关键词：
欢迎访问我的GitHub
关于扩展
-
在之前学习spring环境初始化源码的过程中，见到有些地方能通过子类来实现自定义扩展，从本章开始，我们来逐个实践这些扩展，除了加深对spring的理解，有的扩展也能解决一些通用的问题；
- 文中涉及的spring版本号为4.1.8.RELEASE；
相关文章链接
- 为了方便开发和测试，我们的扩展实战是在SpringBoot框架下进行的，在SpringBoot自定义spring扩展的方式请参考《SpringBoot应用使用自定义的ApplicationContext实现类》
扩展功能介绍
- 今天实战的内容，是通过spring容器来确保环境变量MYSQL_HOST一定存在，如果不存在应用就会启动失败；
分析spring源码
-
通过分析spring源码来确定如何扩展；
- 在spring环境初始化的时候，AbstractApplicationContext的prepareRefresh方法会被调用，源码如下
protected void prepareRefresh()
this.startupDate = System.currentTimeMillis();
this.closed.set(false);
this.active.set(true);
if (logger.isInfoEnabled())
logger.info("Refreshing " + this);
// Initialize any placeholder property sources in the context environment
initPropertySources();
// Validate that all properties marked as required are resolvable
// see ConfigurablePropertyResolver#setRequiredProperties
getEnvironment().validateRequiredProperties();
-
initPropertySources是个空方法，留给子类扩展；
- 来看看getEnvironment().validateRequiredProperties()的源码，对应的是AbstractPropertyResolver类的validateRequiredProperties方法：
public void validateRequiredProperties()
MissingRequiredPropertiesException ex = new MissingRequiredPropertiesException();
for (String key : this.requiredProperties)
if (this.getProperty(key) == null)
ex.addMissingRequiredProperty(key);
if (!ex.getMissingRequiredProperties().isEmpty())
throw ex;
- 可见spring容器初始化的时候，会从集合requiredProperties中取出所有key，然后获取这些key的环境变量（包括系统环境变量和进程环境变量），如果有一个key对应的环境变量为空，就会抛出异常，导致spring容器初始化失败；
扩展功能分析
-
看了AbstractPropertyResolver类的validateRequiredProperties方法源码后，可以确定该方法能强制要求一些环境变量必须存在，否则停止spring启动，我们只要把我们认为必要的环境变量的key存入集合requiredProperties中即可，达到此目标需要解决下面两个问题：
-
如何将环境变量的key存入集合requiredProperties？
调用AbstractPropertyResolver类的setRequiredProperties方法，注意该方法是向集合requiredProperties中添加数据，并不会将已有数据清除； - 在什么时候执行AbstractPropertyResolver类的setRequiredProperties方法设置key？
创建一个AbstractApplicationContext的子类，重写initPropertySources方法，在此方法中执行AbstractPropertyResolver类的setRequiredProperties；
开始实战
- 用maven创建一个SpringBoot工程，工程名为customizepropertyverify，pom.xml内容如下：
<?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>customizepropertyverify</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>jar</packaging>
<name>customizepropertyverify</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>- 创建一个类CustomApplicationContext，继承自AnnotationConfigServletWebServerApplicationContext，重写initPropertySources方法，将"MYSQL_HOST"作为启动时必须要存在的环境变量：
package com.bolingcavalry.customizepropertyverify.context;
import org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext;
/**
* @Description : AnnotationConfigServletWebServerApplicationContext，重写了initPropertySources方法，
* 要求spring启动的时候环境变量MYSQL_HOST必须存在
* @Author : zq2599@gmail.com
* @Date : 2018-08-10 21:40
*/
public class CustomApplicationContext extends AnnotationConfigServletWebServerApplicationContext
@Override
protected void initPropertySources()
super.initPropertySources();
//把"MYSQL_HOST"作为启动的时候必须验证的环境变量
getEnvironment().setRequiredProperties("MYSQL_HOST");
- 创建应用启动类CustomizepropertyverifyApplication，指定ApplicationContext的class为CustomApplicationContext：
package com.bolingcavalry.customizepropertyverify;
import com.bolingcavalry.customizepropertyverify.context.CustomApplicationContext;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
@SpringBootApplication
public class CustomizepropertyverifyApplication
public static void main(String[] args)
SpringApplication springApplication = new SpringApplication(CustomizepropertyverifyApplication.class);
springApplication.setApplicationContextClass(CustomApplicationContext.class);
springApplication.run(args);
- 打包，在pom.xml文件所在目录下执行命令mvn clean package -U -DskipTests，命令执行完成后，即可在target目录找到文件customizepropertyverify-0.0.1-SNAPSHOT.jar；
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customizepropertyverify下，如下图红框所示：
验证
-
接下来我们来验证自定义的ApplicationContext是否实现了环境变量检查的功能；
- "MYSQL_HOST"这个环境变量是不存在的，所以我们先验证环境变量校验不通过导致spring容器启动失败的情况，在target目录执行命令java -jar customizepropertyverify-0.0.1-SNAPSHOT.jar，会发现应用启动失败，日志中显示由于找不到环境变量"MYSQL_HOST"，在AbstractPropertyResolver.validateRequiredProperties位置抛出异常，如下所示：
D:\github\blog_demos\customizepropertyverify\target>java -jar customizepropertyverify-0.0.1-SNAPSHOT.jar
. ____ _ __ _ _
/\\ / ____ __ _ _(_)_ __ __ _ \ \ \ \
( ( )\___ | _ | _| | _ \/ _` | \ \ \ \
\\/ ___)| |_)| | | | | || (_| | ) ) ) )
|____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
:: Spring Boot :: (v2.0.4.RELEASE)
2018-08-12 14:10:16.165 INFO 19624 --- [ main] c.b.c.CustomizepropertyverifyApplication : Starting CustomizepropertyverifyApplication v0.0.1-SNAPSHOT on DESKTOP-82CCEBN with PID 19624 (D:\github\blog_demos\customizepropertyverify\target\customizepropertyverify-0.0.1-SNAPSHOT.jar started by 12167 in D:\github\blog_demos\customizepropertyverify\target)
2018-08-12 14:10:16.168 INFO 19624 --- [ main] c.b.c.CustomizepropertyverifyApplication : No active profile set, falling back to default profiles: default
2018-08-12 14:10:16.218 INFO 19624 --- [ main] c.b.c.context.CustomApplicationContext : Refreshing com.bolingcavalry.customizepropertyverify.context.CustomApplicationContext@6d1e7682: startup date [Sun Aug 12 14:10:16 GMT+08:00 2018]; root of context hierarchy
2018-08-12 14:10:16.221 WARN 19624 --- [ main] o.s.boot.SpringApplication : Error handling failed (ApplicationEventMulticaster not initialized - call refresh before multicasting events via the context: com.bolingcavalry.customizepropertyverify.context.CustomApplicationContext@6d1e7682: startup date [Sun Aug 12 14:10:16 GMT+08:00 2018]; root of context hierarchy)
2018-08-12 14:10:16.226 ERROR 19624 --- [ main] o.s.boot.SpringApplication : Application run failed
org.springframework.core.env.MissingRequiredPropertiesException: The following properties were declared as required but could not be resolved: [MYSQL_HOST]
at org.springframework.core.env.AbstractPropertyResolver.validateRequiredProperties(AbstractPropertyResolver.java:146) ~[spring-core-5.0.8.RELEASE.jar!/:5.0.8.RELEASE]
at org.springframework.core.env.AbstractEnvironment.validateRequiredProperties(AbstractEnvironment.java:519) ~[spring-core-5.0.8.RELEASE.jar!/:5.0.8.RELEASE]
at org.springframework.context.support.AbstractApplicationContext.prepareRefresh(AbstractApplicationContext.java:598) ~[spring-context-5.0.8.RELEASE.jar!/:5.0.8.RELEASE]
at org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext.prepareRefresh(AnnotationConfigServletWebServerApplicationContext.java:200) ~[spring-boot-2.0.4.RELEASE.jar!/:2.0.4.RELEASE]
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:519) ~[spring-context-5.0.8.RELEASE.jar!/:5.0.8.RELEASE]
at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:140) ~[spring-boot-2.0.4.RELEASE.jar!/:2.0.4.RELEASE]
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:762) ~[spring-boot-2.0.4.RELEASE.jar!/:2.0.4.RELEASE]
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:398) ~[spring-boot-2.0.4.RELEASE.jar!/:2.0.4.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:330) ~[spring-boot-2.0.4.RELEASE.jar!/:2.0.4.RELEASE]
at com.bolingcavalry.customizepropertyverify.CustomizepropertyverifyApplication.main(CustomizepropertyverifyApplication.java:13) [classes!/:0.0.1-SNAPSHOT]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_181]
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) ~[na:1.8.0_181]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[na:1.8.0_181]
at java.lang.reflect.Method.invoke(Unknown Source) ~[na:1.8.0_181]
at org.springframework.boot.loader.MainMethodRunner.run(MainMethodRunner.java:48) [customizepropertyverify-0.0.1-SNAPSHOT.jar:0.0.1-SNAPSHOT]
at org.springframework.boot.loader.Launcher.launch(Launcher.java:87) [customizepropertyverify-0.0.1-SNAPSHOT.jar:0.0.1-SNAPSHOT]
at org.springframework.boot.loader.Launcher.launch(Launcher.java:50) [customizepropertyverify-0.0.1-SNAPSHOT.jar:0.0.1-SNAPSHOT]
at org.springframework.boot.loader.JarLauncher.main(JarLauncher.java:51) [customizepropertyverify-0.0.1-SNAPSHOT.jar:0.0.1-SNAPSHOT]
...-
接下来验证环境变量"MYSQL_HOST"存在的时候应用是否能初始化成功，执行命令java -DMYSQL_HOST="192.168.0.1" -jar customizepropertyverify-0.0.1-SNAPSHOT.jar，这个命令可以将"MYSQL_HOST"设置到进程环境变量中，这次顺利通过校验，应用启动成功：
D:\github\blog_demos\customizepropertyverify\target>java -DMYSQL_HOST="192.168.0.1" -jar customizepropertyverify-0.0.1-SNAPSHOT.jar . ____ _ __ _ _ /\\ / ____ __ _ _(_)_ __ __ _ \ \ \ \ ( ( )\___ | _ | _| | _ \/ _` | \ \ \ \ \\/ ___)| |_)| | | | | || (_| | ) ) ) ) |____| .__|_| |_|_| |_\__, | / / / / =========|_|==============|___/=/_/_/_/ :: Spring Boot :: (v2.0.4.RELEASE)
2018-08-12 14:15:31.811 INFO 15328 --- [ main] c.b.c.CustomizepropertyverifyApplication : Starting CustomizepropertyverifyApplication v0.0.1-SNAPSHOT on DESKTOP-82CCEBN with PID 15328 (D:\github\blog_demos\customizepropertyverify\target\customizepropertyverify-0.0.1-SNAPSHOT.jar started by 12167 in D:\github\blog_demos\customizepropertyverify\target)
2018-08-12 14:15:31.813 INFO 15328 --- [ main] c.b.c.CustomizepropertyverifyApplication : No active profile set, falling back to default profiles: default
2018-08-12 14:15:31.850 INFO 15328 --- [ main] c.b.c.context.CustomApplicationContext : Refreshing com.bolingcavalry.customizepropertyverify.context.CustomApplicationContext@3339ad8e: startup date [Sun Aug 12 14:15:31 GMT+08:00 2018]; root of context hierarchy
2018-08-12 14:15:32.776 INFO 15328 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8080 (http)
2018-08-12 14:15:32.796 INFO 15328 --- [ main] o.apache.catalina.core.StandardService : Starting service [Tomcat]
2018-08-12 14:15:32.796 INFO 15328 --- [ main] org.apache.catalina.core.StandardEngine : Starting Servlet Engine: Apache Tomcat/8.5.32
2018-08-12 14:15:32.805 INFO 15328 --- [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:\Program Files (x86)\Common Files\Oracle\Java\javapath;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;;.]
2018-08-12 14:15:32.867 INFO 15328 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext
2018-08-12 14:15:32.868 INFO 15328 --- [ost-startStop-1] o.s.web.context.ContextLoader : Root WebApplicationContext: initialization completed in 1021 ms
2018-08-12 14:15:32.919 INFO 15328 --- [ost-startStop-1] o.s.b.w.servlet.ServletRegistrationBean : Servlet dispatcherServlet mapped to [/]
2018-08-12 14:15:32.923 INFO 15328 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: characterEncodingFilter to: [/]
2018-08-12 14:15:32.923 INFO 15328 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: hiddenHttpMethodFilter to: [/]
2018-08-12 14:15:32.926 INFO 15328 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: httpPutFormContentFilter to: [/]
2018-08-12 14:15:32.927 INFO 15328 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: requestContextFilter to: [/]
2018-08-12 14:15:33.006 INFO 15328 --- [ main] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path [//favicon.ico] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2018-08-12 14:15:33.136 INFO 15328 --- [ main] s.w.s.m.m.a.RequestMappingHandlerAdapter : Looking for @ControllerAdvice: com.bolingcavalry.customizepropertyverify.context.CustomApplicationContext@3339ad8e: startup date [Sun Aug 12 14:15:31 GMT+08:00 2018]; root of context hierarchy
2018-08-12 14:15:33.190 INFO 15328 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "[/hello]" onto public java.lang.String com.bolingcavalry.customizepropertyverify.controller.HelloWorldController.hello()
2018-08-12 14:15:33.194 INFO 15328 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "[/error]" onto public org.springframework.http.ResponseEntity<java.util.Map<java.lang.String, java.lang.Object>> org.springframework.boot.autoconfigure.web.servlet.error.BasicErrorController.error(javax.servlet.http.HttpServletRequest)
2018-08-12 14:15:33.195 INFO 15328 --- [ 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)
2018-08-12 14:15:33.226 INFO 15328 --- [ main] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path [/webjars/] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2018-08-12 14:15:33.227 INFO 15328 --- [ main] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path [/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2018-08-12 14:15:33.314 INFO 15328 --- [ main] o.s.j.e.a.AnnotationMBeanExporter : Registering beans for JMX exposure on startup
2018-08-12 14:15:33.343 INFO 15328 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path
2018-08-12 14:15:33.346 INFO 15328 --- [ main] c.b.c.CustomizepropertyverifyApplication : Started CustomizepropertyverifyApplication in 1.761 seconds (JVM running for 2.113)
2018-08-12 14:15:39.626 INFO 15328 --- [nio-8080-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring FrameworkServlet dispatcherServlet
2018-08-12 14:15:39.626 INFO 15328 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet : FrameworkServlet dispatcherServlet: initialization started
2018-08-12 14:15:39.645 INFO 15328 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet : FrameworkServlet dispatcherServlet: initialization completed in 16 ms
- 验证完成，我们可以通过自定义子类来强制要求指定的环境变量必须存在；
- 至此，我们spring扩展实战的第一章就结束了，接下来的章节我们会进行更多的实战，来了解spring强大的扩展机制；
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