How to obtain Integer data from a postgresql array type

Question

In my database I have a table with smallint[] values. I want to obtain all the values inside this array that match with an id I pass through argument, but when I execute the query it runs me a ClassCastException. What could be the problem?

I think I'm missing something while casting the array value to Integer[].

I've found very few tutorials that teach how to get data from a PostgreSQL array. so I don't know what I'm doing wrong.

Can someone help me?

This is the code, the println and the foreach are only used for """debug""" function.

Integer[] getImportanzaEvento(String nomeCentro) {
    Integer[] valImportanza = null;
    
    String qGetImportanzaEvento = "SELECT importanza FROM eventi_avversi WHERE nomecentro = ?";
    PreparedStatement pstmt;
    ResultSet rs;
    
    try {
        openConnection();
        pstmt = connection.prepareStatement(qGetImportanzaEvento);
        pstmt.setString(1, nomeCentro);
        rs = pstmt.executeQuery();
        
        while(rs.next()) {
            Array importanza = rs.getArray(1);
            valImportanza = (Integer[])importanza.getArray();
            for(Integer s : valImportanza)
                System.out.println(s);
            return valImportanza;
        }
    } catch (SQLException ex) {
        ex.printStackTrace();
    } finally {
        closeConnection();
    }
    return valImportanza;
}

This is the exception:

Exception in thread "AWT-EventQueue-0" java.lang.ClassCastException: class [Ljava.lang.Short; cannot be cast to class [Ljava.lang.Integer; ([Ljava.lang.Short; and [Ljava.lang.Integer; are in module java.base of loader 'bootstrap')
    at server.DB_Engine.getImportanzaEvento(DB_Engine.java:858)
    at server.ServerImpl.getImportanzaEvento(ServerImpl.java:308)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:566)
    at java.rmi/sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:359)
    at java.rmi/sun.rmi.transport.Transport$1.run(Transport.java:200)
    at java.rmi/sun.rmi.transport.Transport$1.run(Transport.java:197)
    at java.base/java.security.AccessController.doPrivileged(Native Method)
    at java.rmi/sun.rmi.transport.Transport.serviceCall(Transport.java:196)

perhaps getting the array as rows would simplify your code a bit : SELECT unnest(importanza) FROM eventi_avversi WHERE nomecentro = ? — Jim Jones
– Jim Jones, Commented Aug 2, 2021 at 11:00
Please edit the question including the complete error message, and the stack trace if possible. Maybe it contains a hint about what you are doing wrong. — RubioRic
– RubioRic, Commented Aug 2, 2021 at 11:14
It seems that you obtain a Short[] from the query and java does not cast directly short to int as you can see in the answers provided here stackoverflow.com/q/33868133/2553194 If you need an Integer[], you've got to convert explicitly and manually the Short[] to Integer[]. This can be achieved easily using Stream operations. — RubioRic
– RubioRic, Commented Aug 2, 2021 at 12:06

Nico · Accepted Answer · 2021-08-02 17:53:04Z

1

I've tryed to convert the Short array into an int array like a user says in the comment and it works.

This is the code:

...
while(rs.next()) {
    Array arrImportanza = rs.getArray("importanza");
    Short[] s = (Short[])arrImportanza.getArray();
    importanza = new int[s.length];
    for(int i=0; i<s.length; i++)
        importanza[i] = (int) s[i];
    return importanza;
}
...

answered Aug 2, 2021 at 17:53

Nico

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