【spring原理】读取xml配置来初始化bean

读取xml配置来初始化bean

根据github 项目学习：tiny-spring，地址：https://github.com/code4craft/tiny-spring

参考博客链接：https://blog.csdn.net/w8253497062015/article/details/90274387

Resource是spring内部定位资源的接口。

public interface Resource {
    InputStream getInputStream() throws IOException;
}

UrlResource 实现 Resource

解决获取IO流的问题:

URL类定位xml文件，url.openConnect().connect()即可定位并打开文件，利用getInputStream获得文件输入流。

public class UrlResource implements Resource {

    private final URL url;

    public UrlResource(URL url) {
        this.url = url;
    }

    @Override
    public InputStream getInputStream() throws IOException{
        URLConnection urlConnection = url.openConnection();
        urlConnection.connect();
        // Returns an input stream that reads from this open connection.
        return urlConnection.getInputStream();
    }
}

ResourceLoader 获取路径

public class ResourceLoader {
    public Resource getResource(String location){
        URL resource = this.getClass().getClassLoader().getResource(location);
        return new UrlResource(resource);
    }
}

AbstractBeanDefinitionReader

public abstract class AbstractBeanDefinitionReader implements BeanDefinitionReader {

    private Map<String,BeanDefinition> registry;

    private ResourceLoader resourceLoader;

    protected AbstractBeanDefinitionReader(ResourceLoader resourceLoader) {
        this.registry = new HashMap<String, BeanDefinition>();
        this.resourceLoader = resourceLoader;
    }

    public Map<String, BeanDefinition> getRegistry() {
        return registry;
    }

    public ResourceLoader getResourceLoader() {
        return resourceLoader;
    }
}

XmlBeanDefinitionReader

通过XMLBeanDefinitionReader类和DocumentBuilder对xml进行解析。先根据bean定位到所有的bean，根据类名和实例名构建一个空实例，然后每一个bean中定位property，利用PVS类和PV类实现对bean属性的赋值

public class XmlBeanDefinitionReader extends AbstractBeanDefinitionReader {

	public XmlBeanDefinitionReader(ResourceLoader resourceLoader) {
		super(resourceLoader);
	}

	@Override
	public void loadBeanDefinitions(String location) throws Exception {
		InputStream inputStream = getResourceLoader().getResource(location).getInputStream();
		doLoadBeanDefinitions(inputStream);
	}

	protected void doLoadBeanDefinitions(InputStream inputStream) throws Exception {
		DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
		DocumentBuilder docBuilder = factory.newDocumentBuilder();
		Document doc = docBuilder.parse(inputStream);
		// 解析bean
		registerBeanDefinitions(doc);
		inputStream.close();
	}

	public void registerBeanDefinitions(Document doc) {
		Element root = doc.getDocumentElement();

		parseBeanDefinitions(root);
	}

	protected void parseBeanDefinitions(Element root) {
		NodeList nl = root.getChildNodes();
		for (int i = 0; i < nl.getLength(); i++) {
			Node node = nl.item(i);
			if (node instanceof Element) {
				Element ele = (Element) node;
				processBeanDefinition(ele);
			}
		}
	}

	protected void processBeanDefinition(Element ele) {
		String name = ele.getAttribute("name");
		String className = ele.getAttribute("class");
        BeanDefinition beanDefinition = new BeanDefinition();
        processProperty(ele,beanDefinition);
        beanDefinition.setBeanClassName(className);
		getRegistry().put(name, beanDefinition);
	}

    private void processProperty(Element ele,BeanDefinition beanDefinition) {
        NodeList propertyNode = ele.getElementsByTagName("property");
        for (int i = 0; i < propertyNode.getLength(); i++) {
            Node node = propertyNode.item(i);
            if (node instanceof Element) {
                Element propertyEle = (Element) node;
                String name = propertyEle.getAttribute("name");
                String value = propertyEle.getAttribute("value");
                beanDefinition.getPropertyValues().addPropertyValue(new PropertyValue(name,value));
            }
        }
    }
}

实现

public class BeanFactoryTest {

	@Test
	public void test() throws Exception {
		// 1.读取配置
		XmlBeanDefinitionReader xmlBeanDefinitionReader = new XmlBeanDefinitionReader(new ResourceLoader());
		xmlBeanDefinitionReader.loadBeanDefinitions("tinyioc.xml");

		// 2.初始化BeanFactory并注册bean
		BeanFactory beanFactory = new AutowireCapableBeanFactory();
		for (Map.Entry<String, BeanDefinition> beanDefinitionEntry : xmlBeanDefinitionReader.getRegistry().entrySet()) {
			beanFactory.registerBeanDefinition(beanDefinitionEntry.getKey(), beanDefinitionEntry.getValue());
		}

		// 3.获取bean
		HelloWorldService helloWorldService = (HelloWorldService) beanFactory.getBean("helloWorldService");
		helloWorldService.helloWorld();

	}
}