Add a 'context' type

This was some example code I found somewhere that seemed interesting.

2 files changed, 100 insertions, 0 deletions

diff --git a/src/main/java/bjc/data/Contexts.java b/src/main/java/bjc/data/Contexts.java
new file mode 100644
index 0000000..0769447
--- /dev/null
+++ b/src/main/java/bjc/data/Contexts.java
@@ -0,0 +1,82 @@
+package bjc.data;
+
+import java.util.*;
+
+public class Contexts {
+	public static final IContext NULL = new NullContextImpl();
+
+	private Contexts() {
+		throw new UnsupportedOperationException();
+	}
+
+	public static IContext create() {
+		return new ContextImpl(NULL);
+	}
+
+	public static IContext create(IContext parent) {
+		return new ContextImpl(parent);
+	}
+
+	private static class NullContextImpl implements IContext {
+		@Override
+		public IContext getParent() {
+			return this;
+		}
+
+		@Override
+		public void register(String name, Object o) {
+			throw new UnsupportedOperationException();
+		}
+
+		@Override
+		public Object get(String name) {
+			throw new NoSuchElementException();
+		}
+		
+		@Override
+		public <T> T get(Class<T> contract) {
+			throw new NoSuchElementException();
+		}
+	}
+
+	private static class ContextImpl implements IContext {
+
+		private final IContext parent;
+
+		private final Map<String, Object> objects;
+
+		public ContextImpl(IContext parent) {
+			this.parent = parent;
+			this.objects = new HashMap<String, Object>();
+		}
+
+		@Override
+		public void register(String name, Object o) {
+			objects.put(name, o);
+		}
+
+		@Override
+		public Object get(String name) {
+			if (objects.containsKey(name)) {
+				return objects.get(name);
+			}
+			return parent.get(name);
+		}
+
+		@SuppressWarnings("unchecked")
+		@Override
+		public <T> T get(Class<T> contract) {
+			for (Object o : objects.values()) {
+				if (contract.isInstance(o)) {
+					return (T) o;
+				}
+			}
+			return parent.get(contract);
+		}
+
+		@Override
+		public IContext getParent() {
+			return parent;
+		}
+	}
+}
diff --git a/src/main/java/bjc/data/IContext.java b/src/main/java/bjc/data/IContext.java
new file mode 100644
index 0000000..a1073f1
--- /dev/null
+++ b/src/main/java/bjc/data/IContext.java
@@ -0,0 +1,18 @@
+package bjc.data;
+
+public interface IContext {
+	void register(String name, Object o);
+
+	IContext getParent();
+
+	Object get(String name);
+	
+	<T> T get(Class<T> contract);
+	
+	default <T> T get(String name, Class<T> contract) {
+		Object obj = get(name);
+		return obj == null 
+				? getParent().get(name, contract) 
+						: contract.cast(obj);
+	};
+}