Java tutorial
/* * Copyright 2013-2016 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.sleuth.annotation; import java.lang.invoke.MethodHandles; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.springframework.expression.Expression; import org.springframework.expression.ExpressionParser; import org.springframework.expression.spel.standard.SpelExpressionParser; /** * Uses SPEL to evaluate the expression. If an exception is thrown will return * the {@code toString()} of the parameter. * * @author Marcin Grzejszczak * @since 1.2.0 */ class SpelTagValueExpressionResolver implements TagValueExpressionResolver { private static final Log log = LogFactory.getLog(MethodHandles.lookup().lookupClass()); @Override public String resolve(String expression, Object parameter) { try { ExpressionParser expressionParser = new SpelExpressionParser(); Expression expressionToEvaluate = expressionParser.parseExpression(expression); return expressionToEvaluate.getValue(parameter, String.class); } catch (Exception e) { log.error("Exception occurred while tying to evaluate the SPEL expression [" + expression + "]", e); } return parameter.toString(); } }