资深小白谈spring（三）：初步了解Resource

旧城等待， 2022-09-10 11:07 130阅读 0赞

### 资深小白谈spring（三）：初步了解Resource ###

1、接着看上一节的loadBeanDefinitions，这个方法的前几行都是构建beanDefinitionReader，最后一行则是调用loadBeanDefinitions进行xml的解析和注册，下面重点看这个方法。

@Override
    	protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
        
    		XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
    		beanDefinitionReader.setEnvironment(this.getEnvironment());
    		beanDefinitionReader.setResourceLoader(this);
    		beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
    		initBeanDefinitionReader(beanDefinitionReader);
    		loadBeanDefinitions(beanDefinitionReader);
    	}

2、其实loadBeanDefinitions主要就是调用XmlBeanDefinitionReader的loadBeanDefinitions方法，加载xml之前会先通过getConfigLocations去获取我们的xml路径

protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
        
    		Resource[] configResources = getConfigResources();
    		if (configResources != null) {
        
    			reader.loadBeanDefinitions(configResources);
    		}
    		String[] configLocations = getConfigLocations();
    		if (configLocations != null) {
        
    			reader.loadBeanDefinitions(configLocations);
    		}
    	}
    
    	protected String[] getConfigLocations() {
        
    		return (this.configLocations != null ? this.configLocations : getDefaultConfigLocations());
    	}

3、至于configLocations的值是怎么来的，我们先看回main方法在new ClassPathXmlApplicationContext时把xml给传了进去。然后在构造方法里调用setConfigLocations，把xml给设置到configLocations

public class XmlApplication {
        
        public static void main(String[] args) {
        
            //通过指定xml加载上下文
            ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("application.xml");
           //启动容器
            context.refresh();
            //从容器中获取A的bean
            A bean = context.getBean(A.class);
            System.out.println(bean.toString());
        }
    }
    
    public class ClassPathXmlApplicationContext{
        
        //构造方法
    	public ClassPathXmlApplicationContext(String configLocation) throws BeansException {
        
    		//调用重载的构造方法
    		this(new String[] {
        configLocation}, true, null);
    	}
    	
    	//重载的构造方法
    	public ClassPathXmlApplicationContext(
    			String[] configLocations, boolean refresh, @Nullable ApplicationContext parent)
    			throws BeansException {
        
    
    		super(parent);
    		//把xml设置到configLocations
    		setConfigLocations(configLocations);
    		if (refresh) {
        
    			refresh();
    		}
    	}
    
      //父类方法，把locations设置到configLocations
    	public void setConfigLocations(@Nullable String... locations) {
        
    		if (locations != null) {
        
    			Assert.noNullElements(locations, "Config locations must not be null");
    			this.configLocations = new String[locations.length];
    			for (int i = 0; i < locations.length; i++) {
        
    				this.configLocations[i] = resolvePath(locations[i]).trim();
    			}
    		}
    		else {
        
    			this.configLocations = null;
    		}
    	}
    }

4、XmlBeanDefinitionReader的loadBeanDefinitions方法也是个重载方法，通过遍历locations，最终会调用到下面的loadBeanDefinitions方法。这个方法虽然有点长，但其实就是用resourceLoader解析location得到Resource或者Resource数组，那什么是Resource呢？

public int loadBeanDefinitions(String location, @Nullable Set<Resource> actualResources) throws BeanDefinitionStoreException {
        
    		ResourceLoader resourceLoader = getResourceLoader();
    		if (resourceLoader == null) {
        
    			throw new BeanDefinitionStoreException(
    					"Cannot load bean definitions from location [" + location + "]: no ResourceLoader available");
    		}
    
    		if (resourceLoader instanceof ResourcePatternResolver) {
        
    			try {
        
    				Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
    				int count = loadBeanDefinitions(resources);
    				if (actualResources != null) {
        
    					Collections.addAll(actualResources, resources);
    				}
    				if (logger.isTraceEnabled()) {
        
    					logger.trace("Loaded " + count + " bean definitions from location pattern [" + location + "]");
    				}
    				return count;
    			}
    			catch (IOException ex) {
        
    				throw new BeanDefinitionStoreException(
    						"Could not resolve bean definition resource pattern [" + location + "]", ex);
    			}
    		}
    		else {
        
    			Resource resource = resourceLoader.getResource(location);
    			int count = loadBeanDefinitions(resource);
    			if (actualResources != null) {
        
    				actualResources.add(resource);
    			}
    			if (logger.isTraceEnabled()) {
        
    				logger.trace("Loaded " + count + " bean definitions from location [" + location + "]");
    			}
    			return count;
    		}
    	}

5、Resource其实就是spring对一些资源文件的一个统一定义，我们知道能通过它获取到文件流供我们操作就可以了。

public interface Resource extends InputStreamSource {
        
        boolean exists();
    
        default boolean isReadable() {
        
            return this.exists();
        }
    
        default boolean isOpen() {
        
            return false;
        }
    
        default boolean isFile() {
        
            return false;
        }
    
        URL getURL() throws IOException;
    
        URI getURI() throws IOException;
    
        File getFile() throws IOException;
    
        default ReadableByteChannel readableChannel() throws IOException {
        
            return Channels.newChannel(this.getInputStream());
        }
    
        long contentLength() throws IOException;
    
        long lastModified() throws IOException;
    
        Resource createRelative(String var1) throws IOException;
    
        @Nullable
        String getFilename();
    
        String getDescription();
    }

6、结语：本节主要讲了在new ClassPathXmlApplicationContext时会把指定的xml赋值给configLocations，然后在refresh创建beanfactory时构建一个XmlBeanDefinitionReader，这个reader在执行loadBeanDefinitions方法时会遍历configLocations，然后在加载前会把这些location封装成Resource对象。

*  上一篇：[初步了解ClassPathXmlApplicationContext][ClassPathXmlApplicationContext]
 *  下一篇：[xml的解析][xml]

[ClassPathXmlApplicationContext]: https://blog.csdn.net/JankeDeng/article/details/120151757?spm=1001.2014.3001.5502
[xml]: https://blog.csdn.net/JankeDeng/article/details/120178660?spm=1001.2014.3001.5502