Spring技术与内幕(一)

Spring生态网： https://spring.io/

1. 简介

可以把IOC和AOP理解为Spring的Kernel。通过IOC管理POJO对象以及它们之间的耦合关系；通过AOP以动态和非侵入式的方式来增强服务的功能。

IOC:Inversion of Control 也称为依赖倒置原理(Dependency Inversion Principle):对象依赖关系的管理被反转了，对象之间的依赖关系由IoC容器进行管理，并且IoC完成对象的注入。

(1)IoC包含了最为基本的IoC容器BeanFactory的接口与实现，比如XmlBeanFactory 就是一个最基本的BeanFactory(IoC容器)。BeanFactory是一个简单容器系列，只实现了容器基本的功能；另一

个是ApplicationContext 上下文，它作为容器的高级形态存在，继承自BeanFactory并增加了许多面向框架的特性，同时对应用环境作了许多适配。在Spring提供的基本Ioc容器的接口定义和实现的

基础上，Spring通过定义BeanDefinition来管理基于Spring的应用中的各种对象以及它们之间的相互依赖关系。BeanDefinition抽象了我们对Bean的定义，是让容器起作用的主要数据类型。

BeanDefinition中维持了Bean是否是单例、是否Primary、是否Lazy等属性。

BeanDefinition源码如下：

package org.springframework.beans.factory.config;

import org.springframework.beans.BeanMetadataElement;
import org.springframework.beans.MutablePropertyValues;
import org.springframework.core.AttributeAccessor;
import org.springframework.lang.Nullable;

public interface BeanDefinition extends AttributeAccessor, BeanMetadataElement {

    /**
     * Scope identifier for the standard singleton scope: "singleton".
     * <p>Note that extended bean factories might support further scopes.
     * @see #setScope
     */
    String SCOPE_SINGLETON = ConfigurableBeanFactory.SCOPE_SINGLETON;

    /**
     * Scope identifier for the standard prototype scope: "prototype".
     * <p>Note that extended bean factories might support further scopes.
     * @see #setScope
     */
    String SCOPE_PROTOTYPE = ConfigurableBeanFactory.SCOPE_PROTOTYPE;


    /**
     * Role hint indicating that a {@code BeanDefinition} is a major part
     * of the application. Typically corresponds to a user-defined bean.
     */
    int ROLE_APPLICATION = 0;

    /**
     * Role hint indicating that a {@code BeanDefinition} is a supporting
     * part of some larger configuration, typically an outer
     * {@link org.springframework.beans.factory.parsing.ComponentDefinition}.
     * {@code SUPPORT} beans are considered important enough to be aware
     * of when looking more closely at a particular
     * {@link org.springframework.beans.factory.parsing.ComponentDefinition},
     * but not when looking at the overall configuration of an application.
     */
    int ROLE_SUPPORT = 1;

    /**
     * Role hint indicating that a {@code BeanDefinition} is providing an
     * entirely background role and has no relevance to the end-user. This hint is
     * used when registering beans that are completely part of the internal workings
     * of a {@link org.springframework.beans.factory.parsing.ComponentDefinition}.
     */
    int ROLE_INFRASTRUCTURE = 2;


    // Modifiable attributes

    /**
     * Set the name of the parent definition of this bean definition, if any.
     */
    void setParentName(@Nullable String parentName);

    /**
     * Return the name of the parent definition of this bean definition, if any.
     */
    @Nullable
    String getParentName();

    /**
     * Specify the bean class name of this bean definition.
     * <p>The class name can be modified during bean factory post-processing,
     * typically replacing the original class name with a parsed variant of it.
     * @see #setParentName
     * @see #setFactoryBeanName
     * @see #setFactoryMethodName
     */
    void setBeanClassName(@Nullable String beanClassName);

    /**
     * Return the current bean class name of this bean definition.
     * <p>Note that this does not have to be the actual class name used at runtime, in
     * case of a child definition overriding/inheriting the class name from its parent.
     * Also, this may just be the class that a factory method is called on, or it may
     * even be empty in case of a factory bean reference that a method is called on.
     * Hence, do <i>not</i> consider this to be the definitive bean type at runtime but
     * rather only use it for parsing purposes at the individual bean definition level.
     * @see #getParentName()
     * @see #getFactoryBeanName()
     * @see #getFactoryMethodName()
     */
    @Nullable
    String getBeanClassName();

    /**
     * Override the target scope of this bean, specifying a new scope name.
     * @see #SCOPE_SINGLETON
     * @see #SCOPE_PROTOTYPE
     */
    void setScope(@Nullable String scope);

    /**
     * Return the name of the current target scope for this bean,
     * or {@code null} if not known yet.
     */
    @Nullable
    String getScope();

    /**
     * Set whether this bean should be lazily initialized.
     * <p>If {@code false}, the bean will get instantiated on startup by bean
     * factories that perform eager initialization of singletons.
     */
    void setLazyInit(boolean lazyInit);

    /**
     * Return whether this bean should be lazily initialized, i.e. not
     * eagerly instantiated on startup. Only applicable to a singleton bean.
     */
    boolean isLazyInit();

    /**
     * Set the names of the beans that this bean depends on being initialized.
     * The bean factory will guarantee that these beans get initialized first.
     */
    void setDependsOn(@Nullable String... dependsOn);

    /**
     * Return the bean names that this bean depends on.
     */
    @Nullable
    String[] getDependsOn();

    /**
     * Set whether this bean is a candidate for getting autowired into some other bean.
     * <p>Note that this flag is designed to only affect type-based autowiring.
     * It does not affect explicit references by name, which will get resolved even
     * if the specified bean is not marked as an autowire candidate. As a consequence,
     * autowiring by name will nevertheless inject a bean if the name matches.
     */
    void setAutowireCandidate(boolean autowireCandidate);

    /**
     * Return whether this bean is a candidate for getting autowired into some other bean.
     */
    boolean isAutowireCandidate();

    /**
     * Set whether this bean is a primary autowire candidate.
     * <p>If this value is {@code true} for exactly one bean among multiple
     * matching candidates, it will serve as a tie-breaker.
     */
    void setPrimary(boolean primary);

    /**
     * Return whether this bean is a primary autowire candidate.
     */
    boolean isPrimary();

    /**
     * Specify the factory bean to use, if any.
     * This the name of the bean to call the specified factory method on.
     * @see #setFactoryMethodName
     */
    void setFactoryBeanName(@Nullable String factoryBeanName);

    /**
     * Return the factory bean name, if any.
     */
    @Nullable
    String getFactoryBeanName();

    /**
     * Specify a factory method, if any. This method will be invoked with
     * constructor arguments, or with no arguments if none are specified.
     * The method will be invoked on the specified factory bean, if any,
     * or otherwise as a static method on the local bean class.
     * @see #setFactoryBeanName
     * @see #setBeanClassName
     */
    void setFactoryMethodName(@Nullable String factoryMethodName);

    /**
     * Return a factory method, if any.
     */
    @Nullable
    String getFactoryMethodName();

    /**
     * Return the constructor argument values for this bean.
     * <p>The returned instance can be modified during bean factory post-processing.
     * @return the ConstructorArgumentValues object (never {@code null})
     */
    ConstructorArgumentValues getConstructorArgumentValues();

    /**
     * Return if there are constructor argument values defined for this bean.
     * @since 5.0.2
     */
    default boolean hasConstructorArgumentValues() {
        return !getConstructorArgumentValues().isEmpty();
    }

    /**
     * Return the property values to be applied to a new instance of the bean.
     * <p>The returned instance can be modified during bean factory post-processing.
     * @return the MutablePropertyValues object (never {@code null})
     */
    MutablePropertyValues getPropertyValues();

    /**
     * Return if there are property values values defined for this bean.
     * @since 5.0.2
     */
    default boolean hasPropertyValues() {
        return !getPropertyValues().isEmpty();
    }

    /**
     * Set the name of the initializer method.
     * @since 5.1
     */
    void setInitMethodName(@Nullable String initMethodName);

    /**
     * Return the name of the initializer method.
     * @since 5.1
     */
    @Nullable
    String getInitMethodName();

    /**
     * Set the name of the destroy method.
     * @since 5.1
     */
    void setDestroyMethodName(@Nullable String destroyMethodName);

    /**
     * Return the name of the destroy method.
     * @since 5.1
     */
    @Nullable
    String getDestroyMethodName();

    /**
     * Set the role hint for this {@code BeanDefinition}. The role hint
     * provides the frameworks as well as tools with an indication of
     * the role and importance of a particular {@code BeanDefinition}.
     * @since 5.1
     * @see #ROLE_APPLICATION
     * @see #ROLE_SUPPORT
     * @see #ROLE_INFRASTRUCTURE
     */
    void setRole(int role);

    /**
     * Get the role hint for this {@code BeanDefinition}. The role hint
     * provides the frameworks as well as tools with an indication of
     * the role and importance of a particular {@code BeanDefinition}.
     * @see #ROLE_APPLICATION
     * @see #ROLE_SUPPORT
     * @see #ROLE_INFRASTRUCTURE
     */
    int getRole();

    /**
     * Set a human-readable description of this bean definition.
     * @since 5.1
     */
    void setDescription(@Nullable String description);

    /**
     * Return a human-readable description of this bean definition.
     */
    @Nullable
    String getDescription();


    // Read-only attributes

    /**
     * Return whether this a <b>Singleton</b>, with a single, shared instance
     * returned on all calls.
     * @see #SCOPE_SINGLETON
     */
    boolean isSingleton();

    /**
     * Return whether this a <b>Prototype</b>, with an independent instance
     * returned for each call.
     * @since 3.0
     * @see #SCOPE_PROTOTYPE
     */
    boolean isPrototype();

    /**
     * Return whether this bean is "abstract", that is, not meant to be instantiated.
     */
    boolean isAbstract();

    /**
     * Return a description of the resource that this bean definition
     * came from (for the purpose of showing context in case of errors).
     */
    @Nullable
    String getResourceDescription();

    /**
     * Return the originating BeanDefinition, or {@code null} if none.
     * Allows for retrieving the decorated bean definition, if any.
     * <p>Note that this method returns the immediate originator. Iterate through the
     * originator chain to find the original BeanDefinition as defined by the user.
     */
    @Nullable
    BeanDefinition getOriginatingBeanDefinition();

}

(2)在Spring具体的注入实现中，接口注入、setter注入、构造器注入是主要的注入方式。在Spring的IOC设计中，setter注入和构造器注入是主要的注入方式；相对而言，使用spring时setter注入是

常见的注入方式，而且为了防止注入异常，spring IOC容器还提供了对特定依赖的检查。

SpringAOP(Aspect-Oriented Programming): 围绕着AOP的增强功能，Spring集成了AsspectJ作为AOP的一个特定实现，同时还在JVM动态代理/Cglib代理的基础上实现了一个AOP框架。

AOP是一种思想而不是一种技术。所以说，如果抛开spring，动态代理甚至静态代理都可以算是一种aop。spring中的aop实现分为两种,基于动态代理的aop和基于AspectJ的aop。AspectJ是完全

独立于Spring存在的一个Eclipse发起的项目。AspectJ甚至可以说是一门独立的语言，在java文件编译期间，织入字节码，改变原有的类。

我们常看到的在spring中用的@Aspect注解只不过是Spring2.0以后使用了AspectJ的风格而已，本质上还是Spring的原生实现。

2.Spring源码构建

Spring 源码是基于Gradle构建的，需要先安装Gradle。

1.  安装Gradle

2. 下载spring源码

https://github.com/spring-projects/spring-framework/tree/5.1.x

3. 到源码目录下执行

点击Sping源码下 gradlew.bat 构建项目

4.测试

(1) build.gradle 如下

plugins {
    id 'java'
}

group 'org.springframework'
version '5.1.20.BUILD-SNAPSHOT'

repositories {
    mavenCentral()
}

dependencies {
    compile(project(":spring-beans"))
    compile(project(":spring-core"))
    implementation(project(":spring-context"))
    testCompile group: 'junit', name: 'junit', version: '4.12'
}

(2) 测试Service

package qz;

import org.springframework.stereotype.Component;

@Component
public class UserService {

    public String method1() {
        System.out.println("method1");
        return "method1";
    }
}

(3) 测试主类

package qz;

import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;

/**
 * @author: 乔利强
 * @date: 2020/12/10 20:09
 * @description:
 */
@ComponentScan("qz")
@Configuration
public class MainApp {

    public static void main(String[] args) {
        AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(MainApp.class);
        UserService bean = applicationContext.getBean(UserService.class);
        String s = bean.method1();
        System.out.println(s);
    }
}

(4) 结果如下：

method1
method1