Generic Enum converter for iBatis

My goal was to create a simple, extensible Enum converter that would work with

iBatis. This seems like a trivial problem, but took me a while to find a proper solution. There were some additional preconditions:
* all given Enums are jaxb generated objects – but any standard Java Enum should work
* conversion was 1-to-1, no special conditions and processing The example Enum for this problem looks like this one (copy&paste from jaxb generated source):

@XmlType(name ="ServiceType") 
@XmlEnum
public enum ServiceType {

    @XmlEnumValue("stationary")
    STATIONARY("stationary"),
    @XmlEnumValue("mobile")
    MOBILE("mobile");
    private final String value;

    ServiceType(String v) {
        value = v;
    }

    public String value() {
        return value;
    }

    public static ServiceType fromValue(String v) {
        for (ServiceType c: ServiceType.values()) {
            if (c.value.equals(v)) {
                return c;
            }
        }
        throw new IllegalArgumentException(v);
    }

}

“No big deal”, you say. I beg to differ. What I wanted to achieve was a simple construction which would look like this when used for another Enum (CommonEnumTypeHandler is the name of my generic converter):

public class ServiceTypeHandler extends CommonEnumTypeHandler { }

Unfortunately due to the fact, that Java does not have reified generics, which is described in

multiple places, I had to stick with passing through a Class type of my enum. So it looks like this:

public class ServiceTypeHandler extends CommonEnumTypeHandler {

    public ServiceTypeHandler() {
        super(ServiceType.class);
    }
}

My final class has to look like this one below:

import java.sql.SQLException;

import com.ibatis.sqlmap.client.extensions.ParameterSetter;
import com.ibatis.sqlmap.client.extensions.ResultGetter;
import com.ibatis.sqlmap.client.extensions.TypeHandlerCallback;

public abstract class CommonEnumTypeHandler implements TypeHandlerCallback {

    Class enumClass;

    public CommonEnumTypeHandler(Class clazz) {
        this.enumClass = clazz;
    }

    public void setParameter(ParameterSetter ps, Object o) throws SQLException {
        if (o.getClass().isAssignableFrom(enumClass)) {
            ps.setString(((T) o).name().toUpperCase());
        } else
            throw new SQLException("Excpected " + enumClass + " object than: " + o);
    }

    public Object getResult(ResultGetter rs) throws SQLException {
        Object o = valueOf(rs.getString());
        if (o == null)
            throw new SQLException("Unknown parameter type: " + rs.getString());
        return o;
    }

    public Object valueOf(String s) {
        return Enum.valueOf(enumClass, s.toUpperCase());
    }
}

 

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Private fields and methods are not private in groovy

I used to code in Java before I met groovy. Like most of you, groovy attracted me with many enhancements. This was to my surprise to discover that method visibility in groovy is handled different than Java!

Consider this example:

class Person {
private String name
public String surname

private Person() {}

private String signature() { "${name?.substring(0, 1)}. $surname" }

public String toString() { "I am $name $surname" }
}

How is this class interpreted with Java?

  1. Person has private constructor that cannot be accessed
  2. Field "name" is private and cannot be accessed
  3. Method signature() is private and cannot be accessed

Let's see how groovy interpretes Person:

public static void main(String[] args) {
def person = new Person() // constructor is private - compilation error in Java
println(person.toString())

person.@name = 'Mike' // access name field directly - compilation error in Java
println(person.toString())

person.name = 'John' // there is a setter generated by groovy
println(person.toString())

person.@surname = 'Foo' // access surname field directly
println(person.toString())

person.surname = 'Bar' // access auto-generated setter
println(person.toString())

println(person.signature()) // call private method - compilation error in Java
}

I was really astonished by its output:

I am null null
I am Mike null
I am John null
I am John Foo
I am John Bar
J. Bar

As you can see, groovy does not follow visibility directives at all! It treats them as non-existing. Code compiles and executes fine. It's contrary to Java. In Java this code has several errors, pointed out in comments.

I've searched a bit on this topic and it seems that this behaviour is known since version 1.1 and there is a bug report on that: http://jira.codehaus.org/browse/GROOVY-1875. It is not resolved even with groovy 2 release. As Tim Yates mentioned in this Stackoverflow question: "It's not clear if it is a bug or by design". Groovy treats visibility keywords as a hint for a programmer.

I need to keep that lesson in mind next time I want to make some field or method private!