ResourceLocator.java

import javax.ws.rs.*;
import java.io.File;
import java.lang.reflect.Method;
import java.net.URISyntaxException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

/**
 * JAX-RS utility class for locating all JAX-RS resources under a given ClassLoader.
 */
public class ResourceLocator {
    /**
     * Returns all of the JAX-RS resources under the given ClassLoader, minus any passed in the exclude list.
     *
     * @param classLoader The ClassLoader instance to search for JAX-RS resources.
     * @param excludeList A list of classes to exclude from the returned list.
     * @return A list of JAX-RS resource classes suitable for use in a JAX-RS Application instance.
     */
    public static List<Class<?>> locateResources(ClassLoader classLoader, Class<?>... excludeList) {
        try {
            List<Class<?>> resourceClasses = new ArrayList<Class<?>>();

            List<File> resources = new ArrayList<File>();
            File root = new File(classLoader.getResource("/").toURI());
            findClasses(root, resources);

            for (File resource : resources) {
                try {
                    String relativePath = resource.getAbsolutePath().substring(root.getAbsolutePath().length() + 1);
                    String className = relativePath.replace("/", ".").replace(".class", ""); // TODO: Need to use the platform path separator? Substring off the .class instead of using replace.
                    Class<?> resourceClass = Class.forName(className, false, classLoader);
                    if (isJaxRsResource(resourceClass)) {
                        resourceClasses.add(resourceClass);
                    }
                } catch (ClassNotFoundException e) {
                    System.err.println("Class returned by class loader cannot be found...this shouldn't happen");
                }
            }

            resourceClasses.removeAll(Arrays.asList(excludeList));

            return resourceClasses;
        } catch (URISyntaxException e) {
            throw new RuntimeException("Got a bad resource URI from the class loader...this shouldn't happen.", e);
        }
    }

    /**
     * Recursively search the File instance for class files. Add them to the list of flies.
     *
     * @param file The File to search recursively.
     * @param classes The list to add class files to.
     */
    private static void findClasses(File file, List<File> classes) {
        if (file.isDirectory()) {
            for (File child : file.listFiles()) {
                if (child.isFile() && child.getName().endsWith(".class")) {
                    classes.add(child);
                } else if (child.isDirectory()) {
                    findClasses(child, classes);
                }
            }
        }
    }

    /**
     * Checks to see if a given class is a JAX-RS resource according to the 1.1 spec:
     *
     * "A resource class is a Java class that uses JAX-RS annotations to implement a corresponding Web resource.
     * Resource classes are POJOs that have at least one method annotated with @Path or a request method designator."
     *
     * https://jsr311.dev.java.net/nonav/releases/1.1/spec/spec.html
     *
     * @param resourceClass The class to check.
     * @return True if the class is a JAX-RS resource, false otherwise.
     */
    private static boolean isJaxRsResource(Class<?> resourceClass) {
        for (Method method : resourceClass.getMethods()) {
            if (hasAnnotation(method, Path.class, HttpMethod.class, GET.class, POST.class, PUT.class, DELETE.class, HEAD.class, OPTIONS.class)) {
                return true;
            }
        }
        return false;
    }

    private static boolean hasAnnotation(Method method, Class... annotations) {
        for (Class annotation : annotations) {
            if (annotation.isAnnotation() && (method.getAnnotation(annotation) != null)) {
                return true;
            }
        }
        return false;
    }
}