spring boot 2.0 源码分析(一)

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在学习spring boot 2.0源码之前,我们先利用spring initializr快速地创建一个基本的简单的示例:

1.先从创建示例中的main函数开始读起:

    package com.example;

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

    /** * spring boot 2.0 源码分析 * author lizongshen * date 2018/06/02 */ 
    @SpringBootApplication
    public class DemoApplication {

        public static void main(String[] args) {
            SpringApplication.run(DemoApplication.class, args);
        }
    }

2.在这里我们可以看到,spring boot是通过SpringApplication.run这个函数来进行启动的,其中args可以传递启动时需要的个性化参数。跳转到源码中继续一探究竟:

        /** * Static helper that can be used to run a {@link SpringApplication} from the * specified source using default settings. * @param primarySource the primary source to load * @param args the application arguments (usually passed from a Java main method) * @return the running {@link ApplicationContext} */
        public static ConfigurableApplicationContext run(Class<?> primarySource,
                String... args) {
            return run(new Class<?>[] { primarySource }, args);
        }

3.在这里我们看到,其把primarySource这个参数包装成数组,跳转到了另外一个同样的方法中。

小发现:SpringApplication.run()函数是允许同时启动多个Application的。

接着往下读

        /** * Static helper that can be used to run a {@link SpringApplication} from the * specified sources using default settings and user supplied arguments. * @param primarySources the primary sources to load * @param args the application arguments (usually passed from a Java main method) * @return the running {@link ApplicationContext} */
        public static ConfigurableApplicationContext run(Class<?>[] primarySources,
                String[] args) {
            return new SpringApplication(primarySources).run(args);
        }

4.在这段代码中,我们可以看到spring boot把我们所使用的静态方法,创建出了一个SpringApplication的实例,并启动了实例中的run方法。

小知识:根据这个发现,我们也可以在main函数中,自己创建SpringApplication的实例,然后调用实例方法run。

我们来看一下SpringApplication的构造函数期间都干了些什么事:

        /** * Create a new {@link SpringApplication} instance. The application context will load * beans from the specified primary sources (see {@link SpringApplication class-level} * documentation for details. The instance can be customized before calling * {@link #run(String...)}. * @param primarySources the primary bean sources * @see #run(Class, String[]) * @see #SpringApplication(ResourceLoader, Class...) * @see #setSources(Set) */
        public SpringApplication(Class<?>... primarySources) {
            this(null, primarySources);
        }

        /** * Create a new {@link SpringApplication} instance. The application context will load * beans from the specified primary sources (see {@link SpringApplication class-level} * documentation for details. The instance can be customized before calling * {@link #run(String...)}. * @param resourceLoader the resource loader to use * @param primarySources the primary bean sources * @see #run(Class, String[]) * @see #setSources(Set) */
        @SuppressWarnings({ "unchecked", "rawtypes" })
        public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
            this.resourceLoader = resourceLoader;
            Assert.notNull(primarySources, "PrimarySources must not be null");
            this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
            this.webApplicationType = deduceWebApplicationType();
            setInitializers((Collection) getSpringFactoriesInstances(
                    ApplicationContextInitializer.class));
            setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
            this.mainApplicationClass = deduceMainApplicationClass();
        }

在这里主要是初始化了SpringApplication的私有属性,在构造的过程中,调用了另外一个构造函数,并传递了ResourceLoader的参数。

小知识:通过ResourceLoader这个参数,我们看到如果自定义SpringApplication在初始化过程中,是可以通过ResourceLoader来引入自定义资源的。

接着往下看,来看看run函数的真面目

        /** * Run the Spring application, creating and refreshing a new * {@link ApplicationContext}. * @param args the application arguments (usually passed from a Java main method) * @return a running {@link ApplicationContext} */
        public ConfigurableApplicationContext run(String... args) {
            StopWatch stopWatch = new StopWatch();
            stopWatch.start();
            ConfigurableApplicationContext context = null;
            Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
            configureHeadlessProperty();
            SpringApplicationRunListeners listeners = getRunListeners(args);
            listeners.starting();
            try {
                ApplicationArguments applicationArguments = new DefaultApplicationArguments(
                        args);
                ConfigurableEnvironment environment = prepareEnvironment(listeners,
                        applicationArguments);
                configureIgnoreBeanInfo(environment);
                Banner printedBanner = printBanner(environment);
                context = createApplicationContext();
                exceptionReporters = getSpringFactoriesInstances(
                        SpringBootExceptionReporter.class,
                        new Class[] { ConfigurableApplicationContext.class }, context);
                prepareContext(context, environment, listeners, applicationArguments,
                        printedBanner);
                refreshContext(context);
                afterRefresh(context, applicationArguments);
                stopWatch.stop();
                if (this.logStartupInfo) {
                    new StartupInfoLogger(this.mainApplicationClass)
                            .logStarted(getApplicationLog(), stopWatch);
                }
                listeners.started(context);
                callRunners(context, applicationArguments);
            }
            catch (Throwable ex) {
                handleRunFailure(context, ex, exceptionReporters, listeners);
                throw new IllegalStateException(ex);
            }

            try {
                listeners.running(context);
            }
            catch (Throwable ex) {
                handleRunFailure(context, ex, exceptionReporters, null);
                throw new IllegalStateException(ex);
            }
            return context;
        }

这段代码很长,我们先来一点一点地分析。
1.通过configureHeadlessProperty();这行代码,配置属性:

        private void configureHeadlessProperty() {
            System.setProperty(SYSTEM_PROPERTY_JAVA_AWT_HEADLESS, System.getProperty(
                    SYSTEM_PROPERTY_JAVA_AWT_HEADLESS, Boolean.toString(this.headless)));
        }

2.通过SpringApplicationRunListeners listeners = getRunListeners(args);这行代码获取了监听器:

        private SpringApplicationRunListeners getRunListeners(String[] args) {
            Class<?>[] types = new Class<?>[] { SpringApplication.class, String[].class };
            return new SpringApplicationRunListeners(logger, getSpringFactoriesInstances(
                    SpringApplicationRunListener.class, types, this, args));
        }

3.通过listeners.starting();这行代码启动监听器:

        public void starting() {
            Iterator var1 = this.listeners.iterator();

            while(var1.hasNext()) {
                SpringApplicationRunListener listener = (SpringApplicationRunListener)var1.next();
                listener.starting();
            }

        }

4.通过context = this.createApplicationContext();创建了容器

        /** * Strategy method used to create the {@link ApplicationContext}. By default this * method will respect any explicitly set application context or application context * class before falling back to a suitable default. * @return the application context (not yet refreshed) * @see #setApplicationContextClass(Class) */
        protected ConfigurableApplicationContext createApplicationContext() {
            Class<?> contextClass = this.applicationContextClass;
            if (contextClass == null) {
                try {
                    switch (this.webApplicationType) {
                    case SERVLET:
                        contextClass = Class.forName(DEFAULT_WEB_CONTEXT_CLASS);
                        break;
                    case REACTIVE:
                        contextClass = Class.forName(DEFAULT_REACTIVE_WEB_CONTEXT_CLASS);
                        break;
                    default:
                        contextClass = Class.forName(DEFAULT_CONTEXT_CLASS);
                    }
                }
                catch (ClassNotFoundException ex) {
                    throw new IllegalStateException(
                            "Unable create a default ApplicationContext, "
                                    + "please specify an ApplicationContextClass",
                            ex);
                }
            }
            return (ConfigurableApplicationContext) BeanUtils.instantiateClass(contextClass);
        }

5.通过prepareContext(context, environment, listeners, applicationArguments,printedBanner);这行代码来准备容器:

        private void prepareContext(ConfigurableApplicationContext context,
                ConfigurableEnvironment environment, SpringApplicationRunListeners listeners,
                ApplicationArguments applicationArguments, Banner printedBanner) {
            context.setEnvironment(environment);
            postProcessApplicationContext(context);
            applyInitializers(context);
            listeners.contextPrepared(context);
            if (this.logStartupInfo) {
                logStartupInfo(context.getParent() == null);
                logStartupProfileInfo(context);
            }

            // Add boot specific singleton beans
            context.getBeanFactory().registerSingleton("springApplicationArguments",
                    applicationArguments);
            if (printedBanner != null) {
                context.getBeanFactory().registerSingleton("springBootBanner", printedBanner);
            }

            // Load the sources
            Set<Object> sources = getAllSources();
            Assert.notEmpty(sources, "Sources must not be empty");
            load(context, sources.toArray(new Object[0]));
            listeners.contextLoaded(context);
        }

6.通过this.refreshContext(context);刷新容器:

        private void refreshContext(ConfigurableApplicationContext context) {
            this.refresh(context);
            if(this.registerShutdownHook) {
                try {
                    context.registerShutdownHook();
                } catch (AccessControlException var3) {
                    ;
                }
            }

        }

在刷新容器完成之后,调用afterRefresh函数,跟踪过去发现是空的,可能是预留了一个扩展点。

通过阅读发现spring boot 2.0的源码和1.x的源码对比起来,细节方面还是变化很大的。当然,这些还只是其中的冰山一角,后面我会继续与大家分享在源码阅读中的一些心得体会,


来源:http://ddrv.cn

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