手写实现lOC和AOP

上一部分我们理解了loC和AOP思想，我们先不考虑Spring是如何实现这两个思想的，此处准备了一个『银行转账」的案例，请分析该案例在代码层次有什么问题？分析之后使用我们已有知识解决这些问题（痛点)。其实这个过程我们就是在一步步分析并手写实现loC和AOP。

第1节银行转账案例界面

![Spring源码高级笔记之——银行案例手写IOC和AOP](https://p6-tt.byteimg.com/origin/pgc-image/9b59c0f8c62d4947aec37161addfbf02?from=pc)

第2节银行转账案例表结构

![Spring源码高级笔记之——银行案例手写IOC和AOP](https://p6-tt.byteimg.com/origin/pgc-image/d3e1a1b78b2c494381d2bff22465b5ff?from=pc)

第3节银行转账案例代码调用关系

![Spring源码高级笔记之——银行案例手写IOC和AOP](https://p3-tt.byteimg.com/origin/pgc-image/8fa2f145073f4cc3b737b34548c387fc?from=pc)

第4节银行转账案例关键代码

TransferServlet

package com.lagou.edu.servlet;import com.lagou.edu.service.impl.TransferServiceImpl;import com.lagou.edu.utils.JsonUtils;import com.lagou.edu.pojo.Result;import com.lagou.edu.service.TransferService;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;/*** @author 斗帝*/@WebServlet(name="transferServlet",urlPatterns = "/transferServlet")public class TransferServlet extends HttpServlet { // 1. 实例化service层对象 private TransferService transferService = new TransferServiceImpl(); @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException { doPost(req,resp); } @Override protected void doPost(HttpServletRequest req, HttpServletResponseresp) throws ServletException, IOException { // 设置请求体的字符编码 req.setCharacterEncoding("UTF-8"); String fromCardNo = req.getParameter("fromCardNo"); String toCardNo = req.getParameter("toCardNo"); String moneyStr = req.getParameter("money"); int money = Integer.parseInt(moneyStr); Result result = new Result(); try { // 2. 调用service层方法 transferService.transfer(fromCardNo,toCardNo,money); result.setStatus("200"); } catch (Exception e) { e.printStackTrace(); result.setStatus("201"); result.setMessage(e.toString()); } // 响应 resp.setContentType("application/json;charset=utf-8"); resp.getWriter().print(JsonUtils.object2Json(result)); }}
TransferService接口及实现****类

package com.lagou.edu.service;/*** @author 斗帝*/public interface TransferService {void transfer(String fromCardNo,String toCardNo,int money) throwsException;}package com.lagou.edu.service.impl;import com.lagou.edu.dao.AccountDao;import com.lagou.edu.dao.impl.JdbcAccountDaoImpl;import com.lagou.edu.pojo.Account;import com.lagou.edu.service.TransferService;/*** @author 斗帝*/public class TransferServiceImpl implements TransferService {private AccountDao accountDao = new JdbcAccountDaoImpl();@Overridepublic void transfer(String fromCardNo, String toCardNo, int money)throws Exception {Account from = accountDao.queryAccountByCardNo(fromCardNo);Account to = accountDao.queryAccountByCardNo(toCardNo);from.setMoney(from.getMoney()-money);to.setMoney(to.getMoney()+money);accountDao.updateAccountByCardNo(from);accountDao.updateAccountByCardNo(to); }
AccountDao层接口及基于Jdbc的实现类

package com.lagou.edu.dao;import com.lagou.edu.pojo.Account;/*** @author 斗帝*/public interface AccountDao { Account queryAccountByCardNo(String cardNo) throws Exception; int updateAccountByCardNo(Account account) throws Exception; }
JdbcAccountDaoImpl（Jdbc技术实现Dao层接口）

package com.lagou.edu.dao.impl;import com.lagou.edu.pojo.Account;import com.lagou.edu.dao.AccountDao;import com.lagou.edu.utils.DruidUtils;import java.sql.Connection;import java.sql.PreparedStatement;import java.sql.ResultSet;/*** @author 斗帝*/public class JdbcAccountDaoImpl implements AccountDao {@Overridepublic Account queryAccountByCardNo(String cardNo) throws Exception {//从连接池获取连接Connection con = DruidUtils.getInstance().getConnection();String sql = "select * from account where cardNo=?";PreparedStatement preparedStatement = con.prepareStatement(sql);preparedStatement.setString(1,cardNo);ResultSet resultSet = preparedStatement.executeQuery();Account account = new Account();while(resultSet.next()) {account.setCardNo(resultSet.getString("cardNo"));account.setName(resultSet.getString("name"));account.setMoney(resultSet.getInt("money")); }resultSet.close();preparedStatement.close();con.close();return account; }@Override public int updateAccountByCardNo(Account account) throws Exception { //从连接池获取连接 Connection con = DruidUtils.getInstance().getConnection(); String sql = "update account set money=? where cardNo=?"; PreparedStatement preparedStatement = con.prepareStatement(sql); preparedStatement.setInt(1,account.getMoney()); preparedStatement.setString(2,account.getCardNo()); int i = preparedStatement.executeUpdate(); preparedStatement.close(); con.close(); return i; }}

第5节银行转账案例代码问题分析

![Spring源码高级笔记之——银行案例手写IOC和AOP](https://p6-tt.byteimg.com/origin/pgc-image/87e22b2842dd4fd180e7330db1faefe9?from=pc)

（1）问题一：在上述案例实现中，service 层实现类在使用 dao 层对象时，直接在TransferServiceImpl 中通过 AccountDao accountDao = new JdbcAccountDaoImpl() 获得了 dao层对象，然而一个 new 关键字却将 TransferServiceImpl 和 dao 层具体的一个实现类JdbcAccountDaoImpl 耦合在了一起，如果说技术架构发生一些变动，dao 层的实现要使用其它技术，比如 Mybatis，思考切换起来的成本？每一个 new 的地方都需要修改源代码，重新编译，面向接口开发的意义将大打折扣？

（2）问题二：service 层代码没有竟然还没有进行事务控制？！如果转账过程中出现异常，将可能导致数据库数据错乱，后果可能会很严重，尤其在金融业务。

第6节问题解决思路

针对问题—思考:

实例化对象的方式除了new之外，还有什么技术?反射(需要把类的全限定类名配置在xml中)

考虑使用设计模式中的工厂模式解耦合，另外项目中往往有很多对象需要实例化，那就在工厂中使用反射技术实例化对象，工厂模式很合适

![Spring源码高级笔记之——银行案例手写IOC和AOP](https://p3-tt.byteimg.com/origin/pgc-image/55249b4a7ecb4c6b8d84991191a13335?from=pc)

更进一步，代码中能否只声明所需实例的接口类型，不出现 new 也不出现工厂类的字眼，如下图？能！声明一个变量并提供 set 方法，在反射的时候将所需要的对象注入进去吧

![Spring源码高级笔记之——银行案例手写IOC和AOP](https://p1-tt.byteimg.com/origin/pgc-image/bc44cff95f8d416397787cd2a41fbc72?from=pc)

针对问题二思考：

service 层没有添加事务控制，怎么办？没有事务就添加上事务控制，手动控制 JDBC 的Connection 事务，但要注意将Connection和当前线程绑定（即保证一个线程只有一个Connection，这样操作才针对的是同⼀个 Connection，进而控制的是同一个事务）

![Spring源码高级笔记之——银行案例手写IOC和AOP](https://p1-tt.byteimg.com/origin/pgc-image/d26d0727532e4465937c35800dd1a929?from=pc)

第7节案例代码改造

（1）针对问题一的代码改造

beans.xml
增加 BeanFactory.java

package com.lagou.edu.factory;import org.dom4j.Document;import org.dom4j.DocumentException;import org.dom4j.Element;import org.dom4j.io.SAXReader;import java.io.InputStream;import java.lang.reflect.InvocationTargetException;import java.lang.reflect.Method;import java.util.HashMap;import java.util.List;import java.util.Map;/*** @author 应癫*/public class BeanFactory { /** * 工厂类的两个任务 * 任务一：加载解析xml，读取xml中的bean信息，通过反射技术实例化bean对象，然后放入map待用 * 任务二：提供接口方法根据id从map中获取bean（静态方法） */ private static Map<String,Object> map = new HashMap<>(); static { InputStream resourceAsStream =BeanFactory.class.getClassLoader().getResourceAsStream("beans.xml"); SAXReader saxReader = new SAXReader(); try { Document document = saxReader.read(resourceAsStream); Element rootElement = document.getRootElement(); List list = rootElement.selectNodes("//bean"); // 实例化bean对象 for (int i = 0; i < list.size(); i++) { Element element = list.get(i); String id = element.attributeValue("id"); String clazz = element.attributeValue("class"); Class<?> aClass = Class.forName(clazz); Object o = aClass.newInstance(); map.put(id,o); } // 维护bean之间的依赖关系 List propertyNodes =rootElement.selectNodes("//property"); for (int i = 0; i < propertyNodes.size(); i++) { Element element = propertyNodes.get(i); // 处理property元素 String name = element.attributeValue("name"); String ref = element.attributeValue("ref"); String parentId =element.getParent().attributeValue("id"); Object parentObject = map.get(parentId); Method[] methods = parentObject.getClass().getMethods(); for (int j = 0; j < methods.length; j++) { Method method = methods[j]; if(("set" + name).equalsIgnoreCase(method.getName())){ // bean之间的依赖关系（注入bean） Object propertyObject = map.get(ref); method.invoke(parentObject,propertyObject); } } // 维护依赖关系后重新将bean放⼊map中 map.put(parentId,parentObject); } } catch (DocumentException e) { e.printStackTrace(); } catch (ClassNotFoundException e) { e.printStackTrace(); } catch (IllegalAccessException e) { e.printStackTrace(); } catch (InstantiationException e) { e.printStackTrace(); } catch (InvocationTargetException e) { e.printStackTrace(); } } public static Object getBean(String id) { return map.get(id); }}
修改 TransferServlet

![Spring源码高级笔记之——银行案例手写IOC和AOP](https://p6-tt.byteimg.com/origin/pgc-image/fad7f58f6b864fe4a9081eed28b6471b?from=pc)

修改 TransferServiceImpl

![Spring源码高级笔记之——银行案例手写IOC和AOP](https://p6-tt.byteimg.com/origin/pgc-image/ccda2c0a0f7346ed85bdcdc9b37eae6a?from=pc)

（2）针对问题二的改造

增加 ConnectionUtils

package com.lagou.edu.utils;import java.sql.Connection;import java.sql.SQLException;/*** @author 斗帝*/public class ConnectionUtils { /private ConnectionUtils() { } private static ConnectionUtils connectionUtils = newConnectionUtils(); public static ConnectionUtils getInstance() { return connectionUtils; }/ private ThreadLocal threadLocal = new ThreadLocal<>(); //存储当前线程的连接 /** * 从当前线程获取连接 / public Connection getCurrentThreadConn() throws SQLException { /* * 判断当前线程中是否已经绑定连接，如果没有绑定，需要从连接池获取一个连接绑定到当前线程 */ Connection connection = threadLocal.get(); if(connection == null) { // 从连接池拿连接并绑定到线程 connection = DruidUtils.getInstance().getConnection(); // 绑定到当前线程 threadLocal.set(connection); } return connection; }}
增加 TransactionManager 事务管理器类

package com.lagou.edu.utils;import java.sql.SQLException;/*** @author 斗帝*/public class TransactionManager { private ConnectionUtils connectionUtils; public void setConnectionUtils(ConnectionUtils connectionUtils) { this.connectionUtils = connectionUtils; } // 开启事务 public void beginTransaction() throws SQLException { connectionUtils.getCurrentThreadConn().setAutoCommit(false); } // 提交事务 public void commit() throws SQLException { connectionUtils.getCurrentThreadConn().commit(); } // 回滚事务 public void rollback() throws SQLException { connectionUtils.getCurrentThreadConn().rollback(); }}
增加 ProxyFactory 代理工厂类

package com.lagou.edu.factory;import com.lagou.edu.utils.TransactionManager;import java.lang.reflect.InvocationHandler;import java.lang.reflect.Method;import java.lang.reflect.Proxy;/*** @author 斗帝*/public class ProxyFactory { private TransactionManager transactionManager; public void setTransactionManager(TransactionManagertransactionManager) { this.transactionManager = transactionManager; } public Object getProxy(Object target) { return Proxy.newProxyInstance(this.getClass().getClassLoader(),target.getClass().getInterfaces(), new InvocationHandler() { @Override public Object invoke(Object proxy, Method method, Object[]args) throws Throwable { Object result = null; try{ // 开启事务 transactionManager.beginTransaction(); // 调用原有业务逻辑 result = method.invoke(target,args); // 提交事务 transactionManager.commit(); }catch(Exception e) { e.printStackTrace(); // 回滚事务 transactionManager.rollback(); // 异常向上抛出,便于servlet中捕获 throw e.getCause(); } return result; } }); }}
修改 beans.xml
修改 JdbcAccountDaoImpl

package com.lagou.edu.dao.impl;import com.lagou.edu.pojo.Account;import com.lagou.edu.dao.AccountDao;import com.lagou.edu.utils.ConnectionUtils;import com.lagou.edu.utils.DruidUtils;import java.sql.Connection;import java.sql.PreparedStatement;import java.sql.ResultSet;/*** @author 斗帝*/public class JdbcAccountDaoImpl implements AccountDao { private ConnectionUtils connectionUtils; public void setConnectionUtils(ConnectionUtils connectionUtils) { this.connectionUtils = connectionUtils; } @Override public Account queryAccountByCardNo(String cardNo) throws Exception { //从连接池获取连接 // Connection con = DruidUtils.getInstance().getConnection(); Connection con = connectionUtils.getCurrentThreadConn(); String sql = "select * from account where cardNo=?"; PreparedStatement preparedStatement = con.prepareStatement(sql); preparedStatement.setString(1,cardNo); ResultSet resultSet = preparedStatement.executeQuery(); Account account = new Account(); while(resultSet.next()) { account.setCardNo(resultSet.getString("cardNo")); account.setName(resultSet.getString("name")); account.setMoney(resultSet.getInt("money")); } resultSet.close(); preparedStatement.close(); //con.close(); return account; } @Override public int updateAccountByCardNo(Account account) throws Exception { // 从连接池获取连接 // 改造为：从当前线程当中获取绑定的connection连接 //Connection con = DruidUtils.getInstance().getConnection(); Connection con = connectionUtils.getCurrentThreadConn(); String sql = "update account set money=? where cardNo=?"; PreparedStatement preparedStatement = con.prepareStatement(sql); preparedStatement.setInt(1,account.getMoney()); preparedStatement.setString(2,account.getCardNo()); int i = preparedStatement.executeUpdate(); preparedStatement.close(); //con.close(); return i; }}
修改 TransferServlet

package com.lagou.edu.servlet;import com.lagou.edu.factory.BeanFactory;import com.lagou.edu.factory.ProxyFactory;import com.lagou.edu.service.impl.TransferServiceImpl;import com.lagou.edu.utils.JsonUtils;import com.lagou.edu.pojo.Result;import com.lagou.edu.service.TransferService;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;/*** @author 斗帝*/@WebServlet(name="transferServlet",urlPatterns = "/transferServlet")public class TransferServlet extends HttpServlet { // 1. 实例化service层对象 //private TransferService transferService = new TransferServiceImpl(); //private TransferService transferService = (TransferService)BeanFactory.getBean("transferService"); // 从工厂获取委托对象（委托对象是增强了事务控制的功能） // 首先从BeanFactory获取到proxyFactory代理工厂的实例化对象 private ProxyFactory proxyFactory = (ProxyFactory)BeanFactory.getBean("proxyFactory"); private TransferService transferService = (TransferService)proxyFactory.getJdkProxy(BeanFactory.getBean("transferService")) ; @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException { doPost(req,resp); } @Override protected void doPost(HttpServletRequest req, HttpServletResponseresp) throws ServletException, IOException { // 设置请求体的字符编码 req.setCharacterEncoding("UTF-8"); String fromCardNo = req.getParameter("fromCardNo"); String toCardNo = req.getParameter("toCardNo"); String moneyStr = req.getParameter("money"); int money = Integer.parseInt(moneyStr); Result result = new Result(); try { // 2. 调用service层方法 transferService.transfer(fromCardNo,toCardNo,money); result.setStatus("200"); } catch (Exception e) { e.printStackTrace(); result.setStatus("201"); result.setMessage(e.toString()); } // 响应 resp.setContentType("application/json;charset=utf-8"); resp.getWriter().print(JsonUtils.object2Json(result)); }}

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初学源码之——银行案例手写IOC和AOP