Spring阅读笔记 (一) : XmlBeanFactory

项目准备:

环境:

java 8

gradle 4.10

代码:

build.gradle :

plugins {
    id 'java'
}

group 'cn.fancy.spring.test'
version '1.0-SNAPSHOT'

sourceCompatibility = 1.8

repositories {
    mavenCentral()
}

dependencies {
    // https://mvnrepository.com/artifact/org.springframework/spring-core
    compile group: 'org.springframework', name: 'spring-core', version: '5.1.2.RELEASE'
    // https://mvnrepository.com/artifact/org.springframework/spring-beans
    compile group: 'org.springframework', name: 'spring-beans', version: '5.1.2.RELEASE'
    testCompile group: 'junit', name: 'junit', version: '4.12'
}

MyTestBean

package cn.fancy.testbean;

/**
 * @author fancy
 * @date 2018-11-23 08:48
 */
public class MyTestBean {

    private String name = "fancy";


    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

beanFactoryTest.xml

<?xml version="1.0" encoding="utf-8" ?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
                           http://www.springframework.org/schema/beans/spring-beans.xsd " >

    <bean id="myTestBean" class="cn.fancy.testbean.MyTestBean">
        <property name="name" value="张三"/>
    </bean>
</beans>

MyBeanFactoryTest

package cn.fancy.testbean;

import org.junit.Test;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.support.BeanDefinitionReader;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.beans.factory.xml.XmlBeanDefinitionReader;
import org.springframework.beans.factory.xml.XmlBeanFactory;
import org.springframework.core.io.ClassPathResource;
import org.springframework.core.io.Resource;

import javax.management.loading.ClassLoaderRepository;

/**
 * @author fancy
 * @date 2018-11-23 08:49
 */
public class MyBeanFactoryTest {

    @Test
    public void testSimpleLoad () {
        XmlBeanFactory xmlBeanFactory = new XmlBeanFactory(new ClassPathResource("beanFactoryTest.xml"));
        MyTestBean myTestBean = (MyTestBean)xmlBeanFactory.getBean("myTestBean");
        System.out.println(myTestBean.getName());
    }
}

我们发现XmlBeanFactory过时了,那我们不使用XmlBeanFactory,怎么去读取配置生成bean呢?
我们先看下下面这行代码XmlBeanFactory 做了什么工作?

	/**
	 * Create a new XmlBeanFactory with the given resource,
	 * which must be parsable using DOM.
	 * @param resource the XML resource to load bean definitions from
	 * @throws BeansException in case of loading or parsing errors
	 */
	public XmlBeanFactory(Resource resource) throws BeansException {
		this(resource, null);
	}

/**
	 * Create a new XmlBeanFactory with the given input stream,
	 * which must be parsable using DOM.
	 * @param resource the XML resource to load bean definitions from
	 * @param parentBeanFactory parent bean factory
	 * @throws BeansException in case of loading or parsing errors
	 */
	public XmlBeanFactory(Resource resource, BeanFactory parentBeanFactory) throws BeansException {
		super(parentBeanFactory);
		this.reader.loadBeanDefinitions(resource);
	}

我们在调用new XmlBeanFactory(new ClassPathResource(“beanFactoryTest.xml”))的时候,主要讲resource 资源传入this.reader.loadBeanDefinitions(resource);
那么this.reader是什么呢?
先看一下以下代码:

public class XmlBeanFactory extends DefaultListableBeanFactory {

	private final XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(this);
...
}

XmlBeanDefinitionReader 的构造器

/**
	 * Create new XmlBeanDefinitionReader for the given bean factory.
	 * @param registry the BeanFactory to load bean definitions into,
	 * in the form of a BeanDefinitionRegistry
	 */
	public XmlBeanDefinitionReader(BeanDefinitionRegistry registry) {
		super(registry);
	}

根据以上,我们可以仿写一个XmlBeanFactory读取xml的逻辑
代码如下:

   DefaultListableBeanFactory factory = new DefaultListableBeanFactory();
   BeanDefinitionReader beanDefinitionReader=new XmlBeanDefinitionReader(factory);
   beanDefinitionReader.loadBeanDefinitions(new ClassPathResource("beanFactoryTest.xml"));
   MyTestBean myTestBean = (MyTestBean)factory.getBean("myTestBean");
   System.out.println(myTestBean.getName());

根据代码上面的代码,我们能看出XmlBeanFactory继承DefaultListableBeanFactory,同时只比DefaultListableBeanFactory多实现了this.reader.loadBeanDefinitions(resource);这个方法.
那么这个方法干了件什么事情呢?下节在讨论!