spring-IOC控制反转

IoC(Inversion of Control)控制反转，对象创建责任的反转，在spring中BeanFacotory是IoC容器的核心接口，负责实例化，定位，配置应用程序中的对象及建立这些对象间的依赖。XmlBeanFacotory实现BeanFactory接口，通过获取xml配置文件数据，组成应用对象及对象间的依赖关系。

spring中有三种注入方式，一种是set注入，一种是接口注入，另一种是构造方法注入。

注:本实例是在idea软件上执行的,

一.导包:

<dependency>
  <groupId>junit</groupId>
  <artifactId>junit</artifactId>
  <version>4.12</version>
  <scope>test</scope>
</dependency>
<dependency>
  <groupId>org.springframework</groupId>
  <artifactId>spring-context</artifactId>
  <version>4.3.9.RELEASE</version>
</dependency>
<dependency>
  <groupId>org.hibernate</groupId>
  <artifactId>hibernate-core</artifactId>
  <version>5.2.11.Final</version>
</dependency>

二.实体类

package com.yztc.ioc.bean;

/**
 * @author
 */
public class User {
    private Integer uid;
    private String name;
    public void init(){
        System.out.println("初始化对象");
    }


    public User() {
    }

    public User(Integer uid, String name) {
        this.uid = uid;
        this.name = name;
    }

    public Integer getUid() {
        return uid;
    }

    public void setUid(Integer uid) {
        this.uid = uid;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

三.配置beans.xml文件

<beans>
    <bean id="user" class="com.yztc.ioc.bean.User">

        <property name="name" value="11111"/>
    </bean>
</beans>

四.BeanFactory类

package com.yztc.ioc.bean;

import org.dom4j.Attribute;
import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;

import java.lang.reflect.Field;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * @author bindu
 *
 *
 */
public class BeanFactory {
    public static final String DEFAULT_XML_NAME ="beans.xml";
    private String xmlName;
    private Map<String ,Object> beans = new HashMap<>();

    public BeanFactory() {
        this.xmlName =DEFAULT_XML_NAME;
        init();

    }

    public BeanFactory(String xmlName) {
        this.xmlName = xmlName != null&& !"".equals(xmlName)? xmlName:DEFAULT_XML_NAME;
        init();
    }

    /**
     * 1.xml解析
     * 2.实例化注册bean
     */
    private void init(){
        SAXReader reader = new SAXReader();
        try {
            //获得dom操作对象
            Document document = reader.read(this.getClass().getClassLoader().getResourceAsStream(xmlName));
            //获得xml文件的根元素
            Element root = document.getRootElement();
            //获得根元素下的所有子元素
            List<Element> elements = root.elements();
            //遍历所有bean子元素
            for (Element element : elements) {
                //获得bean元素下的id元素
                Attribute idAttr = element.attribute("id");
                //获得id元素属性的值
                String id = idAttr.getValue();
                //获取bean元素下的class属性
                Attribute claAttr = element.attribute("class");
                //获取class属性的值
                String value = claAttr.getValue();
                //class对象实例化的三种方式
                Class<?> cls = Class.forName(value);
                Object o = cls.newInstance();
                List<Element> properties = element.elements("property");
                for (Element property : properties) {
                    Attribute nameAttr = property.attribute("name");
                    String value1 = nameAttr.getValue();
                    Field field = cls.getDeclaredField(value1);
                    //取消jvm运行时的访问检测机制
                    field.setAccessible(true);
                    Attribute valueAttr = property.attribute("value");
                    String value2 = valueAttr.getValue();
                    //给属性赋值
                    field.set(o,value2);
                }
                beans.put(id,o);


            }


        } catch (DocumentException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (NoSuchFieldException e) {
            e.printStackTrace();
        }
    }
    public <T> T getBean(String name){
        return (T) beans.get(name);
    }
    public <T> T getBean(String name ,Class<T> cls){
        return (T) beans.get(name);
    }


}

五.测试类

package com.yztc.ioc;

import com.yztc.ioc.bean.BeanFactory;
import com.yztc.ioc.bean.User;

/**
 * @author
 */
public class TestMain {
    public static void main(String[] args) {
        BeanFactory factory = new BeanFactory();
        User user1 = factory.getBean("user", User.class);

        System.out.println(user1);
    }


}