JDBC returning MySQLSyntaxError Exception with correct statement

I'm writing an application in java which communicates with a MySQL db, and while I was testing it I noticed that the code to insert new rows in a table threw a MySQLSyntaxError Exception, so I tried to execute the same INSERT using MySQL Workbench, and it worked. The code in question is this:

public static boolean aggiungiElem(String nome, GrafoGenerico g){
    if(connessioneAperta()){
        try{
            String sqlCommandUser="SELECT USER()";
            String sqlCommandInserim="INSERT INTO salvataggi VALUES ( ? , ? , DEFAULT , NULL );";
            PreparedStatement sUser=conn.prepareStatement(sqlCommandUser);
            ResultSet risultatiUtente=sUser.executeQuery();
            String utente = null;
            while(risultatiUtente.next()){
                utente=risultatiUtente.getString(1);
            }
            sUser.close();
            PreparedStatement sInserim=conn.prepareStatement(sqlCommandInserim);
            sInserim.setString(1, utente);
            sInserim.setString(2, nome);
            //sInserim.setObject(3,g);
            System.out.println(sInserim.toString());
            sInserim.executeUpdate(sqlCommandInserim);
            sInserim.close();
            return true;
        }
        catch(SQLException e){
            e.printStackTrace();
            return false;
        }
    }
    else
        return false;
}

EDIT: sorry, the stack trace is:

com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '? , ? , DEFAULT , NULL )' at line 1
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:407)
at com.mysql.jdbc.Util.getInstance(Util.java:382)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1052)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3603)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3535)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1989)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2150)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2620)
at com.mysql.jdbc.StatementImpl.executeUpdate(StatementImpl.java:1664)
at com.mysql.jdbc.StatementImpl.executeUpdate(StatementImpl.java:1583)
at se.diag.control.clientspec.UtilsClientSQL.aggiungiElem(UtilsClientSQL.java:67)
at se.diag.control.clientspec.UtilsClientSQLTest.testAggiungiElem(UtilsClientSQLTest.java:67)
at se.diag.control.clientspec.UtilsClientSQLTest.testCaricaElem(UtilsClientSQLTest.java:99)
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 org.junit.internal.runners.TestMethodRunner.executeMethodBody(TestMethodRunner.java:99)
at org.junit.internal.runners.TestMethodRunner.runUnprotected(TestMethodRunner.java:81)
at org.junit.internal.runners.BeforeAndAfterRunner.runProtected(BeforeAndAfterRunner.java:34)
at org.junit.internal.runners.TestMethodRunner.runMethod(TestMethodRunner.java:75)
at org.junit.internal.runners.TestMethodRunner.run(TestMethodRunner.java:45)
at org.junit.internal.runners.TestClassMethodsRunner.invokeTestMethod(TestClassMethodsRunner.java:66)
at org.junit.internal.runners.TestClassMethodsRunner.run(TestClas开发者_Python百科sMethodsRunner.java:35)
at org.junit.internal.runners.TestClassRunner$1.runUnprotected(TestClassRunner.java:42)
at org.junit.internal.runners.BeforeAndAfterRunner.runProtected(BeforeAndAfterRunner.java:34)
at org.junit.internal.runners.TestClassRunner.run(TestClassRunner.java:52)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:45)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:460)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:673)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:386)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:196)

---

com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '? , ? , DEFAULT , NULL )' at line 1

Those placeholders ? should not appear in the MySQL side at all.

Look here,

sInserim.executeUpdate(sqlCommandInserim);

you're passing the raw SQL string into executeUpdate() instead of executing the PreparedStatement with the set values.

Replace it by

sInserim.executeUpdate();

The executeUpdate(sqlString) should be used on Statement only.

---

Unrelated to the concrete problem, you should be closing the PreparedStatement in the finally block to prevent resource leaking in case of exceptions. The same applies to Connection, Statement and ResultSet by the way.