spring创建bean的方式

构造方法
1. 无参构造方法
2. 有参构造方法
工厂方法
1. 静态工厂方法
2. 实例工厂方法
实现FactoryBean接口

前两篇《Spring源码分析系列——bean创建过程分析（一）——默认无参构造方法创建bean》和《Spring源码分析系列——bean创建过程分析（二）——有参构造方法创建bean》介绍了构造方法创建bean的主要流程，本篇分析一下工厂方式创建bean，包括静态工厂和实例工厂方式

测试代码准备

xml配置如下

<bean id="boyService" class="yxf.instantiate.InstantiateFactory" factory-method="getBoyFromStaticFactoryMethod" ><!--<property name="friend" ref="grilService"></property>-->
</bean>
<bean id="instantiateFactory" class="yxf.instantiate.InstantiateFactory" />

实体类代码

public class Lad implements Boy {private String name;private Gril friend;private Money money;public Lad(String name) {this.name = name;}
}public class MagicGril implements Gril {private String name;private Boy friend;public MagicGril(){}public MagicGril(String name) {this.name = name;}
}

工厂方法代码

public class InstantiateFactory {public static Lad getBoyFromStaticFactoryMethod() {return new Lad("swk");}public MagicGril getGrilFromMemberFactoryMethod(String name) {return new MagicGril(name);}
}

运行测试代码

public class MyXmlConfig {public static void main(String[] args) {ApplicationContext ac = new ClassPathXmlApplicationContext("/application.xml");Lad lad = (Lad) ac.getBean("boyService");System.out.println(lad);}
}

createBeanInstance()方法分析

基于之前的分析，创建单例bean的步骤都是经getBean、doGetBean、createBean、doCreateBean、createBeanInstance等步骤，本次直接从createBeanInstance方法开始分析

代码精简后

protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {// Make sure bean class is actually resolved at this point.Class<?> beanClass = resolveBeanClass(mbd, beanName);if (beanClass != null && !Modifier.isPublic(beanClass.getModifiers()) && !mbd.isNonPublicAccessAllowed()) {throw new BeanCreationException(mbd.getResourceDescription(), beanName,"Bean class isn't public, and non-public access not allowed: " + beanClass.getName());}Supplier<?> instanceSupplier = mbd.getInstanceSupplier();if (instanceSupplier != null) {return obtainFromSupplier(instanceSupplier, beanName);}if (mbd.getFactoryMethodName() != null) {return instantiateUsingFactoryMethod(beanName, mbd, args);}
}

很直观的，如果bean定义中有factoryMethodName，则直接走工厂方式创建bean。

instantiateUsingFactoryMethod()方法分析

protected BeanWrapper instantiateUsingFactoryMethod(String beanName, RootBeanDefinition mbd, @Nullable Object[] explicitArgs) {return new ConstructorResolver(this).instantiateUsingFactoryMethod(beanName, mbd, explicitArgs);}

跟有参构造方法创建的autowireConstructor()方法一样，都是委托给ConstructorResolver类处理，看一下它的instantiateUsingFactoryMethod()方法。
精简之后

public BeanWrapper instantiateUsingFactoryMethod(String beanName, RootBeanDefinition mbd, @Nullable Object[] explicitArgs) {BeanWrapperImpl bw = new BeanWrapperImpl();this.beanFactory.initBeanWrapper(bw);Object factoryBean;Class<?> factoryClass;boolean isStatic;//工厂bean名称String factoryBeanName = mbd.getFactoryBeanName();//如果有工厂bean，则走实例工厂创建，没有则走静态工厂创建if (factoryBeanName != null) {if (factoryBeanName.equals(beanName)) {throw new BeanDefinitionStoreException(mbd.getResourceDescription(), beanName,"factory-bean reference points back to the same bean definition");}//从bean工厂中获取factoryBean实例factoryBean = this.beanFactory.getBean(factoryBeanName);if (mbd.isSingleton() && this.beanFactory.containsSingleton(beanName)) {throw new ImplicitlyAppearedSingletonException();}factoryClass = factoryBean.getClass();isStatic = false;}//如果有工厂bean，则走实例工厂创建，没有则走静态工厂创建else {// It's a static factory method on the bean class.if (!mbd.hasBeanClass()) {throw new BeanDefinitionStoreException(mbd.getResourceDescription(), beanName,"bean definition declares neither a bean class nor a factory-bean reference");}factoryBean = null;factoryClass = mbd.getBeanClass();isStatic = true;}Method factoryMethodToUse = null;ArgumentsHolder argsHolderToUse = null;Object[] argsToUse = null;if (explicitArgs != null) {argsToUse = explicitArgs;}else {Object[] argsToResolve = null;//从缓存中找，第一次没有synchronized (mbd.constructorArgumentLock) {factoryMethodToUse = (Method) mbd.resolvedConstructorOrFactoryMethod;if (factoryMethodToUse != null && mbd.constructorArgumentsResolved) {// Found a cached factory method...argsToUse = mbd.resolvedConstructorArguments;if (argsToUse == null) {argsToResolve = mbd.preparedConstructorArguments;}}}if (argsToResolve != null) {argsToUse = resolvePreparedArguments(beanName, mbd, bw, factoryMethodToUse, argsToResolve, true);}}//决定是用哪个静态方法if (factoryMethodToUse == null || argsToUse == null) {// Need to determine the factory method...// Try all methods with this name to see if they match the given arguments.factoryClass = ClassUtils.getUserClass(factoryClass);List<Method> candidates = null;         if (candidates == null) {candidates = new ArrayList<>();//找到工厂类所有的方法Method[] rawCandidates = getCandidateMethods(factoryClass, mbd);for (Method candidate : rawCandidates) {//找到静态的，并且是定义的工厂方法名的方法if (Modifier.isStatic(candidate.getModifiers()) == isStatic && mbd.isFactoryMethod(candidate)) {candidates.add(candidate);}}}//如果只有一个符合的静态方法，并且没有指定构造方法参数if (candidates.size() == 1 && explicitArgs == null && !mbd.hasConstructorArgumentValues()) {Method uniqueCandidate = candidates.get(0);//方法的形参数为0，则直接用反射创建if (uniqueCandidate.getParameterCount() == 0) {mbd.factoryMethodToIntrospect = uniqueCandidate;synchronized (mbd.constructorArgumentLock) {//放入缓存mbd.resolvedConstructorOrFactoryMethod = uniqueCandidate;mbd.constructorArgumentsResolved = true;mbd.resolvedConstructorArguments = EMPTY_ARGS;}bw.setBeanInstance(instantiate(beanName, mbd, factoryBean, uniqueCandidate, EMPTY_ARGS));return bw;}}//如果有多个候选方法，则需要排序if (candidates.size() > 1) {  // explicitly skip immutable singletonListcandidates.sort(AutowireUtils.EXECUTABLE_COMPARATOR);}ConstructorArgumentValues resolvedValues = null;boolean autowiring = (mbd.getResolvedAutowireMode() == AutowireCapableBeanFactory.AUTOWIRE_CONSTRUCTOR);int minTypeDiffWeight = Integer.MAX_VALUE;Set<Method> ambiguousFactoryMethods = null;int minNrOfArgs;if (explicitArgs != null) {minNrOfArgs = explicitArgs.length;}else {//解析bean定义中定义的构造方法参数if (mbd.hasConstructorArgumentValues()) {ConstructorArgumentValues cargs = mbd.getConstructorArgumentValues();resolvedValues = new ConstructorArgumentValues();minNrOfArgs = resolveConstructorArguments(beanName, mbd, bw, cargs, resolvedValues);}else {minNrOfArgs = 0;}}LinkedList<UnsatisfiedDependencyException> causes = null;for (Method candidate : candidates) {int parameterCount = candidate.getParameterCount();if (parameterCount >= minNrOfArgs) {ArgumentsHolder argsHolder;Class<?>[] paramTypes = candidate.getParameterTypes();if (explicitArgs != null) {// Explicit arguments given -> arguments length must match exactly.if (paramTypes.length != explicitArgs.length) {continue;}argsHolder = new ArgumentsHolder(explicitArgs);}else {// Resolved constructor arguments: type conversion and/or autowiring necessary.try {String[] paramNames = null;ParameterNameDiscoverer pnd = this.beanFactory.getParameterNameDiscoverer();if (pnd != null) {paramNames = pnd.getParameterNames(candidate);}//根据bean定义的参数，转换给工厂方法需要的参数argsHolder = createArgumentArray(beanName, mbd, resolvedValues, bw,paramTypes, paramNames, candidate, autowiring, candidates.size() == 1);}catch (UnsatisfiedDependencyException ex) {}}int typeDiffWeight = (mbd.isLenientConstructorResolution() ?argsHolder.getTypeDifferenceWeight(paramTypes) : argsHolder.getAssignabilityWeight(paramTypes));if (typeDiffWeight < minTypeDiffWeight) {factoryMethodToUse = candidate;argsHolderToUse = argsHolder;argsToUse = argsHolder.arguments;minTypeDiffWeight = typeDiffWeight;ambiguousFactoryMethods = null;}}}if (explicitArgs == null && argsHolderToUse != null) {mbd.factoryMethodToIntrospect = factoryMethodToUse;//将第一次找到的方法、及参数放入缓存，以备下次查找时直接从缓存中取argsHolderToUse.storeCache(mbd, factoryMethodToUse);}}//根据指定的工厂bean和指定的工厂方法或者找到的静态工厂方法创建beanbw.setBeanInstance(instantiate(beanName, mbd, factoryBean, factoryMethodToUse, argsToUse));return bw;

总结

工厂方法创建bean与构造方法创建bean大致步骤差不多，都是先确定方法和参数，然后反射创建bean。

Spring源码分析系列——bean创建过程分析（三）——工厂方法创建bean相关推荐

【四】Spring源码分析之启动主流程---AbstractApplicationContext的refresh方法
入口: 在SpringBoot启动的时候,SpringApplication的run方法中 refreshContext(context); 里面最终调用的是AbstractApplicationCo ...
Spring源码分析系列-Bean的生命周期（总结篇）
ApplicationContext和BeanFactory BeanFactory是Spring中的顶层接口,只负责管理bean,而ApplicationContext也实现了BeanFacto ...
【Spring源码分析系列】bean的加载
前言以 BeanFactory bf = new XmlBeanFactory(new ClassPathResource("beans.xml"));为例查看bean的加载过 ...
spring源码分析系列（一）
本系列以官方开发文档+spring5的源码为主一.IOC 控制反转(Inversion of Control,缩写为IoC),是面向对象编程中的一种设计原则,可以用来减低计算机代码之间的耦合度.其中 ...
Spring源码分析系列-循环依赖和三级缓存
目录循环依赖多级缓存一级缓存二级缓存当循环依赖遇上AOP 三级缓存 Spring三级缓存源码实现总结循环依赖 BeanFactory作为bean工厂管理我们的单例bean,那么肯定需 ...
spring源码分析系列（二）AOP应用
这里讲AOP应用先来说说一个比较虚无缥缈的问题:什么是AOP? 1.OOP 在说AOP之前,我们需要先看看什么是OOP:Object Oriented Programming,翻译过来就是面向对象编 ...
Spring源码分析之BeanPostProcessor接口和BeanFactoryPostProcessor接口方法不执行原因分析
首先下面是我的Bean /** Copyright 2002-2017 the original author or authors.** Licensed under the Apache Lice ...
Spring源码分析之Bean的创建过程详解
前文传送门: Spring源码分析之预启动流程 Spring源码分析之BeanFactory体系结构 Spring源码分析之BeanFactoryPostProcessor调用过程详解本文内容: 在 ...
Spring IOC 容器源码分析系列文章导读
1. 简介前一段时间,我学习了 Spring IOC 容器方面的源码,并写了数篇文章对此进行讲解.在写完 Spring IOC 容器源码分析系列文章中的最后一篇后,没敢懈怠,趁热打铁,花了3天时间阅 ...

Spring源码分析系列——bean创建过程分析（三）——工厂方法创建bean

前言

spring创建bean的方式

测试代码准备

createBeanInstance()方法分析

instantiateUsingFactoryMethod()方法分析

总结

Spring源码分析系列——bean创建过程分析（三）——工厂方法创建bean相关推荐

最新文章

热门文章