Using reflection to get the value of a final static field

[Struan Kerr]

I'm writing code to automatically generate database access code. In order to do this it needs to call the stored procedure with parameters extracted from an xml file. I've given each parameter an attribute sqltype which should take the name of one of the fields of java.sql.Types and then I'm using reflection to get the actual value of that field.

Now my problem is that to get the value of the field you need an instance of the class to reflect on, but Types can't be instantiated, so this is my work around, is there a better way?

//************************
// The following is a nasty hack to make the constructor
// of java.sql.types visible, so we can instanciate it
// in order to get the values by reflection.
 
Constructor[] c = Types.class.getDeclaredConstructors();
c[0].setAccessible(true);
Types types=null;
try {
types= (Types)c[0].newInstance(new Object[0]);
} catch (Exception e1) {
System.out.prinln("An error occured accessing Types constructor");
}
// *****************************
 
int fieldValue=Types.class.getField(fieldName).getInt(types))

Thanks

Struan

[Jeff Albertson]

You don't need to instantiate the class because the fields you want are
all static, and for static fields, you pass null to methods like getInt.

    import java.lang.reflect.*;
import java.sql.Types;
import java.util.*;
 
public class TypeFields {
    private Map<String, Integer> map = new HashMap<String, Integer>();
 
    public TypeFields() {
        try {
            for(Field f : Types.class.getFields())
                map.put(f.getName(), f.getInt(null));
        } catch (SecurityException e) {
            throw new RuntimeException("unexpected", e);
        } catch (IllegalAccessException e) {
            throw new RuntimeException("unexpected", e);
        }
    }
 
    public int get(String fieldName) {return map.get(fieldName);}
 
    public static void main(String... args) {
        String[] fields = {"ARRAY", "BIGINT", "BINARY", "BIT", "BLOB", "BOOLEAN", "CHAR",
            "CLOB", "DATALINK", "DATE", "DECIMAL", "DISTINCT", "DOUBLE", "FLOAT", "INTEGER",
            "JAVA_OBJECT", "LONGVARBINARY", "LONGVARCHAR", "NULL", "NUMERIC", "OTHER", "REAL",
            "REF", "SMALLINT", "STRUCT", "TIME", "TIMESTAMP", "TINYINT", "VARBINARY", "VARCHAR"};
        TypeFields app = new TypeFields();
        for(String f : fields)
            System.out.format("%13s=%4d%n", f, app.get(f));
    }
}

[Struan Kerr]

Many thanks,

Shows its pays to read more of the javadocs than just the method you're interested in!

Regards

Struan