Spring （一） 加载配置文件，实例化类, 三种实例化bean的方式

Spring （一） 加载配置文件，实例化类

jar：
dom4j.jar; jason-full.jar

public class JmiracleClassPathXmlApplicationContext {
    private List bds = new ArrayList();
    private Map sigletons = new HashMap();

    public JmiracleClassPathXmlApplicationContext (String filename) {
        readXml(filename);
        instanceBeans();
    }

    private void readXml(String filename) {
        SAXReader reader = new SAXReader();
        Document doc = null;
        try {
            URL xmlPath = this.getClass().getClassLoader().getResource(filename); // 可以获取bin目录下的资源文件
            doc = reader.read(xmlPath);
            Map nsMap = new HashMap();
            // 加入命名空间
            nsMap.put("ns", "http://www.springframework.org/schema/beans");
            // 创建beans/bean查询路径
            XPath xsub = document.createXPath("//ns:beans/ns:bean");
            // 设置命名空间
            xsub.setNamespaceURIs(nsMap);
            // 获取文档下所有的bean
            List beans = xsub.selectNodes(document);
            for (Element e : beans) {
                String id = e.attributeValue("id");
                String clazz = e.attributeValue("class");
                BeanDefinition d = new BeanDefinition(id, clazz);
                bds.add(d);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private void instanceBeans() {
        for ( BeanDefinition beanD : bds ) {
            try {
                if ( beanD.getClassname() != null && !"".equals(beanD.getClassname())) {
                    // 通过反射获取类名对应的实例
                    sigletons.put(beanD.getId(), Class.forName(beanD.getClassname()).newInstance());
                }
            }catch (Exception e) {
                e.printStackTrace()
            }
        }
    }

    public Object getBean(String beanName) {
        return this.sigletons.get(beanName);
    }

    public static void main(String[] args) {
        JmiracleClassPathXmlApplicationContext ctx = new JmiracleClassPathXmlApplicationContext("application.xml");
        IService service = (IService)ctx.getBean("service");
        service.sayHello();
    }
}

class BeanDefinition {
    private String id;
    private String classname;

    public BeanDefinition (String id, String classname) {
        this.id = id;
        this.classname = classname;
    }
    public String getId() {
        return this.id;
    }
    public void setId(String id ) {
        this.id = id;
    }

    public String getClassname () {
        return this.classname;
    }

    public void setClassname(String classname ) {
        this.classname = classname;
    }
}

interface IService {
    void sayHello();
}

class ServiceImpl implements IService {
    public void sayHello () {
        System.out.println("ServiceImp -> sayHello");
    }
}

// application.xml
"service" class="ServiceImp" >

1、 三种实例化bean的方式
a. 使用类构造器实例化

<bean id="service" class="ServiceImpl" >bean>

b. 使用静态工厂方法

"service" class="com.test.serviceFactory" factory-method="createService" >

public class serviceFactory {
public static ServiceImpl createService () {
return new ServiceImpl();
}
}

c. 使用实例工厂方法实例化

"serviceFactory" class="com.test.serviceFactory">
"service" factory-bean="serviceFactory" factory-method="createService" >

public class serviceFactory {
    public ServiceImpl createService () {
        return new ServiceImpl();
    }
}