SpringBoot应用使用自定义的ApplicationContext实现类

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：

代码语言：javascript复制

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：

代码语言：javascript复制

@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：

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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： 1. 基于maven创建一个SpringBoot的web应用，pom.xml如下：

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<?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>

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

代码语言：javascript复制

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");
    }
}

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

代码语言：javascript复制

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);
    }
}

4. 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：

代码语言：javascript复制

2018-08-11 17:21:18.833  INFO 5132 --- [           main] c.CustomizeapplicationcontextApplication : Starting CustomizeapplicationcontextApplication on zhaoqinwin10 with PID 5132 (D:temp2018089customizeapplicationcontexttargetclasses started by 12167 in D:temp2018089customizeapplicationcontext)
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:jdkbin;C:WINDOWSSunJavabin;C:WINDOWSsystem32;C:WINDOWS;C:ProgramDataOracleJavajavapath;C:Program Files (x86)InteliCLS Client;C:Program FilesInteliCLS Client;C:Windowssystem32;C:Windows;C:WindowsSystem32Wbem;C:WindowsSystem32WindowsPowerShellv1.0;C:Program Files (x86)IntelIntel(R) Management Engine ComponentsDAL;C:Program FilesIntelIntel(R) Management Engine ComponentsDAL;C:Program Files (x86)IntelIntel(R) Management Engine ComponentsIPT;C:Program FilesIntelIntel(R) Management Engine ComponentsIPT;C:Program Files (x86)NVIDIA CorporationPhysXCommon;C:Program FilesIntelWiFibin;C:Program FilesCommon FilesIntelWirelessCommon;C:softwareapache-maven-3.3.3bin;C:softwareGitbin;E:workdubbozookeeper-3.3.6/bin;E:workdubbozookeeper-3.3.6/conf;D:softgradle-1.1bin;C:jdkbin;C:softwaresvnbin;D:softwareAndroidSdkplatform-tools;D:softwarecalibre;D:softwaregradle-2.14.1bin;C:WINDOWSsystem32;C:WINDOWS;C:WINDOWSSystem32Wbem;C:WINDOWSSystem32WindowsPowerShellv1.0;C:Program FilesGitcmd;C:Users12167AppDataLocalMicrosoftWindowsApps;C:Users12167AppDataLocalProgramsFiddler;%USERPROFILE%AppDataLocalMicrosoftWindowsApps;.]
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：

名称	链接	备注
项目主页	https://github.com/zq2599/blog_demos	该项目在GitHub上的主页
git仓库地址(https)	https://github.com/zq2599/blog_demos.git	该项目源码的仓库地址，https协议
git仓库地址(ssh)	git@github.com:zq2599/blog_demos.git	该项目源码的仓库地址，ssh协议

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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