Spring 依赖注入控制反转实现，及编码解析（自制容器）

定义：

在运行期，由外部容器动态的将依赖对象动态地注入到组件中。

两种方式：

手工装配

-set方式

-构造器

-注解方式

自动装配（不推荐）

1利用构造器

2set方法注入

dao：

package dao;

public interface PersonDao {
	public void add();
}

daoimpl：

package dao.impl;

import dao.PersonDao;

public class PersonDaoBean implements PersonDao{

	@Override
	public void add() {
		System.out.println("I am person dao");
	}

}

service：

package service;

public interface PersonService {

	public void save();

}

serviceimpl（set实现依赖注入）：

package service.impl;

import dao.PersonDao;
import service.PersonService;

public class PersonServiceBean implements PersonService {

	private PersonDao personDao;

	public PersonDao getPersonDao() {
		return personDao;
	}

	public void setPersonDao(PersonDao personDao) {
		this.personDao = personDao;
	}

	public void save(){
		personDao.add();
	}

}

applicationContext.xml：

<?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-3.1.xsd">

        <bean id = "personDao" class = "dao.impl.PersonDaoBean"></bean>    

        <!-- 默认构造方法 -->
        <bean id = "personService" class = "service.impl.PersonServiceBean">
              <property name = "personDao" ref = "personDao">
              </property>
        </bean>

</beans>

这样一来，dao方法会直接被spring注入到service里。运行service的save方法可以调用dao的save方法。　

　

　除了注入bean还可以注入基本属性类型，以及各种集合类。

编码剖析：

bean定义类：

package test;

import java.util.ArrayList;
import java.util.List;

public class BeanDefinition {
    private String id;
    private String className;
    private List<PropertyDefinition> propertys = new ArrayList<PropertyDefinition>();

    public BeanDefinition(String id, String className) {
        this.id = id;
        this.className = className;
    }
    public String getId() {
        return id;
    }
    public void setId(String id) {
        this.id = id;
    }
    public String getClassName() {
        return className;
    }
    public void setClassName(String className) {
        this.className = className;
    }
    public List<PropertyDefinition> getPropertys() {
        return propertys;
    }
    public void setPropertys(List<PropertyDefinition> propertys) {
        this.propertys = propertys;
    }

}

property定义类：

package test;

public class PropertyDefinition {
    private String name;
    private String ref;
    private String value;

    public String getValue() {
        return value;
    }

    public void setValue(String value) {
        this.value = value;
    }

    public PropertyDefinition(String name, String ref, String value) {
        this.name = name;
        this.ref = ref;
        this.value = value;
    }

    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getRef() {
        return ref;
    }
    public void setRef(String ref) {
        this.ref = ref;
    }

}

自制spring容器

package test;

import java.beans.Introspector;
import java.beans.PropertyDescriptor;
import java.lang.reflect.Method;
import java.net.URL;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.apache.commons.beanutils.ConvertUtils;
import org.dom4j.Document;
import org.dom4j.Element;
import org.dom4j.XPath;
import org.dom4j.io.SAXReader;

public class MyClassPathXMLApplicationContext {
    private List<BeanDefinition> beanDefines = new ArrayList<BeanDefinition>();
    private Map<String, Object> sigletons = new HashMap<String, Object>();

    public MyClassPathXMLApplicationContext(String filename){
        this.readXML(filename);
        this.instanceBeans();
        this.injectObject();
    }

    /**
     * 为bean对象的属性注入值
     */
    private void injectObject() {
        for(BeanDefinition beanDefinition : beanDefines){
            Object bean = sigletons.get(beanDefinition.getId());
            if(bean!=null){
                try {
                    PropertyDescriptor[] ps = Introspector.getBeanInfo(bean.getClass()).getPropertyDescriptors();
                    for(PropertyDefinition propertyDefinition : beanDefinition.getPropertys()){
                        for(PropertyDescriptor properdesc : ps){
                            if(propertyDefinition.getName().equals(properdesc.getName())){
                                Method setter = properdesc.getWriteMethod();//获取属性的setter方法 ,private
                                if(setter!=null){
                                    Object value = null;
                                    if(propertyDefinition.getRef()!=null && !"".equals(propertyDefinition.getRef().trim())){
                                        value = sigletons.get(propertyDefinition.getRef());
                                    }else{
                                        value = ConvertUtils.convert(propertyDefinition.getValue(), properdesc.getPropertyType());
                                    }
                                    setter.setAccessible(true);
                                    setter.invoke(bean, value);//把引用对象注入到属性
                                }
                                break;
                            }
                        }
                    }
                } catch (Exception e) {
                }
            }
        }
    }
    /**
     * 完成bean的实例化
     */
    private void instanceBeans() {
        for(BeanDefinition beanDefinition : beanDefines){
            try {
                if(beanDefinition.getClassName()!=null && !"".equals(beanDefinition.getClassName().trim()))
                    sigletons.put(beanDefinition.getId(), Class.forName(beanDefinition.getClassName()).newInstance());
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

    }
    /**
     * 读取xml配置文件
     * @param filename
     */
    private void readXML(String filename) {
            SAXReader saxReader = new SAXReader();
            Document document=null;
            try{
             URL xmlpath = this.getClass().getClassLoader().getResource(filename);
             document = saxReader.read(xmlpath);
             Map<String,String> nsMap = new HashMap<String,String>();
             nsMap.put("ns","http://www.springframework.org/schema/beans");//加入命名空间
             XPath xsub = document.createXPath("//ns:beans/ns:bean");//创建beans/bean查询路径
             xsub.setNamespaceURIs(nsMap);//设置命名空间
             List<Element> beans = xsub.selectNodes(document);//获取文档下所有bean节点
             for(Element element: beans){
                String id = element.attributeValue("id");//获取id属性值
                String clazz = element.attributeValue("class"); //获取class属性值
                BeanDefinition beanDefine = new BeanDefinition(id, clazz);
                XPath propertySub = element.createXPath("ns:property");
                propertySub.setNamespaceURIs(nsMap);        //设置命名空间
                List<Element> propertys = propertySub.selectNodes(element);
                for(Element property:propertys){
                    String propertyName = property.attributeValue("name");
                    String propertyref = property.attributeValue("ref");
                    String propertyValue = property.attributeValue("value");
                    PropertyDefinition propertyDefinition =
                            new PropertyDefinition(propertyName, propertyref, propertyValue);
                    beanDefine.getPropertys().add(propertyDefinition);
                }
                beanDefines.add(beanDefine);
             }
            }catch(Exception e){
                e.printStackTrace();
            }
    }
    /**
     * 获取bean实例
     * @param beanName
     * @return
     */
    public Object getBean(String beanName){
        return this.sigletons.get(beanName);
    }
}