mdma - Developer IT

java-COM interop: Implement COM interface in Java

- by mdma

How can I implement a vtable COM interface in java? In the old days, I'd use the Microsft JVM, which had built in java-COM interop. What's the equivalent for a modern JRE? Answers to a similar SO question proposed JACOB. I've looked at JACOB, but that is based on IDispatch, and is aimed at controlling Automation serers. The COM interfaces I need are custom vtable (extend IUnknown), e.g. IPersistStream, IOleWindow, IContextMenu etc. For my use case, I could implement all the COM specifics in JNI, and have the JNI layer call corresponding interfaces in java. But I'm hoping for a less painful solution. It's for an open source project, so open source alternatives are preferred.

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Annotation to make available generic type

- by mdma

Given an generic interface like interface DomainObjectDAO<T> { T newInstance(); add(T t); remove(T t); T findById(int id); // etc... } I'd like to create a subinterface that specifies the type parameter: interface CustomerDAO extends DomainObjectDAO<Customer> { // customer-specific queries - incidental. } The implementation needs to know the actual template parameter type, but of course type erasure means isn't available at runtime. Is there some annotation that I could include to declare the interface type? Something like @GenericParameter(Customer.class) interface CustomerDAO extends DomainObjectDAO<Customer> { } The implementation could then fetch this annotation from the interface and use it as a substitute for runtime generic type access. Some background: This interface is implemented using JDK dynamic proxies as outlined here. The non-generic version of this interface has been working well, but it would be nicer to use generics and not have to create a subinterface for each domain object type. The actual type is needed at runtime to implement the newInstance method, amongst others.

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why is java.lang.Throwable a class?

- by mdma

In java adjectives ending in -able are interfaces Serializable, Comparable etc... So why is Throwable a class? Wouldn't exception handling be easier if Throwable were an interface? Obviously, changing it now is out the question. But could it be made abstract? Wouldn't that avoid the bad practice of throw new Throwable();

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java serialization and final fields

- by mdma

I have an class defining an immutable value type that I now need to serialize. The immutability comes from the final fields which are set in the constructor. I've tried serializing, and it works (surprisingly?) - but I've no idea how. Here's an example of the class public class MyValueType implements Serializable { private final int value; private transient int derivedValue; public MyValueType(int value) { this.value = value; this.derivedValue = derivedValue(value); } // getters etc... } Given that the class doesn't have a no arg constructor, how can it be instantiated and the final field set? (An aside - I noticed this class particularly because IDEA wasn't generating a "no serialVersionUID" inspection warning for this class, yet successfully generated warnings for other classes that I've just made serializable.)

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Reducing the pain writing integration and system tests

- by mdma

I would like to make integration tests and system tests for my applications but producing good integration and system tests have often needed so much effort that I have not bothered. The few times I tried, I wrote custom, application-specific test harnesses, which felt like re-inventing the wheel each time. I wonder if this is the wrong approach. Is there a "standard" approach to integration and full system testing? EDIT: To clarify, it's automated tests, for desktop and web applications. Ideally a complete test suite that exercises the full functionality of the application.

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lightweight publish/subscribe framework in java

- by mdma

Is there a good lightweight framework for java that provides the publish/subscribe pattern? Some ideal features Support for generics Registration of multiple subscribers to a publisher API primarily interfaces and some useful implementations purely in-memory, persistence and transaction guarantees not required. I know about JMS but that is overkill for my need. The publish/subscribed data are the result of scans of a file system, with scan results being fed to another component for processing, which are then processed before being fed to another and so on.

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Spring bean creation via deserialization

- by mdma

Spring has many different ways of creating beans, but is it possible to create a bean by deserializing a resource? My application has a number of Components, and each manipulates a certain type of data. During test, the data object is instantiated directly and set directly on the component, e.g. component.setData(someDataObject). At runtime, the data is available as a serialized object and read in from the serialized stream by the component. Rather than having each component explicitly deserialize it's data from the stream, it would be more consistent and flexible to have Spring deserialize the data object from a resource. Is there a DeserializerBeanFactory or something similar?

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spring - constructor injection and overriding parent definition of nested bean

- by mdma

I've read the Spring 3 reference on inheriting bean definitions, but I'm confused about what is possible and not possible. For example, a bean that takes a collaborator bean, configured with the value 12 <bean name="beanService12" class="SomeSevice"> <constructor-arg index="0"> <bean name="beanBaseNested" class="SomeCollaborator"> <constructor-arg index="0" value="12"/> </bean> </constructor-arg> </bean> I'd then like to be able to create similar beans, with slightly different configured collaborators. Can I do something like <bean name="beanService13" parent="beanService12"> <constructor-arg index="0"> <bean> <constructor-arg index="0" value="13"/> </bean> </constructor> </bean> I'm not sure this is possible and, if it were, it feels a bit clunky. Is there a nicer way to override small parts of a large nested bean definition? It seems the child bean has to know quite a lot about the parent, e.g. constructor index. I'd prefer not to change the structure - the parent beans use collaborators to perform their function, but I can add properties and use property injection if that helps. This is a repeated pattern, would creating a custom schema help? Thanks for any advice!

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Java - when to use notify or notifyAll?

- by mdma

Why does java.lang.Object have two notify methods - notify and notifyAll? It seems that notifyAll does at least everything notify does, so why not just use notifyAll all the time? If notifyAll is used instead of notify, is the program still correct, and vice versa? What influences the choice between these two methods?

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