spring ListableBeanFactory接口中getBeansOfType和BeanFactory接口的isTypeMatch方法实现分析

public interface ListableBeanFactory extends BeanFactory {

........

<T> Map<String, T> getBeansOfType(Class<T> type) throws BeansException;

........

}

public interface ListableBeanFactory extends BeanFactory {

........

boolean isTypeMatch(String name, Class<?> targetType) throws NoSuchBeanDefinitionException;

........

}

ListableBeanFactory接口，继承自BeanFactory接口。DefaultListableBeanFactory类可以认为是ListableBeanFactory接口的一个常用实现。

根据类型获取bean，即getBeansOfType方法，依赖于isTypeMatch。

以DefaultListableBeanFactory为例，getBeansOfType方法内部的核心实现是调用doGetBeanNamesForType方法，private String[] doGetBeanNamesForType(Class<?> type, boolean includeNonSingletons, boolean allowEagerInit) 。在spring中，真正干事的都是do×××方法。

doGetBeanNamesForType方法内，会先获取目前已有的所有的bean名字String[] beanDefinitionNames = getBeanDefinitionNames();，然后循环比较每个bean是否符合类型要求，如果符合，添加到结果集合内，List<String> result = new ArrayList<String>();，最后将result结合返回。

判断bean是否符合类型要求时，需要用到isTypeMatch接口实现，在AbstractBeanFactory类内。AbstractBeanFactory.isTypeMatch方法内，会根据beanName获取对应的RootBeanDefinition对象属性RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);，然后通过调用AbstractAutowireCapableBeanFactory.predictBeanType方法找到beanName对应的class类，Class<?> beanType = predictBeanType(beanName, mbd, typesToMatch);。predictBeanType方法内，会根据beanName找到对应的class值，一般是从RootBeanDefinition属性中getBeanClass方法获取mbd.getBeanClass();，如果有hasInstantiationAwareBeanPostProcessors的情况，会稍微复杂一点，这里不做说明。总之，predictBeanType方法会返回beanName对应的class类。isTypeMatch方法内，最终是用这个返回类和参数中的class类进行对应的。

对比两个类型是否相等的代码只有一句，typeToMatch.isAssignableFrom(beanType);，这是个本地方法，无法追查代码。typeToMatch是isTypeMatch(String name, Class<?>targetType)中targetType的简单处理后的值，Class<?>typeToMatch = (targetType != null ? targetType : Object.class);，beanType是predictBeanType方法中根据beanName获取的对应的class类，Class<?> beanType = predictBeanType(beanName, mbd, typesToMatch);

Class类isAssignableFrom方法说明

public final class Class<T> implements java.io.Serializable,
                              GenericDeclaration,
                              Type,
                              AnnotatedElement {

...........

public native boolean isAssignableFrom(Class<?> cls);

...........

}

instanceof 针对实例 
isAssignableFrom针对class对象

 

isAssignableFrom   是用来判断一个类Class1和另一个类Class2是否相同或是另一个类的超类或接口。   
通常调用格式是  

Java代码  

1. Class1.isAssignableFrom(Class2)     

 

调用者和参数都是   java.lang.Class   类型。   

1. public class Test {  
2.     public static void main(String[] args) {  
3.         List<String> list = new ArrayList<String>();  
4.         System.out.println(list instanceof List);  
5.         System.out.println(list instanceof ArrayList);  
6.           
7.         System.out.println(list.getClass().isAssignableFrom(List.class));  
8.         System.out.println(List.class.isAssignableFrom(list.getClass()));  
9.     }  
10. }  

结果：

true
true
false
true

其中instanceof是子-->父 
isAssignableFrom是父-->子

list.getClass() = class java.util.ArrayList
List.class = interface java.util.List

List ×× = ArrayList 可以

ArrayList ×× = List 报错

boolean java.lang.Class.isAssignableFrom(Class<?> cls)

Determines if the class or interface represented by this Class object is either the same as, or is a superclass or superinterface of, the class or interface represented by the specifiedClass parameter. It returnstrue if so; otherwise it returnsfalse. If this Class object represents a primitive type, this method returnstrue if the specifiedClass parameter is exactly thisClass object; otherwise it returnsfalse.

Specifically, this method tests whether the type represented by the specified Class parameter can be converted to the type represented by this Class object via an identity conversion or via a widening reference conversion. SeeThe Java Language Specification, sections 5.1.1 and 5.1.4 , for details.

Parameters:

cls the Class object to be checked

Returns:

the boolean value indicating whether objects of the type cls can be assigned to objects of this class

Throws:

NullPointerException - if the specified Class parameter is null.

Since:

JDK1.1