### 歡迎訪問我的GitHub
> 這裡分類和彙總了欣宸的全部原創(含配套原始碼)：[https://github.com/zq2599/blog_demos](https://github.com/zq2599/blog_demos)

### 本篇概覽
- Aware.java是個沒有定義任何方法的介面，擁有眾多子介面，在spring原始碼中有多處都在使用這些子介面完成各種場景下的回撥操作，當業務有需要時，我們只需建立類來實現相關介面，再宣告為bean，就可以被spring容器主動回撥；

### spring原始碼分析Aware子類的使用場景
- 接下來通過分析spring原始碼，我們來看看典型的Aware子類有哪些，使用場景是什麼？

- 在spring容器初始化過程中，會執行AbstractApplicationContext類的prepareBeanFactory方法，這裡面會建立一個bean後置處理器**ApplicationContextAwareProcessor**，如下圖紅框所示：
![image.png](https://bbs-img.huaweicloud.com/blogs/img/20220612/1655046342073680532.png)

- 在bean被初始化之前，所有的bean後置處理器的postProcessBeforeInitialization方法都會被執行，如下圖紅框所示：
![image.png](https://bbs-img.huaweicloud.com/blogs/img/20220612/1655046367889673468.png)

- 由以上兩步可以確定：**對於每個bean後置處理器來說，它的postProcessBeforeInitialization方法會在每個bean的初始化之前被呼叫一次；**

- 來看看ApplicationContextAwareProcessor類的postProcessBeforeInitialization方法，按照前面的分析，該方法在每個bean被初始化之前都會被執行，如下圖紅框所示，invokeAwareInterfaces方法會被呼叫，這是我們要關注的重點：
![image.png](https://bbs-img.huaweicloud.com/blogs/img/20220612/1655046387430573360.png)

- 展開invokeAwareInterfaces方法看看：

```java
private void invokeAwareInterfaces(Object bean) {
		if (bean instanceof Aware) {
			if (bean instanceof EnvironmentAware) {
				((EnvironmentAware) bean).setEnvironment(this.applicationContext.getEnvironment());
			}
			if (bean instanceof EmbeddedValueResolverAware) {
				((EmbeddedValueResolverAware) bean).setEmbeddedValueResolver(
						new EmbeddedValueResolver(this.applicationContext.getBeanFactory()));
			}
			if (bean instanceof ResourceLoaderAware) {
				((ResourceLoaderAware) bean).setResourceLoader(this.applicationContext);
			}
			if (bean instanceof ApplicationEventPublisherAware) {
				((ApplicationEventPublisherAware) bean).setApplicationEventPublisher(this.applicationContext);
			}
			if (bean instanceof MessageSourceAware) {
				((MessageSourceAware) bean).setMessageSource(this.applicationContext);
			}
			if (bean instanceof ApplicationContextAware) {
				((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);
			}
		}
	}
```

- 從上述程式碼可以看出，如果當前的bean實現了某個介面，那麼它的某個對應的方法就會被呼叫，例如我們建立了一個bean實現了ApplicationContextAware介面，那麼這個bean的setApplicationContext方法就會被呼叫，入參是applicationContext成員變數，這樣我們的bean就能得到applicationContext物件了；

- 以上就是Aware的介面使用原理：**業務按需要實現特定的Aware介面，spring容器會主動找到該bean，然後呼叫特定的方法，將特定的引數傳遞給bean；**

### BeanNameAware介面的呼叫場景
- BeanNameAware也是Aware的子介面，不過它的呼叫場景和前面分析的幾個Aware子介面不同，並未出現在ApplicationContextAwareProcessor類的invokeAwareInterfaces方法中，我們來看看它是如何被呼叫的；

- 如下圖所示，紅框中就是BeanNameAware介面被呼叫的地方，而綠框中的applyBeanPostProcessorsBeforeInitialization方法就是前面我們分析的那些Aware子介面被呼叫的位置：
![image.png](https://bbs-img.huaweicloud.com/blogs/img/20220612/1655046427837597106.png)

- 方法invokeAwareMethods如下所示，和前面的討論一樣，特定型別的bean，其特定的方法被呼叫，傳入特定的入參：
```java
private void invokeAwareMethods(final String beanName, final Object bean) {
		if (bean instanceof Aware) {
			if (bean instanceof BeanNameAware) {
				((BeanNameAware) bean).setBeanName(beanName);
			}
			if (bean instanceof BeanClassLoaderAware) {
				((BeanClassLoaderAware) bean).setBeanClassLoader(getBeanClassLoader());
			}
			if (bean instanceof BeanFactoryAware) {
				((BeanFactoryAware) bean).setBeanFactory(AbstractAutowireCapableBeanFactory.this);
			}
		}
	}
```

### 實戰，通過Aware介面得到想要的物件
- 瞭解Aware介面在spring環境中的用法之後，我們可以通過實戰來驗證前面所學了，本次實戰我們建立兩個類，分別實現ApplicationContextAware和BeanNameAware這兩個介面，看宣告的方法是否能被呼叫，並驗證傳入的物件是否有效（文章結尾處提供本次實戰的工程原始碼下載）；
- 基於maven新建一個SpringBoot的web工程**customizeaware**；
- 新建工具類Utils，提供靜態方法printTrack用於列印當前執行緒堆疊資訊：

```java
package com.bolingcavalry.customizeaware.util;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * @Description : 提供一些常用的工具方法
 * @Author : zq2599@gmail.com
 * @Date : 2018-08-14 05:51
 */
public class Utils {
    private static final Logger logger = LoggerFactory.getLogger(Utils.class);

/**
     * 列印當前執行緒堆疊資訊
     * @param prefix
     */
    public static void printTrack(String prefix){
        StackTraceElement[] st = Thread.currentThread().getStackTrace();

if(null==st){
            logger.info("invalid stack");
            return;
        }

StringBuffer sbf =new StringBuffer();

for(StackTraceElement e:st){
 if(sbf.length()>0){
 sbf.append(" ）
 for(String name : beanDefinitionNames){
 stringBuilder.append(name).append(" ");
 }
 }

return "hello, "
 + new Date()
 + " CustomizeBeanNameAware instance bean name : "
 + customizeBeanNameAware.getBeanName()
 + " bean definition names, size "
 + arrayLength
 + ", detail : "
 + stringBuilder;
 }

}
```

- 啟動應用，看到啟動日誌中帶有CustomizeBeanNameAware和CustomizeApplicationContextAware的介面方法被呼叫時輸出的日誌，並且執行緒堆疊和我們之前看的spring原始碼位置一致，分別是ApplicationContextAwareProcessor.invokeAwareInterfaces()和AbstractAutowireCapableBeanFactory.invokeAwareMethods()：

```shell
C:\jdk\bin\java.exe -XX:TieredStopAtLevel=1 -noverify -Dspring.output.ansi.enabled=always -Dcom.sun.management.jmxremote -Dcom.sun.management.jmxremote.port=63257 -Dcom.sun.management.jmxremote.authenticate=false -Dcom.sun.management.jmxremote.ssl=false -Djava.rmi.server.hostname=localhost -Dspring.liveBeansView.mbeanDomain -Dspring.application.admin.enabled=true -javaagent:C:\software\JetBrains\IntelliJIDEA\lib\idea_rt.jar=63258:C:\software\JetBrains\IntelliJIDEA\bin -Dfile.encoding=UTF-8 -classpath C:\jdk\jre\lib\charsets.jar;C:\jdk\jre\lib\deploy.jar;C:\jdk\jre\lib\ext\access-bridge-64.jar;C:\jdk\jre\lib\ext\cldrdata.jar;C:\jdk\jre\lib\ext\dnsns.jar;C:\jdk\jre\lib\ext\jaccess.jar;C:\jdk\jre\lib\ext\jfxrt.jar;C:\jdk\jre\lib\ext\localedata.jar;C:\jdk\jre\lib\ext\nashorn.jar;C:\jdk\jre\lib\ext\sunec.jar;C:\jdk\jre\lib\ext\sunjce_provider.jar;C:\jdk\jre\lib\ext\sunmscapi.jar;C:\jdk\jre\lib\ext\sunpkcs11.jar;C:\jdk\jre\lib\ext\zipfs.jar;C:\jdk\jre\lib\javaws.jar;C:\jdk\jre\lib\jce.jar;C:\jdk\jre\lib\jfr.jar;C:\jdk\jre\lib\jfxswt.jar;C:\jdk\jre\lib\jsse.jar;C:\jdk\jre\lib\management-agent.jar;C:\jdk\jre\lib\plugin.jar;C:\jdk\jre\lib\resources.jar;C:\jdk\jre\lib\rt.jar;D:\github\blog_demos\customizeaware\target\classes;C:\Users\12167\.m2\repository\org\springframework\boot\spring-boot-starter-web\2.0.4.RELEASE\spring-boot-starter-web-2.0.4.RELEASE.jar;C:\Users\12167\.m2\repository\org\springframework\boot\spring-boot-starter\2.0.4.RELEASE\spring-boot-starter-2.0.4.RELEASE.jar;C:\Users\12167\.m2\repository\org\springframework\boot\spring-boot\2.0.4.RELEASE\spring-boot-2.0.4.RELEASE.jar;C:\Users\12167\.m2\repository\org\springframework\boot\spring-boot-autoconfigure\2.0.4.RELEASE\spring-boot-autoconfigure-2.0.4.RELEASE.jar;C:\Users\12167\.m2\repository\org\springframework\boot\spring-boot-starter-logging\2.0.4.RELEASE\spring-boot-starter-logging-2.0.4.RELEASE.jar;C:\Users\12167\.m2\repository\ch\qos\logback\logback-classic\1.2.3\logback-classic-1.2.3.jar;C:\Users\12167\.m2\repository\ch\qos\logback\logback-core\1.2.3\logback-core-1.2.3.jar;C:\Users\12167\.m2\repository\org\apache\logging\log4j\log4j-to-slf4j\2.10.0\log4j-to-slf4j-2.10.0.jar;C:\Users\12167\.m2\repository\org\apache\logging\log4j\log4j-api\2.10.0\log4j-api-2.10.0.jar;C:\Users\12167\.m2\repository\org\slf4j\jul-to-slf4j\1.7.25\jul-to-slf4j-1.7.25.jar;C:\Users\12167\.m2\repository\javax\annotation\javax.annotation-api\1.3.2\javax.annotation-api-1.3.2.jar;C:\Users\12167\.m2\repository\org\yaml\snakeyaml\1.19\snakeyaml-1.19.jar;C:\Users\12167\.m2\repository\org\springframework\boot\spring-boot-starter-json\2.0.4.RELEASE\spring-boot-starter-json-2.0.4.RELEASE.jar;C:\Users\12167\.m2\repository\com\fasterxml\jackson\core\jackson-databind\2.9.6\jackson-databind-2.9.6.jar;C:\Users\12167\.m2\repository\com\fasterxml\jackson\core\jackson-annotations\2.9.0\jackson-annotations-2.9.0.jar;C:\Users\12167\.m2\repository\com\fasterxml\jackson\core\jackson-core\2.9.6\jackson-core-2.9.6.jar;C:\Users\12167\.m2\repository\com\fasterxml\jackson\datatype\jackson-datatype-jdk8\2.9.6\jackson-datatype-jdk8-2.9.6.jar;C:\Users\12167\.m2\repository\com\fasterxml\jackson\datatype\jackson-datatype-jsr310\2.9.6\jackson-datatype-jsr310-2.9.6.jar;C:\Users\12167\.m2\repository\com\fasterxml\jackson\module\jackson-module-parameter-names\2.9.6\jackson-module-parameter-names-2.9.6.jar;C:\Users\12167\.m2\repository\org\springframework\boot\spring-boot-starter-tomcat\2.0.4.RELEASE\spring-boot-starter-tomcat-2.0.4.RELEASE.jar;C:\Users\12167\.m2\repository\org\apache\tomcat\embed\tomcat-embed-core\8.5.32\tomcat-embed-core-8.5.32.jar;C:\Users\12167\.m2\repository\org\apache\tomcat\embed\tomcat-embed-el\8.5.32\tomcat-embed-el-8.5.32.jar;C:\Users\12167\.m2\repository\org\apache\tomcat\embed\tomcat-embed-websocket\8.5.32\tomcat-embed-websocket-8.5.32.jar;C:\Users\12167\.m2\repository\org\hibernate\validator\hibernate-validator\6.0.11.Final\hibernate-validator-6.0.11.Final.jar;C:\Users\12167\.m2\repository\javax\validation\validation-api\2.0.1.Final\validation-api-2.0.1.Final.jar;C:\Users\12167\.m2\repository\org\jboss\logging\jboss-logging\3.3.2.Final\jboss-logging-3.3.2.Final.jar;C:\Users\12167\.m2\repository\com\fasterxml\classmate\1.3.4\classmate-1.3.4.jar;C:\Users\12167\.m2\repository\org\springframework\spring-web\5.0.8.RELEASE\spring-web-5.0.8.RELEASE.jar;C:\Users\12167\.m2\repository\org\springframework\spring-beans\5.0.8.RELEASE\spring-beans-5.0.8.RELEASE.jar;C:\Users\12167\.m2\repository\org\springframework\spring-webmvc\5.0.8.RELEASE\spring-webmvc-5.0.8.RELEASE.jar;C:\Users\12167\.m2\repository\org\springframework\spring-aop\5.0.8.RELEASE\spring-aop-5.0.8.RELEASE.jar;C:\Users\12167\.m2\repository\org\springframework\spring-context\5.0.8.RELEASE\spring-context-5.0.8.RELEASE.jar;C:\Users\12167\.m2\repository\org\springframework\spring-expression\5.0.8.RELEASE\spring-expression-5.0.8.RELEASE.jar;C:\Users\12167\.m2\repository\org\slf4j\slf4j-api\1.7.25\slf4j-api-1.7.25.jar;C:\Users\12167\.m2\repository\org\springframework\spring-core\5.0.8.RELEASE\spring-core-5.0.8.RELEASE.jar;C:\Users\12167\.m2\repository\org\springframework\spring-jcl\5.0.8.RELEASE\spring-jcl-5.0.8.RELEASE.jar com.bolingcavalry.customizeaware.CustomizeawareApplication

.   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.0.4.RELEASE)

2018-08-14 06:07:11.512  INFO 18940 --- [           main] c.b.c.CustomizeawareApplication          : Starting CustomizeawareApplication on DESKTOP-82CCEBN with PID 18940 (D:\github\blog_demos\customizeaware\target\classes started by 12167 in D:\github\blog_demos\customizeaware)
2018-08-14 06:07:11.514  INFO 18940 --- [           main] c.b.c.CustomizeawareApplication          : No active profile set, falling back to default profiles: default
2018-08-14 06:07:11.546  INFO 18940 --- [           main] ConfigServletWebServerApplicationContext : Refreshing org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext@6ab7a896: startup date [Tue Aug 14 06:07:11 GMT+08:00 2018]; root of context hierarchy
2018-08-14 06:07:12.165  INFO 18940 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2018-08-14 06:07:12.177  INFO 18940 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2018-08-14 06:07:12.177  INFO 18940 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet Engine: Apache Tomcat/8.5.32
2018-08-14 06:07:12.180  INFO 18940 --- [ost-startStop-1] o.a.catalina.core.AprLifecycleListener   : The APR based Apache Tomcat Native library which allows optimal performance in production environments was not found on the java.library.path: [C:\jdk\bin;C:\WINDOWS\Sun\Java\bin;C:\WINDOWS\system32;C:\WINDOWS;C:\Program Files (x86)\Common Files\Oracle\Java\javapath;C:\Program Files (x86)\Intel\Intel(R) Management Engine Components\iCLS\;C:\Program Files\Intel\Intel(R) Management Engine Components\iCLS\;C:\windows\system32;C:\windows;C:\windows\System32\Wbem;C:\windows\System32\WindowsPowerShell\v1.0\;C:\Program Files (x86)\Intel\Intel(R) Management Engine Components\DAL;C:\Program Files\Intel\Intel(R) Management Engine Components\DAL;C:\Program Files (x86)\Intel\Intel(R) Management Engine Components\IPT;C:\Program Files\Intel\Intel(R) Management Engine Components\IPT;C:\Program Files (x86)\NVIDIA Corporation\PhysX\Common;C:\jdk\bin;C:\software\Git\cmd;C:\software\apache-maven-3.5.0\bin;;%SystemRoot%\system32;%SystemRoot%;%SystemRoot%\System32\Wbem;%SYSTEMROOT%\System32\WindowsPowerShell\v1.0\;%SYSTEMROOT%\System32\OpenSSH\;C:\Users\12167\AppData\Local\Microsoft\WindowsApps;;.]
2018-08-14 06:07:12.244  INFO 18940 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2018-08-14 06:07:12.244  INFO 18940 --- [ost-startStop-1] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 700 ms
2018-08-14 06:07:12.281  INFO 18940 --- [ost-startStop-1] o.s.b.w.servlet.ServletRegistrationBean  : Servlet dispatcherServlet mapped to [/]
2018-08-14 06:07:12.284  INFO 18940 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'characterEncodingFilter' to: [/*]
2018-08-14 06:07:12.284  INFO 18940 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'hiddenHttpMethodFilter' to: [/*]
2018-08-14 06:07:12.284  INFO 18940 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'httpPutFormContentFilter' to: [/*]
2018-08-14 06:07:12.285  INFO 18940 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'requestContextFilter' to: [/*]
2018-08-14 06:07:12.305  INFO 18940 --- [           main] c.b.customizeaware.util.Utils            : applicationContext is set to org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext@6ab7a896: startup date [Tue Aug 14 06:07:11 GMT+08:00 2018]; root of context hierarchy
************************************************************
java.lang.Thread.getStackTrace() 1,559 > org.springframework.boot.autoconfigure.web.servlet.error.BasicErrorController.error(javax.servlet.http.HttpServletRequest)
2018-08-14 06:07:12.511  INFO 18940 --- [           main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/error],produces=[text/html]}" onto public org.springframework.web.servlet.ModelAndView org.springframework.boot.autoconfigure.web.servlet.error.BasicErrorController.errorHtml(javax.servlet.http.HttpServletRequest,javax.servlet.http.HttpServletResponse)
2018-08-14 06:07:12.524  INFO 18940 --- [           main] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/webjars/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2018-08-14 06:07:12.524  INFO 18940 --- [           main] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2018-08-14 06:07:12.602  INFO 18940 --- [           main] o.s.j.e.a.AnnotationMBeanExporter        : Registering beans for JMX exposure on startup
2018-08-14 06:07:12.622  INFO 18940 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2018-08-14 06:07:12.625  INFO 18940 --- [           main] c.b.c.CustomizeawareApplication          : Started CustomizeawareApplication in 1.311 seconds (JVM running for 1.932)
```

- 瀏覽器訪問web服務，地址：http://localhost:8080/hello，如下圖，兩個實現了Aware介面的bean的被設定的資訊都列印出來了，都是來自spring環境的內容：
![image.png](https://bbs-img.huaweicloud.com/blogs/img/20220612/1655046469484248838.png)

- 驗證結束，自定義的Aware介面實現類如果宣告為bean，在初始化的時候就會被spring容器按照介面型別找出來，通過呼叫介面方法的方式將特定的物件例項傳遞給bean；

### 實戰原始碼下載
- 本章實戰的原始碼可以在github下載，地址和連結資訊如下表所示：

| 名稱      |   連結 |   備註|
| :-------- | :----| :----|
| 專案主頁| https://github.com/zq2599/blog_demos | 該專案在GitHub上的主頁 |
| git倉庫地址(https)| https://github.com/zq2599/blog_demos.git | 該專案原始碼的倉庫地址，https協議 |
| git倉庫地址(ssh)| git@github.com:zq2599/blog_demos.git | 該專案原始碼的倉庫地址，ssh協議 |

- 這個git專案中有多個資料夾，本章原始碼在資料夾customizeaware/下，如下圖紅框所示：
![image.png](https://bbs-img.huaweicloud.com/blogs/img/20220612/1655046490620299573.png)

- 至此，spring的Aware介面實戰就結束了，由於篇幅所限，本章只選擇了BeanNameAware和ApplicationContextAware這兩個介面來實戰，您可以結合spring原始碼去分析其他Aware介面的用處，再在demo用去驗證它們；

### 歡迎關注ITpub：程式設計師欣宸
> [學習路上，你不孤單，欣宸原創一路相伴...](http://blog.itpub.net/70017844/)

spring4.1.8擴充套件實戰之二：Aware介面揭祕

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