Add a converter String->Expression

spring-cloud-stream/src/main/java/org/springframework/cloud/stream/config/SpelExpressionConverterConfiguration.java

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+/*
+ * Copyright 2015 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.cloud.stream.config;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.core.convert.converter.Converter;
+import org.springframework.expression.Expression;
+import org.springframework.expression.ParseException;
+import org.springframework.expression.spel.standard.SpelExpressionParser;
+
+/**
+ * Adds a Converter from String to SpEL Expression in the context.
+ * By default, ConfigurationPropertiesBindingPostProcessor adds all converters it finds
+ * in the context to its own conversionService, so this is useful for binding properties
+ * of type Expression in {@literal @}ConfigurationProperties annotated classes.
+ *
+ * @author Eric Bottard
+ */
+@Configuration
+public class SpelExpressionConverterConfiguration {
+
+	@Bean
+	public Converter<String, Expression> spelConverter() {
+		return new SpelConverter();
+	}
+
+	/**
+	 * A simple converter from String to Expression.
+	 *
+	 * @author Eric Bottard
+	 */
+	public static class SpelConverter implements Converter<String, Expression> {
+
+		private SpelExpressionParser parser = new SpelExpressionParser();
+
+		@Override
+		public Expression convert(String source) {
+			try {
+				return parser.parseExpression(source);
+			}
+			catch (ParseException e) {
+				throw new IllegalArgumentException(String.format("Could not convert '%s' into a SpEL expression", source), e);
+			}
+		}
+	}
+}