Java – com.google.gwt.user.client.rpc.StatusCodeException: 500 The call failed on the server; see server log for details

gwtjava

my GWT project give me a lot of problems, can someone help me??

Here the Client:

server.SQL_tutti_clienti(new AsyncCallback<Cliente>() {


        public void onSuccess(Cliente result) {

            log = log + " 1 - Cliente ";

            tutti_clienti = result;

            cliente.addItem("- Seleziona un Cliente -","null");

            int n_clienti = tutti_clienti.getN();


            for(int i=0; i<n_clienti; i++){
                cliente.addItem(tutti_clienti.getCliente(i), String.valueOf(tutti_clienti.getId(i)));

            }
        }


        public void onFailure(Throwable caught) {

            log = log + " 1.1 - ERRORE Cliente " + caught;
            System.out.println("Errore server.SQL_tutti_clienti(): " + caught);
        }

    });

    server.SQL_tutti_tipi_prodotto(new AsyncCallback<Tipo_Prodotto>() {

        @Override
        public void onSuccess(Tipo_Prodotto result) {

            log = log + " 2 - Tutti Tipi ";

            tutti_tipi = result;

            tipo.addItem("- Seleziona Tipo Prodotto -");

            int n_tipi = tutti_tipi.getN();

            for(int i=0; i<n_tipi; i++)
                tipo.addItem(tutti_tipi.getTipoProdotto(i), String.valueOf(tutti_tipi.getId(i)));


        }

        @Override
        public void onFailure(Throwable caught) {
            log = log +" 2.1 - ERRORE Tutti Tipi: " + caught;
            System.out.println("Errore server.tutti_tipi_prodotto(): " + caught);
        }
    });

GreetingServiceAsync server = GWT.create(GreetingService.class);
SQL_tutti_clienti() is a method instead a server and it is only a SELECT * FROM table
SQL_tutti_tipi_prodotto() is another server's method and it is a SELECT * FROM table2

Class Cliente:

public class Cliente  implements Serializable{

private ArrayList<Integer> id_cliente = new ArrayList<Integer>();
private ArrayList<String> nome_cliente = new ArrayList<String>();

// Costruttori
public Cliente(){

}


// Metodi
public void add_cliente(int id, String nome){

    this.id_cliente.add(id);
    this.nome_cliente.add(nome);

}

public int getN(){
    return this.id_cliente.size();
}

public String getCliente(int id){
    return this.nome_cliente.get(id);
}

public int getId(int id){
    return this.id_cliente.get(id);
}
}

Class Tipo_Prodotto:

public class Tipo_Prodotto implements Serializable{

private static final long serialVersionUID = 1L;
private ArrayList<Integer> id_tipo_prodotto = new ArrayList<Integer>();
private ArrayList<String> tipo_prodotto = new ArrayList<String>();


// Costruttori
public Tipo_Prodotto(){

}


// Metodi
public void add_tipo_prodotto(int id, String nome){

    this.id_tipo_prodotto.add(id);
    this.tipo_prodotto.add(nome);

}

public int getN(){
    return this.id_tipo_prodotto.size();
}

public String getTipoProdotto(int id){
    return this.tipo_prodotto.get(id);
}

public int getId(int id){
    return this.id_tipo_prodotto.get(id);
}
}

Server Code:

public Cliente SQL_tutti_clienti() throws Exception{

    Statement stmt1 = stmt;
    ResultSet rset1 = stmt1.executeQuery("SELECT * FROM cliente"); // Query
    Cliente c = new Cliente();


    while (rset1.next()){
        c.add_cliente(rset1.getInt("id_cliente"), rset1.getString("nome_cliente"));
    }

    rset1.close();
    stmt1.close();

    return c;

}

public Tipo_Prodotto SQL_tutti_tipi_prodotto() throws Exception{

    Statement stmt1 = stmt;
    ResultSet rset1 = stmt1.executeQuery("SELECT * FROM tipo_prodotto"); // Query
    Tipo_Prodotto t = new Tipo_Prodotto();


    while (rset1.next()){
        t.add_tipo_prodotto(rset1.getInt("id_prodotto"), rset1.getString("nome_prodotto"));
    }

    rset1.close();
    stmt1.close();

    return t;
}

Here the errors:

[WARN] Exception while dispatching incoming RPC call
com.google.gwt.user.client.rpc.SerializationException: Type 'com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException' was not included in the set of types which can be serialized by this SerializationPolicy or its Class object could not be loaded. For security purposes, this type will not be serialized.: instance = com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: No operations allowed after statement closed.
at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter.serialize(ServerSerializationStreamWriter.java:667)
at com.google.gwt.user.client.rpc.impl.AbstractSerializationStreamWriter.writeObject(AbstractSerializationStreamWriter.java:126)
at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter$ValueWriter$8.write(ServerSerializationStreamWriter.java:153)
at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter.serializeValue(ServerSerializationStreamWriter.java:587)
at com.google.gwt.user.server.rpc.RPC.encodeResponse(RPC.java:605)
at com.google.gwt.user.server.rpc.RPC.encodeResponseForFailure(RPC.java:393)
at com.google.gwt.user.server.rpc.RPC.invokeAndEncodeResponse(RPC.java:579)
at com.google.gwt.user.server.rpc.RemoteServiceServlet.processCall(RemoteServiceServlet.java:208)
at com.google.gwt.user.server.rpc.RemoteServiceServlet.processPost(RemoteServiceServlet.java:248)
at com.google.gwt.user.server.rpc.AbstractRemoteServiceServlet.doPost(AbstractRemoteServiceServlet.java:62)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:487)
at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:362)
at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:181)
at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:729)
at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:405)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at org.mortbay.jetty.handler.RequestLogHandler.handle(RequestLogHandler.java:49)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at org.mortbay.jetty.Server.handle(Server.java:324)
at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:505)
at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:843)
at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:647)
at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:211)
at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:380)
at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:395)
at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:488)
[ERROR] 500 – POST /meccanicagervasoni/greet ( ) 57 bytes
Request headers
Host: :8888
Connection: keep-alive
Accept: /
User-Agent: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/31.0.1650.63 Safari/537.36
Accept-Encoding: gzip,deflate,sdch
Accept-Language: it-IT,it;q=0.8,en-US;q=0.6,en;q=0.4
Referer: http:// :8888/Meccanicagervasoni.html?gwt.codesvr= :9997
Content-Length: 155
X-GWT-Module-Base: http:// :8888/meccanicagervasoni/
X-GWT-Permutation: HostedMode
Origin: http:// :8888
Content-Type: text/x-gwt-rpc; charset=UTF-8
Response headers
Content-Type: text/plain
[WARN] Exception while dispatching incoming RPC call
com.google.gwt.user.client.rpc.SerializationException: Type 'com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException' was not included in the set of types which can be serialized by this SerializationPolicy or its Class object could not be loaded. For security purposes, this type will not be serialized.: instance = com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: No operations allowed after statement closed.
at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter.serialize(ServerSerializationStreamWriter.java:667)
at com.google.gwt.user.client.rpc.impl.AbstractSerializationStreamWriter.writeObject(AbstractSerializationStreamWriter.java:126)
at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter$ValueWriter$8.write(ServerSerializationStreamWriter.java:153)
at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter.serializeValue(ServerSerializationStreamWriter.java:587)
at com.google.gwt.user.server.rpc.RPC.encodeResponse(RPC.java:605)
at com.google.gwt.user.server.rpc.RPC.encodeResponseForFailure(RPC.java:393)
at com.google.gwt.user.server.rpc.RPC.invokeAndEncodeResponse(RPC.java:579)
at com.google.gwt.user.server.rpc.RemoteServiceServlet.processCall(RemoteServiceServlet.java:208)
at com.google.gwt.user.server.rpc.RemoteServiceServlet.processPost(RemoteServiceServlet.java:248)
at com.google.gwt.user.server.rpc.AbstractRemoteServiceServlet.doPost(AbstractRemoteServiceServlet.java:62)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:487)
at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:362)
at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:181)
at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:729)
at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:405)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at org.mortbay.jetty.handler.RequestLogHandler.handle(RequestLogHandler.java:49)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at org.mortbay.jetty.Server.handle(Server.java:324)
at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:505)
at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:843)
at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:647)
at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:211)
at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:380)
at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:395)
at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:488)
[ERROR] 500 – POST /meccanicagervasoni/greet ( ) 57 bytes
Request headers
Host: :8888
Connection: keep-alive
Content-Length: 168
X-GWT-Module-Base: http:// :8888/meccanicagervasoni/
X-GWT-Permutation: HostedMode
Origin: http:// :8888
User-Agent: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/31.0.1650.63 Safari/537.36
Content-Type: text/x-gwt-rpc; charset=UTF-8
Accept: /
Referer: http:// :8888/Meccanicagervasoni.html?gwt.codesvr= :9997
Accept-Encoding: gzip,deflate,sdch
Accept-Language: it-IT,it;q=0.8,en-US;q=0.6,en;q=0.4
Response headers
Content-Type: text/plain
[WARN] Exception while dispatching incoming RPC call
com.google.gwt.user.client.rpc.SerializationException: Type 'com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException' was not included in the set of types which can be serialized by this SerializationPolicy or its Class object could not be loaded. For security purposes, this type will not be serialized.: instance = com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: No operations allowed after statement closed.
at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter.serialize(ServerSerializationStreamWriter.java:667)
at com.google.gwt.user.client.rpc.impl.AbstractSerializationStreamWriter.writeObject(AbstractSerializationStreamWriter.java:126)
at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter$ValueWriter$8.write(ServerSerializationStreamWriter.java:153)
at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter.serializeValue(ServerSerializationStreamWriter.java:587)
at com.google.gwt.user.server.rpc.RPC.encodeResponse(RPC.java:605)
at com.google.gwt.user.server.rpc.RPC.encodeResponseForFailure(RPC.java:393)
at com.google.gwt.user.server.rpc.RPC.invokeAndEncodeResponse(RPC.java:579)
at com.google.gwt.user.server.rpc.RemoteServiceServlet.processCall(RemoteServiceServlet.java:208)
at com.google.gwt.user.server.rpc.RemoteServiceServlet.processPost(RemoteServiceServlet.java:248)
at com.google.gwt.user.server.rpc.AbstractRemoteServiceServlet.doPost(AbstractRemoteServiceServlet.java:62)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:487)
at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:362)
at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:181)
at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:729)
at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:405)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at org.mortbay.jetty.handler.RequestLogHandler.handle(RequestLogHandler.java:49)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at org.mortbay.jetty.Server.handle(Server.java:324)
at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:505)
at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:843)
at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:647)
at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:211)
at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:380)
at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:395)
at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:488)
[ERROR] 500 – POST /meccanicagervasoni/greet ( ) 57 bytes
Request headers
Host: :8888
Connection: keep-alive
Content-Length: 154
X-GWT-Module-Base: http:// :8888/meccanicagervasoni/
X-GWT-Permutation: HostedMode
Origin: http:// :8888
User-Agent: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/31.0.1650.63 Safari/537.36
Content-Type: text/x-gwt-rpc; charset=UTF-8
Accept: /
Referer: http:// :8888/Meccanicagervasoni.html?gwt.codesvr= :9997
Accept-Encoding: gzip,deflate,sdch
Accept-Language: it-IT,it;q=0.8,en-US;q=0.6,en;q=0.4
Response headers
Content-Type: text/plain
[WARN] Exception while dispatching incoming RPC call
com.google.gwt.user.client.rpc.SerializationException: Type 'com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException' was not included in the set of types which can be serialized by this SerializationPolicy or its Class object could not be loaded. For security purposes, this type will not be serialized.: instance = com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: No operations allowed after statement closed.
at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter.serialize(ServerSerializationStreamWriter.java:667)
at com.google.gwt.user.client.rpc.impl.AbstractSerializationStreamWriter.writeObject(AbstractSerializationStreamWriter.java:126)
at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter$ValueWriter$8.write(ServerSerializationStreamWriter.java:153)
at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter.serializeValue(ServerSerializationStreamWriter.java:587)
at com.google.gwt.user.server.rpc.RPC.encodeResponse(RPC.java:605)
at com.google.gwt.user.server.rpc.RPC.encodeResponseForFailure(RPC.java:393)
at com.google.gwt.user.server.rpc.RPC.invokeAndEncodeResponse(RPC.java:579)
at com.google.gwt.user.server.rpc.RemoteServiceServlet.processCall(RemoteServiceServlet.java:208)
at com.google.gwt.user.server.rpc.RemoteServiceServlet.processPost(RemoteServiceServlet.java:248)
at com.google.gwt.user.server.rpc.AbstractRemoteServiceServlet.doPost(AbstractRemoteServiceServlet.java:62)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:487)
at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:362)
at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:181)
at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:729)
at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:405)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at org.mortbay.jetty.handler.RequestLogHandler.handle(RequestLogHandler.java:49)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at org.mortbay.jetty.Server.handle(Server.java:324)
at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:505)
at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:843)
at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:647)
at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:211)
at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:380)
at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:395)
at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:488)
[ERROR] 500 – POST /meccanicagervasoni/greet ( ) 57 bytes
Request headers
Host: :8888
Connection: keep-alive
Content-Length: 156
X-GWT-Module-Base: http:// :8888/meccanicagervasoni/
X-GWT-Permutation: HostedMode
Origin: http:// :8888
User-Agent: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/31.0.1650.63 Safari/537.36
Content-Type: text/x-gwt-rpc; charset=UTF-8
Accept: /
Referer: http:// :8888/Meccanicagervasoni.html?gwt.codesvr= :9997
Accept-Encoding: gzip,deflate,sdch
Accept-Language: it-IT,it;q=0.8,en-US;q=0.6,en;q=0.4
Response headers
Content-Type: text/plain
[WARN] Exception while dispatching incoming RPC call
com.google.gwt.user.client.rpc.SerializationException: Type 'com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException' was not included in the set of types which can be serialized by this SerializationPolicy or its Class object could not be loaded. For security purposes, this type will not be serialized.: instance = com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: No operations allowed after statement closed.
at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter.serialize(ServerSerializationStreamWriter.java:667)
at com.google.gwt.user.client.rpc.impl.AbstractSerializationStreamWriter.writeObject(AbstractSerializationStreamWriter.java:126)
at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter$ValueWriter$8.write(ServerSerializationStreamWriter.java:153)
at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter.serializeValue(ServerSerializationStreamWriter.java:587)
at com.google.gwt.user.server.rpc.RPC.encodeResponse(RPC.java:605)
at com.google.gwt.user.server.rpc.RPC.encodeResponseForFailure(RPC.java:393)
at com.google.gwt.user.server.rpc.RPC.invokeAndEncodeResponse(RPC.java:579)
at com.google.gwt.user.server.rpc.RemoteServiceServlet.processCall(RemoteServiceServlet.java:208)
at com.google.gwt.user.server.rpc.RemoteServiceServlet.processPost(RemoteServiceServlet.java:248)
at com.google.gwt.user.server.rpc.AbstractRemoteServiceServlet.doPost(AbstractRemoteServiceServlet.java:62)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:487)
at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:362)
at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:181)
at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:729)
at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:405)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at org.mortbay.jetty.handler.RequestLogHandler.handle(RequestLogHandler.java:49)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at org.mortbay.jetty.Server.handle(Server.java:324)
at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:505)
at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:843)
at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:647)
at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:211)
at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:380)
at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:395)
at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:488)
[ERROR] 500 – POST /meccanicagervasoni/greet ( ) 57 bytes
Request headers
Host: :8888
Connection: keep-alive
Content-Length: 159
X-GWT-Module-Base: http:// :8888/meccanicagervasoni/
X-GWT-Permutation: HostedMode
Origin: http:// :8888
User-Agent: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/31.0.1650.63 Safari/537.36
Content-Type: text/x-gwt-rpc; charset=UTF-8
Accept: /
Referer: http:// :8888/Meccanicagervasoni.html?gwt.codesvr= :9997
Accept-Encoding: gzip,deflate,sdch
Accept-Language: it-IT,it;q=0.8,en-US;q=0.6,en;q=0.4
Response headers
Content-Type: text/plain
[WARN] Exception while dispatching incoming RPC call
com.google.gwt.user.client.rpc.SerializationException: Type 'com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException' was not included in the set of types which can be serialized by this SerializationPolicy or its Class object could not be loaded. For security purposes, this type will not be serialized.: instance = com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: No operations allowed after statement closed.
at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter.serialize(ServerSerializationStreamWriter.java:667)
at com.google.gwt.user.client.rpc.impl.AbstractSerializationStreamWriter.writeObject(AbstractSerializationStreamWriter.java:126)
at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter$ValueWriter$8.write(ServerSerializationStreamWriter.java:153)
at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter.serializeValue(ServerSerializationStreamWriter.java:587)
at com.google.gwt.user.server.rpc.RPC.encodeResponse(RPC.java:605)
at com.google.gwt.user.server.rpc.RPC.encodeResponseForFailure(RPC.java:393)
at com.google.gwt.user.server.rpc.RPC.invokeAndEncodeResponse(RPC.java:579)
at com.google.gwt.user.server.rpc.RemoteServiceServlet.processCall(RemoteServiceServlet.java:208)
at com.google.gwt.user.server.rpc.RemoteServiceServlet.processPost(RemoteServiceServlet.java:248)
at com.google.gwt.user.server.rpc.AbstractRemoteServiceServlet.doPost(AbstractRemoteServiceServlet.java:62)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:487)
at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:362)
at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:181)
at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:729)
at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:405)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at org.mortbay.jetty.handler.RequestLogHandler.handle(RequestLogHandler.java:49)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at org.mortbay.jetty.Server.handle(Server.java:324)
at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:505)
at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:843)
at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:647)
at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:211)
at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:380)
at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:395)
at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:488)
[ERROR] 500 – POST /meccanicagervasoni/greet ( ) 57 bytes
Request headers
Host: :8888
Connection: keep-alive
Accept: /
User-Agent: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/31.0.1650.63 Safari/537.36
Referer: http:// :8888/Meccanicagervasoni.html?gwt.codesvr= :9997
Accept-Encoding: gzip,deflate,sdch
Accept-Language: it-IT,it;q=0.8,en-US;q=0.6,en;q=0.4
Content-Length: 148
X-GWT-Module-Base: http:// :8888/meccanicagervasoni/
X-GWT-Permutation: HostedMode
Origin: http:// :8888
Content-Type: text/x-gwt-rpc; charset=UTF-8
Response headers
Content-Type: text/plain
<

Best Answer

I think the Exception is pretty clear: 

com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: No operations allowed after statement closed.

I think this is the error. I have no idea, where stmt is created, but you reuse it, and it will be closed.

Statement stmt1 = stmt;

The second servercall will fail, because the statement is closed:

stmt1.close();
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