code>public interface HelpConnection extends RemoteService { public String[] sensors() throws Exception;} public interface HelpConnectionAsync { public void sensors(AsyncCallback<String[]> callback);} </code></pre> <p>This is my Server side Program</p> <pre><code>public class MySQLConnection extends RemoteServiceServlet implements HelpConnection { private Connection conn = null; private ResultSet rs = null; private PreparedStatement pstmt = null; public static Connection getConnection() throws Exception { String driver = "com.mysql.jdbc.Driver"; String url = "jdbc:mysql://localhost:3306/temperature"; String username = "root"; String password = "123456"; Class.forName(driver); Connection conn = DriverManager.getConnection(url, username, password); return conn; } @Override public String[] sensors() throws Exception { String [] user = null; try { conn = getConnection(); rs = pstmt.executeQuery("SELECT ID, times FROM sensor ORDER BY id DESC LIMIT 1;"); // extract data from the ResultSet while (rs.next()) { user = new String[] {rs.getString(1),rs.getString(2)}; } } catch(SQLException e) { e.printStackTrace(); } finally { try { rs.close(); pstmt.close(); conn.close(); } catch (SQLException e) { e.printStackTrace(); } } return user; }} </code></pre> <p>And lastly this is the code generated out by the console</p> <pre><code>java.lang.NullPointerException at com.google.gwt.user.client.rpc.core.java.lang.NullPointerException_FieldSerializer.instantiate(NullPointerException_FieldSerializer.java:16) at com.google.gwt.user.client.rpc.core.java.lang.NullPointerException_FieldSerializer.create(NullPointerException_FieldSerializer.java:25) at com.google.gwt.user.client.rpc.impl.SerializerBase.instantiate(SerializerBase.java:115) at com.google.gwt.user.client.rpc.impl.ClientSerializationStreamReader.deserialize(ClientSerializationStreamReader.java:396) at com.google.gwt.user.client.rpc.impl.AbstractSerializationStreamReader.readObject(AbstractSerializationStreamReader.java:119) at com.google.gwt.user.client.rpc.impl.RequestCallbackAdapter.onResponseReceived(RequestCallbackAdapter.java:216) at com.google.gwt.http.client.Request.fireOnResponseReceived(Request.java:258) at com.google.gwt.http.client.RequestBuilder$1.onReadyStateChange(RequestBuilder.java:412) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103) at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71) at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:172) at com.google.gwt.dev.shell.BrowserChannelServer.reactToMessagesWhileWaitingForReturn(BrowserChannelServer.java:338) at com.google.gwt.dev.shell.BrowserChannelServer.invokeJavascript(BrowserChannelServer.java:219) at com.google.gwt.dev.shell.ModuleSpaceOOPHM.doInvoke(ModuleSpaceOOPHM.java:136) at com.google.gwt.dev.shell.ModuleSpace.invokeNative(ModuleSpace.java:571) at com.google.gwt.dev.shell.ModuleSpace.invokeNativeObject(ModuleSpace.java:279) at com.google.gwt.dev.shell.JavaScriptHost.invokeNativeObject(JavaScriptHost.java:91) at com.google.gwt.core.client.impl.Impl.apply(Impl.java) at com.google.gwt.core.client.impl.Impl.entry0(Impl.java:242) at sun.reflect.GeneratedMethodAccessor38.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103) at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71) at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:172) at com.google.gwt.dev.shell.BrowserChannelServer.reactToMessages(BrowserChannelServer.java:293) at com.google.gwt.dev.shell.BrowserChannelServer.processConnection(BrowserChannelServer.java:547) at com.google.gwt.dev.shell.BrowserChannelServer.run(BrowserChannelServer.java:364) at java.lang.Thread.run(Unknown Source) </code></pre> <p>Error on the Development Mode</p> <pre><code>[ERROR] Uncaught exception escaped </code></pre> <p>com.google.gwt.event.shared.UmbrellaException: Exception caught: Service implementation URL not specified at com.google.gwt.event.shared.HandlerManager.fireEvent(HandlerManager.java:129) at com.google.gwt.user.client.ui.Widget.fireEvent(Widget.java:129) at com.google.gwt.event.dom.client.DomEvent.fireNativeEvent(DomEvent.java:116) at com.google.gwt.user.client.ui.Widget.onBrowserEvent(Widget.java:177) at com.google.gwt.user.client.DOM.dispatchEventImpl(DOM.java:1351) at com.google.gwt.user.client.DOM.dispatchEvent(DOM.java:1307) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103) at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71) at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:172) at com.google.gwt.dev.shell.BrowserChannelServer.reactToMessagesWhileWaitingForReturn(BrowserChannelServer.java:338) at com.google.gwt.dev.shell.BrowserChannelServer.invokeJavascript(BrowserChannelServer.java:219) at com.google.gwt.dev.shell.ModuleSpaceOOPHM.doInvoke(ModuleSpaceOOPHM.java:136) at com.google.gwt.dev.shell.ModuleSpace.invokeNative(ModuleSpace.java:571) at com.google.gwt.dev.shell.ModuleSpace.invokeNativeObject(ModuleSpace.java:279) at com.google.gwt.dev.shell.JavaScriptHost.invokeNativeObject(JavaScriptHost.java:91) at com.google.gwt.core.client.impl.Impl.apply(Impl.java) at com.google.gwt.core.client.impl.Impl.entry0(Impl.java:242) at sun.reflect.GeneratedMethodAccessor43.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103) at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71) at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:172) at com.google.gwt.dev.shell.BrowserChannelServer.reactToMessages(BrowserChannelServer.java:293) at com.google.gwt.dev.shell.BrowserChannelServer.processConnection(BrowserChannelServer.java:547) at com.google.gwt.dev.shell.BrowserChannelServer.run(BrowserChannelServer.java:364) at java.lang.Thread.run(Unknown Source) Caused by: com.google.gwt.user.client.rpc.ServiceDefTarget$NoServiceEntryPointSpecifiedException: Service implementation URL not specified at com.google.gwt.user.client.rpc.impl.RemoteServiceProxy.doPrepareRequestBuilderImpl(RemoteServiceProxy.java:430) at com.google.gwt.user.client.rpc.impl.RemoteServiceProxy.doInvoke(RemoteServiceProxy.java:368) at com.google.gwt.user.client.rpc.impl.RemoteServiceProxy$ServiceHelper.finish(RemoteServiceProxy.java:74) at com.mycompany.project.client.HelpConnection_Proxy.sensors(HelpConnection_Proxy.java:30) at com.mycompany.project.client.PleaseWork$1.onClick(PleaseWork.java:30) at com.google.gwt.user.client.ui.ListenerWrapper$WrappedClickListener.onClick(ListenerWrapper.java:245) at com.google.gwt.event.dom.client.ClickEvent.dispatch(ClickEvent.java:56) at com.google.gwt.event.dom.client.ClickEvent.dispatch(ClickEvent.java:1) at com.google.gwt.event.shared.GwtEvent.dispatch(GwtEvent.java:1) at com.google.web.bindery.event.shared.EventBus.dispatchEvent(EventBus.java:40) at com.google.web.bindery.event.shared.SimpleEventBus.doFire(SimpleEventBus.java:193) at com.google.web.bindery.event.shared.SimpleEventBus.fireEvent(SimpleEventBus.java:88) at com.google.gwt.event.shared.HandlerManager.fireEvent(HandlerManager.java:127) at com.google.gwt.user.client.ui.Widget.fireEvent(Widget.java:129) at com.google.gwt.event.dom.client.DomEvent.fireNativeEvent(DomEvent.java:116) at com.google.gwt.user.client.ui.Widget.onBrowserEvent(Widget.java:177) at com.google.gwt.user.client.DOM.dispatchEventImpl(DOM.java:1351) at com.google.gwt.user.client.DOM.dispatchEvent(DOM.java:1307) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103) at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71) at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:172) at com.google.gwt.dev.shell.BrowserChannelServer.reactToMessagesWhileWaitingForReturn(BrowserChannelServer.java:338) at com.google.gwt.dev.shell.BrowserChannelServer.invokeJavascript(BrowserChannelServer.java:219) at com.google.gwt.dev.shell.ModuleSpaceOOPHM.doInvoke(ModuleSpaceOOPHM.java:136) at com.google.gwt.dev.shell.ModuleSpace.invokeNative(ModuleSpace.java:571) at com.google.gwt.dev.shell.ModuleSpace.invokeNativeObject(ModuleSpace.java:279) at com.google.gwt.dev.shell.JavaScriptHost.invokeNativeObject(JavaScriptHost.java:91) at com.google.gwt.core.client.impl.Impl.apply(Impl.java) at com.google.gwt.core.client.impl.Impl.entry0(Impl.java:242) at sun.reflect.GeneratedMethodAccessor43.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103) at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71) at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:172) at com.google.gwt.dev.shell.BrowserChannelServer.reactToMessages(BrowserChannelServer.java:293) at com.google.gwt.dev.shell.BrowserChannelServer.processConnection(BrowserChannelServer.java:547) at com.google.gwt.dev.shell.BrowserChannelServer.run(BrowserChannelServer.java:364) at java.lang.Thread.run(Unknown Source)</p> <p>Another attempt based on changing the return User to return String[] {"text1","text2"} There was this error genererated in the Developmentmode again,</p> <pre><code>[ERROR] Uncaught exception escaped </code></pre> <p>java.lang.ClassCastException: [Ljava.lang.String; cannot be cast to java.lang.String at com.mycompany.project.client.PleaseWork$1$1.onSuccess(PleaseWork.java:40) at com.google.gwt.user.client.rpc.impl.RequestCallbackAdapter.onResponseReceived(RequestCallbackAdapter.java:232) at com.google.gwt.http.client.Request.fireOnResponseReceived(Request.java:258) at com.google.gwt.http.client.RequestBuilder$1.onReadyStateChange(RequestBuilder.java:412) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103) at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71) at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:172) at com.google.gwt.dev.shell.BrowserChannelServer.reactToMessagesWhileWaitingForReturn(BrowserChannelServer.java:338) at com.google.gwt.dev.shell.BrowserChannelServer.invokeJavascript(BrowserChannelServer.java:219) at com.google.gwt.dev.shell.ModuleSpaceOOPHM.doInvoke(ModuleSpaceOOPHM.java:136) at com.google.gwt.dev.shell.ModuleSpace.invokeNative(ModuleSpace.java:571) at com.google.gwt.dev.shell.ModuleSpace.invokeNativeObject(ModuleSpace.java:279) at com.google.gwt.dev.shell.JavaScriptHost.invokeNativeObject(JavaScriptHost.java:91) at com.google.gwt.core.client.impl.Impl.apply(Impl.java) at com.google.gwt.core.client.impl.Impl.entry0(Impl.java:242) at sun.reflect.GeneratedMethodAccessor43.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103) at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71) at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:172) at com.google.gwt.dev.shell.BrowserChannelServer.reactToMessages(BrowserChannelServer.java:293) at com.google.gwt.dev.shell.BrowserChannelServer.processConnection(BrowserChannelServer.java:547) at com.google.gwt.dev.shell.BrowserChannelServer.run(BrowserChannelServer.java:364) at java.lang.Thread.run(Unknown Source)</p>

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