GWT file not found trouble during database connection - database

Question

I'm trying to create a GWT app and I'm working with a local postgreSQL Database.
I'm working with GWT 2.4 on eclipse Juno.
I implemented in this way the Server-side implementation (TaskServiceImpl):
public class TaskServiceImpl extends ServiceImpl implements TaskService {
#Override
public List<Task> getAllTasks() {
em = this.getEntityManager();
Query q = em.createQuery("SELECT x FROM Task x");
List<Task> list = createList(q.getResultList().toArray(),
new ArrayList<Task>(), em);
em.close();
return list;
}
and this is the Database connection class in the client-side:
public class DatabaseConnection {
public static final TaskServiceAsync taskService;
static {
taskService = GWT.create(TaskService.class);
}
}
I try now to run a getAllTask() in this way
public void onModuleLoad() {
DatabaseConnection.taskService.getAllTasks(new AsyncCallback<List<Task>>() {
#Override
public void onSuccess(List<Task> result) {
System.out.println("Success!");
}
#Override
public void onFailure(Throwable caught) {
System.out.println("Fail!");
}
});
}
And always returns "fail!" and gives me this error:
com.google.appengine.tools.development.LocalResourceFileServlet doGet
WARNING: No file found for: /fantapgl/task
This is my web.xml
<servlet>
<servlet-name>taskServiceImpl</servlet-name>
<servlet-class>fieldProject.server.service.TaskServiceImpl</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>taskServiceImpl</servlet-name>
<url-pattern>/fantaPGL/task</url-pattern>
</servlet-mapping>
to open the connection to the DB I have this code in the persistence.xml:
<properties>
<property name="openjpa.jdbc.DBDictionary" value="postgres" />
<property name="openjpa.jdbc.SynchronizeMappings" value="buildSchema()"/>
<property name="openjpa.ConnectionDriverName" value="org.postgresql.Driver"/>
<property name="openjpa.ConnectionURL" value="jdbc:postgresql://localhost:5432/db" />
<property name="openjpa.ConnectionUserName" value="postgres" />
<property name="openjpa.ConnectionPassword" value="password" />
</properties>
I don't understand where I'm wrong. Can someone plz help me!?

Answer 1

I'm not sure what the problem is. But the error messages seems to suggest you have google appengine enabled. That doesn't make sense because you would only need that if you want to deploy on Google app engine, and you are clearly developing for something else since you can't run PostgreSql on Google appengine.
Futhremore, make sure to close database connections by placing the close in a finally statement and prefer to return specific datatypes; that is, ArrayList instead of List. Otherwise the compiler will generate code for all subclasses of List, because at compile time the compiler can't know what subclass will be used.

Answer 2

Before executing the query:
1) Use jdbc driver
try {
Class.forName("org.postgresql.Driver");
} catch (ClassNotFoundException e) {
System.out.println("Your PostgreSQL JDBC Driver is missing! "
+ "Include in your library path!");
e.printStackTrace();
return "error";
}
2) Connect to database
Connection connection = null;
connection =
DriverManager.getConnection( "jdbc:postgresql://127.0.0.1:5432/"YourDB",
"admin",
"pass" );
3) Then Execute the query
if (connection != null) { //Your query }

Answer 3

you need to add #RemoteServiceRelativePath annotation at the begin of the serviceImpl class.
please refer to https://developers.google.com/web-toolkit/doc/latest/tutorial/RPC
or if you have installed google eclipse plugin, create a new project with sample code, you can refer to the sample code as well.