freewxy

Spring装配基本属性的原理分析与代码实现

首先，做一个配置属性的基本测试。修改beans.xml,使引用外部类变成内部bean属性：

<?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-2.5.xsd">

</bean>

</beans>

测试：

public class Test {

public static void main(String[] args) {

//IOC容器实例化

ClassPathXmlApplicationContext ac = new ClassPathXmlApplicationContext("beans.xml");

PeopleService peopleService = (PeopleService) ac.getBean("peopleService");

peopleService.save();

}

结果正常！能够引用得到（这不是废话么）

使用ref，ref所指向的bean可以被多个bean引用；ref依赖对象将作为一个属性被注入。

Spring是如何实现装配基本属性的呢？下面用源码模拟实现之：

1、在xml配置文件中增加属性：

<?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-2.5.xsd">

</bean>

</beans>

2、在属性Bean：PorpertyDefinition中定义相应的属性，用来存放xml文件中定义的属性：

package com.wxy.bean;

/**

* 存放bean的property属性

* @creator xiaoyu.wang

* @create-time 2011-8-10 下午04:40:07

* @revision $Id

public class PropertyDefinition {

private String name; //属性名

private String ref; //属性依赖对象

private String value;

/**

* @return the name

public String getName() {

return name;

}

/**

* @param name the name to set

public void setName(String name) {

this.name = name;

}

/**

* @return the ref

public String getRef() {

return ref;

}

/**

* @param ref the ref to set

public void setRef(String ref) {

this.ref = ref;

}

public PropertyDefinition(String name, String ref, String value) {

super();

this.name = name;

this.ref = ref;

this.value = value;

}

/**

* @return the value

public String getValue() {

return value;

}

/**

* @param value the value to set

public void setValue(String value) {

this.value = value;

}

/* (non-Javadoc)

* @see java.lang.Object#toString()

@Override

public String toString() {

return "PropertyDefinition [name=" + name + ", ref=" + ref + ", value=" + value + "]";

}

3、修改PeopelServiceBean ，添加相对应的属性：

public class PeopleServiceBean implements PeopleService {

private PeopleDao peopleDao;

private String name;

private Integer id;

/**

* @return the peopleDao

public PeopleDao getPeopleDao() {

return peopleDao;

}

/**

* @param peopleDao the peopleDao to set

public void setPeopleDao(PeopleDao peopleDao) {

this.peopleDao = peopleDao;

}

/**

* @return the name

public String getName() {

return name;

}

/**

* @param name the name to set

public void setName(String name) {

this.name = name;

}

/**

* @return the id

public Integer getId() {

return id;

}

/**

* @param id the id to set

public void setId(Integer id) {

this.id = id;

}

public void save() {

System.out.println("--> the method is called save()! name=" + name + ",id=" + id);

peopleDao.add();

}

4、读取属性值，修改WxyClassPathXMLApplicationContext.java, 添加注入属性功能：

package com.wxy.content;

import java.beans.IntrospectionException;

import java.beans.Introspector;

import java.beans.PropertyDescriptor;

import java.lang.reflect.InvocationTargetException;

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;

import com.wxy.bean.BeanDefinition;

import com.wxy.bean.PropertyDefinition;

/**

* 自定义IoC容器

* BeanDefinition的resource定位:readXML();

* BeanDefinition的载入和解析 :readXML();

* BeanDefinition在IoC容器中的注册 instanceBeans();

* @create-time 2011-8-10 上午09:19:17

* @revision $Id

public class WxyClassPathXMLApplicationContext {

//存放BeanDefinition的列表，在beans.xml中定义的bean可能不止一个

private final List<BeanDefinition> beanDefines = new ArrayList<BeanDefinition>();

//将类名作为索引，将创建的Bean对象存入到Map中

private final Map<String, Object> sigletons = new HashMap<String, Object>();

public WxyClassPathXMLApplicationContext(String fileName) {

//读取xml配置文件

this.readXML(fileName);

//实例化bean

this.instanceBeans();

//注入对象

this.injectObject();

}

/**

*为bean对象的属性注入值

private void injectObject() {

for (BeanDefinition beanDefinition : beanDefines) {

//获取beanDefines中的对象

Object bean = sigletons.get(beanDefinition.getId());

if (bean != null) {

//如果存在，利用反射技术将值注入

try {

//获取Bean的描述属性类

PropertyDescriptor[] ps = Introspector.getBeanInfo(bean.getClass())

.getPropertyDescriptors();

for (PropertyDefinition propertyDefinition : beanDefinition.getProperties()) {

for (PropertyDescriptor properdesc : ps) {

//取得属性名字与propertyDefinition中的属性做比较

if (propertyDefinition.getName().equals(properdesc.getName())) {

//获得属性的setter方法

Method setter = properdesc.getWriteMethod();

if (setter != null) {

Object value = null;

if (propertyDefinition.getRef() != null

&& !propertyDefinition.getRef().isEmpty()) {//注入依赖对象

value = sigletons.get(propertyDefinition.getRef());

} else {//注入基本类型

//将字符串类型装换成用户需要的类型，需要用到jar包中的commons-beanutils.jar

value = ConvertUtils.convert(propertyDefinition.getValue(),

properdesc.getPropertyType());

}

//允许访私有方法

setter.setAccessible(true);

//把引用对象注入到属性

setter.invoke(bean, value);

}

} catch (SecurityException e) {