#19 - Exceptions on plugin lookup can now be submitted lazily.

Introduced overloads on PluginRegistry which instead of taking an exception instance immediately (which requires instance creation beforehand) now accept a Supplier<E> so that the exception creation can actually be delayed until it's really needed.

Deprecated the old methods taking exception instances directly.

core/src/main/java/org/springframework/plugin/core/PluginRegistry.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2008-2012 the original author or authors.
+ * Copyright 2008-2016 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -51,19 +51,48 @@ public interface PluginRegistry<T extends Plugin<S>, S> extends Iterable<T> {
 	 * @param ex the exception to be thrown in case no plugin can be found
 	 * @return a single plugin for the given delimiter
 	 * @throws E if no plugin can be found for the given delimiter
+	 * @deprecated prefer {@link #getPluginFor(Object, Supplier)} to avoid the exceptions to be created for every plugin
+	 *             lookup.
 	 */
+	@Deprecated
 	<E extends Exception> T getPluginFor(S delimiter, E ex) throws E;
 
+	/**
+	 * Retrieves a required plugin from the registry or throw the given exception if none can be found. If more than one
+	 * plugins are found the first one will be returned.
+	 * 
+	 * @param <E> the exception type to be thrown in case no plugin can be found.
+	 * @param delimiter
+	 * @param ex a lazy {@link Supplier} to produce an exception in case no plugin can be found.
+	 * @return a single plugin for the given delimiter
+	 * @throws E if no plugin can be found for the given delimiter
+	 */
+	<E extends Exception> T getPluginFor(S delimiter, Supplier<E> ex) throws E;
+
 	/**
 	 * Retrieves all plugins for the given delimiter or throws an exception if no plugin can be found.
 	 * 
-	 * @param <E> the exception type to be thrown
+	 * @param <E> the exception type to be thrown.
 	 * @param delimiter
-	 * @param ex
+	 * @param ex the exception to be thrown in case no plugin can be found.
+	 * @return all plugins for the given delimiter.
+	 * @throws E if no plugin can be found
+	 * @deprecated prefer {@link #getPluginFor(Object, Supplier)} to avoid the exceptions to be created for every plugin
+	 *             lookup.
+	 */
+	@Deprecated
+	<E extends Exception> List<T> getPluginsFor(S delimiter, E ex) throws E;
+
+	/**
+	 * Retrieves all plugins for the given delimiter or throws an exception if no plugin can be found.
+	 * 
+	 * @param <E> the exception type to be thrown.
+	 * @param delimiter
+	 * @param ex a lazy {@link Supplier} to produce an exception in case no plugin can be found.
 	 * @return all plugins for the given delimiter
 	 * @throws E if no plugin can be found
 	 */
-	<E extends Exception> List<T> getPluginsFor(S delimiter, E ex) throws E;
+	<E extends Exception> List<T> getPluginsFor(S delimiter, Supplier<E> ex) throws E;
 
 	/**
 	 * Returns the first {@link Plugin} supporting the given delimiter or the given plugin if none can be found.
@@ -113,4 +142,9 @@ public interface PluginRegistry<T extends Plugin<S>, S> extends Iterable<T> {
 	 * @return
 	 */
 	List<T> getPlugins();
-}
+
+	interface Supplier<E extends Exception> {
+
+		E get();
+	}
+}

core/src/main/java/org/springframework/plugin/core/SimplePluginRegistry.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2008-2012 the original author or authors.
+ * Copyright 2008-2016 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -104,12 +104,28 @@ public class SimplePluginRegistry<T extends Plugin<S>, S> extends PluginRegistry
 	 * (non-Javadoc)
 	 * @see org.springframework.plugin.core.PluginRegistry#getPluginFor(java.lang.Object, java.lang.Exception)
 	 */
-	public <E extends Exception> T getPluginFor(S delimiter, E ex) throws E {
+	public <E extends Exception> T getPluginFor(S delimiter, final E ex) throws E {
+
+		return getPluginFor(delimiter, new Supplier<E>() {
+
+			@Override
+			public E get() {
+				return ex;
+			}
+		});
+	}
+
+	/* 
+	 * (non-Javadoc)
+	 * @see org.springframework.plugin.core.PluginRegistry#getPluginFor(java.lang.Object, org.springframework.plugin.core.PluginRegistry.Supplier)
+	 */
+	@Override
+	public <E extends Exception> T getPluginFor(S delimiter, Supplier<E> ex) throws E {
 
 		T plugin = getPluginFor(delimiter);
 
 		if (null == plugin) {
-			throw ex;
+			throw ex.get();
 		}
 
 		return plugin;
@@ -119,12 +135,28 @@ public class SimplePluginRegistry<T extends Plugin<S>, S> extends PluginRegistry
 	 * (non-Javadoc)
 	 * @see org.springframework.plugin.core.PluginRegistry#getPluginsFor(java.lang.Object, java.lang.Exception)
 	 */
-	public <E extends Exception> List<T> getPluginsFor(S delimiter, E ex) throws E {
+	public <E extends Exception> List<T> getPluginsFor(S delimiter, final E ex) throws E {
+
+		return getPluginsFor(delimiter, new Supplier<E>() {
+
+			@Override
+			public E get() {
+				return ex;
+			}
+		});
+	}
+
+	/* 
+	 * (non-Javadoc)
+	 * @see org.springframework.plugin.core.PluginRegistry#getPluginsFor(java.lang.Object, org.springframework.plugin.core.PluginRegistry.ExceptionProvider)
+	 */
+	@Override
+	public <E extends Exception> List<T> getPluginsFor(S delimiter, Supplier<E> ex) throws E {
 
 		List<T> result = getPluginsFor(delimiter);
 
 		if (result.isEmpty()) {
-			throw ex;
+			throw ex.get();
 		}
 
 		return result;

core/src/test/java/org/springframework/plugin/core/SimplePluginRegistryUnitTest.java

@@ -21,10 +21,12 @@ import static org.junit.Assert.*;
 
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collections;
 import java.util.List;
 
 import org.junit.Before;
 import org.junit.Test;
+import org.springframework.plugin.core.PluginRegistry.Supplier;
 
 /**
  * Unit test for {@link SimplePluginRegistry}.
@@ -130,4 +132,21 @@ public class SimplePluginRegistryUnitTest {
 
 		assertThat(registry.countPlugins(), is(0));
 	}
+
+	/**
+	 * @see #19
+	 */
+	@Test(expected = IllegalStateException.class)
+	public void testname() throws Exception {
+
+		registry = SimplePluginRegistry.create(Collections.<SamplePlugin> emptyList());
+
+		registry.getPluginFor("FOO", new Supplier<Exception>() {
+
+			@Override
+			public Exception get() {
+				return new IllegalStateException();
+			}
+		});
+	}
 }