Spring源碼之BeanDefinition類是什么

這篇文章主要介紹了Spring源碼之BeanDefinition類是什么，具有一定借鑒價值，需要的朋友可以參考下。希望大家閱讀完這篇文章后大有收獲。下面讓小編帶著大家一起了解一下。

Spring版本為5.1.5

用過spring的人都知道，我們將對象注入到spring容器中，交給spring來幫我們管理。這種對象我們稱之為bean對象。但是這些bean對象在spring容器中，到底是以什么形式存在，具有哪些屬性、行為呢？今天我們進入到spring源碼來一探究竟。

bean的創建工廠BeanFactory有個默認實現類DefaultListableBeanFactory，內部有個存放所有注入bean對象信息的Map

/** Map of bean definition objects, keyed by bean name. */
private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<>(256);

Map的value對象BeanDefinition就是spring中對bean的定義和描述，具體概述如下：

注意：BeanDefinition是一個接口，內部只定義了bean對象的一些基本行為。上表中的屬性在BeanDefinition中并不是真實存在的，只是通過set、get方法來設置和獲取。以下抽取出部分BeanDefinition源代碼供大家感知下

public interface BeanDefinition extends AttributeAccessor, BeanMetadataElement {
    /**
     * 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();
}

實際使用

假設有以下兩個bean，Java代碼如下

MyTestBean

package com.yuanweiquan.learn.bean;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Description;

public class MyTestBean {
    @Autowired
    private AutowireCandidateBean autowireCandidateBean;

    public void init() {
        System.out.println("inti MyTestBean");
    }

    public AutowireCandidateBean getAutowireCandidateBean() {
        return autowireCandidateBean;
    }
    public void setAutowireCandidateBean(AutowireCandidateBean bean) {
        this.autowireCandidateBean = bean;
    }
}

AutowireCandidateBean

package com.yuanweiquan.learn.bean;

public class AutowireCandidateBean {
    public void initBean() {
        System.out.println("init AutowireCandidateBean");
    }

    public void destroyBean() {
        System.out.println("destroy AutowireCandidateBean");
    }
}

下面看如何在配置文件applicationContext.xml來進行配置

   <bean id="myTestBean" class="com.yuanweiquan.learn.bean.MyTestBean" 
         depends-on="autowireCandidateBean" 
         init-method="init"/>
         
   <bean id="autowireCandidateBean" 
         class="com.yuanweiquan.learn.bean.AutowireCandidateBean"
         init-method="initBean"
         autowire-candidate="true"
         destroy-method="destroyBean"
         scope="singleton"
         parent="myTestBean"
         lazy-init="default"
         primary="true">
      <description>autowireCandidateBean description</description>
   </bean>

接下來就是測試代碼

FileSystemXmlApplicationContext factory = 
        new FileSystemXmlApplicationContext("classpath:applicationContext.xml");
BeanDefinition myTestBeanDefinition = 
        factory.getBeanFactory().getBeanDefinition("autowireCandidateBean");
//輸出
System.out.println("bean description:" + myTestBeanDefinition.getDescription());
System.out.println("bean class name:" + myTestBeanDefinition.getBeanClassName());
System.out.println("parent name:" + myTestBeanDefinition.getParentName());
System.out.println("scope:" + myTestBeanDefinition.getScope());
System.out.println("is lazyinit:" + myTestBeanDefinition.isLazyInit());
System.out.println("depends On:" + myTestBeanDefinition.getDependsOn());
System.out.println("is autowireCandidate:" + myTestBeanDefinition.isAutowireCandidate());
System.out.println("is primary:" + myTestBeanDefinition.isPrimary());
System.out.println("factory bean name:"+myTestBeanDefinition.getFactoryBeanName());
System.out.println("factory bean method name:" + myTestBeanDefinition.getFactoryMethodName());
System.out.println("init method name:" + myTestBeanDefinition.getInitMethodName());
System.out.println("destory method name:" + myTestBeanDefinition.getDestroyMethodName());
System.out.println("role:" + myTestBeanDefinition.getRole());
//關閉context，否則不會調用bean的銷毀方法
factory.close();

控制臺輸出如下

init AutowireCandidateBean
inti MyTestBean
bean description:autowireCandidateBean description
bean class name:com.yuanweiquan.learn.bean.AutowireCandidateBean
parent name:myTestBean
scope:singleton
is lazyinit:false
depends On:null
is autowireCandidate:true
is primary:true
factory bean name:null
factory bean method name:null
init method name:initBean
destory method name:destroyBean
role:0
destroy AutowireCandidateBean

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