前言

通过前面的文章了解到在spring boot的启动时，利用的是编写的Application类，使用了注解@SpringBootApplication，本篇将阐述该Bean的加载过程。

[html] view plain copy

@SpringBootApplication
public class Application {
public static void main(String[] args) {
SpringApplication app = new SpringApplication(Application.class);
app.addListeners(new MyApplicationStartedEventListener());
app.run(args);
}
}

Application

上篇中讲述了上下文的创建，在run方法中接下来会执行

[html] view plain copy

load(context, sources.toArray(new Object[sources.size()]));

这个的sources表示的为Application类，在创建SpringApplication时手动传递

[html] view plain copy

SpringApplication app = new SpringApplication(Application.class);

load方法如下：

[html] view plain copy

protected void load(ApplicationContext context, Object[] sources) {
if (this.log.isDebugEnabled()) {
this.log.debug("Loading source "
+ StringUtils.arrayToCommaDelimitedString(sources));
}
BeanDefinitionLoader loader = createBeanDefinitionLoader(
getBeanDefinitionRegistry(context), sources);
if (this.beanNameGenerator != null) {
loader.setBeanNameGenerator(this.beanNameGenerator);
}
if (this.resourceLoader != null) {
loader.setResourceLoader(this.resourceLoader);
}
if (this.environment != null) {
loader.setEnvironment(this.environment);
}
loader.load();
}

调用loader.load()；

[html] view plain copy

private int load(Object source) {
Assert.notNull(source, "Source must not be null");
if (source instanceof Class<?>) {
return load((Class<?>) source);
}
if (source instanceof Resource) {
return load((Resource) source);
}
if (source instanceof Package) {
return load((Package) source);
}
if (source instanceof CharSequence) {
return load((CharSequence) source);
}
throw new IllegalArgumentException("Invalid source type " + source.getClass());
}

执行load((Class<?>) source)

[html] view plain copy

private int load(Class<?> source) {
if (isGroovyPresent()) {
// Any GroovyLoaders added in beans{} DSL can contribute beans here
if (GroovyBeanDefinitionSource.class.isAssignableFrom(source)) {
GroovyBeanDefinitionSource loader = BeanUtils.instantiateClass(source,
GroovyBeanDefinitionSource.class);
load(loader);
}
}
if (isComponent(source)) {
this.annotatedReader.register(source);
return 1;
}
return 0;
}

isComponent判断Application是否存在注解Compent

[html] view plain copy

private boolean isComponent(Class<?> type) {
// This has to be a bit of a guess. The only way to be sure that this type is
// eligible is to make a bean definition out of it and try to instantiate it.
if (AnnotationUtils.findAnnotation(type, Component.class) != null) {
return true;
}
// Nested anonymous classes are not eligible for registration, nor are groovy
// closures
if (type.getName().matches(".*\\$_.*closure.*") || type.isAnonymousClass()
|| type.getConstructors() == null || type.getConstructors().length == 0) {
return false;
}
return true;
}

AnnotationUtils.findAnnotation(type, Component.class) 工具类获取执行类对应的注解信息，该工具类在自己编码代码时可用得到

由于Application使用注解@SpringBootApplication，其定义如下

[html] view plain copy

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Configuration
@EnableAutoConfiguration
@ComponentScan
public @interface SpringBootApplication {
/**
* Exclude specific auto-configuration classes such that they will never be applied.
* @return the classes to exclude
*/
Class<?>[] exclude() default {};
}

发现不存在Compoment注解，是不是表明Application不是一个Component呢？其实不然，来看下@Configuration注解

[html] view plain copy

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface Configuration {
/**
* Explicitly specify the name of the Spring bean definition associated
* with this Configuration class. If left unspecified (the common case),
* a bean name will be automatically generated.
* <p>The custom name applies only if the Configuration class is picked up via
* component scanning or supplied directly to a {@link AnnotationConfigApplicationContext}.
* If the Configuration class is registered as a traditional XML bean definition,
* the name/id of the bean element will take precedence.
* @return the specified bean name, if any
* @see org.springframework.beans.factory.support.DefaultBeanNameGenerator
*/
String value() default "";
}

发现Configuration注解上存在Component注解，表明Application为Component

接下来执行this.annotatedReader.register(source);

[html] view plain copy

public void register(Class<?>... annotatedClasses) {
for (Class<?> annotatedClass : annotatedClasses) {
registerBean(annotatedClass);
}
}

调用registerBean注册Application对应的bean信息

[html] view plain copy

public void registerBean(Class<?> annotatedClass, String name,
@SuppressWarnings("unchecked") Class<? extends Annotation>... qualifiers) {
AnnotatedGenericBeanDefinition abd = new AnnotatedGenericBeanDefinition(annotatedClass);
if (this.conditionEvaluator.shouldSkip(abd.getMetadata())) {
return;
}
ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(abd);
abd.setScope(scopeMetadata.getScopeName());
String beanName = (name != null ? name : this.beanNameGenerator.generateBeanName(abd, this.registry));
AnnotationConfigUtils.processCommonDefinitionAnnotations(abd);
if (qualifiers != null) {
for (Class<? extends Annotation> qualifier : qualifiers) {
if (Primary.class.equals(qualifier)) {
abd.setPrimary(true);
}
else if (Lazy.class.equals(qualifier)) {
abd.setLazyInit(true);
}
else {
abd.addQualifier(new AutowireCandidateQualifier(qualifier));
}
}
}
BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(abd, beanName);
definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
BeanDefinitionReaderUtils.registerBeanDefinition(definitionHolder, this.registry);
}

首先来看

[html] view plain copy

if (this.conditionEvaluator.shouldSkip(abd.getMetadata())) {
return;
}

判断是否需要跳过，其代码如下：

[html] view plain copy

public boolean shouldSkip(AnnotatedTypeMetadata metadata, ConfigurationPhase phase) {
if (metadata == null || !metadata.isAnnotated(Conditional.class.getName())) {
return false;
}
if (phase == null) {
if (metadata instanceof AnnotationMetadata &&
ConfigurationClassUtils.isConfigurationCandidate((AnnotationMetadata) metadata)) {
return shouldSkip(metadata, ConfigurationPhase.PARSE_CONFIGURATION);
}
return shouldSkip(metadata, ConfigurationPhase.REGISTER_BEAN);
}
List<Condition> conditions = new ArrayList<Condition>();
for (String[] conditionClasses : getConditionClasses(metadata)) {
for (String conditionClass : conditionClasses) {
Condition condition = getCondition(conditionClass, this.context.getClassLoader());
conditions.add(condition);
}
}
AnnotationAwareOrderComparator.sort(conditions);
for (Condition condition : conditions) {
ConfigurationPhase requiredPhase = null;
if (condition instanceof ConfigurationCondition) {
requiredPhase = ((ConfigurationCondition) condition).getConfigurationPhase();
}
if (requiredPhase == null || requiredPhase == phase) {
if (!condition.matches(this.context, metadata)) {
return true;
}
}
}
return false;
}

该代码判断Application上是否存在Conditional注解，如果不满足Conditional对应条件则该bean不被创建；

Conditional注解

代码分析到这里可以先看看Conditional注解的使用，其定义为：

[html] view plain copy

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE, ElementType.METHOD})
public @interface Conditional {
/**
* All {@link Condition}s that must {@linkplain Condition#matches match}
* in order for the component to be registered.
*/
Class<? extends Condition>[] value();
}

从源码可以看出，首先判断Application上是否存在Conditional，如果存在，则获取Conditional注解中的value数组值，对应的Class必须实现Condition接口：

[html] view plain copy

public interface Condition {
boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata);
}

如果matches返回true 表明该bean需要被创建，否则表明该bean不需要被创建。

明白了该注解的用法后，来一个实际案例

[html] view plain copy

package com.lkl.springboot.condition;
import org.springframework.context.annotation.Conditional;
import org.springframework.stereotype.Component;
@Component("MyCondition")
@Conditional(MyCondition.class)
public class ConditionBean {
}

创建ConditionBean，使用注解@Conditional(MyCondition.class)调用MyCondition类

[html] view plain copy

/**
* 自定义condition 修改返回值，查看bean是否创建
*
* @author liaokailin
*/
public class MyCondition implements Condition {
/**
* 返回true 生成bean
* 返回false 不生成bean
*/
@Override
public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
Map<String, Object> map = metadata.getAnnotationAttributes(Component.class.getName());
return "MyCondition".equals(map.get("value").toString());
}
}

MyCondition实现接口Condition，在matches方法中获取bean上注解Component信息，如果bean名称等于MyCondition返回true，否则返回false，bean不会被创建。

回到前面Application的分析，Application上不存在Conditional，因此shouldSkip返回false，代码继续执行

[html] view plain copy

ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(abd);

处理Scope注解信息，默认是单例bean

执行

[html] view plain copy

AnnotationConfigUtils.processCommonDefinitionAnnotations(abd);

处理一些常见注解信息

[html] view plain copy

static void processCommonDefinitionAnnotations(AnnotatedBeanDefinition abd, AnnotatedTypeMetadata metadata) {
if (metadata.isAnnotated(Lazy.class.getName())) {
abd.setLazyInit(attributesFor(metadata, Lazy.class).getBoolean("value"));
}
else if (abd.getMetadata() != metadata && abd.getMetadata().isAnnotated(Lazy.class.getName())) {
abd.setLazyInit(attributesFor(abd.getMetadata(), Lazy.class).getBoolean("value"));
}
if (metadata.isAnnotated(Primary.class.getName())) {
abd.setPrimary(true);
}
if (metadata.isAnnotated(DependsOn.class.getName())) {
abd.setDependsOn(attributesFor(metadata, DependsOn.class).getStringArray("value"));
}
if (abd instanceof AbstractBeanDefinition) {
AbstractBeanDefinition absBd = (AbstractBeanDefinition) abd;
if (metadata.isAnnotated(Role.class.getName())) {
absBd.setRole(attributesFor(metadata, Role.class).getNumber("value").intValue());
}
if (metadata.isAnnotated(Description.class.getName())) {
absBd.setDescription(attributesFor(metadata, Description.class).getString("value"));
}
}
}

处理Lazy、Primary、DependsOn、Role、Description等注解

最后调用

[html] view plain copy

BeanDefinitionReaderUtils.registerBeanDefinition(definitionHolder, this.registry);

注册bean信息，在注册bean信息之前通过

[html] view plain copy

String beanName = (name != null ? name : this.beanNameGenerator.generateBeanName(abd, this.registry));

获取bean名称

bean的注册调用为

[html] view plain copy

registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());

该代码在上篇中已有说明。

此时Application对应bean已创建完成。

spring boot实战(第九篇)Application创建源码分析相关推荐

spring boot 超市进销存系统源码
spring boot 超市进销存系统源码功能:本系统根据权限划分为三种用户:系统管理员,货物管理员,商品管理员(具体角色可以根据权限划分多个) 系统管理员默认功能:客户管理,供应商管理,商品管理, ...
番外篇——直流电机桥源码分析LED驱动例程开发
[番外篇]直流电机桥源码分析&LED驱动例程开发直流电机桥测试代码分析直流电机桥驱动代码分析仿写HBLED驱动程序利用芯片手册修改设备树利用原理图寻找引脚仿写代码仿写HBLED测 ...
Spring自定义注解驱动开发使用及源码分析
目录前言注解驱动开发使用需求代码实现测试效果源码分析 BeanDefinitionRegistryPostProcessor接口解析BeanDefinition 处理Bean上配置的注解 ...
聊聊Spring中的数据绑定 --- DataBinder本尊（源码分析）【享学Spring】
每篇一句唯有热爱和坚持,才能让你在程序人生中屹立不倒,切忌跟风什么语言或就学什么去~ 前言数据绑定这个概念在任何一个成型的框架中都是特别重要的(尤其是web框架),它能让框架更多的自动化,更好容 ...
Java集合篇：LinkedList源码分析
(注:本文内容基于JDK1.6) 一.概述: LinkedList与ArrayList一样实现List接口,只是ArrayList是List接口的大小可变数组的实现,LinkedList是List接口 ...
Linux项目实战C++轻量级Web服务器源码分析TinyWebServer
目录文章简介一. 先跑起来项目二.再看项目核心三.逐个击破!立下flag 文章简介 TinyWebServer是Linux下C++轻量级Web服务器,助力初学者快速实践网络编程,搭建属于自己的 ...
聊聊Spring中的数据绑定 --- DataBinder本尊（源码分析）
每篇一句唯有热爱和坚持,才能让你在程序人生中屹立不倒,切忌跟风什么语言或就学什么去~ 相关阅读 [小家Spring]聊聊Spring中的数据转换:Converter.ConversionServic ...
【小家Spring】聊聊Spring中的数据绑定 --- DataBinder本尊（源码分析）
每篇一句 > 唯有热爱和坚持,才能让你在程序人生中屹立不倒,切忌跟风什么语言或就学什么去~ 相关阅读 [小家Spring]聊聊Spring中的数据绑定 --- 属性访问器PropertyAcce ...
spring boot实战(第二篇)事件监听
前言 spring boot在启动过程中增加事件监听机制,为用户功能拓展提供极大的便利. 支持的事件类型四种 ApplicationStartedEvent ApplicationEnvironmen ...

spring boot实战(第九篇)Application创建源码分析

前言

Application

Conditional注解

spring boot实战(第九篇)Application创建源码分析相关推荐

最新文章

热门文章