Question

I’m creating a login application on Eclipse using Google Web Toolkit(GWT). The code checks for the username and password and if its correct, it shows the o/p as welcome. Still after compiling it is giving me errors.I’m sharing both code and the error message. Please help me out.

    package com.vin.client;
import java.sql.DriverManager;
import java.sql.ResultSet;
import com.google.gwt.core.client.EntryPoint;
import com.google.gwt.dev.generator.ast.Statement;
import com.google.gwt.event.dom.client.ClickEvent;
import com.google.gwt.event.dom.client.ClickHandler;
import com.google.gwt.user.client.Window;
import com.google.gwt.user.client.ui.*;

public class HelloWorld implements EntryPoint{
    public void onModuleLoad() {
        Button click=new Button("Click Here");
        Label name=new Label("Enter Name");
        Label passwrd=new Label("Enter Password");
        final TextBox t_name=new TextBox();
        final TextBox t_passwrd=new TextBox();
        click.addClickHandler(new ClickHandler() {
        public void onClick(ClickEvent ev) {
            try {
                String temp_user=t_name.getText();
                String temp_pass=t_passwrd.getText();
                java.sql.Connection con = null;
                Class.forName("org.hsqldb.jdbcDriver");
                con = DriverManager.getConnection("jdbc:hsqldb:hsql://localhost/", "SA", "");
                Statement st=(Statement) con.createStatement();
                ResultSet rs=((java.sql.Statement) st).executeQuery("select username,password from lgfrm");
                String user=rs.getString(1);
                String pass=rs.getString(2);
                if(temp_user.equals(user) && temp_pass.equals(pass)) {
                    Window.alert("Welcome");
                }
                else {
                    Window.alert("Please enter valid details");
                }
        }
        catch (Exception ae) {}
        }
    });
        RootPanel.get().add(name);
        RootPanel.get().add(t_name);
        RootPanel.get().add(passwrd);
        RootPanel.get().add(t_passwrd);
        RootPanel.get().add(click);
    }
    }

Error Message is———-

Compiling module com.vin.HelloWorld Exception in thread
“UnitCacheLoader” java.lang.RuntimeException: Unable to read from byte
cache at
com.google.gwt.dev.util.DiskCache.transferFromStream(DiskCache.java:166)
at
com.google.gwt.dev.util.DiskCacheToken.readObject(DiskCacheToken.java:87)
at sun.reflect.GeneratedMethodAccessor19.invoke(Unknown Source)
…………..and many more like this….Please help me out

Answer 1

Try something like following for Server side :

UserService.java

@RemoteServiceRelativePath("userService")
public interface UserService extends RemoteService {
    String loginUser(String username,String password);
}

UserServiceAsync.java

public interface UserServiceAsync {
    void loginUser(String username, String password, AsyncCallback<String> callback);
}

UserServiceImpl.java

public class UserServiceImpl extends RemoteServiceServlet  implements UserService {

        public String loginUser(String username, String password){
            //database interaction
            return "result"; //return success or failure depending upon logic
    }
}

Follow Communicate with a Server in GWT and the Anatomy of service

For Client Side :

public class HelloWorld implements EntryPoint{
    //(1) Create the client proxy.
    private UserServiceAsync userService = (UserServiceAsync) GWT.create(UserService.class);
    public void onModuleLoad() {
        Button click=new Button("Click Here");
        Label name=new Label("Enter Name");
        Label passwrd=new Label("Enter Password");
        final TextBox t_name=new TextBox();
        final TextBox t_passwrd=new TextBox();
        click.addClickHandler(new ClickHandler() {
        public void onClick(ClickEvent ev) {
                 String temp_user=t_name.getText();
                 String temp_pass=t_passwrd.getText();   
                 /// (2) Create an asynchronous callback and Make the call
                 userService.loginUser(temp_user, temp_pass, new AsyncCallback<String>() {
                     public void onFailure(Throwable caught) {
                             Window.alert("Please enter valid details");
                      }

                     public void onSuccess(String result) {
                         Window.alert("Welcome");
                     }
                 });//end of service call
       });//end of clickhandler
        RootPanel.get().add(name);
        RootPanel.get().add(t_name);
        RootPanel.get().add(passwrd);
        RootPanel.get().add(t_passwrd);
        RootPanel.get().add(click);
    }
 }