用工厂模式+反射对依赖注入做个探究

概述

创建不同但是相关类型的对象&＃xff08;继承同一父类或者接口的一组子类&＃xff09;&＃xff0c;由给定的参数来决定创建哪种类型的对象的模式叫工厂模式&＃xff0c;结合以前学的反射来对依赖注入做个简单的探究

大体思路是有一个实体BeanDefinition记录类的信息&＃xff0c;而XmlBeanConfigParser负责解析xml文件&＃xff0c;并将实体信息传给BeansFactory&＃xff0c;BeansFactory根据实体信息创建相应的对象&＃xff0c;如图

demo

ClassPathXmlApplication类:

public class ClassPathXmlApplication {private BeansFactory beansFactory;private XmlBeanConfigParser beanConfigParser;public ClassPathXmlApplication(String config){this.beansFactory &＃61; new BeansFactory();this.beanConfigParser &＃61; new XmlBeanConfigParser();loadBeanDefinition(config);}private void loadBeanDefinition(String config) {InputStream in &＃61; null;try {in &＃61; this.getClass().getResourceAsStream("/"&＃43;config);if (in &＃61;&＃61; null){throw new RuntimeException("can not find config file:"&＃43;config);}List<BeanDefinition> beanDefinitions &＃61; beanConfigParser.parse(in);beansFactory.addBeanDefinitions(beanDefinitions);} catch (DocumentException e) {e.printStackTrace();}finally {if (in!&＃61;null){try {in.close();} catch (IOException e) {e.printStackTrace();}}}}public Object getBean(String beanId){return beansFactory.getBean(beanId);}public static void main(String[] args) {ClassPathXmlApplication xmlApplication &＃61; new ClassPathXmlApplication("beans.xml");Person person &＃61; (Person) xmlApplication.getBean("person");System.out.println(person);}}


XmlBeanConfigParser 类:解析xml配置文件&＃xff0c;生成BeanDefinition的List传给BeanFactory

public class XmlBeanConfigParser {public List<BeanDefinition> parse(InputStream inputStream) throws DocumentException {List<BeanDefinition> beanDefinitions &＃61; new ArrayList<>();SAXReader reader &＃61; new SAXReader();;Document document &＃61; reader.read(inputStream);Element root &＃61; document.getRootElement();Iterator<Element> it&＃61;root.elementIterator("bean");while (it.hasNext()){BeanDefinition beanDefinition &＃61; new BeanDefinition();Element child &＃61; it.next();Iterator<Attribute> attribute &＃61; child.attributeIterator();while(attribute.hasNext()) {Attribute attr &＃61; attribute.next();if ("id".equalsIgnoreCase(attr.getName())){beanDefinition.setId(attr.getValue());}if ("class".equalsIgnoreCase(attr.getName())){beanDefinition.setClassName(attr.getValue());}}beanDefinitions.add(beanDefinition);}return beanDefinitions;}}


BeansFactory:把解析过来的

List<BeanDefinition> beanDefinitionList


存到一个Map对象中&＃xff0c;需要的时候从Map中拿

public class BeansFactory {private ConcurrentHashMap<String, BeanDefinition> beanDefinitions &＃61; new ConcurrentHashMap<>();public void addBeanDefinitions(List<BeanDefinition> beanDefinitionList){for (BeanDefinition bean:beanDefinitionList) {this.beanDefinitions.put(bean.getId(),bean);}}public Object getBean(String beanId){BeanDefinition beanDefinition &＃61; beanDefinitions.get(beanId);if (beanDefinition&＃61;&＃61;null){throw new NoSuchBeanDefinitionException("没有这个bean类");}//创建类return createBean(beanDefinition);
}private Object createBean(BeanDefinition beanDefinition) {Object bean &＃61; null;try {Class beanClass &＃61; Class.forName(beanDefinition.getClassName());bean &＃61; beanClass.newInstance();} catch (ClassNotFoundException e) {e.printStackTrace();} catch (IllegalAccessException e) {e.printStackTrace();} catch (InstantiationException e) {e.printStackTrace();}return bean;}
}


BeanDefinition:保存xml中bean对象的信息

public class BeanDefinition {private String id;private String className;public void setId(String id) {this.id &＃61; id;}public void setClassName(String className) {this.className &＃61; className;}public String getId() {return id;}public String getClassName() {return className;}
}


测试一下: