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<p>Spring 通常使用三种方式注入对象：</p>
<ol>
<li>字段注入：字段上使用 <em>@Autowired</em>、<em>@Resource</em> 注解</li>
<li>setter 注入：使用 setter 方法注入</li>
<li>构造器注入：使用构造方法参数注入依赖</li>
</ol>
<h3 id="字段注入">字段注入</h3>
<p>在字段上使用 <em>@Autowired</em>、<em>@Resource</em> 注解注入。</p>
<ul>
<li>优点：
<ol>
<li>方便快捷，不需要写其他和业务无关的代码</li>
</ol>
</li>
<li>缺点：
<ol>
<li>不能注入不可变对象</li>
<li>依赖对外部不可见（外界无法看到 private 字段，无法了解所需依赖）</li>
<li><strong>重要：组件月 IoC 容器紧密耦合</strong></li>
<li><strong>单元测试时也需要使用 IoC 容器</strong></li>
<li>依赖过多时不够明显（比如使用 setter 注入，十个依赖最少会有 50 行代码，这时候就需要考虑该组件是否违反单一职责原则）</li>
</ol>
</li>
</ul>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@Autowired</span></span><br><span class="line"><span class="keyword">private</span> UserInfoMapper userInfoMapper;</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="meta">@Resource</span></span><br><span class="line"><span class="keyword">private</span> UserInfoMapper userInfoMapper;</span><br></pre></td></tr></table></figure>
<ul>
<li>注意<br>
在 idea 中，使用 <em>@Autowired</em> 注解会提示 <code>Field injection is not recommended</code>；<em>@Resource</em> 则不会提示该信息。
<ol>
<li><em>@Autowired</em> 是 Spring 框架提供的，导致了注解与框架的绑定，一旦更换其他 IoC 框架将会无法使用；</li>
<li><em>@Resource</em> 注解是 Java 标准，即使更换容器也可以正常工作。</li>
</ol>
</li>
</ul>
<h2 id="Component和-Bean">@Component和@Bean</h2>
<ol>
<li>
<p>相同</p>
<ul>
<li>目的：注册 bean 到 Spring 容器中。</li>
</ul>
</li>
<li>
<p>区别</p>
<ul>
<li>
<p><strong>作用范围</strong></p>
<ul>
<li>@Component 作用范围：<strong>类</strong><br>
表明这个类为组件类，Spring 需要为其创建 bean。</li>
<li>@Bean 作用范围：<strong>方法</strong><br>
告知 Spring 该方法需要返回一个对象，该对象要注册为 Spring 上下文中的 bean。</li>
</ul>
</li>
<li>
<p><strong>作用形式</strong></p>
<ul>
<li>@Component（@Controller、@Service、@Repository）都是通过类路径自动扫描检测并注入到 Spring 容器中。</li>
<li>@Bean 在使用该注解的方法上产生这个 bean。</li>
</ul>
</li>
</ul>
</li>
<li>
<p>总结</p>
<ul>
<li>都是为了注册 bean 并且装配到 Sping 容器中。</li>
<li>@Bean 的自定义性更强，比如引用第三方库中的类装配到 Sping 容器中，只能使用 @Bean 注解。</li>
</ul>
</li>
</ol>
<h2 id="Service-注解">@Service 注解</h2>
<p>一定注意要在 <strong>ServiceImpl</strong> 类上添加。</p>
<h2 id="参考-22">参考</h2>
<div id="refer-anchor-1"></div>
<ul>
<li>[1] <a target="_blank" rel="noopener" href="https://www.rainng.com/field-injection-is-not-recommend">不推荐使用@Autowired进行Field注入的原因</a></li>
</ul>
</article><div class="post-copyright"><div class="post-copyright__author"><span class="post-copyright-meta">文章作者: </span><span class="post-copyright-info"><a href="mailto:undefined">huy</a></span></div><div class="post-copyright__type"><span class="post-copyright-meta">文章链接: </span><span class="post-copyright-info"><a href="http://example.com/44660.html">http://example.com/44660.html</a></span></div><div class="post-copyright__notice"><span class="post-copyright-meta">版权声明: </span><span class="post-copyright-info">本博客所有文章除特别声明外，均采用 <a href="https://creativecommons.org/licenses/by-nc-sa/4.0/" target="_blank">CC BY-NC-SA 4.0</a> 许可协议。转载请注明来自 <a href="http://example.com" target="_blank">征蓬</a>！</span></div></div><div class="tag_share"><div class="post-meta__tag-list"><a class="post-meta__tags" href="/tags/SpringBoot/">SpringBoot</a></div><div class="post_share"><div class="social-share" data-image="/pics/scenery/29.jpg" data-sites="facebook,twitter,wechat,weibo,qq"></div><link rel="stylesheet" href="https://jsdelivr.pai233.top/npm/social-share.js/dist/css/share.min.css" media="print" onload="this.media='all'"><script src="https://jsdelivr.pai233.top/npm/social-share.js/dist/js/social-share.min.js" defer></script></div></div><div class="relatedPosts"><div class="headline"><i class="fas fa-thumbs-up fa-fw"></i><span>相关推荐</span></div><div class="relatedPosts-list"><div><a href="/11802.html" title="Bean的加载和控制"><img class="cover" src="/pics/scenery/03.jpg" alt="cover"><div class="content is-center"><div class="date"><i class="far fa-calendar-alt fa-fw"></i> 2022-05-02</div><div class="title">Bean的加载和控制</div></div></a></div><div><a href="/48587.html" title="SpringBoot（一）：日志框架配置"><img class="cover" src="/pics/scenery/03.jpg" alt="cover"><div class="content is-center"><div class="date"><i class="far fa-calendar-alt fa-fw"></i> 2021-01-29</div><div class="title">SpringBoot（一）：日志框架配置</div></div></a></div><div><a href="/35740.html" title="SpringBoot（七）：Application文件配置"><img class="cover" src="/pics/scenery/01.jpg" alt="cover"><div class="content is-center"><div class="date"><i class="far fa-calendar-alt fa-fw"></i> 2022-01-20</div><div class="title">SpringBoot（七）：Application文件配置</div></div></a></div><div><a href="/23140.html" title="SpringBoot（三）：数据库"><img class="cover" src="/pics/scenery/18.jpg" alt="cover"><div class="content is-center"><div class="date"><i class="far fa-calendar-alt fa-fw"></i> 2021-02-10</div><div class="title">SpringBoot（三）：数据库</div></div></a></div><div><a href="/3737.html" title="SpringBoot（五）：Swagger2配置和服务器部署"><img class="cover" src="/pics/scenery/15.jpg" alt="cover"><div class="content is-center"><div class="date"><i class="far fa-calendar-alt fa-fw"></i> 2021-12-09</div><div class="title">SpringBoot（五）：Swagger2配置和服务器部署</div></div></a></div><div><a href="/4811.html" title="SpringBoot（八）：Thymeleaf基础功能"><img class="cover" src="/pics/scenery/03.jpg" alt="cover"><div class="content is-center"><div class="date"><i class="far fa-calendar-alt fa-fw"></i> 2022-02-03</div><div class="title">SpringBoot（八）：Thymeleaf基础功能</div></div></a></div></div></div></div><div class="aside-content" id="aside-content"><div class="sticky_layout"><div class="card-widget" id="card-toc"><div class="item-headline"><i class="fas fa-stream"></i><span>目录</span></div><div class="toc-content"><ol class="toc"><li class="toc-item toc-level-2"><a class="toc-link" href="#%E6%B3%A8%E5%85%A5%E6%96%B9%E5%BC%8F%E7%9A%84%E5%8C%BA%E5%88%AB-sup-1-sup"><span class="toc-number">1.</span> <span class="toc-text">注入方式的区别 1</span></a><ol class="toc-child"><li class="toc-item toc-level-3"><a class="toc-link" href="#%E5%AD%97%E6%AE%B5%E6%B3%A8%E5%85%A5"><span class="toc-number">1.1.</span> <span class="toc-text">字段注入</span></a></li></ol></li><li class="toc-item toc-level-2"><a class="toc-link" href="#Component%E5%92%8C-Bean"><span class="toc-number">2.</span> <span class="toc-text">@Component和@Bean</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#Service-%E6%B3%A8%E8%A7%A3"><span class="toc-number">3.</span> <span class="toc-text">@Service 注解</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#%E5%8F%82%E8%80%83-22"><span class="toc-number">4.</span> <span class="toc-text">参考</span></a></li></ol></div></div></div></div></main><footer id="footer" style="background-image: url('/pics/scenery/29.jpg')"><div id="footer-wrap"><div class="copyright">©2021 - 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