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POJava annotation to set field to a static instance?
 

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  1. POJava annotation to set field to a static instance?
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    <p>I've been playing with annotations, and I'm wondering how to go about doing this. What I'd like to do is to be able to have a field declared in a class and annotated such that the field will be initialized with a static instance of the class.</p> <p>Given an annotation like this:</p> <pre><code>@Target(ElementType.FIELD) @Retention(RetentionPolicy.RUNTIME) //or would this be RetentionPolicy.CLASS? public @interface SetThisField { } </code></pre> <p>Something like this:</p> <pre><code>public class Foo { @SetThisField private Bar bar; } </code></pre> <p>I've played around with using a parser and setting this at runtime, which works but isn't as elegant as I'd like.</p> <p>I can't find any really good examples of RetentionPolicy.CLASS but the documentation seems to indicate that I could somehow make the declaration of "bar" get compiled into this:</p> <pre><code>private Bar bar = Bar.getInstance(); </code></pre> <p>It wouldn't look that way in the source code of course, but it would in the byte code and it would behave like that at runtime.</p> <p>So am I off base here? Is this possible? Or is the parser the way to go with it?</p> <p>UPDATE: This is the guts of the parser I'm using</p> <pre><code>public static void parse(Object instance) throws Exception { Field[] fields = instance.getClass().getDeclaredFields(); for (Field field : fields) { //"Property" annotated fields get set to an application.properties value //using the value of the annotation as the key into the properties if (field.isAnnotationPresent(Property.class)) { Property property = field.getAnnotation(Property.class); String value = property.value(); if (!"".equals(value)) { setFieldValue(instance, field, properties.getProperty(value)); } } //"Resource" annotated fields get static instances of the class allocated //based upon the type of the field. if (field.isAnnotationPresent(Resource.class)) { String name = field.getType().getName(); setFieldValue(instance, field, MyApplication.getResources().get(name)); } } } private static void setFieldValue(Object instance, Field field, Object value) throws IllegalAccessException { boolean accessibleState = field.isAccessible(); field.setAccessible(true); field.set(instance, value); field.setAccessible(accessibleState); } </code></pre>
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    1. USPeter Lawrey
    1. USwbj
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    1. COAnd what about just using a singleton?
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    2. COUltimately, I'm trying to replace some specific parts of the spring framework that I and my colleagues like and then not use the spring framework. I could just use spring, or I could use a custom parser, or I could use a singleton as you suggest. Mostly I'm just trying to figure out if it *could* be done this way.
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      1. USwbj
 

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