Spring基础第一章

运行环境苛刻可以移植性差重量级框架

Spring是一个轻量级JavaEE解决方案，整合了多种设计模式

轻量级

1.对运行环境要求低，可以运行在web容器中 tomcat resion jetty

2.代码移植性好，不需要实现额外的接口

整合了设计模式

1.工厂

2.代理

3.模板

4.策略

1.概念:通过工厂类创建对象
	User user = new User();
2.目的:解耦合
	耦合:代码间的强关联关系
	问题:不利于代码维护
	把接口的实现类硬编码在了程序中
	UserService userService = new UserServiceImpl();
	=>
	UserService userservice = new UserServiceImplNew();
	如果要改变UserService的实现类就需要修改代码,那么就需要重新编译

package com.xia.basic;

import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;

public class BeanFactory {

    private static Properties properties = new Properties();

    static {
        InputStream inputStream = null;
        try {
            inputStream = BeanFactory.class.getResourceAsStream("/applicationContext.properties");
            properties.load(inputStream);
            inputStream.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static UserService getUserService() {
        UserService userService = null;
        try {
            String userServiceImpl = properties.getProperty("userService");
            Class clazz = Class.forName(userServiceImpl);
            userService = (UserService)clazz.newInstance();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        }
        return userService;
    }

    public static UserDAO getUserDAO() {
        UserDAO userDAO = null;
        try {
            Class clazz = Class.forName(properties.getProperty("userDAO"));
             userDAO = (UserDAO)clazz.newInstance();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        }
        return userDAO;
    }
}

显然简单工厂中每一个实现类都需要一个方法，那么有没有什么办法可以只设计一个通用方法呢?

package com.xia.basic;

import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;

public class BeanFactory {

    private static Properties properties = new Properties();

    static {
        InputStream inputStream = null;
        try {
            inputStream = BeanFactory.class.getResourceAsStream("/applicationContext.properties");
            properties.load(inputStream);
            inputStream.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    // 通用工厂方法
    public static Object getBean(String beanName) {
        Object object = null;
        try {
            Class clazz = Class.forName(properties.getProperty(beanName));
            object = clazz.newInstance();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        }
        return object;
    }
}

Spring本质上就是一个工厂，可以用来创建对象，解耦合