初学源码之——银行案例手写IOC和AOP

  • 2020 年 9 月 28 日
  • 筆記

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

 

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

 

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

 

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

 

Spring源码高级笔记之——银行案例手写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
Spring源码高级笔记之——银行案例手写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

 

Spring源码高级笔记之——银行案例手写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)

Spring源码高级笔记之——银行案例手写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
Spring源码高级笔记之——银行案例手写IOC和AOP

 

  • 修改 TransferServiceImpl
Spring源码高级笔记之——银行案例手写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;

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