spring源码阅读(1/4) - Bean生成

上午去缴了上次没带驾驶证的扣分罚款，最近在图书馆没事就看曾国藩家书，曾国藩说人要明强。光强没有用，你要明强。也就是说要强的有道理。曾国藩又说，作学问不能作死学问，作学问其实很重要的事就是能懂得孝悌，把家持好，能作事。能作事很重要，学问再高，不能作事，也是无用。相反即便没什么学问，写不出来，可是能作事，事事作的条理，家庭安排的和气，家族事宜可以有积极的贡献，再到更大的方面，都能作好，这才是学问的意义。看了一下，上一篇文章已是2号的了，这个月已经9号了，1/3了，但是这重头的Bean加载尚未什么大的进展，这样怎么能行，家里的事情还要办，不少事情还没弄好，这可不行呀。

想要人生有所突破，下一番苦工是不可能省略的。一半努力一半为所欲为，是不可能成就的。

“须是策励此心，勇猛奋发，拨出心肝与他去作！如两边擂起战鼓，莫问前头如何，只认卷将去！如此，方作得工夫。若半上落下，半沉半浮，济得甚事！” 朱熹 .《朱子语录》

咱们继续上节的内容，这节主要是bean的加载。

咱们从ServerMain的方法中的getBean("")做为入口来看：

public Object getBean(String name) throws BeansException {
        return this.doGetBean(name, (Class)null, (Object[])null, false);
    }

继续调用，都在AbstractBeanFactory中进行，下边这段就是恐怖的bean加载了。咱们能够翻到最后看下返回了Bean，固然bean是范性的，先抛开中间的过程不说，这里返回的就是实实在在的咱们须要的Bean了，彷佛一切都在这个方法里，没错全部的“恩怨”都在这里。

protected <T> T doGetBean(String name, Class<T> requiredType, final Object[] args, boolean typeCheckOnly) throws BeansException {
        final String beanName = this.transformedBeanName(name);
        Object sharedInstance = this.getSingleton(beanName);
        Object bean;
        if (sharedInstance != null && args == null) {
            if (this.logger.isDebugEnabled()) {
                if (this.isSingletonCurrentlyInCreation(beanName)) {
                    this.logger.debug("Returning eagerly cached instance of singleton bean '" + beanName + "' that is not fully initialized yet - a consequence of a circular reference");
                } else {
                    this.logger.debug("Returning cached instance of singleton bean '" + beanName + "'");
                }
            }

            bean = this.getObjectForBeanInstance(sharedInstance, name, beanName, (RootBeanDefinition)null);
        } else {
            if (this.isPrototypeCurrentlyInCreation(beanName)) {
                throw new BeanCurrentlyInCreationException(beanName);
            }

            BeanFactory parentBeanFactory = this.getParentBeanFactory();
            if (parentBeanFactory != null && !this.containsBeanDefinition(beanName)) {
                String nameToLookup = this.originalBeanName(name);
                if (args != null) {
                    return parentBeanFactory.getBean(nameToLookup, args);
                }

                return parentBeanFactory.getBean(nameToLookup, requiredType);
            }

            if (!typeCheckOnly) {
                this.markBeanAsCreated(beanName);
            }

            try {
                final RootBeanDefinition mbd = this.getMergedLocalBeanDefinition(beanName);
                this.checkMergedBeanDefinition(mbd, beanName, args);
                String[] dependsOn = mbd.getDependsOn();
                String[] var11;
                if (dependsOn != null) {
                    var11 = dependsOn;
                    int var12 = dependsOn.length;

                    for(int var13 = 0; var13 < var12; ++var13) {
                        String dependsOnBean = var11[var13];
                        if (this.isDependent(beanName, dependsOnBean)) {
                            throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Circular depends-on relationship between '" + beanName + "' and '" + dependsOnBean + "'");
                        }

                        this.registerDependentBean(dependsOnBean, beanName);
                        this.getBean(dependsOnBean);
                    }
                }

                if (mbd.isSingleton()) {
                    sharedInstance = this.getSingleton(beanName, new ObjectFactory<Object>() {
                        public Object getObject() throws BeansException {
                            try {
                                return AbstractBeanFactory.this.createBean(beanName, mbd, args);
                            } catch (BeansException var2) {
                                AbstractBeanFactory.this.destroySingleton(beanName);
                                throw var2;
                            }
                        }
                    });
                    bean = this.getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
                } else if (mbd.isPrototype()) {
                    var11 = null;

                    Object prototypeInstance;
                    try {
                        this.beforePrototypeCreation(beanName);
                        prototypeInstance = this.createBean(beanName, mbd, args);
                    } finally {
                        this.afterPrototypeCreation(beanName);
                    }

                    bean = this.getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
                } else {
                    String scopeName = mbd.getScope();
                    Scope scope = (Scope)this.scopes.get(scopeName);
                    if (scope == null) {
                        throw new IllegalStateException("No Scope registered for scope '" + scopeName + "'");
                    }

                    try {
                        Object scopedInstance = scope.get(beanName, new ObjectFactory<Object>() {
                            public Object getObject() throws BeansException {
                                AbstractBeanFactory.this.beforePrototypeCreation(beanName);

                                Object var1;
                                try {
                                    var1 = AbstractBeanFactory.this.createBean(beanName, mbd, args);
                                } finally {
                                    AbstractBeanFactory.this.afterPrototypeCreation(beanName);
                                }

                                return var1;
                            }
                        });
                        bean = this.getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
                    } catch (IllegalStateException var21) {
                        throw new BeanCreationException(beanName, "Scope '" + scopeName + "' is not active for the current thread; " + "consider defining a scoped proxy for this bean if you intend to refer to it from a singleton", var21);
                    }
                }
            } catch (BeansException var23) {
                this.cleanupAfterBeanCreationFailure(beanName);
                throw var23;
            }
        }

        if (requiredType != null && bean != null && !requiredType.isAssignableFrom(bean.getClass())) {
            try {
                return this.getTypeConverter().convertIfNecessary(bean, requiredType);
            } catch (TypeMismatchException var22) {
                if (this.logger.isDebugEnabled()) {
                    this.logger.debug("Failed to convert bean '" + name + "' to required type [" + ClassUtils.getQualifiedName(requiredType) + "]", var22);
                }

                throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
            }
        } else {
            return bean;
        }
    }

好，下边咱们就开始这场江湖的血雨腥风。

首先第一句就是：

final String beanName = this.transformedBeanName(name);

这句作的事情，好像不知道所云，由于beanName不是做为参数传进来了吗，还要再转换是什么意思，稍微想一下就知道了，咱们获取bean的时候传过来的name参数，有多是别名。

若是是别名这里就须要转换一下了，由于咱们须要真正的名称。

翻看下代码：

protected String transformedBeanName(String name) {
        return this.canonicalName(BeanFactoryUtils.transformedBeanName(name));
    }

括号里边的部分的代码以下：

public static String transformedBeanName(String name) {
        Assert.notNull(name, "'name' must not be null");

        String beanName;
        for(beanName = name; beanName.startsWith("&"); beanName = beanName.substring("&".length())) {
        }

        return beanName;
    }

若是name是以&开头的，那么去除开头的&符号。继续：

public String canonicalName(String name) {
        String canonicalName = name;

        String resolvedName;
        do {
            resolvedName = (String)this.aliasMap.get(canonicalName);
            if (resolvedName != null) {
                canonicalName = resolvedName;
            }
        } while(resolvedName != null);

        return canonicalName;
    }

这里很容易看出来，就是根据名称去别名map中获取有没有对应的名称。目的就是获取别名对应的真实Bean名称。

接下来这句getSingleton就涉及到伟大的又扯淡的各类面试都会问到的循环依赖问题了，其实不复杂，可是没认真研究过代码。关于循环依赖的问题，能够看下个章节。这里重点仍是建立Bean这个主题。

咱们继续上边的doCreateBean(name, requiredType, args[], typeCheckOnly)的代码。转换完名字以后，紧接的一句是getSingleton(beanName).

@Override
    @Nullable
    public Object getSingleton(String beanName) {
        return getSingleton(beanName, true);
    }

    /**
     * Return the (raw) singleton object registered under the given name.
     * <p>Checks already instantiated singletons and also allows for an early
     * reference to a currently created singleton (resolving a circular reference).
     * @param beanName the name of the bean to look for
     * @param allowEarlyReference whether early references should be created or not
     * @return the registered singleton object, or {@code null} if none found
     */
    @Nullable
    protected Object getSingleton(String beanName, boolean allowEarlyReference) {
        Object singletonObject = this.singletonObjects.get(beanName);
        if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
            synchronized (this.singletonObjects) {
                singletonObject = this.earlySingletonObjects.get(beanName);
                if (singletonObject == null && allowEarlyReference) {
                    ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);
                    if (singletonFactory != null) {
                        singletonObject = singletonFactory.getObject();
                        this.earlySingletonObjects.put(beanName, singletonObject);
                        this.singletonFactories.remove(beanName);
                    }
                }
            }
        }
        return singletonObject;
    }

这里咱们观察注释，可以了解一部分：返回已这个beanName注册的实例。而且检查已经初始化的实例，容许当前建立的实例有一个早期的引用（用来解决循环依赖问题）。

咱们深刻代码来看一下：

首先从singletonObjects.get(beanName)从缓存里获取一下，看有没有，若是有直接返回。若是没有，而且当前beanName正在建立，那么加锁后边的这部分代码：

判断beanName是否在earlySingletonObjects列表中，若是不在而且容许早期引用，那么就获取beanName对应的ObjectFactory。而后调用ObjectFactory.getObject()返回实例。并将该实例添加到earlySingletonObjects中。这里确实就是解决循环引用的核心了，解决循环依赖的核心就是这里的这个singletonFactories.get(beanName)获取singletonFactory，而后调用getOjbect返回实例。说的通俗一点儿就是可能对象尚未建立，可是可以建立这个对象的ObjectFactroy会提早放入缓存中，这样，当后续建立过程当中，须要引用一个以前尚未建立完的bean时，就会调用这里的ObjectFactory.getObject()返回一个实例对象。

这个部分咱们在下一篇专门将循环依赖的文章里详细阐述。在这里，这个getSingleton在总体流程上，最核心的是从缓存中尝试获取bean。

咱们继续看下代码，咱们用粗体标示了一个方法：getObjectForBeanInstance(scopedInstance, name, beanName, mdb)。咱们看到，后续的几种状况里，不管是singleton/prototype/仍是其余实例模式，获得bean以后，作的事情都是这个getObjectForBeanInstance方法，咱们来跟进看下：

    /** 获取给定bean实例的对象，要么bean实例自己，要么当它是一个FactroyBean时，它建立出来的对象
     **/
    protected Object getObjectForBeanInstance(
            Object beanInstance, String name, String beanName, @Nullable RootBeanDefinition mbd) {

        // 若是指定的name是&开头即工厂相关的，但又不是FactoryBean类型，则抛出异常，类型验证不经过
        if (BeanFactoryUtils.isFactoryDereference(name)) {
            if (beanInstance instanceof NullBean) {
                return beanInstance;
            }
            if (!(beanInstance instanceof FactoryBean)) {
                throw new BeanIsNotAFactoryException(beanName, beanInstance.getClass());
            }
        }
// 如今咱们有个这个bean实例，可是这个bean实例多是普通bean也多是FactoryBean，若是是FactoryBean，那么咱们使用它来获取工厂实例，若是调用者须要的是
FactoryBean自己，那么beanName参数须要带"&"
        if (!(beanInstance instanceof FactoryBean) || BeanFactoryUtils.isFactoryDereference(name)) {
            return beanInstance;
        }
        // 到这里就明确是一个FactoryBean，由于若是不是上边已经返回了
        Object object = null;
        if (mbd == null) {
            object = getCachedObjectForFactoryBean(beanName);
        }
        if (object == null) {
            // Return bean instance from factory.
            FactoryBean<?> factory = (FactoryBean<?>) beanInstance;
            // Caches object obtained from FactoryBean if it is a singleton.
            if (mbd == null && containsBeanDefinition(beanName)) {
                mbd = getMergedLocalBeanDefinition(beanName);
            }
            boolean synthetic = (mbd != null && mbd.isSynthetic());
            object = getObjectFromFactoryBean(factory, beanName, !synthetic);
        }
        return object;
    }

1:判断是不是FactoryBean，判断依据是 beanName是不是"&"开头的。若是是&开头，则表示是获取FactoryBean自己，若是不是&开头，则是获取FactroyBean的方法返回的Bean。若是是&开头，可是自己并非FactoryBean类型，则抛出异常。

2:若是自己不是FactoryBean类型或者beanName不是以“&”开头的，那么直接返回Bean自己。

3:判断BeanDefinitions中是否存在该beanName。这里作的事情实际上是将咱们解析时候生成的GenericBeanDefinition转换成RootBeanDefinition.细节这里就不说了。

4:最后委托给getObjectFromFactoryBean(factory, beanName, !synthetic)方法类获取真正的实例。

咱们继续往下看：

     /**  得到从给定的FactoryBean获取出来的对象*/
    protected Object getObjectFromFactoryBean(FactoryBean<?> factory, String beanName, boolean shouldPostProcess) {
        if (factory.isSingleton() && containsSingleton(beanName)) {
            synchronized (getSingletonMutex()) {
                Object object = this.factoryBeanObjectCache.get(beanName);
                if (object == null) {
                    object = doGetObjectFromFactoryBean(factory, beanName); // Only post-process and store if not put there already during getObject() call above
                    // (e.g. because of circular reference processing triggered by custom getBean calls)
                    Object alreadyThere = this.factoryBeanObjectCache.get(beanName);
                    if (alreadyThere != null) {
                        object = alreadyThere;
                    }
                    else {
                        if (shouldPostProcess) {
                            if (isSingletonCurrentlyInCreation(beanName)) {
                                // Temporarily return non-post-processed object, not storing it yet..
                                return object;
                            }
                            beforeSingletonCreation(beanName);
                            try {
                                object = postProcessObjectFromFactoryBean(object, beanName);
                            }
                            catch (Throwable ex) {
                                throw new BeanCreationException(beanName,
                                        "Post-processing of FactoryBean's singleton object failed", ex);
                            }
                            finally {
                                afterSingletonCreation(beanName);
                            }
                        }
                        if (containsSingleton(beanName)) {
                            this.factoryBeanObjectCache.put(beanName, object);
                        }
                    }
                }
                return object;
            }
        }
        else {
            Object object = doGetObjectFromFactoryBean(factory, beanName); if (shouldPostProcess) {
                try {
                    object = postProcessObjectFromFactoryBean(object, beanName);
                }
                catch (Throwable ex) {
                    throw new BeanCreationException(beanName, "Post-processing of FactoryBean's object failed", ex);
                }
            }
            return object;
        }
    }

核心其实就是这句doGetObjectFromFactoryBean(factory, beanName)。里边的if里是判断是不是单例，而里边的内容跟else的区别就是若是是单例，那么就尝试从缓存中获取，若是缓存中没有才调用到doGetObjectFactoryBean(factory, beanName)。还有里边的beforeSingletonCreation和afterSingletonCreation则都是保证建立过程当中，不会重复建立实例，是为了保证单例性。

好了，咱们仍是继续一层一层的往下看吧。

private Object doGetObjectFromFactoryBean(final FactoryBean<?> factory, final String beanName)
            throws BeanCreationException {

        Object object;
        try {
            if (System.getSecurityManager() != null) {
                AccessControlContext acc = getAccessControlContext();
                try {
                    object = AccessController.doPrivileged((PrivilegedExceptionAction<Object>) factory::getObject, acc);
                }
                catch (PrivilegedActionException pae) {
                    throw pae.getException();
                }
            }
            else {
                object = factory.getObject();
            }
        }
        catch (FactoryBeanNotInitializedException ex) {
            throw new BeanCurrentlyInCreationException(beanName, ex.toString());
        }
        catch (Throwable ex) {
            throw new BeanCreationException(beanName, "FactoryBean threw exception on object creation", ex);
        }

        // Do not accept a null value for a FactoryBean that's not fully
        // initialized yet: Many FactoryBeans just return null then.
        if (object == null) {
            if (isSingletonCurrentlyInCreation(beanName)) {
                throw new BeanCurrentlyInCreationException(
                        beanName, "FactoryBean which is currently in creation returned null from getObject");
            }
            object = new NullBean();
        }
        return object;
    }

终于到了最后获取对象的地方了，这里getObject()的调用为整个经过FactoryBean获取实例的解析过程画上美丽的句号。

承接上文，咱们对缓存中获取bean和FactoryBean方式获取Bean进行了阐述。对getBean("")方法进行了阐述。这一篇咱们先深刻单例的建立来详细说一下spring循环依赖问题的解决。

咱们从doGetBean方法继续，咱们主要看下singleton这一部分：

// Create bean instance.
                if (mbd.isSingleton()) {
                    sharedInstance = getSingleton(beanName, () -> {
                        try {
                            return createBean(beanName, mbd, args);
                        }
                        catch (BeansException ex) {
                            // Explicitly remove instance from singleton cache: It might have been put there
                            // eagerly by the creation process, to allow for circular reference resolution.
                            // Also remove any beans that received a temporary reference to the bean.
                            destroySingleton(beanName);
                            throw ex;
                        }
                    });
                    bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
                }

咱们继续getSingleton(beanName, singletonFactory)。

    /**
     * 返回beanName注册过的单例对象，若是没有，那么建立并注册该beanName的实例*/
    public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
        Assert.notNull(beanName, "Bean name must not be null");
        synchronized (this.singletonObjects) {
            Object singletonObject = this.singletonObjects.get(beanName); // 1 if (singletonObject == null) {
                if (this.singletonsCurrentlyInDestruction) {
                    throw new BeanCreationNotAllowedException(beanName,
                            "Singleton bean creation not allowed while singletons of this factory are in destruction " +
                            "(Do not request a bean from a BeanFactory in a destroy method implementation!)");
                }
                if (logger.isDebugEnabled()) {
                    logger.debug("Creating shared instance of singleton bean '" + beanName + "'");
                }
                beforeSingletonCreation(beanName); // 2 boolean newSingleton = false;
                boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
                if (recordSuppressedExceptions) {
                    this.suppressedExceptions = new LinkedHashSet<>();
                }
                try {
                    singletonObject = singletonFactory.getObject(); // 3
                    newSingleton = true;
                }
                catch (IllegalStateException ex) {
                    // Has the singleton object implicitly appeared in the meantime ->
                    // if yes, proceed with it since the exception indicates that state.
                    singletonObject = this.singletonObjects.get(beanName);
                    if (singletonObject == null) {
                        throw ex;
                    }
                }
                catch (BeanCreationException ex) {
                    if (recordSuppressedExceptions) {
                        for (Exception suppressedException : this.suppressedExceptions) {
                            ex.addRelatedCause(suppressedException);
                        }
                    }
                    throw ex;
                }
                finally {
                    if (recordSuppressedExceptions) {
                        this.suppressedExceptions = null;
                    }
                    afterSingletonCreation(beanName); // 4
                }
                if (newSingleton) {
                    addSingleton(beanName, singletonObject);
                }
            }
            return singletonObject;
        }
    }

这里其实最核心的就是singletonFactory.getObject()。咱们梳理下步骤：

1:尝试从缓存获取beanName对应的bean

2:若是没有，调用beforeSingletonCreation(beanName)，将beanName放入singletonCurrentlyInCreation列表。

3:经过调用参数传入的FactoryBean的getObject方法，获取实例化bean

4:加载完成后，处理以后的方法调用。这里作的事情跟beforeSingletonCreation正好相反，把beanName从singletonCurrentlyInCreation中删除

5:缓存生成的object。并删除生成过程当中的相关状态。

/**
     * Add the given singleton object to the singleton cache of this factory.
     * <p>To be called for eager registration of singletons.
     * @param beanName the name of the bean
     * @param singletonObject the singleton object
     */
    protected void addSingleton(String beanName, Object singletonObject) {
        synchronized (this.singletonObjects) {
            this.singletonObjects.put(beanName, singletonObject); // 放入缓存
            this.singletonFactories.remove(beanName);
            this.earlySingletonObjects.remove(beanName);
            this.registeredSingletons.add(beanName);
        }
    }

6:返回bean，这个bean就是上边getSingleton(beanName, singletonFactory)的这个参数，在doGetBean中定义的方法。

                    sharedInstance = getSingleton(beanName, () -> { // 这里是jdk8引入的函数是写法，这里其实就是ObjectFactroy的一个匿名类实现 try {
                            return createBean(beanName, mbd, args);
                        }
                        catch (BeansException ex) {
                            // Explicitly remove instance from singleton cache: It might have been put there
                            // eagerly by the creation process, to allow for circular reference resolution.
                            // Also remove any beans that received a temporary reference to the bean.
                            destroySingleton(beanName);
                            throw ex;
                        }
                    });

接下来就是建立bean的代码了。

咱们来详细看下这个createBean(beanName, mdb, args)

/**
     * Central method of this class: creates a bean instance,
     * populates the bean instance, applies post-processors, etc.
     * @see #doCreateBean
     */
    @Override
    protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
            throws BeanCreationException {

        if (logger.isTraceEnabled()) {
            logger.trace("Creating instance of bean '" + beanName + "'");
        }
        RootBeanDefinition mbdToUse = mbd;

        // Make sure bean class is actually resolv1ed at this point, and
        // clone the bean definition in case of a dynamically resolved Class
        // which cannot be stored in the shared merged bean definition.
        Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
        if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
            mbdToUse = new RootBeanDefinition(mbd);
            mbdToUse.setBeanClass(resolvedClass);
        }

        // Prepare method overrides.
        try {
            mbdToUse.prepareMethodOverrides();
        }
        catch (BeanDefinitionValidationException ex) {
            throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(),
                    beanName, "Validation of method overrides failed", ex);
        }

        try {
            // Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
            Object bean = resolveBeforeInstantiation(beanName, mbdToUse); if (bean != null) {
                return bean;
            }
        }
        catch (Throwable ex) {
            throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName,
                    "BeanPostProcessor before instantiation of bean failed", ex);
        }

        try {
            Object beanInstance = doCreateBean(beanName, mbdToUse, args); if (logger.isTraceEnabled()) {
                logger.trace("Finished creating instance of bean '" + beanName + "'");
            }
            return beanInstance;
        }
        catch (BeanCreationException | ImplicitlyAppearedSingletonException ex) {
            // A previously detected exception with proper bean creation context already,
            // or illegal singleton state to be communicated up to DefaultSingletonBeanRegistry.
            throw ex;
        }
        catch (Throwable ex) {
            throw new BeanCreationException(
                    mbdToUse.getResourceDescription(), beanName, "Unexpected exception during bean creation", ex);
        }
    }

1:根据mdb获取beanName对应的class。

2:对override属性进行处理

3:应用初始化前的处理器

4:建立bean

咱们来详细看下override 的处理

/**
     * Validate and prepare the method overrides defined for this bean.
     * Checks for existence of a method with the specified name.
     * @throws BeanDefinitionValidationException in case of validation failure
     */
    public void prepareMethodOverrides() throws BeanDefinitionValidationException {
        // Check that lookup methods exists.
        if (hasMethodOverrides()) {
            Set<MethodOverride> overrides = getMethodOverrides().getOverrides();
            synchronized (overrides) {
                for (MethodOverride mo : overrides) {
                    prepareMethodOverride(mo);
                }
            }
        }
    }

    /**
     * Validate and prepare the given method override.
     * Checks for existence of a method with the specified name,
     * marking it as not overloaded if none found.
     * @param mo the MethodOverride object to validate
     * @throws BeanDefinitionValidationException in case of validation failure
     */
    protected void prepareMethodOverride(MethodOverride mo) throws BeanDefinitionValidationException {
        int count = ClassUtils.getMethodCountForName(getBeanClass(), mo.getMethodName());
        if (count == 0) {
            throw new BeanDefinitionValidationException(
                    "Invalid method override: no method with name '" + mo.getMethodName() +
                    "' on class [" + getBeanClassName() + "]");
        }
        else if (count == 1) {
            // Mark override as not overloaded, to avoid the overhead of arg type checking.
            mo.setOverloaded(false);
        }
    }

这里咱们要理解下lookup-method和override-method的问题。这两个配置咱们在解析xml的时候说过但没有太详细介绍，这两个的做用lookup-method。（这里不太明白还，暂时放这里，后续bean生成的时候看下到底代码如何实现的，再过来看）