Looks to me like this is saying your server-side code throws a
NullPointerException, so you get it on the client-side.
On Saturday, November 2, 2013 9:15:37 PM UTC+1, zhenli...@gmail.com wrote:
>
> 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 onFailure
> command is being triggered always.
> Below is my Code for the program.
>
> 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);}
>
> And this is my Serverside 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;
> }
>
> }
>
> While running the application it generates this error message on the console
> side which is telling me why onFailure Command is always being
> triggered but i do not understand about it.
> 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)
>
>
>
>
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