#41 - Added PluginRegistry.getRequiredPlugin(…).

Added aforementioned method for clients to look up a required plugin with the registry throwing a default exception if none is found. An overload taking a Supplier<String> is available to customize the exception message if needed.

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

@@ -36,6 +36,27 @@ public interface PluginRegistry<T extends Plugin<S>, S> extends Iterable<T> {
 	 */
 	Optional<T> getPluginFor(S delimiter);
 
+	/**
+	 * Returns the first {@link Plugin} found for the given delimiter. Thus, further configured {@link Plugin}s are
+	 * ignored.
+	 * 
+	 * @param delimiter
+	 * @return a {@link Plugin} for the given originating system or {@link Optional#empty()} if none found.
+	 * @throws IllegalArgumentException in case no {@link Plugin} for the given delimiter
+	 */
+	T getRequiredPluginFor(S delimiter) throws IllegalArgumentException;
+
+	/**
+	 * Returns the first {@link Plugin} found for the given delimiter. Thus, further configured {@link Plugin}s are
+	 * ignored.
+	 * 
+	 * @param delimiter
+	 * @param message a {@link Supplier} to produce an exception message in case no plugin is found.
+	 * @return a {@link Plugin} for the given originating system or {@link Optional#empty()} if none found.
+	 * @throws IllegalArgumentException in case no {@link Plugin} for the given delimiter
+	 */
+	T getRequiredPluginFor(S delimiter, Supplier<String> message) throws IllegalArgumentException;
+
 	/**
 	 * Returns all plugins for the given delimiter.
 	 * 

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

@@ -22,6 +22,8 @@ import java.util.Optional;
 import java.util.function.Supplier;
 import java.util.stream.Collectors;
 
+import org.springframework.util.Assert;
+
 /**
  * Basic implementation of {@link PluginRegistry}. Simply holds all given plugins in a list dropping {@literal null}
  * values silently on adding.
@@ -83,6 +85,29 @@ public class SimplePluginRegistry<T extends Plugin<S>, S> extends PluginRegistry
 				.findFirst();
 	}
 
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.plugin.core.PluginRegistry#getRequiredPluginFor(java.lang.Object)
+	 */
+	@Override
+	public T getRequiredPluginFor(S delimiter) {
+
+		return getRequiredPluginFor(delimiter,
+				() -> String.format("No plugin found for delimiter %s! Registered plugins: %s.", delimiter, getPlugins()));
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.plugin.core.PluginRegistry#getRequiredPluginFor(java.lang.Object, java.util.function.Supplier)
+	 */
+	@Override
+	public T getRequiredPluginFor(S delimiter, Supplier<String> message) throws IllegalArgumentException {
+
+		Assert.notNull(message, "Message must not be null!");
+
+		return getPluginFor(delimiter, () -> new IllegalArgumentException(message.get()));
+	}
+
 	/*
 	 * (non-Javadoc)
 	 * @see org.springframework.plugin.core.PluginRegistry#getPluginsFor(java.lang.Object)

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

@@ -25,7 +25,9 @@ import java.util.Collections;
 import java.util.List;
 
 import org.junit.Before;
+import org.junit.Rule;
 import org.junit.Test;
+import org.junit.rules.ExpectedException;
 
 /**
  * Unit test for {@link SimplePluginRegistry}.
@@ -38,6 +40,8 @@ public class SimplePluginRegistryUnitTest {
 
 	SimplePluginRegistry<SamplePlugin, String> registry;
 
+	public @Rule ExpectedException o_O = ExpectedException.none();
+
 	/**
 	 * Initializes a {@code PluginRegistry} and equips it with an {@code EmailNotificationProvider}.
 	 */
@@ -142,4 +146,29 @@ public class SimplePluginRegistryUnitTest {
 
 		registry.getPluginFor("FOO", () -> new IllegalStateException());
 	}
+
+	/**
+	 * @see #41
+	 */
+	public void throwsExceptionIfRequiredPluginIsNotFound() {
+
+		registry = SimplePluginRegistry.create(Collections.emptyList());
+
+		o_O.expect(IllegalArgumentException.class);
+
+		registry.getRequiredPluginFor("FOO");
+	}
+
+	/**
+	 * @see #41
+	 */
+	public void throwsExceptionWithMessafeIfRequiredPluginIsNotFound() {
+
+		registry = SimplePluginRegistry.create(Collections.emptyList());
+
+		o_O.expect(IllegalArgumentException.class);
+		o_O.expectMessage("message");
+
+		registry.getRequiredPluginFor("FOO", () -> "message");
+	}
 }