So I have a problem that I'm not sure is solvable well.
I have a library that has a method annotation
#Retention(RetentionPolicy.RUNTIME)
public #interface CallbackHandler {...}
For the next version of the library, I would like to copy this annotation and rename it, but leave this old annotation around with #Deprecated for backward compatibility, so there isnt a hard break while people make the switch.
The problem is since I can't subclass the annotation, I have to write all of the code twice to handle the two different annotations. I would like to avoid this at it's problematic and a big time sink.
So the question is there any way to rename the annotation for the new version but keep backward compatibililty while not having to write two versions of the code?
One way coming to my mind is using an annotation proxy such as this one or or this one from the Hibernate Validator project (disclaimer: I'm a committer of the latter).
You could create a proxy for your old, now deprecated annotation based on the attribute values from the new annotation. That way your code for processing the annotation can stay unchanged.
Or you refactor your code to process the new annotation type and create a proxy for the new annotation type when discovering the old one, which you can phase out that way later on.
Related
Is there something special to the #Deprecated annotation that I cannot reproduce?
I need to create an annotation similar to #Deprecated to produce warnings in Eclipse and also at build time. When I mark a method as #Deprecated I get nice warnings. For example, if I have an old method (that I may still keep for compatibility reasons):
#Deprecated
public List<Account> getClientAccounts(final int clientId) {
// Implement search...
}
Then, if I try to use it in Eclipse I can see it strikethrough, and a yellow icon in the left bar:
Also when building I can see the:
[WARNING] app1/src/test/java/com/app1/MyApp.java: app1/src/test/java/com/app1/MyApp.java uses or overrides a deprecated API.
Now, depending on external factors I cannot control (e.g. absence of database indexes) some methods are not optimal, and I would like to clearly mark them as such... with my brand new #NonOptimal annotation. I need to add visibility to the problem. So far I have:
#Retention(RUNTIME)
#Target(METHOD)
// What else here?
public #interface NonOptimal {
}
How can I create this annotation?
I wish I could extend Deprecated, but no can do.
After reading about this quite a bit I ended up with an ugly workaround. It works, though I don't like it.
I decided to mark the bad methods with both the #Deprecated and #NonOptimal annotations. It's conceptually wrong (the methods are not actually deprecated) but it works well out of the box. No need to develop an overkill Eclipse plugin:
The #Deprecated annnotation bugs developers all around the place (in Eclipse and when building), and that's a good thing.
The #NonOptimal annotation provides details on why this is a bad method to use.
Ugly but works. As of now Eclipse does not provide any better option.
Note: to make things worse, the NonOptimal annotation does not work well in Maven when using toolchains: warnings go silent, disappear, nada... Therefore, AnnotationProcessors are kind of useless in the end.
#TheImpaler This is actually not a true answer for your problem, but some time ago I came across the Google Annotations Library (a.k.a. gag) while using Zalando's Problem API.
This library provides a great number of custom annotations that, in some cases, can be used to instrument your actual code by using a ASM and a custom java agent.
Maybe it can give you some ideas regarding your actual issue.
The project is no longer maintained but there is a fork in Github.
I'm a bit new to annotations in Java. Is it possible to design a custom annotation which when used in a class automatically invokes a method present inside another Class. TIA.
The answer is "sort of": annotations by themselves do nothing (except "compile time" annotations that affect the compile process).
Meaning: just attaching an annotation to something doesn't magically cause a method to be called at some arbitrary point in time.
This works differently: you have some sort of framework - and at some point you ask the framework to process an object, class, ... And then the framework might check for the presence of certain annotations to "do" something based on that check.
Thus: it is possible to implement custom annotations, and it is also possible to make some "framework" react to the presence of that annotation.
In case you find this answer too generic - well, it can't be more precise/specific than the question ...
Eclipse has the #NonNullByDefault annotation, which treats all values as #NonNull unless you explicitly annotate them as #Nullable.
Is there an equivalent option in IntelliJ IDEA, or do you have to always use #Nonnull?
Idea version 14 will include support for the JSR 305 "#TypeQualifierDefault" annotation, which allows the user to create a custom annotation, to be used on a package declaration in a package-info.java file, that specifies that everything in that package (not just parameters, but method return values, local variables, etc.) will be implicitly annotated as not allowing null values.
Unfortunately, this doesn't (currently) recursively affect subpackages, so each subpackage has to have a package-info.java file too, declaring that subpackage to use the annotation.
See here for details and an example of use:
http://youtrack.jetbrains.com/issue/IDEA-125281
Note that this is already implemented in Early Access Program (EAP) builds.
No, it is currently not supported by IDEA.
As a proof, see lena's link about the open feature request to allow 'NotNull' as the default element behavior for a given class or package.
Maybe a similar feature will be become standard with JSR-305, which may include the #ParametersAreNonnullByDefault annotation and also the opposite annotation #ParametersAreNullableByDefault. Note that in contrast to #NonNullByDefault, return values are not covered by those two annotations. So, you still had to annotate the return value explicitely.
All that doesn't change the current state, though. Neither has JSR-305 become a standard, nor does IDEA implement it.
I was wondering if I can easily annotate Acceleo templates and then get these annotations when working with TraceabilityModel.
Acceleo is now using an annotation to determine entry points for generation:
[comment #main]
So I am asking, if I can use this mechanism to annotate my templates for other purposes, for example:
[comment #org.project.SimpleStatement]
[template public generateSimpleStatement(...)]
...
[/template]
Then, I could be able to get the annotation programmatically when working with traceability model (probably using the org.eclipse.acceleo.traceability.ModuleElement interface).
Acceleo's traceability does not support either annotations or comments : we only record traceability information for the actually generated text bits, not for any of the "extra" information (comments of the module, main annotation, metamodels ...).
That being answered, and though not possible through the means of an annotation, maybe your use case would be worth an enhancement request? Can you describe what you were expecting to achieve through this? (preferrably through the Eclipse M2T forum since stack overflow does not seem to be appropriate for such discussions ;)).
(Note : I am an active developper on Acceleo)
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Closed 12 years ago.
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How and where are Annotations used in Java?
Java beans, annotations: What do they do? How do they help me?
Over and over, I read about Java 5's annotations being an 'advanced feature' of the language. Until recently, I haven't much used annotations (other than the usual #Override, &c), but work on a number of webservice-related projects has forced my hand. Since I learned Java pre-5, I never really took the time to sit down and grok the annotation system.
My question- do you guys actually use annotations? How helpful are they to you, day-to-day? How many StackOverflow-ers have had to write a custom annotation?
Perhaps the most useful and used case of Java Annotations is to use POJO + Annotation instead of xml configuration files
I use it a lot since (as you already stated) if you use a web framework (like spring or seam) they usually have plenty of annotations to help you.
I have recently wrote some annotations to build a custom statemachine, validations purpose and annotations of annotations (using the metadata aspect of it). And IMO they help a lot making the code cleaner, easier to understand and manage.
Current project (200KLOC), annotations I use all the time are:
#NotNull / #Nullabe
#Override
#Test
#Ignore
#ThreadSafe
#Immutable
But I haven't written yet my own annotation... Yet!
I have used annotations for:
Hibernate, so I don't need to keep those huge XML files;
XML Serialization, so I describe how the object should be rendered in the object itself;
Warning removal for warnings that I don't want to disable (and for which the particular case cannot be properly solved).
I have created annotations for:
Describe the state required in order for my method to be executed (for example, that a user must be logged in);
Mark my method as executable from a specific platform with additional properties for that platform;
And probably some other similar operations.
The annotations that I have created are read with Reflection when I need to get more information about the object I am working with. It works and it works great.
Annotations are just for frameworks and they do work great in hibernate/jpa. until you write a framework that needs some extra information from passed to it objects you wont write your own annotations.
however there is new and cool junit feature that let you write your own annotations in tests - http://blog.mycila.com/2009/11/writing-your-own-junit-extensions-using.html
I use annotations daily and they are wonderful. I use them with jsf and jpa and find them much easier to manage and work with than the alternative XML configurations.
I use annotations for describing in my state synchronisation system what classes are specialisations of the annotated classes, and the environment in which they should be used (when an object is created, it will work out for its entity lists which are the best entity classes to create for the nodes on the network; i.e., a Player entity for a server node is instead a ServerPlayer entity). Additionally, the attributes inside the classes are described and how they should be synchronised across machines.
We just used annotations to create a simple way to validate our POJO's:
#NotEmpty
#Pattern(regex = "I")
private String value;
Then we run this through the Hibernate validator which will do all our validation for us:
import org.hibernate.validator.ClassValidator;
import org.hibernate.validator.InvalidValue;
public void validate(T validateMe) {
ClassValidator<T> validator = new ClassValidator<T>((Class<T>) validateMe.getClass());
InvalidValue[] errors = validator.getInvalidValues(validateMe);
}
Works great. Nice clean code.
We use custom annotations as a part of our integration testing system:
#Artifact: Associates an integration test with an issue ID. Trace matrices are then automatically generated for our testing and regulatory departments.
#Exclude: Ignores an integration test based on the browser platform / version. Keeps the IE 6 bugs from clogging up our nightly test runs :)
#SeleniumSession: Defines test specific selenium settings for each integration test.
They are a very powerful tool, but you gotta use them carefully. Just have a look at those early .NET Enterprise class files to see what a nightmare mandatory annotations can be :)
We have a report builder as part of our webapp. A user can add a large number of widgets that are all small variations on the same set of themes (graphs, tables, etc).
The UI builds itself based on custom annotations in the widget classes. (e.g. an annotation might contain default value and valid values that would render as a dropdown. Or a flag indicating if the field is mandatory).
It has turned out be be a good way to allow devs to crank out widgets without having to touch the UI.