【Java Web】条件Bean@ConditionalOnResource
【Java Web】条件Bean@ConditionalOnResource
注解仅仅会加载classpath中指定的资源,资源存在则创建对象,资源不存在则不创建对象。外部资源文件无法加载,想要使用外部资源文件参考:
resources目录下资源application.properties,存在则创建对象
import org.springframework.boot.autoconfigure.condition.ConditionalOnResource; import org.springframework.context.annotation.Configuration; @ConditionalOnResource(resources = {"application.properties"}) @Configuration public class TestConditionalOnResource { }
@Autowired(required = false) TestConditionalOnResource bean;
实现类
/* * Copyright 2012-2019 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 * * https://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.boot.autoconfigure.condition; import java.util.ArrayList; import java.util.List; import org.springframework.boot.autoconfigure.condition.ConditionMessage.Style; import org.springframework.context.annotation.Condition; import org.springframework.context.annotation.ConditionContext; import org.springframework.core.Ordered; import org.springframework.core.annotation.Order; import org.springframework.core.io.ResourceLoader; import org.springframework.core.type.AnnotatedTypeMetadata; import org.springframework.util.Assert; import org.springframework.util.MultiValueMap; /** * {@link Condition} that checks for specific resources. * * @author Dave Syer * @see ConditionalOnResource */ @Order(Ordered.HIGHEST_PRECEDENCE + 20) class OnResourceCondition extends SpringBootCondition { @Override public ConditionOutcome getMatchOutcome(ConditionContext context, AnnotatedTypeMetadata metadata) { MultiValueMap<String, Object> attributes = metadata .getAllAnnotationAttributes(ConditionalOnResource.class.getName(), true); ResourceLoader loader = context.getResourceLoader(); List<String> locations = new ArrayList<>(); collectValues(locations, attributes.get("resources")); Assert.isTrue(!locations.isEmpty(), "@ConditionalOnResource annotations must specify at least one resource location"); List<String> missing = new ArrayList<>(); for (String location : locations) { String resource = context.getEnvironment().resolvePlaceholders(location); if (!loader.getResource(resource).exists()) { missing.add(location); } } if (!missing.isEmpty()) { return ConditionOutcome.noMatch(ConditionMessage.forCondition(ConditionalOnResource.class) .didNotFind("resource", "resources").items(Style.QUOTE, missing)); } return ConditionOutcome.match(ConditionMessage.forCondition(ConditionalOnResource.class) .found("location", "locations").items(locations)); } private void collectValues(List<String> names, List<Object> values) { for (Object value : values) { for (Object item : (Object[]) value) { names.add((String) item); } } } }