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

第2节银行转账案例表结构

第3节银行转账案例代码调用关系

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")publicclassTransferServletextendsHttpServlet{// 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*/publicinterfaceTransferService{voidtransfer(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*/publicclassTransferServiceImplimplementsTransferService{private AccountDao accountDao = new JdbcAccountDaoImpl();@Overridepublicvoidtransfer(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*/publicinterfaceAccountDao{Account queryAccountByCardNo(String cardNo)throws Exception;intupdateAccountByCardNo(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*/publicclassJdbcAccountDaoImplimplementsAccountDao{@OverridepublicAccount 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

（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

• 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

• 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）

第7节 案例代码改造

（1）针对问题一的代码改造

• beans.xml

<?xml version="1.0" encoding="UTF-8"?><beans><beanid="transferService"class="com.lagou.edu.service.impl.TransferServiceImpl"><propertyname="AccountDao"ref="accountDao"></property></bean><beanid="accountDao"class="com.lagou.edu.dao.impl.JdbcAccountDaoImpl"></bean></beans>

• 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<Element> 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<Element> 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

• 修改 TransferServiceImpl

（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*/publicclassConnectionUtils{/*private ConnectionUtils() { } private static ConnectionUtils connectionUtils = newConnectionUtils(); public static ConnectionUtils getInstance() { return connectionUtils; }*/private ThreadLocal<Connection> 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*/publicclassTransactionManager{private ConnectionUtils connectionUtils;publicvoidsetConnectionUtils(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*/publicclassProxyFactory{private TransactionManager transactionManager;publicvoidsetTransactionManager(TransactionManagertransactionManager){this.transactionManager = transactionManager; } public Object getProxy(Object target){return Proxy.newProxyInstance(this.getClass().getClassLoader(),target.getClass().getInterfaces(), new InvocationHandler() {@Overridepublic 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

<?xml version="1.0" encoding="UTF-8"?><!--跟标签beans，里面配置一个又一个的bean子标签，每一个bean子标签都代表一个类的配置--><beans><!--id标识对象，class是类的全限定类名--><beanid="accountDao"class="com.lagou.edu.dao.impl.JdbcAccountDaoImpl"><propertyname="ConnectionUtils"ref="connectionUtils"/></bean><beanid="transferService"class="com.lagou.edu.service.impl.TransferServiceImpl"><!--set+ name 之后锁定到传值的set方法了，通过反射技术可以调用该方法传入对应的值--><propertyname="AccountDao"ref="accountDao"></property></bean><!--配置新增的三个Bean--><beanid="connectionUtils"class="com.lagou.edu.utils.ConnectionUtils"></bean><!--事务管理器--><beanid="transactionManager"class="com.lagou.edu.utils.TransactionManager"><propertyname="ConnectionUtils"ref="connectionUtils"/></bean><!--代理对象工厂--><beanid="proxyFactory"class="com.lagou.edu.factory.ProxyFactory"><propertyname="TransactionManager"ref="transactionManager"/></bean></beans>

• 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*/publicclassJdbcAccountDaoImplimplementsAccountDao{private ConnectionUtils connectionUtils;publicvoidsetConnectionUtils(ConnectionUtils connectionUtils){this.connectionUtils = connectionUtils; } @Overridepublic 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")publicclassTransferServletextendsHttpServlet{// 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)); }}

好了，银行的案例今天就写到这里，喜欢的朋友可以关注一下小编，此系列文章持续更新中；



推荐阅读：为什么阿里巴巴的程序员成长速度这么快，看完他们的内部资料我明白了

看完三件事❤️

如果你觉得这篇内容对你还蛮有帮助，我想邀请你帮我三个小忙：

1. 点赞，转发，有你们的 『点赞和评论』，才是我创造的动力。

2. 关注公众号 『 Java斗帝 』，不定期分享原创知识。

3. 同时可以期待后续文章ing🚀