spring boot 的 ApplicationContext 及 getbean

在spring中，我们通过如下代码取得一个spring托管类：

 ApplicationContext ac = new FileSystemXmlApplicationContext("applicationContext.xml");
 ac.getBean("beanId");

在spring boot中，我参考了如下三篇文章：

让非Spring管理的类获得一个Bean

http://blog.sina.com.cn/s/blog_72ef7bea0102wcvk.htmlblog.sina.com.cn/s/blog_72ef7bea0102wcvk.html

Spring Boot普通类调用bean

http://blog.csdn.net/u014695188/article/details/52396880

SpringBoot-获取上下文

http://www.2cto.com/kf/201701/582935.html

做了一些实践。

首先，我们需要一个媒介，来取得AppicationContext——SpringUtil

这个类有两种方式：

1. 实现ApplicationContextAware接口

@Component

public class SpringUtil implements ApplicationContextAware {


<span class="hljs-keyword">private</span> <span class="hljs-keyword">static</span> ApplicationContext applicationContext = <span class="hljs-keyword">null</span>;</br>

// 非@import显式注入，@Component是必须的，且该类必须与main同包或子包


// 若非同包或子包，则需手动import 注入，有没有@Component都一样


// 可复制到Test同包测试


<span class="hljs-annotation">@Override</span></br>
<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">setApplicationContext</span><span class="hljs-params">(ApplicationContext applicationContext)</span> <span class="hljs-keyword">throws</span> BeansException </span>{</br>
    <span class="hljs-keyword">if</span>(SpringUtil.applicationContext == <span class="hljs-keyword">null</span>){</br>
        SpringUtil.applicationContext  = applicationContext;</br>
    }</br>
    System.out.println(<span class="hljs-string">"---------------com.ilex.jiutou.util.Test.Main.SubPackage.SpringUtil---------------"</span>);</br>
}</br></br>

<span class="hljs-comment">//获取applicationContext</span></br>
<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> ApplicationContext <span class="hljs-title">getApplicationContext</span><span class="hljs-params">()</span> </span>{</br>
    <span class="hljs-keyword">return</span> applicationContext;</br>
}</br>



    //通过name获取 Bean.

    public static Object getBean(String name){

        return getApplicationContext().getBean(name);


}</br></br>

<span class="hljs-comment">//通过class获取Bean.</span></br>
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> &lt;T&gt; <span class="hljs-function">T <span class="hljs-title">getBean</span><span class="hljs-params">(Class&lt;T&gt; clazz)</span></span>{</br>
    <span class="hljs-keyword">return</span> getApplicationContext().getBean(clazz);</br>
}</br></br>

<span class="hljs-comment">//通过name,以及Clazz返回指定的Bean</span></br>
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> &lt;T&gt; <span class="hljs-function">T <span class="hljs-title">getBean</span><span class="hljs-params">(String name,Class&lt;T&gt; clazz)</span></span>{</br>
    <span class="hljs-keyword">return</span> getApplicationContext().getBean(name, clazz);</br>
}</br>

}

需要被spring注入，覆写setApplicationContext

2. 普通类

//@Component  在不可扫描区域，且不需要注入，作为一个普通的util类

public class SpringUtil{




    private static ApplicationContext applicationContext = null;


<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title">setApplicationContext</span><span class="hljs-params">(ApplicationContext applicationContext)</span></span>{</br>
    <span class="hljs-keyword">if</span>(SpringUtil.applicationContext == <span class="hljs-keyword">null</span>){</br>
        SpringUtil.applicationContext  = applicationContext;</br>
    }</br></br>

}</br></br>

<span class="hljs-comment">//获取applicationContext</span></br>
<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> ApplicationContext <span class="hljs-title">getApplicationContext</span><span class="hljs-params">()</span> </span>{</br>
    <span class="hljs-keyword">return</span> applicationContext;</br>
}</br></br>

<span class="hljs-comment">//通过name获取 Bean.</span></br>
<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> Object <span class="hljs-title">getBean</span><span class="hljs-params">(String name)</span></span>{</br>
    <span class="hljs-keyword">return</span> getApplicationContext().getBean(name);</br></br>

}</br>

<span class="hljs-comment">//通过class获取Bean.</span></br>
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> &lt;T&gt; <span class="hljs-function">T <span class="hljs-title">getBean</span><span class="hljs-params">(Class&lt;T&gt; clazz)</span></span>{</br>
    <span class="hljs-keyword">return</span> getApplicationContext().getBean(clazz);</br>
}</br>

<span class="hljs-comment">//通过name,以及Clazz返回指定的Bean</span></br>
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> &lt;T&gt; <span class="hljs-function">T <span class="hljs-title">getBean</span><span class="hljs-params">(String name,Class&lt;T&gt; clazz)</span></span>{</br>
    <span class="hljs-keyword">return</span> getApplicationContext().getBean(name, clazz);</br>
}</br>

}

不需要被注入，但需要手动调用

主函数

@SpringBootApplication
@Import(value={UserFooterService.class})
public class Test {
    public static void main(String[] args) {
        ApplicationContext ctx = SpringApplication.run(Test.class, args);
<span class="hljs-comment">//    SpringUtil.setApplicationContext(ctx);  这个对应于AnoStatic</span></br></br>

    String[] beanNames =  ctx.getBeanDefinitionNames();</br>
    System.out.println(<span class="hljs-string">"beanNames个数："</span>+beanNames.length);</br>
    <span class="hljs-keyword">for</span>(String bn:beanNames){</br>
        System.out.println(bn);</br>
    }</br></br>

    <span class="hljs-comment">// 测试加载UserFooterService</span></br>
    UserFooterService userFooterService = (UserFooterService) SpringUtil.getBean(UserFooterService.class);</br>
    List&lt;Map&lt;String,Object&gt;&gt; list = userFooterService.hotTopic(<span class="hljs-string">"0"</span>, <span class="hljs-string">"5"</span>);</br>
    System.out.println(list.toString());</br></br>

    <span class="hljs-comment">// 测试加载SpringUtil</span></br>
    SpringUtil springUtil = (SpringUtil)SpringUtil.getBean(SpringUtil.class);</br>
    System.out.println(springUtil);</br>
}</br></br>

//    @Bean


//    public SpringUtil springUtil() {


//        return new SpringUtil();


//    }


}

UserFooterService是一个业务类，这里不榕树

建立如下的测试结构：

Main/Test 主函数

AnoStatic/SpringUtil  普通类

Main/SubPackage/SpringUtil 实现ApplicationContextAware，但为主函数子包

NonSubPackage/SpringUtil 实现ApplicationContextAware，但非主函数子包和同包

SpringUtil注入方式有三种，在参考的三篇博客均有说明，在此仅总结：

1. 类与SpringBootApplication同包或子包，此在ComponentScan的扫描范围之内，在类上@Component注解即可，会被自动注入；

2. 无论位置，都可通过在主函数用@import或@bean来手动注入。

第一种SpringUtil方式必须被spring注入，否则会报

Exception in thread "main" java.lang.NullPointerException

at com.ilex.jiutou.util.Test.NonSubPackage.SpringUtil.getBean(SpringUtil.java:40)

at com.ilex.jiutou.util.Test.Main.Test.main(Test.java:34)

表示applicationContext获取失败

第二种方式，SpringUtil可被注入可不被注入

当不注入时，主函数这一段：

        // 测试加载SpringUtil
        SpringUtil springUtil = (SpringUtil)SpringUtil.getBean(SpringUtil.class);
        System.out.println(springUtil);

报错：

No qualifying bean of type [＊＊.Test.AnoStatic.SpringUtil