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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