手撸Mybatis（三）——收敛SQL操作到SqlSession

本文主要是介绍手撸Mybatis（三）——收敛SQL操作到SqlSession，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

本专栏的源码：https://gitee.com/dhi-chen-xiaoyang/yang-mybatis。

引言

在上一章中，我们实现了读取mapper配置并构造相关的mapper代理对象，读取mapper.xml文件中的sql信息等操作，现在，在上一章的基础上，我们接着开始链接数据库，通过封装JDBC，来实现我们数据库操作。

数据库准备

我们创建一个user表，用于后续进行测试，user表的结构如下图所示：

user表的内容如下：

添加User类

我们根据表结构，创建对应的user类，user类的结构如下：

package com.yang.mybatis.test;import java.io.Serializable;
import java.util.Date;public class User implements Serializable {private Integer id;private String userName;private String password;private Integer age;private Date createTime;public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getUserName() {return userName;}public void setUserName(String userName) {this.userName = userName;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}public Integer getAge() {return age;}public void setAge(Integer age) {this.age = age;}public Date getCreateTime() {return createTime;}public void setCreateTime(Date createTime) {this.createTime = createTime;}
}

JDBC基础操作

在使用jdbc之前，我们先引入mysql的依赖

<dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>8.0.27</version></dependency>

jdbc的操作，一般分为下面几个步骤：
1）加载JDBC驱动程序
2）创建数据库链接
3）创建一个preparedStatement
4）执行SQL语句
5）遍历数据集
6）处理异常，关闭JDBC对象资源
示例代码如下：

 public static void main(String[] args) throws SQLException {String url = "jdbc:mysql://localhost:3306/test?useSSL=false";String username = "用户名";String password = "密码";Connection conn = null;try {// 1. 加载驱动Class.forName("com.mysql.cj.jdbc.Driver");// 2. 创建数据库链接conn = DriverManager.getConnection(url, username, password);conn.setAutoCommit(false);// 3. 创建preparedStatementString sql = "select user_name from user where id = ?";PreparedStatement preparedStatement = conn.prepareStatement(sql);preparedStatement.setInt(1, 1);// 4. 执行sqlResultSet resultSet = preparedStatement.executeQuery();// 5. 遍历结果if (resultSet.next()) {System.out.println(resultSet.getString(1));}conn.commit();} catch (SQLException | ClassNotFoundException e) {conn.rollback();e.printStackTrace();} finally {// 6. 释放连接conn.close();}}

执行上述代码，结果如下：

将sql操作，收敛到SqlSession

在上一章，当我们调用mapper的方法时，最终是通过在MapperProxy中获取对应的MybatisStatement，然后打印出sql信息的，但是如果后续操作数据库是，也在MapperProxy中执行sql的话，不太方便管理。因此，我们添加一个IMybatisSqlSession类，后续对于数据库的操作，收敛到此类进行。
首先，我们添加IMybatisSqlSession：

package com.yang.mybatis.session;public interface IMybatisSqlSession {<T> T execute(String method, Object parameter);<T> T getMapper(Class<T> type);
}

然后添加其默认实现：

package com.yang.mybatis.session;import com.yang.mybatis.proxy.MapperProxyFactory;public class DefaultMybatisSqlSession implements IMybatisSqlSession {private MapperProxyFactory mapperProxyFactory;public DefaultMybatisSqlSession(MapperProxyFactory mapperProxyFactory) {this.mapperProxyFactory = mapperProxyFactory;}@Overridepublic <T> T execute(String method, Object parameter) {return (T)("你被代理了!" + method + ",入参:" + parameter);}@Overridepublic <T> T getMapper(Class<T> type) {return (T) mapperProxyFactory.newInstance(type, this);}
}

添加IMybatisSqlSession的工厂接口

package com.yang.mybatis.session;public interface MybatisSqlSessionFactory {IMybatisSqlSession openSession();
}

添加工厂的默认实现：

package com.yang.mybatis.session;import com.yang.mybatis.proxy.MapperProxyFactory;public class DefaultMybatisSqlSessionFactory implements IMybatisSqlSessionFactory {private MapperProxyFactory mapperProxyFactory;public DefaultMybatisSqlSessionFactory(MapperProxyFactory mapperProxyFactory) {this.mapperProxyFactory = mapperProxyFactory;}@Overridepublic IMybatisSqlSession openSession() {return new DefaultMybatisSqlSession(mapperProxyFactory);}
}

修改MapperProxyFactory，在新建MapperProxy的时候，将imybatisSqlSession传递给MapperProxy。

package com.yang.mybatis.proxy;import com.yang.mybatis.config.MybatisConfiguration;
import com.yang.mybatis.session.IMybatisSqlSession;import java.lang.reflect.Proxy;public class MapperProxyFactory {private MybatisConfiguration mybatisConfiguration;public MapperProxyFactory(MybatisConfiguration mybatisConfiguration) {this.mybatisConfiguration = mybatisConfiguration;}public Object newInstance(Class mapperType, IMybatisSqlSession mybatisSqlSession) {MapperProxy mapperProxy = new MapperProxy(mapperType, mybatisSqlSession);return Proxy.newProxyInstance(mapperType.getClassLoader(),new Class[]{mapperType},mapperProxy);}public MybatisConfiguration getMybatisConfiguration() {return mybatisConfiguration;}public void setMybatisConfiguration(MybatisConfiguration mybatisConfiguration) {this.mybatisConfiguration = mybatisConfiguration;}
}

然后修改MapperProxy，在真正执行的时候，通过iMybatisSqlSession的execute，来执行sql操作，以此实现sql操作由iMybatisSqlSession来统一管理。

package com.yang.mybatis.proxy;import com.yang.mybatis.session.IMybatisSqlSession;import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;public class MapperProxy<T> implements InvocationHandler {private Class<T> mapperInterface;private IMybatisSqlSession sqlSession;public MapperProxy(Class<T> mapperInterface, IMybatisSqlSession mybatisSqlSession) {this.mapperInterface = mapperInterface;this.sqlSession = mybatisSqlSession;}@Overridepublic Object invoke(Object proxy, Method method, Object[] args) throws Throwable {if (Object.class.equals(method.getDeclaringClass())) {return method.invoke(this, args);}String methodName = this.mapperInterface.getName() + "." + method.getName();return sqlSession.execute(methodName, args);}
}

最后，我们添加sqlSession工厂类的创建者，通过创建者模式，来创建SqlSession工厂

package com.yang.mybatis.session;import com.yang.mybatis.config.MybatisConfiguration;
import com.yang.mybatis.config.MybatisSqlStatement;
import com.yang.mybatis.config.parser.IMybatisConfigurationParser;
import com.yang.mybatis.config.parser.IMybatisMapperParser;
import com.yang.mybatis.proxy.MapperProxyFactory;import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;public class MybatisSqlSessionFactoryBuilder {private IMybatisConfigurationParser mybatisConfigurationParser;private IMybatisMapperParser mybatisMapperParser;private String configPath;public IMybatisSqlSessionFactory buildSqlSessionFactory() {if (configPath == null || configPath.isEmpty()) {throw new RuntimeException("配置文件路径不合法==========");}if (this.mybatisMapperParser == null || this.mybatisConfigurationParser == null) {throw new RuntimeException("缺少解析器=======");}MybatisConfiguration mybatisConfiguration = mybatisConfigurationParser.parser(configPath);List<String> mapperPaths = mybatisConfiguration.getMapperPaths();for (String mapperPath : mapperPaths) {List<MybatisSqlStatement> mybatisSqlStatements = this.mybatisMapperParser.parseMapper(mapperPath);Map<String, List<MybatisSqlStatement>> mapperNameGroupMap = mybatisSqlStatements.stream().collect(Collectors.groupingBy(MybatisSqlStatement::getNamespace));for (Map.Entry<String, List<MybatisSqlStatement>> entry : mapperNameGroupMap.entrySet()) {String mapperName = entry.getKey();List<MybatisSqlStatement> sqlSessionList = entry.getValue();mybatisConfiguration.putMybatisSqlStatementList(mapperName, sqlSessionList);}}MapperProxyFactory mapperProxyFactory = new MapperProxyFactory(mybatisConfiguration);return new DefaultMybatisSqlSessionFactory(mapperProxyFactory);}public MybatisSqlSessionFactoryBuilder setConfigPath(String configPath) {this.configPath = configPath;return this;}public MybatisSqlSessionFactoryBuilder setMybatisConfigurationParser(IMybatisConfigurationParser iMybatisConfigurationParser) {this.mybatisConfigurationParser = iMybatisConfigurationParser;return this;}public MybatisSqlSessionFactoryBuilder setMybatisMapperParser(IMybatisMapperParser iMybatisMapperParser) {this.mybatisMapperParser = iMybatisMapperParser;return this;}
}

添加测试代码，进行测试：

package com.yang.mybatis.test;import com.yang.mybatis.config.parser.XmlMybatisConfigurationParser;
import com.yang.mybatis.config.parser.XmlMybatisMapperParser;
import com.yang.mybatis.session.IMybatisSqlSession;
import com.yang.mybatis.session.IMybatisSqlSessionFactory;
import com.yang.mybatis.session.MybatisSqlSessionFactoryBuilder;public class Main {public static void main(String[] args) {String configPath = "mybatis-config.xml";IMybatisSqlSessionFactory mybatisSqlSessionFactory = new MybatisSqlSessionFactoryBuilder().setMybatisMapperParser(new XmlMybatisMapperParser()).setMybatisConfigurationParser(new XmlMybatisConfigurationParser()).setConfigPath(configPath).buildSqlSessionFactory();IMybatisSqlSession mybatisSqlSession = mybatisSqlSessionFactory.openSession();IUserMapper userMapper = mybatisSqlSession.getMapper(IUserMapper.class);System.out.println(userMapper.queryUserName(1));}
}

SqlSession获取执行方法对应的sql语句

首先，修改MybatisConfiguration，之前是将每一个mapper和他所拥有的MybatisSqlStatement列表关联起来，现在感觉粒度太大，因此，该为每一个mapper的方法和对应的MybatisSqlStatement关联。

package com.yang.mybatis.config;import java.io.Serializable;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;public class MybatisConfiguration implements Serializable {private Map<String, MybatisEnvironment> id2EnvironmentMap = new HashMap<>();private MybatisEnvironment defaultMybatisEnvironment;private List<String> mapperPaths = new ArrayList<>();private Map<String, MybatisSqlStatement> mapperMethod2SqlStatementsMap = new HashMap<>();public void putMapperMethod2MybatisSqlStatement(String mapperMethod, MybatisSqlStatement mybatisSqlStatement) {this.mapperMethod2SqlStatementsMap.put(mapperMethod, mybatisSqlStatement);}public MybatisSqlStatement getMybatisSqlStatement(String mapperMethod) {return this.mapperMethod2SqlStatementsMap.get(mapperMethod);}public Map<String, MybatisSqlStatement> getMapperMethod2SqlStatementsMap() {return this.mapperMethod2SqlStatementsMap;}public void addEnvironment(String id, MybatisEnvironment mybatisEnvironment) {this.id2EnvironmentMap.put(id, mybatisEnvironment);}public MybatisEnvironment getEnvironment(String id) {return id2EnvironmentMap.get(id);}public MybatisEnvironment getDefaultMybatisEnvironment() {return defaultMybatisEnvironment;}public void setDefaultMybatisEnvironment(MybatisEnvironment defaultMybatisEnvironment) {this.defaultMybatisEnvironment = defaultMybatisEnvironment;}public void addMapperPath(String mapperPath) {this.mapperPaths.add(mapperPath);}public List<String> getMapperPaths() {return this.mapperPaths;}public List<MybatisEnvironment> getEnvironments() {return new ArrayList<>(id2EnvironmentMap.values());}}

然后修改MybatisSqlSessionFactoryBuilder:

package com.yang.mybatis.session;import com.yang.mybatis.config.MybatisConfiguration;
import com.yang.mybatis.config.MybatisSqlStatement;
import com.yang.mybatis.config.parser.IMybatisConfigurationParser;
import com.yang.mybatis.config.parser.IMybatisMapperParser;
import com.yang.mybatis.proxy.MapperProxyFactory;import java.util.List;public class MybatisSqlSessionFactoryBuilder {private IMybatisConfigurationParser mybatisConfigurationParser;private IMybatisMapperParser mybatisMapperParser;private String configPath;public IMybatisSqlSessionFactory buildSqlSessionFactory() {if (configPath == null || configPath.isEmpty()) {throw new RuntimeException("配置文件路径不合法==========");}if (this.mybatisMapperParser == null || this.mybatisConfigurationParser == null) {throw new RuntimeException("缺少解析器=======");}MybatisConfiguration mybatisConfiguration = mybatisConfigurationParser.parser(configPath);List<String> mapperPaths = mybatisConfiguration.getMapperPaths();for (String mapperPath : mapperPaths) {List<MybatisSqlStatement> mybatisSqlStatements = this.mybatisMapperParser.parseMapper(mapperPath);for (MybatisSqlStatement mybatisSqlStatement : mybatisSqlStatements) {String methodName = mybatisSqlStatement.getNamespace() + "." + mybatisSqlStatement.getId();mybatisConfiguration.putMapperMethod2MybatisSqlStatement(methodName, mybatisSqlStatement);}}MapperProxyFactory mapperProxyFactory = new MapperProxyFactory(mybatisConfiguration);return new DefaultMybatisSqlSessionFactory(mapperProxyFactory);}public MybatisSqlSessionFactoryBuilder setConfigPath(String configPath) {this.configPath = configPath;return this;}public MybatisSqlSessionFactoryBuilder setMybatisConfigurationParser(IMybatisConfigurationParser iMybatisConfigurationParser) {this.mybatisConfigurationParser = iMybatisConfigurationParser;return this;}public MybatisSqlSessionFactoryBuilder setMybatisMapperParser(IMybatisMapperParser iMybatisMapperParser) {this.mybatisMapperParser = iMybatisMapperParser;return this;}
}

修改DefaultMybatisSqlSession类，获取方法对应的MybatisStatement

package com.yang.mybatis.session;import com.yang.mybatis.config.MybatisSqlStatement;
import com.yang.mybatis.proxy.MapperProxyFactory;public class DefaultMybatisSqlSession implements IMybatisSqlSession {private MapperProxyFactory mapperProxyFactory;public DefaultMybatisSqlSession(MapperProxyFactory mapperProxyFactory) {this.mapperProxyFactory = mapperProxyFactory;}@Overridepublic <T> T execute(String method, Object parameter) {MybatisSqlStatement mybatisSqlStatement = this.mapperProxyFactory.getMybatisConfiguration().getMybatisSqlStatement(method);return (T)("method:" + method + "sql:"+ mybatisSqlStatement.getSql() + ",入参:" + parameter);}@Overridepublic <T> T getMapper(Class<T> type) {return (T) mapperProxyFactory.newInstance(type, this);}
}

添加测试方法进行测试：

 public static void main(String[] args) {String configPath = "mybatis-config.xml";MybatisSqlSessionFactory mybatisSqlSessionFactory = new MybatisSqlSessionFactoryBuilder().setMybatisMapperParser(new XmlMybatisMapperParser()).setMybatisConfigurationParser(new XmlMybatisConfigurationParser()).setConfigPath(configPath).buildSqlSessionFactory();IMybatisSqlSession mybatisSqlSession = mybatisSqlSessionFactory.openSession();IUserMapper userMapper = mybatisSqlSession.getMapper(IUserMapper.class);System.out.println(userMapper.queryUserAge(1));}