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spring-binding/src/main/java/org/springframework/binding/expression/el/DefaultExpressionFactoryUtils.java

@@ -0,0 +1,74 @@
+package org.springframework.binding.expression.el;
+
+import javax.el.ExpressionFactory;
+
+import org.springframework.beans.BeanInstantiationException;
+import org.springframework.beans.BeanUtils;
+import org.springframework.util.ClassUtils;
+import org.springframework.util.ReflectionUtils;
+
+/**
+ * A helper for creating a new expression factory instance using the default expression factory class configured for the
+ * VM.
+ * 
+ * @author Keith Donald
+ */
+public class DefaultExpressionFactoryUtils {
+	private static final String EXPRESSION_FACTORY_PROPERTY = "javax.el.ExpressionFactory";
+
+	static {
+		if (!System.getProperties().containsKey(EXPRESSION_FACTORY_PROPERTY)) {
+			// TODO - change default to Spring EL when it becomes available
+			setDefaultExpressionFactoryClassName("org.jboss.el.ExpressionFactoryImpl");
+		}
+	}
+
+	/**
+	 * Returns the type of ExpressionFactory configured for this VM.
+	 */
+	public static String getDefaultExpressionFactoryClassName() {
+		return System.getProperty(EXPRESSION_FACTORY_PROPERTY);
+	}
+
+	/**
+	 * Sets the type of ExpressionFactory configured for this VM.
+	 */
+	public static void setDefaultExpressionFactoryClassName(String expressionFactoryClassName) {
+		System.setProperty(EXPRESSION_FACTORY_PROPERTY, expressionFactoryClassName);
+	}
+
+	/**
+	 * Creates a new instance of the expression factory configured for this VM.
+	 * @throws IllegalStateException if the ExpressionFactory class cannot be found
+	 * @throws RuntimeException if the ExpressionFactory cannot be instantiated
+	 */
+	public static ExpressionFactory createExpressionFactory() throws IllegalStateException, RuntimeException {
+		if (ReflectionUtils.findMethod(ExpressionFactory.class, "newInstance") != null) {
+			return ExpressionFactory.newInstance();
+		} else {
+			// Fallback in the case of using an older version of the EL API
+			try {
+				Class expressionFactoryClass = ClassUtils.forName(getDefaultExpressionFactoryClassName());
+				return (ExpressionFactory) BeanUtils.instantiateClass(expressionFactoryClass);
+			} catch (ClassNotFoundException e) {
+				throw new IllegalStateException(
+						"The default ExpressionFactory class '"
+								+ getDefaultExpressionFactoryClassName()
+								+ "' could not be found in the classpath.  "
+								+ "Please add this to your classpath or set the default ExpressionFactory class name to something that is in the classpath.",
+						e);
+			} catch (NoClassDefFoundError e) {
+				throw new IllegalStateException(
+						"The default ExpressionFactory class '"
+								+ getDefaultExpressionFactoryClassName()
+								+ "' could not be found in the classpath.  "
+								+ "Please add this to your classpath or set the default ExpressionFactory class name to something that is in the classpath.",
+						e);
+			} catch (BeanInstantiationException e) {
+				throw new RuntimeException("An instance of the default ExpressionFactory '"
+						+ getDefaultExpressionFactoryClassName()
+						+ "' could not be instantiated.  Check your EL implementation configuration.", e);
+			}
+		}
+	}
+}