简单模拟 spring的bean容器的实现

  原理：从配置文件读取类的地址，通过Class.forName()方法实例化对象。方法静态化，使其工厂启动时，所有的bean以被实例化，可以随时取。

  思路 ：1.定义beanFactory  接口  2.  beanFactoryFactory的实现

定义javabean

public class Hello {    public void hello(){        System.out.println("hello spring");    }}

写配置文件

<?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">    <!--    xmlns 即 xml namespace xml 使用的命名空间    xmlns:xsi 即 xml schema instance xml 遵守的具体规范    xsi:schemaLocation 本文档 xml 遵守的规范 官方指定    -->    <bean id="hello" class="com.shsxt.Hello"/></beans>

描述对象属性的类

public class Entry {    String name;    String clazz;    public Entry(String name,String clazz){        this.name=name;        this.clazz=clazz;    }}

beanFactory接口定义

public interface BeanFactory {    Object getBean(String id);}

beanFactory实现类

public class BeanFactoryImpl implements BeanFactory {    private static final String BEAN_ID = "id";    private static final String BEAN_CLASS = "class";    //对象存放的容器    private static Map<String,Object> container = new ConcurrentHashMap<String,Object>();    //从配置文件读取出来的id和class的键值对才存入list    private static List<Entry> list = new LinkedList<Entry>();    /**     * 构造器，传入配置文件，并初始化bean池     * @param filePath     */    public BeanFactoryImpl(String filePath){        readXMLHelper(filePath);        beanInit();    }    /**     * 读取配置文件，获取id和class，list     * @param filePath     */    private static void readXMLHelper(String filePath) {        URL url = BeanFactoryImpl.class.getClassLoader().getResource(filePath);        SAXReader saxReader = new SAXReader();        try{            Document document = saxReader.read(url);            Map<String,Object> map = new HashMap<String,Object>();            map.put("sxt","http://www.springframework.org/schema/beans");            XPath xPath = document.createXPath("//sxt:bean");            xPath.setNamespaceURIs(map);            List<Element> elements = xPath.selectNodes(document);            for (Element element:elements){                list.add(new Entry(element.attributeValue(BEAN_ID),element.attributeValue(BEAN_CLASS)));            }        } catch (DocumentException e) {            e.printStackTrace();        }    }    /**     * 根据list中的class值，实例化对象，并将对应的id-Object存入容器container内     */    private static void beanInit() {        Iterator<Entry> iterator = list.iterator();        while(iterator.hasNext()){            Entry en = iterator.next();            try{                Class<?> cls = Class.forName(en.clazz);                Object obj = cls.newInstance();                container.put(en.name,obj);            }catch (Exception e){                e.printStackTrace();            }        }    }    /**     * 重写接口的getBean方法，从容器container中取值     * @param name     * @return     */    public Object getBean(String name) {        return container.get(name);    }}

测试类

public class HelloTest {    public static void main(String[] args) {        BeanFactoryImpl ac = new BeanFactoryImpl("spring.xml");        Object object = ac.getBean("hello");        Hello hello = (Hello) object;        hello.hello();    }}