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POJava field injection via annotation
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  1. POJava field injection via annotation
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    copied!<p>I'm trying to write the code to annotate a field in a class so that the value of that field is set from a config file. This is virtually identical to the @Value attribute that the spring framework has, but for reasons I won't go into, I'm not using the spring framework.</p> <p>The project I'm working on is a web app using the Jersey framework. I apologize for all the up-front information, but for the sake of completeness, here's a basic setup of what I have:</p> <p>This is the main application class:</p> <pre><code>package com.ttrr.myservice; import com.ttrr.myservice.controllers.MyController; import javax.ws.rs.ApplicationPath; import javax.ws.rs.core.Application; import java.util.HashSet; import java.util.Set; @ApplicationPath("/") public class MyApplication extends Application { @Override public Set&lt;Class&lt;?&gt;&gt; getClasses() { final Set&lt;Class&lt;?&gt;&gt; classes = new HashSet&lt;Class&lt;?&gt;&gt;(); // register root resources classes.add(MyController.class); return classes; } } </code></pre> <p>This is the MyController class, that I want annotations to work in:</p> <pre><code>package com.ttrr.myservice.controllers; import com.ttrr.myservice.annotations.Property; import javax.servlet.ServletContext; import javax.ws.rs.GET; import javax.ws.rs.Path; import javax.ws.rs.Produces; import javax.ws.rs.core.Context; @Path("test") public class MyController { @Property("my.value.from.config") private String myValue; @GET @Produces("text/html") @Path("/testPage") public String testPage(@Context ServletContext context) { return "&lt;p&gt;" + myValue + "&lt;/p&gt;"; } } </code></pre> <p>My annotations interface is pretty straight forward:</p> <pre><code>package com.ttrr.myservice.annotations; import java.lang.annotation.ElementType; import java.lang.annotation.Retention; import java.lang.annotation.RetentionPolicy; import java.lang.annotation.Target; @Target(ElementType.FIELD) @Retention(RetentionPolicy.RUNTIME) public @interface Property { String value() default ""; } </code></pre> <p>And I have an annotation parser class:</p> <pre><code>package com.ttrr.myservice.annotations; import java.io.IOException; import java.lang.reflect.Field; import java.util.Properties; public class PropertyParser { public static Properties properties; static { properties = new Properties(); try { Property.class.getClassLoader(); Properties defaults = new Properties(); defaults.load(Property.class.getClassLoader().getResourceAsStream("application.properties")); for(Object key : defaults.keySet()) { properties.put(key, defaults.get(key)); } } catch (IOException e) { //in this case do nothing, properties will simply be empty } } public void parse(Class&lt;?&gt; clazz) throws Exception { Field[] fields = clazz.getDeclaredFields(); for (Field field : fields) { if (field.isAnnotationPresent(Property.class)) { Property property = field.getAnnotation(Property.class); String value = property.value(); if (!"".equals(value)) { field.set(clazz, properties.getProperty(value)); } } } } } </code></pre> <p>Where I'm really struggling is putting it all together, and getting the value from my application.properties file into an instance of the MyController class.</p> <p>Thanks for taking the time to read all that! Any help will be greatly appreciated.</p>
 

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