Spring源码之Context的创建核心逻辑(上)

我们前一章介绍了spring的整体架构以及模块划分，也已经将代码导入ide中，那么接下来就要开始让人心动的Spring源码之旅了。

1、默认的Spring启动器

1. @SpringBootApplication

2. @ComponentScan(basePackages = {"com"})

3. public class SpringSourceApplication {

4. public static void main(String[] args) {

5. ApplicationContext ctx = SpringApplication.run(SpringSourceApplication.class, args);

6. }

7. }

该方法是Springboot的启动类

2、进入SpringApplication.java

1. public static ConfigurableApplicationContext run(Object source, String... args) {

2. return run(new Object[] { source }, args);

3. }

4. public static ConfigurableApplicationContext run(Object[] sources, String[] args) {

5. return new SpringApplication(sources).run(args);

6. }

这里创建了一个SpringApplication方法，执行run方法，返回一个ConfigurableApplicationContext,这只是一个接口而已，根据名称来看，这是一个可配置的应用程序上下文。

3、进入RUN方法

SpringApplication(sources)这个类的初始化就先不看，这里面调用了initialize()方法，主要完成了当前的运行环境，以及设置了ApplicationListener相关的东西，这里我们先不做分析，直接进入run方法。

1. public ConfigurableApplicationContext run(String... args) {

2. //记录程序运行时间

3. StopWatch stopWatch = new StopWatch();

4. stopWatch.start();

5. ConfigurableApplicationContext context = null;

6. FailureAnalyzers analyzers = null;

7. /**

8. * 设置headless模式

9. * 在我们的例子中该属性会被设置为true，因为我们开发的是服务器程序，

10. * 一般运行在没有显示器和键盘的环境。关于java中的headless模式

11. */

12. configureHeadlessProperty();

13. SpringApplicationRunListeners listeners = getRunListeners(args);

14. listeners.starting();

15. try {

16. ApplicationArguments applicationArguments = new DefaultApplicationArguments(

17. args);

18. ConfigurableEnvironment environment = prepareEnvironment(listeners,

19. applicationArguments);

20. configureIgnoreBeanInfo(environment);

21. bindToSpringApplication(environment);

22. Banner printedBanner = printBanner(environment);

23. /**

24. * 它创建出来的是ConfigurableApplicationContext类的实例对象

25. *AnnotationConfigEmbeddedWebApplicationContext

26. */

27. context = createApplicationContext();

28. analyzers = new FailureAnalyzers(context);

29. /**

30. * 该方法对context进行了预设置，设置了ResourceLoader和ClassLoader，

31. * 并向bean工厂中添加了一个beanNameGenerator

32. */

33. prepareContext(context, environment, listeners, applicationArguments,

34. printedBanner);

35. /**

36. * prepareContext()已经做好了refresh上下文的基础准备工作

37. * spring对ApplicationContext进行了向下转型，

38. * 转型后的类型为：AbstractApplicationContex，并调用了它的refresh()方法

39. * 详见方法内部实现

40. */

41. refreshContext(context);

42. afterRefresh(context, applicationArguments);

43. listeners.finished(context, null);

44. stopWatch.stop();

45. if (this.logStartupInfo) {

46. new StartupInfoLogger(this.mainApplicationClass)

47. .logStarted(getApplicationLog(), stopWatch);

48. }

49. return context;

50. }

51. catch (Throwable ex) {

52. handleRunFailure(context, listeners, analyzers, ex);

53. throw new IllegalStateException(ex);

54. }

55. }

try代码块中是我们最核心的功能，代码中也添加了一部分的注释。我们先看context的创建过程即进入到createApplicationContext()方法。

1. protected ConfigurableApplicationContext createApplicationContext() {

2. Class<?> contextClass = this.applicationContextClass;

3. if (contextClass == null) {

4. try {

5. switch (this.webApplicationType) {

6. case SERVLET:

7. //此处采用反射获取WebApplicationContext

8. contextClass = Class.forName(DEFAULT_WEB_CONTEXT_CLASS);

9. break;

10. case REACTIVE:

11. contextClass = Class.forName(DEFAULT_REACTIVE_WEB_CONTEXT_CLASS);

12. break;

13. default:

14. contextClass = Class.forName(DEFAULT_CONTEXT_CLASS);

15. }

16. }

17. catch (ClassNotFoundException ex) {

18. throw new IllegalStateException(

19. "Unable create a default ApplicationContext, "

20. + "please specify an ApplicationContextClass",

21. ex);

22. }

23. }

24. return (ConfigurableApplicationContext) BeanUtils.instantiateClass(contextClass);

25. }

DEFAULT_WEB_CONTEXT_CLASS—>AnnotationConfigEmbeddedWebApplicationContext接下来执行AnnotationConfigEmbeddedWebApplicationContext的构造方法

1. public AnnotationConfigEmbeddedWebApplicationContext() {

2. this.reader = new AnnotatedBeanDefinitionReader(this);

3. this.scanner = new ClassPathBeanDefinitionScanner(this);

4. }

上面实例化了 AnnotatedBeanDefinitionReader以及 ClassPathBeanDefinitionScanner实例化 AnnotatedBeanDefinitionReader

1. public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry) {

2. this(registry, getOrCreateEnvironment(registry));

3. }

接下来是调用

1. public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry, Environment environment) {

2. Assert.notNull(registry, "BeanDefinitionRegistry must not be null");

3. Assert.notNull(environment, "Environment must not be null");

4. this.registry = registry;

5. this.conditionEvaluator = new ConditionEvaluator(registry, environment, null);

6. AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);

7. }

实例化 ConditionEvaluator，将其属性 ConditionContextImpl赋值

1. AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);

具体实现如下:

1. public static Set<BeanDefinitionHolder> registerAnnotationConfigProcessors(

2. BeanDefinitionRegistry registry, @Nullable Object source) {

3. //获取beanfactory信息,Spring IOC的核心

4. DefaultListableBeanFactory beanFactory = unwrapDefaultListableBeanFactory(registry)

5. if (beanFactory != null) {

6. if (!(beanFactory.getDependencyComparator() instanceof AnnotationAwareOrderComparator)) {

7. beanFactory.setDependencyComparator(AnnotationAwareOrderComparator.INSTANCE);

8. }

9. if (!(beanFactory.getAutowireCandidateResolver() instanceof ContextAnnotationAutowireCandidateResolver)) {

10. beanFactory.setAutowireCandidateResolver(new ContextAnnotationAutowireCandidateResolver());

11. }

12. }

13. Set<BeanDefinitionHolder> beanDefs = new LinkedHashSet<>(4);

14. if (!registry.containsBeanDefinition(CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME)) {

15. RootBeanDefinition def = new RootBeanDefinition(ConfigurationClassPostProcessor.class);

16. def.setSource(source);

17. beanDefs.add(registerPostProcessor(registry, def, CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME));

18. }

19. if (!registry.containsBeanDefinition(AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {

20. RootBeanDefinition def = new RootBeanDefinition(AutowiredAnnotationBeanPostProcessor.class);

21. def.setSource(source);

22. beanDefs.add(registerPostProcessor(registry, def, AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME));

23. }

24. if (!registry.containsBeanDefinition(REQUIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {

25. RootBeanDefinition def = new RootBeanDefinition(RequiredAnnotationBeanPostProcessor.class);

26. def.setSource(source);

27. beanDefs.add(registerPostProcessor(registry, def, REQUIRED_ANNOTATION_PROCESSOR_BEAN_NAME));

28. }

29. // Check for JSR-250 support, and if present add the CommonAnnotationBeanPostProcessor.

30. if (jsr250Present && !registry.containsBeanDefinition(COMMON_ANNOTATION_PROCESSOR_BEAN_NAME)) {

31. RootBeanDefinition def = new RootBeanDefinition(CommonAnnotationBeanPostProcessor.class);

32. def.setSource(source);

33. beanDefs.add(registerPostProcessor(registry, def, COMMON_ANNOTATION_PROCESSOR_BEAN_NAME));

34. }

35. // Check for JPA support, and if present add the PersistenceAnnotationBeanPostProcessor.

36. if (jpaPresent && !registry.containsBeanDefinition(PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME)) {

37. RootBeanDefinition def = new RootBeanDefinition();

38. try {

39. def.setBeanClass(ClassUtils.forName(PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME,

40. AnnotationConfigUtils.class.getClassLoader()));

41. }

42. catch (ClassNotFoundException ex) {

43. throw new IllegalStateException(

44. "Cannot load optional framework class: " + PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME, ex);

45. }

46. def.setSource(source);

47. beanDefs.add(registerPostProcessor(registry, def, PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME));

48. }

49. if (!registry.containsBeanDefinition(EVENT_LISTENER_PROCESSOR_BEAN_NAME)) {

50. RootBeanDefinition def = new RootBeanDefinition(EventListenerMethodProcessor.class);

51. def.setSource(source);

52. beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_PROCESSOR_BEAN_NAME));

53. }

54. if (!registry.containsBeanDefinition(EVENT_LISTENER_FACTORY_BEAN_NAME)) {

55. RootBeanDefinition def = new RootBeanDefinition(DefaultEventListenerFactory.class);

56. def.setSource(source);

57. beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_FACTORY_BEAN_NAME));

58. }

59. return beanDefs;

60. }

上面代码比较长，我们来分开解析

1. DefaultListableBeanFactory beanFactory = unwrapDefaultListableBeanFactory(registry);

2. 由wrap就可以看出此处使用的是装饰器模式，registry包裹成一个指定的beanFactory

3. private static DefaultListableBeanFactory unwrapDefaultListableBeanFactory(BeanDefinitionRegistry registry) {

4. if (registry instanceof DefaultListableBeanFactory) {

5. return (DefaultListableBeanFactory) registry;

6. }

7. else if (registry instanceof GenericApplicationContext) {

8. //此处 GenericApplicationContext构造函数初始化beanFactory为DefaultListableBeanFactory

9. return ((GenericApplicationContext) registry).getDefaultListableBeanFactory();

10. }

11. else {

12. return null;

13. }

14. }

15. 代码执行到`registry instanceof GenericApplicationContext`(通过类继承结构可得到)，随后调用`GenericApplicationContext#getDefaultListableBeanFactory()方法，GenericApplicationContext`在构造方法中实例化了属性`beanFactory`的值为`DefaultListableBeanFactory`:

16. public GenericApplicationContext() {

17. this.beanFactory = new DefaultListableBeanFactory();

18. }

19. 其构造优先于`AnnotationConfigEmbeddedWebApplicationContext`构造方法执行。

20. 以上获得了BeanFactory信息

代码的构建请参考 github该地址有相应代码的注释

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