chapter05_从spring.xml读取Bean
一、简化Bean的注册
如果每次注册一个Bean，都要像上节一样，手动写PropertyValues相关的代码，那太复杂了，我们希望读取XML文件，自动注册Bean，这样对于使用者，甚至不知道有BeanDefinition的存在
二、统一处理资源文件
新建资源接口，Spring对所有的资源文件，统一处理
- 一个资源，最重要的就是拿到输入流，拿到输入流就可以读取文件
public interface Resource {InputStream getInputStream() throws IOException;
}
提供三个资源实现类，分别读取不同类型的文件，这就是策略模式
类路径下的文件（最常用）
public class ClassPathResource implements Resource{private final String path;private final ClassLoader classLoader;public ClassPathResource(String path) {this(path, null);}public ClassPathResource(String path, ClassLoader classLoader) {Assert.notNull(path, "Path must not be null");this.path = path;this.classLoader = classLoader != null ? classLoader : ClassUtil.getClassLoader();}@Overridepublic InputStream getInputStream() throws IOException {InputStream is = classLoader.getResourceAsStream(path);if (is == null) {throw new FileNotFoundException(path + " cannot be opened because it does not exist");}return is;}
}
文件系统下的文件
public class FileSystemResource implements Resource{private File file;public FileSystemResource(File file) {this.file = file;}@Overridepublic InputStream getInputStream() throws IOException {return Files.newInputStream(file.toPath());}
}
网络文件
public class UrlResource implements Resource{private final URL url;public UrlResource(URL url) {Assert.notNull(url,"URL must not be null");this.url = url;}@Overridepublic InputStream getInputStream() throws IOException {URLConnection con = url.openConnection();return con.getInputStream();}
}
资源加载器接口，简化资源类的使用，自动根据路径选择合适的加载类
- 这又属于工厂方法设计模式
/*** @Author 孤风雪影* @Email gitee.com/efairy520* @Date 2025/1/2 22:16* @Version 1.0*/
public interface ResourceLoader {String CLASSPATH_URL_PREFIX = "classpath:";Resource getResource(String location);
}
资源加载器接口实现
- 根据路径前缀，默认就是使用classpath策略
/*** @Author 孤风雪影* @Email gitee.com/efairy520* @Date 2025/1/2 22:18* @Version 1.0*/
public class DefaultResourceLoader implements ResourceLoader{@Overridepublic Resource getResource(String location) {Assert.notNull(location, "Location must not be null");if (location.startsWith(CLASSPATH_URL_PREFIX)) {//使用类路径加载器，去掉前缀return new ClassPathResource(location.substring(CLASSPATH_URL_PREFIX.length()));}else {try {URL url = new URL(location);return new UrlResource(url);} catch (MalformedURLException e) {return new FileSystemResource(new File(location));}}}
}
三、从文件中读取Bean
定义BeanDefinitionReader接口，从文件中读取BeanDefinition，并且注册到Bean工厂，这里有三要素
- 资源文件
- Bean工厂
- 读取BeanDefinition的逻辑（单个资源，多个资源，位置字符串）
/*** @Author 孤风雪影* @Email gitee.com/efairy520* @Date 2025/1/2 22:26* @Version 1.0*/
public interface BeanDefinitionReader {BeanDefinitionRegistry getRegistry();ResourceLoader getResourceLoader();void loadBeanDefinitions(Resource resource);void loadBeanDefinitions(Resource... resources);void loadBeanDefinitions(String location);
}
用抽象类AbstractBeanDefinitionReader实现接口，模板方法设计模式
- Bean工厂和资源加载器都是确定的，抽象类直接实现
- 只有加载BeanDefinition是不确定的逻辑，交给具体的策略子类实现
public abstract class AbstractBeanDefinitionReader implements BeanDefinitionReader {private final BeanDefinitionRegistry registry;private final ResourceLoader resourceLoader;public AbstractBeanDefinitionReader(BeanDefinitionRegistry registry, ResourceLoader resourceLoader) {this.registry = registry;this.resourceLoader = resourceLoader;}public AbstractBeanDefinitionReader(BeanDefinitionRegistry registry) {this(registry, new DefaultResourceLoader());}@Overridepublic BeanDefinitionRegistry getRegistry() {return registry;}@Overridepublic ResourceLoader getResourceLoader() {return resourceLoader;}}
XmlBeanDefinitionReader做具体实现，策略模式
public class XmlBeanDefinitionReader extends AbstractBeanDefinitionReader {public XmlBeanDefinitionReader(BeanDefinitionRegistry registry, ResourceLoader resourceLoader) {super(registry, resourceLoader);}public XmlBeanDefinitionReader(BeanDefinitionRegistry registry) {super(registry);}@Overridepublic void loadBeanDefinitions(Resource resource) {try {InputStream is = resource.getInputStream();doLoadBeanDefinitions(is);} catch (IOException e) {throw new RuntimeException("IOException parsing XML document from " + resource, e);}}@Overridepublic void loadBeanDefinitions(Resource... resources) {for (Resource resource : resources) {loadBeanDefinitions(resource);}}@Overridepublic void loadBeanDefinitions(String location) {ResourceLoader resourceLoader = getResourceLoader();Resource resource = resourceLoader.getResource(location);loadBeanDefinitions(resource);}/*** 真正解析XMl文件的方法** @param inputStream*/private void doLoadBeanDefinitions(InputStream inputStream) {Document doc = XmlUtil.readXML(inputStream);Element root = doc.getDocumentElement();NodeList childNodes = root.getChildNodes();for (int i = 0; i < childNodes.getLength(); i++) {// 判断元素if (!(childNodes.item(i) instanceof Element)) continue;// 判断对象if (!"bean".equals(childNodes.item(i).getNodeName())) continue;// 解析标签Element bean = (Element) childNodes.item(i);String id = bean.getAttribute("id");String name = bean.getAttribute("name");String className = bean.getAttribute("class");// 获取 Class，方便获取类中的名称Class<?> clazz = null;try {clazz = Class.forName(className);} catch (ClassNotFoundException e) {throw new RuntimeException("不存在的类名" + className);}// 优先级 id > name，此处是Bean自己的id和nameString beanName = StrUtil.isNotEmpty(id) ? id : name;if (StrUtil.isEmpty(beanName)) {beanName = StrUtil.lowerFirst(clazz.getSimpleName());}// 定义BeanBeanDefinition beanDefinition = new BeanDefinition(clazz);// 读取属性并填充for (int j = 0; j < bean.getChildNodes().getLength(); j++) {if (!(bean.getChildNodes().item(j) instanceof Element)) continue;if (!"property".equals(bean.getChildNodes().item(j).getNodeName())) continue;// 解析标签：propertyElement property = (Element) bean.getChildNodes().item(j);String attrName = property.getAttribute("name");String attrValue = property.getAttribute("value");String attrRef = property.getAttribute("ref");// 获取属性值：引入对象、值对象Object value = StrUtil.isNotEmpty(attrRef) ? new BeanReference(attrRef) : attrValue;// 创建属性信息PropertyValue propertyValue = new PropertyValue(attrName, value);beanDefinition.getPropertyValues().addPropertyValue(propertyValue);}if (getRegistry().containsBeanDefinition(beanName)) {throw new RuntimeException("Duplicate beanName[" + beanName + "] is not allowed");}// 注册 BeanDefinitiongetRegistry().registerBeanDefinition(beanName, beanDefinition);}}
}
BeanDefinitionReader接口、资源接口，层次结构图
四、测试
新建Person类
@Data
@ToString
@NoArgsConstructor
@AllArgsConstructor
@EqualsAndHashCode
public class Person {private String name;private int age;private Cat cat;
}
新建Cat类
@Data
@ToString
@NoArgsConstructor
@AllArgsConstructor
@EqualsAndHashCode
public class Cat {private String name;private int weight;
}
编写一个spring.xml文件
<?xml version="1.0" encoding="UTF-8"?>
<beans><bean id="cat" class="cn.shopifymall.springframework.test.bean.Cat"><property name="name" value="tomcat"/><property name="weight" value="2000"/></bean><bean id="person" class="cn.shopifymall.springframework.test.bean.Person"><property name="name" value="10001"/><property name="age" value="18"/><property name="cat" ref="cat"/></bean></beans>新建测试类
public class ApiTest {@Testpublic void testGetBeanFromXml() {// 1.初始化 BeanFactoryDefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();// 2. 读取配置文件&注册BeanXmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(beanFactory);reader.loadBeanDefinitions("classpath:spring.xml");// 3. 获取Bean对象调用方法Person person = (Person) beanFactory.getBean("person");System.out.println("person：" + person);}
}
控制台输出
person：Person(name=10001, age=18, cat=Cat(name=tomcat, weight=2000))
五、总结
- 通过引入spring.xml配置文件，我们就可以简化Bean的注册
- 用户只需要编写一个xml文件，由XmlBeanDefinitionReader自动解析xml文件，生成BeanDefinition并注册到BeanFactory