模拟Spring IOC的简易实现

模拟Spring IOC的简易实现

IOC是Inversion of Control的缩写，即控制反转，是一个种面向对象的编程和设计思想。主要目的：解耦

即对象不是自己new出来的，而是由框架来生成的（工厂）。

下面来简单模拟一下Spring获得bean的过程

首先需要一个外部配置的xml以及bean所对应的具体类。

<?xml version="1.0" encoding="UTF-8"?><beans>    <bean id="items" class="com.easzz.ioc.Items"/>    <bean id="users" class="com.easzz.ioc.Users">        <property name="userName" value="mike"/>    </bean></beans>

public interface UniversalApp {    void add();}/** * Created by easzz on 2017/8/30 9:46 */public class Users implements UniversalApp {    private String userName;    @Override    public void add() {        System.out.println("userName is "+userName);    }}/** * Created by easzz on 2017/8/30 9:29 */public class Items implements UniversalApp{    @Override    public void add() {        System.out.println("item add...");    }}

下面定义一个接口BeanFactory，用于获得bean。

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

Ioc容器，context，用于存储bean，通过解析xml，使用反射获取其对象，将bean对象和它的id放入一个map中。需要使用的时候get即可。

/** * Created by easzz on 2017/8/30 9:30 */public class XmlContext implements BeanFactory {    //bean context    private Map<String, Object> context = new HashMap<>();    public XmlContext(String xmlName) {        SAXReader saxReader = new SAXReader();        try {            Document read = saxReader.read(this.getClass()                            .getClassLoader().getResourceAsStream(xmlName));            Element rootElement = read.getRootElement();            Iterator iterator = rootElement.elementIterator();            while (iterator.hasNext()){                Element next = (Element)iterator.next();                Object o=null;                if ("bean".equals(next.getName())){                    String id = next.attributeValue("id");                    String className = next.attributeValue("class");                    Class<?> aClass = Class.forName(className);                    Iterator iterator1 = next.elementIterator();                    while (iterator1.hasNext()){                        Element next1 = (Element) iterator1.next();                        if ("property".equals(next1.getName())){                            //设置属性值                            String name = next1.attributeValue("name");                            String value = next1.attributeValue("value");                            o = aClass.newInstance();                            Field declaredField = aClass.getDeclaredField(name);                            //允许访问私有属性                            declaredField.setAccessible(true);                            declaredField.set(o,value);                            declaredField.setAccessible(false);                        }                    }                    context.put(id, o);                }            }        } catch (IllegalAccessException | InstantiationException | ClassNotFoundException | DocumentException | NoSuchFieldException e) {            e.printStackTrace();        }    }    @Override    public Object getBean(String id) {        return context.get(id);    }}

编写测试类

public class Test {    public static void main(String[] args){        BeanFactory beanFactory=new XmlContext("beans.xml");        //由Ioc容器帮我们创建对象，注入依赖。        Users users = (Users) beanFactory.getBean("users");        users.add();    }}

输出

userName is mike

正确的获取到了xml里面所定义的bean以及依赖(userName)…