SpringBoot应用使用自定义的ApplicationContext实现类

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为什么要自定义application context

• 在学习spring容器初始化的过程中，发现spring容器预留了一些扩展点，我们可以写子类来做功能扩展，例如AbstractApplicationContext类的initPropertySources、postProcessBeanFactory、onRefresh等方法都是空方法，留给子类来扩展用；

在传统spring框架下的扩展方式

• 传统的spring框架下使用哪个ApplicationContext实现类，是自己写代码来指定的，下面是基于spring框架的应用的启动代码：

public static void main(String[] args) {
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("classpath:applicationContext.xml");
        Simple bean = context.getBean(Simple.class);
        bean.execute();
        context.close();
    }

• 如果我们要用自定的ApplicationContext实现类，只要将上面的ClassPathXmlApplicationContext改成我们做的类即可；

探寻SpringBoot框架下的扩展方式

• 先看一段代码，以下是一个SpringBoot应用启动的代码：

@SpringBootApplication
public class CustomizeapplicationcontextApplication {

	public static void main(String[] args) {
		SpringApplication springApplication = new SpringApplication(CustomizeapplicationcontextApplication.class);
		springApplication.run(args);
	}
}

• 从上述代码可知，我们需要去查看SpingApplication的run方法源码，那里应该有ApplicationContext初始化相关的信息，在SpingApplication的run方法中，果然找到了有用信息，如下图红框所示，是createApplicationContext方法创建了ApplicationContext实现类：

• 去看看createApplicationContext方法，如下图：

• 上图中有两点需要注意：

1. 红框中显示，ApplicationContext实现类来自成员变量applicationContextClass，只要我们能设置成员变量applicationContextClass，就达到了目的：在应用中使用自定义的ApplicationContext实现类；
2. 绿框中显示，如果没有设置成员变量applicationContextClass，就把AnnotationConfigServletWebServerApplicationContext作为ApplicationContext实现类，用在spring环境中，所以，我们在自定义ApplicationContext实现类时，用AnnotationConfigServletWebServerApplicationContext作为父类最合适（除了我们自己扩展的东西，其他部分都和默认的保持一致）；

如何设置自定义的ApplicationContext实现类

• 从createApplicationContext方法可以看出，设置了成员变量applicationContextClass，就达到了使用自定义ApplicationContext实现类的目的，那么如何设置成员变量applicationContextClass呢？就在下面这个setApplicationContextClass方法：

public void setApplicationContextClass(
			Class<? extends ConfigurableApplicationContext> applicationContextClass) {
		this.applicationContextClass = applicationContextClass;
		if (!isWebApplicationContext(applicationContextClass)) {
			this.webApplicationType = WebApplicationType.NONE;
		}
	}

• 我们只要在启动应用的时候，在调用springApplication的run方法之前先调用setApplicationContextClass方法就能指定ApplicationContext实现类了；

• 分析到此，您是否和我一样有疑虑：setApplicationContextClass方法会不会被在其他地方被调用，导致我们的设置无效呢？通过以下两种方法来检查：

1. 在IntelliJ IDEA中，通过"Find Usages"的方式查找该方法被调用的地方，结果只发现了一处SpringBootServletInitializer类的onStartup方法，这是war包形式的应用在配置Initializer的时候才会用到，main方法启动的方式中不会用到；
2. 在setApplicationContextClass方法中打断点，debug启动应用，确认不会走进来；

实战使用自定义的ApplicationContext实现类

• 理论分析完毕，可以实战验证了：
• 基于maven创建一个SpringBoot的web应用，pom.xml如下：

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>

	<groupId>com.bolingcavalry</groupId>
	<artifactId>customizeapplicationcontext</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<packaging>jar</packaging>

	<name>customizeapplicationcontext</name>
	<description>Demo project for Spring Boot</description>

	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.0.4.RELEASE</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>

	<properties>
		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
		<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
		<java.version>1.8</java.version>
	</properties>

	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>

		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
		</dependency>
	</dependencies>

	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>
</project>

• 创建类CustomizeApplicationContext，继承自AnnotationConfigServletWebServerApplicationContext，重写了父类的几个方法，如下：

package com.bolingcavalry.customizeapplicationcontext;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext;

/**
 * @Description : 自定义的ApplicationContext实现类
 * @Author : zq2599@gmail.com
 * @Date : 2018-08-11 17:12
 */
public class CustomizeApplicationContext extends AnnotationConfigServletWebServerApplicationContext {

    Log logger = LogFactory.getLog(CustomizeApplicationContext.class);

    @Override
    protected void initPropertySources() {
        super.initPropertySources();
        logger.info("execute override initPropertySources");
    }

    @Override
    protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
        super.postProcessBeanFactory(beanFactory);
        logger.info("execute override postProcessBeanFactory");
    }

    @Override
    protected void onRefresh() {
        super.onRefresh();
        logger.info("execute override onRefresh");
    }
}

• 启动类CustomizeapplicationcontextApplication的main方法中，调用setApplicationContextClass方法，将ApplicationContext实现类设置为CustomizeApplicationContext：

package com.bolingcavalry.customizeapplicationcontext;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class CustomizeapplicationcontextApplication {

	public static void main(String[] args) {
		SpringApplication springApplication = new SpringApplication(CustomizeapplicationcontextApplication.class);
		springApplication.setApplicationContextClass(CustomizeApplicationContext.class);
		springApplication.run(args);
	}
}

• 启动应用，查看日志如下，CustomizeApplicationContext中重写的方法都被执行了，并且initPropertySources被执行了两次，那是因为除了AbstractApplicationContext类中有调用，在ServletWebServerApplicationContext类的onRefresh中会执行createWebServer方法，而createWebServer方法中也会调用一次initPropertySources方法：

2018-08-11 17:21:18.833  INFO 5132 --- [           main] c.CustomizeapplicationcontextApplication : Starting CustomizeapplicationcontextApplication on zhaoqinwin10 with PID 5132 (D:\temp\201808\09\customizeapplicationcontext\target\classes started by 12167 in D:\temp\201808\09\customizeapplicationcontext)
2018-08-11 17:21:18.840  INFO 5132 --- [           main] c.CustomizeapplicationcontextApplication : No active profile set, falling back to default profiles: default
2018-08-11 17:21:18.957  INFO 5132 --- [           main] c.b.c.CustomizeApplicationContext        : Refreshing com.bolingcavalry.customizeapplicationcontext.CustomizeApplicationContext@5906ebcb: startup date [Sat Aug 11 17:21:18 CST 2018]; root of context hierarchy
2018-08-11 17:21:18.958  INFO 5132 --- [           main] c.b.c.CustomizeApplicationContext        : execute override initPropertySources
2018-08-11 17:21:18.967  INFO 5132 --- [           main] c.b.c.CustomizeApplicationContext        : execute override postProcessBeanFactory
2018-08-11 17:21:20.085  INFO 5132 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2018-08-11 17:21:20.102  INFO 5132 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2018-08-11 17:21:20.103  INFO 5132 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet Engine: Apache Tomcat/8.5.32
2018-08-11 17:21:20.106  INFO 5132 --- [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:\ProgramData\Oracle\Java\javapath;C:\Program Files (x86)\Intel\iCLS Client\;C:\Program Files\Intel\iCLS Client\;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:\Program Files\Intel\WiFi\bin\;C:\Program Files\Common Files\Intel\WirelessCommon\;C:\software\apache-maven-3.3.3\bin\;C:\software\Git\bin;E:\work\dubbo\zookeeper-3.3.6/bin;E:\work\dubbo\zookeeper-3.3.6/conf;D:\soft\gradle-1.1\bin;C:\jdk\bin;C:\software\svn\bin;D:\software\AndroidSdk\platform-tools;D:\software\calibre\;D:\software\gradle-2.14.1\bin;C:\WINDOWS\system32;C:\WINDOWS;C:\WINDOWS\System32\Wbem;C:\WINDOWS\System32\WindowsPowerShell\v1.0\;C:\Program Files\Git\cmd;C:\Users\12167\AppData\Local\Microsoft\WindowsApps;C:\Users\12167\AppData\Local\Programs\Fiddler;%USERPROFILE%\AppData\Local\Microsoft\WindowsApps;.]
2018-08-11 17:21:20.226  INFO 5132 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2018-08-11 17:21:20.227  INFO 5132 --- [ost-startStop-1] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 1273 ms
2018-08-11 17:21:20.305  INFO 5132 --- [ost-startStop-1] o.s.b.w.servlet.ServletRegistrationBean  : Servlet dispatcherServlet mapped to [/]
2018-08-11 17:21:20.310  INFO 5132 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'characterEncodingFilter' to: [/*]
2018-08-11 17:21:20.310  INFO 5132 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'hiddenHttpMethodFilter' to: [/*]
2018-08-11 17:21:20.310  INFO 5132 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'httpPutFormContentFilter' to: [/*]
2018-08-11 17:21:20.310  INFO 5132 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'requestContextFilter' to: [/*]
2018-08-11 17:21:20.330  INFO 5132 --- [           main] c.b.c.CustomizeApplicationContext        : execute override initPropertySources
2018-08-11 17:21:20.330  INFO 5132 --- [           main] c.b.c.CustomizeApplicationContext        : execute override onRefresh

实战源码下载

• 本章实战的源码可以在github下载，地址和链接信息如下表所示：

• 这个git项目中有多个文件夹，本章源码在文件夹customizeapplicationcontext下，如下图红框所示：
  

• 至此，我们通过查看SpringApplication的源码，搞清楚了spring环境的ApplicationContext实现类在SpringBoot框架下如何指定，也做了一次简单的自定义实战，今后在研究和学习spring过程中，如果需要扩展spring容器就能在SpringBoot环境下进行了，相比传统的war包部署、以及指定多个jar包的classpath等操作，springboot应用的单个jar包更方便省事。

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