本篇我们一起来看一下Spring Framework IoC的字段依赖注入。这里我总结了以下几种方式：

* 手动模式	* Java 注解配置元信息		* @Autowired		* @Resource		* @Inject

字段的依赖注入只有手动的模式，并没有自动模式。接下来我们就一起通过实际的案例来实践一下。代码如下：

/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements.  See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You 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 * *      * * 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.eleven.thinking.in.spring.ioc.dependency.injection;import org.eleven.thinking.in.spring.ioc.overview.domain.User;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.beans.factory.xml.XmlBeanDefinitionReader;import org.springframework.context.annotation.AnnotationConfigApplicationContext;import org.springframework.context.annotation.Bean;import javax.annotation.Resource;/** * 基于 Java 注解的依赖字段注入示例 * * @author <a href="mailto:eleven.hm@vip.163.com">eleven</a> * @since */public class AnnotationDependencyFieldInjectionDemo {    @Autowired    private//    static // @Autowired 会忽略掉静态字段            UserHolder userHolder;    @Resource    private UserHolder userHolder2;    public static void main(String[] args) {        // 创建 BeanFactory 容器        AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext();        // 注册 Configuration Class（配置类） -> Spring Bean        applicationContext.register(AnnotationDependencyFieldInjectionDemo.class);        XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(applicationContext);        String xmlResourcePath = "classpath:/META-INF/dependency-lookup-context.xml";        // 加载 XML 资源，解析并且生成 BeanDefinition        beanDefinitionReader.loadBeanDefinitions(xmlResourcePath);        // 启动 Spring 应用上下文        applicationContext.refresh();        // 依赖查找 AnnotationDependencyFieldInjectionDemo Bean        AnnotationDependencyFieldInjectionDemo demo = applicationContext.getBean(AnnotationDependencyFieldInjectionDemo.class);        // @Autowired 字段关联        UserHolder userHolder = demo.userHolder;        System.out.println(userHolder);        System.out.println(demo.userHolder2);        System.out.println(userHolder == demo.userHolder2);        // 显示地关闭 Spring 应用上下文        applicationContext.close();    }    @Bean    public UserHolder userHolder(User user) {        return new UserHolder(user);    }}

以上就是我们通过字段的方式进行依赖注入的实践。这里需要注意的一个问题就是：@Autowired 会忽略掉静态字段。