revised expression parser API design

org.springframework.beans/src/main/java/org/springframework/beans/factory/config/BeanExpressionContext.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2008 the original author or authors.
+ * Copyright 2002-2009 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.
@@ -17,6 +17,7 @@
 package org.springframework.beans.factory.config;
 
 import org.springframework.beans.factory.BeanFactory;
+import org.springframework.util.Assert;
 
 /**
  * Context object for evaluating an expression within a bean definition.
@@ -32,6 +33,7 @@ public class BeanExpressionContext {
 
 
 	public BeanExpressionContext(BeanFactory beanFactory, Scope scope) {
+		Assert.notNull(beanFactory, "BeanFactory must not be null");
 		this.beanFactory = beanFactory;
 		this.scope = scope;
 	}
@@ -47,16 +49,37 @@ public class BeanExpressionContext {
 
 	public boolean containsObject(String key) {
 		return (this.beanFactory.containsBean(key) ||
-				this.scope.resolveContextualObject(key) != null);
+				(this.scope != null && this.scope.resolveContextualObject(key) != null));
 	}
 
 	public Object getObject(String key) {
 		if (this.beanFactory.containsBean(key)) {
 			return this.beanFactory.getBean(key);
 		}
-		else {
+		else if (this.scope != null){
 			return this.scope.resolveContextualObject(key);
 		}
+		else {
+			return null;
+		}
+	}
+
+
+	@Override
+	public boolean equals(Object other) {
+		if (this == other) {
+			return true;
+		}
+		if (!(other instanceof BeanExpressionContext)) {
+			return false;
+		}
+		BeanExpressionContext otherContext = (BeanExpressionContext) other;
+		return (this.beanFactory == otherContext.beanFactory && this.scope == otherContext.scope);
+	}
+
+	@Override
+	public int hashCode() {
+		return this.beanFactory.hashCode();
 	}
 
 }