Spring源码解析

通过 new RuntimeException().getStackTrace() 从方法调用栈的栈帧 StackTraceElement 里面来找到主启动类

执行流程

// 获取initializer, 排序
SpringApplication application = new SpringApplication(primaryClass);

application.run();

// 利用前面分类好的bootstrapInitializer来初始化DefaultBootstrapContext
createBootstrapContext();

// 为系统变量 SYSTEM_PROPERTY_JAVA_AWT_HEADLESS 设置默认值为 "true"
configureHeadlessProperty();

SpringApplicationRunListeners listeners = new SpringApplicationRunListeners();

// 比较复杂, 暂时略过
listeners.starting(bootstrapContext, this.mainApplicationClass);

// Servlet方式, 非WebFlux方式
ConfigurableEnvironment environment = new ApplicationServletEnvironment();

// 类型转换器的设置(核心方法)
ApplicationConversionService conversionService = new ApplicationConversionService();

// 添加各种类型转换器和类型转换器工厂, GenericConversionService
conversionService.addConverterFactory(converterFactory);

// 获取factory上的两个泛型: FromType 和 ToType
ResolvableType[] typeInfo = getRequiredTypeInfo(factory.getClass(), ConverterFactory.class);
addConverter(new ConverterFactoryAdapter(factory, new ConvertiblePair(typeInfo[0].toClass(), typeInfo[1].toClass())));

ConverterFactory、ConvertiblePair 和 Converter 类

• ConverterFactory 通过调用 getConverter() 来获取具体的 Converter
• ConvertiblePair 封装 ConverterFactory 中的两个泛型：sourceType 和 targetType

final class NumberToNumberConverterFactory implements ConverterFactory<Number, Number>, ConditionalConverter {

    @Override
    public <T extends Number> Converter<Number, T> getConverter(Class<T> targetType) {
        return new NumberToNumber<>(targetType);
    }

    // Integer没有必要转换成Integer
    @Override
    public boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType) {
        return !sourceType.equals(targetType);
    }


    private static final class NumberToNumber<T extends Number> implements Converter<Number, T> {

        private final Class<T> targetType;

        NumberToNumber(Class<T> targetType) {
            this.targetType = targetType;
        }

        @Override
        public T convert(Number source) {
            return NumberUtils.convertNumberToTargetClass(source, this.targetType);
        }
    }

}

ResolvableType 类