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:
```java
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:
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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