欢迎您访问程序员文章站本站旨在为大家提供分享程序员计算机编程知识!
您现在的位置是: 首页  >  IT编程

Java开发银行系统案例手写IOC和AOP

程序员文章站 2022-03-10 10:28:48
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TransferServletpackage com.lagou.edu......

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

Java开发银行系统案例手写IOC和AOP


第2节银行转账案例表结构

Java开发银行系统案例手写IOC和AOP


第3节银行转账案例代码调用关系

Java开发银行系统案例手写IOC和AOP


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, HttpServletResponse
resp) 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) throws
Exception;
}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();
@Override
public 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 {
@Override
public 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


Java开发银行系统案例手写IOC和AOP


(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

Java开发银行系统案例手写IOC和AOP


  • 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


Java开发银行系统案例手写IOC和AOP


  • 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)

Java开发银行系统案例手写IOC和AOP


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>
<bean id="transferService"
class="com.lagou.edu.service.impl.TransferServiceImpl">
<property name="AccountDao" ref="accountDao"></property>
</bean>
<bean id="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

Java开发银行系统案例手写IOC和AOP


  • 修改 TransferServiceImpl

Java开发银行系统案例手写IOC和AOP


(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 = new
ConnectionUtils();
 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
*/
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(TransactionManager
transactionManager) {
 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
<?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-->
 <bean id="accountDao"
class="com.lagou.edu.dao.impl.JdbcAccountDaoImpl">
 <property name="ConnectionUtils" ref="connectionUtils"/>
 </bean>
 <bean id="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-->
 <property name="AccountDao" ref="accountDao"></property>
 </bean>
 <!--配置新增的三个Bean-->
 <bean id="connectionUtils"
class="com.lagou.edu.utils.ConnectionUtils"></bean>
 <!--事务管理器-->
 <bean id="transactionManager"
class="com.lagou.edu.utils.TransactionManager">
 <property name="ConnectionUtils" ref="connectionUtils"/>
 </bean>
 <!--代理对象工厂-->
 <bean id="proxyFactory" class="com.lagou.edu.factory.ProxyFactory">
 <property name="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
*/
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, HttpServletResponse
resp) 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。

本文地址:https://blog.csdn.net/Java0258/article/details/108849256