仿照MyBatis手寫一個持久層框架學習

首先數據準備，創建MySQL數據庫mybatis，創建表并插入數據。

DROP TABLE IF EXISTS user_t;
CREATE TABLE user_t ( id INT PRIMARY KEY, username VARCHAR ( 128 ) );
INSERT INTO user_t VALUES(1,'Tom');
INSERT INTO user_t VALUES(2,'Jerry');

JDBC API允許應用程序訪問任何形式的表格數據，特別是存儲在關系數據庫中的數據。

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JDBC代碼示例：

    @Test@DisplayName("JDBC模式訪問數據庫示例")public void jdbc_test() {Connection connection = null;PreparedStatement preparedStatement = null;ResultSet resultSet = null;try {// 加載數據庫驅動Class.forName("com.mysql.cj.jdbc.Driver");// 通過驅動管理類來獲取數據庫連接connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/mybatis?characterEncoding=utf-8", "root", "123456");// 定義SQL語句 ?表示占位符String sql = "select * from user_t where username = ?";// 獲取預處理StatementpreparedStatement = connection.prepareStatement(sql);// 設置參數，第一個參數為SQL語句中參數的序號（從1開始），第二個參數為設置的參數值preparedStatement.setString(1, "Tom");// 向數據庫發出SQL執行查詢，查詢出結果集resultSet = preparedStatement.executeQuery();// 遍歷查詢結果集while (resultSet.next()) {int id = resultSet.getInt("id");String username = resultSet.getString("username");// 封裝UserUser user = new User();user.setId(id);user.setUsername(username);System.out.println(user);}} catch (ClassNotFoundException e) {throw new RuntimeException(e);} catch (SQLException e) {throw new RuntimeException(e);} finally {if (resultSet != null) {try {resultSet.close();} catch (SQLException e) {throw new RuntimeException(e);}}if (preparedStatement != null) {try {preparedStatement.close();} catch (SQLException e) {throw new RuntimeException(e);}}if (connection != null) {try {connection.close();} catch (SQLException e) {throw new RuntimeException(e);}}}}

我們發現使用過程中存在以下問題：

數據庫配置信息硬編碼
頻繁創建釋放數據庫連接，而數據庫連接是寶貴的資源
SQL語句、參數、返回結果集獲取均存在硬編碼問題
需要手動封裝返回結果集，較為繁瑣

手寫持久層框架思路分析

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創建一個maven項目mybatis-demo，作為使用端,引入自定義持久層框架jar包。

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其中文件內容如下：

package com.mybatis.it.dao;import com.mybatis.it.pojo.User;import java.util.List;public class UserDaoImpl implements IUserDao {@Overridepublic List<User> findAll() {return null;}@Overridepublic User findByCondition(User user) {return null;}
}

package com.mybatis.it.pojo;public class User {private int id;private String username;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}@Overridepublic String toString() {return "User{" +"id=" + id +", username='" + username + '\'' +'}';}
}

創建SqlMapConfig.xml配置文件：存放數據庫配置信息、存放mapper.xml路徑

<?xml version="1.0" encoding="utf-8" ?>
<configuration><!-- 1. 配置數據庫信息--><dataSource><property name="driverClassName" value="com.mysql.cj.jdbc.Driver"></property><property name="url" value="jdbc:mysql://localhost:3306/mybatis?characterEncoding=utf-8&amp;serverTimezone=UTC"></property><property name="username" value="root"></property><property name="password" value="123456"></property></dataSource><!-- 2. 引入映射配置文件--><mappers><mapper resource="mapper/UserMapper.xml"></mapper></mappers></configuration>

創建mapper.xml配置文件：存放SQL信息、參數類型、返回值類型等

<?xml version="1.0" encoding="UTF-8" ?>
<!-- 唯一標識：namespace.id 取名字叫statementId -->
<mapper namespace="com.mybatis.it.dao.IUserDao"><!--規范：接口的全路徑要和namespace的值保持一致接口中的方法名要和id的值保持一致--><!-- 查詢所有--><select id="findAll" resultType="com.mybatis.it.pojo.User">select * from user_t</select><!-- 按照條件進行查詢--><select id="findByCondition" resultType="com.mybatis.it.pojo.User" parameterType="com.mybatis.it.pojo.User">select * from user_t where id = #{id} and username = #{username}</select>
</mapper>

單元測試用例：

package com.mybatis.it;import com.mybatis.it.dao.IUserDao;
import com.mybatis.it.pojo.User;
import com.mybatis.it.sdk.io.Resources;
import com.mybatis.it.sdk.session.SqlSession;
import com.mybatis.it.sdk.session.SqlSessionFactory;
import com.mybatis.it.sdk.session.SqlSessionFactoryBuilder;
import jdk.nashorn.internal.ir.annotations.Ignore;
import org.junit.jupiter.api.DisplayName;
import org.junit.jupiter.api.Test;import java.io.InputStream;
import java.util.List;public class MyBatisSDKTest {@Ignore@DisplayName("測試手寫版本1MyBatis使用")public void test() {// 1. 根據配置文件的路徑，加載成字節輸入流，存到內存中 注意：配置文件還未解析InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");// 2. 解析了配置文件，封裝了Configuration對象 ； 創建sqlSessionFactory工廠對象SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);// 3. 生產sqlSession 創建了執行器對象SqlSession sqlSession = sqlSessionFactory.openSession();// 4. 調用sqlSession方法User user = new User();user.setId(1);user.setUsername("Tom");User user2 = sqlSession.selectOne("user.selectOne", user);System.out.println(user2);List<Object> list = sqlSession.selectList("user.selectList", null);System.out.println(list);// 釋放資源sqlSession.close();}@Test@DisplayName("測試手寫版本2MyBatis使用")public void test2() {// 1. 根據配置文件的路徑，加載成字節輸入流，存到內存中 注意：配置文件還未解析InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");// 2. 解析了配置文件，封裝了Configuration對象 ； 創建sqlSessionFactory工廠對象SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);// 3. 生產sqlSession 創建了執行器對象SqlSession sqlSession = sqlSessionFactory.openSession();// 4. 調用sqlSession方法User user = new User();user.setId(1);user.setUsername("Tom");IUserDao userDao = sqlSession.getMapper(IUserDao.class);User user2 = userDao.findByCondition(user);System.out.println(user2);List<User> list = userDao.findAll();System.out.println(list);// 釋放資源sqlSession.close();}
}

項目pom.xml內容如下：

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><groupId>com.mybatis.it</groupId><artifactId>mybatis-demo</artifactId><version>1.0-SNAPSHOT</version><properties><maven.compiler.source>8</maven.compiler.source><maven.compiler.target>8</maven.compiler.target><project.build.sourceEncoding>UTF-8</project.build.sourceEncoding></properties><dependencies><!-- 引入自定義持久層框架的jar包 --><dependency><groupId>com.mybatis.it.sdk</groupId><artifactId>mybatis-sdk</artifactId><version>1.0-SNAPSHOT</version></dependency><!-- 引入單元測試依賴 --><dependency><groupId>org.junit.jupiter</groupId><artifactId>junit-jupiter-engine</artifactId><version>5.10.1</version><scope>test</scope></dependency></dependencies></project>

同時創建一個maven模塊：mybatis-sdk

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引入依賴如下（pom.xml）

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><groupId>com.mybatis.it.sdk</groupId><artifactId>mybatis-sdk</artifactId><version>1.0-SNAPSHOT</version><properties><maven.compiler.source>8</maven.compiler.source><maven.compiler.target>8</maven.compiler.target><project.build.sourceEncoding>UTF-8</project.build.sourceEncoding></properties><dependencies><!-- 解析xml --><dependency><groupId>dom4j</groupId><artifactId>dom4j</artifactId><version>1.6.1</version></dependency><!-- xpath --><dependency><groupId>jaxen</groupId><artifactId>jaxen</artifactId><version>1.1.6</version></dependency><!-- mysql數據庫驅動 --><dependency><groupId>com.mysql</groupId><artifactId>mysql-connector-j</artifactId><version>8.2.0</version></dependency><!-- 數據庫連接池 --><dependency><groupId>com.alibaba</groupId><artifactId>druid</artifactId><version>1.2.20</version></dependency><!-- 日志 --><dependency><groupId>org.apache.logging.log4j</groupId><artifactId>log4j-slf4j-impl</artifactId><version>2.22.0</version><scope>test</scope></dependency><!-- 單元測試 --><dependency><groupId>org.junit.jupiter</groupId><artifactId>junit-jupiter-engine</artifactId><version>5.10.1</version><scope>test</scope></dependency><dependency><groupId>org.projectlombok</groupId><artifactId>lombok</artifactId><version>1.18.30</version><scope>provided</scope></dependency></dependencies></project>

創建Resources類：負責加載配置文件，加載成字節流，存到內存中

package com.mybatis.it.sdk.io;import java.io.InputStream;public class Resources {/*** 根據配置文件的路徑，加載配置文件成字節輸入流，存到內存中，注意配置文件還未解析** @param path* @return*/public static InputStream getResourceAsStream(String path) {InputStream inputStream = Resources.class.getClassLoader().getResourceAsStream(path);return inputStream;}
}

Configuration：全局配置類：存儲SqlMapConfig.xml配置文件解析出來的內容

package com.mybatis.it.sdk.pojo;import javax.sql.DataSource;
import java.util.HashMap;
import java.util.Map;/*** 全局配置類：存放核心配置文件解析出來的內容*/
public class Configuration {// 數據源對象private DataSource dataSource;/*** 聲明一個Map集合* key:statementId:namespace.id* MappedStatement: 封裝好的MappedStatement對象*/private Map<String, MappedStatement> mappedStatementMap = new HashMap<>();public DataSource getDataSource() {return dataSource;}public void setDataSource(DataSource dataSource) {this.dataSource = dataSource;}public Map<String, MappedStatement> getMappedStatementMap() {return mappedStatementMap;}public void setMappedStatementMap(Map<String, MappedStatement> mappedStatementMap) {this.mappedStatementMap = mappedStatementMap;}
}

MappedStatement：映射配置類：存儲mapper.xml配置文件解析出來的內容

package com.mybatis.it.sdk.pojo;/*** 映射配置類：存放mapper.xml解析內容*/
public class MappedStatement {// 唯一標識：statementId:namespace.idprivate String statementId;// 返回值類型private String resultType;// 參數值類型private String parameterType;// SQL語句private String sql;// 判斷當前是什么操作的一個屬性private String sqlCommandType;public String getStatementId() {return statementId;}public void setStatementId(String statementId) {this.statementId = statementId;}public String getResultType() {return resultType;}public void setResultType(String resultType) {this.resultType = resultType;}public String getParameterType() {return parameterType;}public void setParameterType(String parameterType) {this.parameterType = parameterType;}public String getSql() {return sql;}public void setSql(String sql) {this.sql = sql;}public String getSqlCommandType() {return sqlCommandType;}public void setSqlCommandType(String sqlCommandType) {this.sqlCommandType = sqlCommandType;}
}

解析配置文件，填充容器對象。創建SqlSessionFactoryBuilder類

提供方法：build(InputStream stream) 方法：

(1) 解析配置文件（dom4j + xpath），封裝Configuration

(2) 創建SqlSessionFactory

package com.mybatis.it.sdk.session;import com.mybatis.it.sdk.config.XMLConfigBuilder;
import com.mybatis.it.sdk.pojo.Configuration;import java.io.InputStream;public class SqlSessionFactoryBuilder {/*** 1.解析配置文件，封裝容器對象* 2.創建SqlSessionFactory工廠對象** @param inputStream* @return*/public SqlSessionFactory build(InputStream inputStream) {// 1. 解析配置文件，封裝容器對象 XMLConfigBuilder：專門解析核心配置文件的解析類XMLConfigBuilder xmlConfigBuilder = new XMLConfigBuilder();Configuration configuration = xmlConfigBuilder.parse(inputStream);// 2. 創建SqlSessionFactory工廠對象DefaultSqlSessionFactory defaultSqlSessionFactory = new DefaultSqlSessionFactory(configuration);return defaultSqlSessionFactory;}}

創建SqlSessionFactory接口及DefaultSqlSessionFactory實現類

提供方法：SqlSession openSession(); 工廠模式

提供接口類：

package com.mybatis.it.sdk.session;public interface SqlSessionFactory {/*** 1.生產sqlSession對象* 2. 創建執行器對象** @return*/SqlSession openSession();
}

提供實現類：

package com.mybatis.it.sdk.session;import com.mybatis.it.sdk.executor.Executor;
import com.mybatis.it.sdk.executor.SimpleExecutor;
import com.mybatis.it.sdk.pojo.Configuration;public class DefaultSqlSessionFactory implements SqlSessionFactory {private Configuration configuration;public DefaultSqlSessionFactory(Configuration configuration) {this.configuration = configuration;}@Overridepublic SqlSession openSession() {// 1. 創建執行器對象Executor executor = new SimpleExecutor();// 2. 生產sqlSession對象DefaultSqlSession defaultSqlSession = new DefaultSqlSession(configuration, executor);return defaultSqlSession;}
}

創建SqlSession接口和DefaultSqlSession實現類：

提供方法：

selectList(); 查詢所有
selectOne(); 查詢單個
update(); 更新
delete(); 刪除
insert(); 添加
close();
getMapper();

package com.mybatis.it.sdk.session;import java.util.List;public interface SqlSession {/*** 查詢多個結果** @param statementId* @param param       SQL參數* @param <E>         元素* @return*/<E> List<E> selectList(String statementId, Object param);/*** 查詢單個結果** @param statementId* @param param       SQL參數* @param <T>         類型* @return*/<T> T selectOne(String statementId, Object param);/*** 清除資源*/void close();/*** 生成代理對象*/<T> T getMapper(Class<?> mapperClass);
}

DefaultSqlSession實現類：

package com.mybatis.it.sdk.session;import com.mybatis.it.sdk.executor.Executor;
import com.mybatis.it.sdk.pojo.Configuration;
import com.mybatis.it.sdk.pojo.MappedStatement;import java.lang.reflect.*;
import java.util.List;public class DefaultSqlSession implements SqlSession {private Configuration configuration;private Executor executor;public DefaultSqlSession(Configuration configuration, Executor executor) {this.configuration = configuration;this.executor = executor;}@Overridepublic <E> List<E> selectList(String statementId, Object param) {// 將查詢操作委托給底層的執行器// query()：執行底層的JDBC操作：1.數據庫配置信息 2.SQL配置信息MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);List<E> list = executor.query(configuration, mappedStatement, param);return list;}@Overridepublic <T> T selectOne(String statementId, Object param) {// 去調用selectList方法List<Object> list = this.selectList(statementId, param);if (list.size() == 1) {return (T) list.get(0);} else if (list.size() > 1) {throw new RuntimeException("返回結果大于預期");} else {return null;}}@Overridepublic void close() {executor.close();}@Overridepublic <T> T getMapper(Class<?> mapperClass) {// 使用JDK動態代理生成基于接口的代理對象Object proxy = Proxy.newProxyInstance(DefaultSqlSession.class.getClassLoader(), new Class[]{mapperClass}, new InvocationHandler() {/**** @param proxy 代理對象的引用，很少用* @param method 被調用的方法的字節碼對象* @param args 調用的方法參數** @return* @throws Throwable*/@Overridepublic Object invoke(Object proxy, Method method, Object[] args) throws Throwable {// 具體的邏輯：執行底層的JDBC// 通過調用sqlSession里面的方法來完成方法調用// 參數準備：1.statementId 2.param// 問題1：無法獲取現有的statementId// 規范：接口的全路徑要和namespace的值保持一致；接口中的方法名要和id的值保持一致String methodName = method.getName();String className = method.getDeclaringClass().getName();String statementId = className + "." + methodName;// 方法調用：問題2：要調用sqlSession中增刪改查的什么方法？// 改造當前工程：sqlCommandType：判斷當前是什么操作的一個屬性MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);// sqlCommandType取值范圍(insert delete update select)String sqlCommandType = mappedStatement.getSqlCommandType();switch (sqlCommandType) {case "select":// 執行查詢方法調用// 問題3：該調用selectList還是selectOne？Type genericReturnType = method.getGenericReturnType();// 判斷是否實現了 泛型類型參數化if (genericReturnType instanceof ParameterizedType) {// 表示返回結果是帶泛型的if (args != null) {return selectList(statementId, args[0]);}return selectList(statementId, null);}if (args != null) {return selectOne(statementId, args[0]);}return selectOne(statementId, null);case "update":// 執行更新方法調用case "delete":// 執行刪除方法調用case "insert":// 執行插入方法調用}return null;}});return (T) proxy;}
}

創建Executor接口和實現類SimpleExecutor

提供方法：query(Configuration,MappedStatement,Object parameter); 執行的就是底層JDBC代碼（數據庫配置信息、SQL配置信息）

package com.mybatis.it.sdk.executor;import com.mybatis.it.sdk.pojo.Configuration;
import com.mybatis.it.sdk.pojo.MappedStatement;import java.sql.SQLException;
import java.util.List;public interface Executor {<E> List<E> query(Configuration configuration, MappedStatement mappedStatement, Object param);void close();
}

SimpleExecutor實現類：

package com.mybatis.it.sdk.executor;import com.mybatis.it.sdk.config.BoundSql;
import com.mybatis.it.sdk.pojo.Configuration;
import com.mybatis.it.sdk.pojo.MappedStatement;
import com.mybatis.it.sdk.utils.GenericTokenParser;
import com.mybatis.it.sdk.utils.ParameterMapping;
import com.mybatis.it.sdk.utils.ParameterMappingTokenHandler;import java.beans.PropertyDescriptor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;public class SimpleExecutor implements Executor {private Connection connection = null;private PreparedStatement preparedStatement = null;private ResultSet resultSet = null;@Overridepublic <E> List<E> query(Configuration configuration, MappedStatement mappedStatement, Object param) {try {// 1. 加載驅動，獲取數據源連接connection = configuration.getDataSource().getConnection();// 2. 獲取preparedStatement預編譯對象// 獲取要執行的SQL語句/*** select * from user_t where id = #{id} and username = #{username}* 替換成* select * from user_t where id = ? and username = ?* 解析替換過程中：自定義占位符#{id}里面的值保存下來*/String sql = mappedStatement.getSql();BoundSql boundSql = getBoundSql(sql);String finalSql = boundSql.getFinalSql();preparedStatement = connection.prepareStatement(finalSql);// 3.設置參數String parameterType = mappedStatement.getParameterType();if (parameterType != null) {Class<?> parameterTypeClass = Class.forName(parameterType);List<ParameterMapping> parameterMappingList = boundSql.getList();for (int i = 0; i < parameterMappingList.size(); i++) {ParameterMapping parameterMapping = parameterMappingList.get(i);// 值為#{}里面的內容String paramName = parameterMapping.getContent();// 反射Field declaredField = parameterTypeClass.getDeclaredField(paramName);// 暴力訪問declaredField.setAccessible(true);Object value = declaredField.get(param);// 賦值占位符preparedStatement.setObject(i + 1, value);}}// 4. 執行SQL，發起查詢resultSet = preparedStatement.executeQuery();// 5. 處理返回結果集List<E> list = new ArrayList<>();while (resultSet.next()) {// 元數據信息 包含了：字段名以及字段的值ResultSetMetaData metaData = resultSet.getMetaData();String resultType = mappedStatement.getResultType();Class<?> resultTypeClass = Class.forName(resultType);Object object = resultTypeClass.newInstance();for (int i = 1; i <= metaData.getColumnCount(); i++) {// 字段名String columnName = metaData.getColumnName(i);// 字段值Object value = resultSet.getObject(columnName);// 封裝// 屬性描述器：通過API方法獲取某個屬性的讀寫方法PropertyDescriptor propertyDescriptor = new PropertyDescriptor(columnName, resultTypeClass);Method writeMethod = propertyDescriptor.getWriteMethod();// 參數1：實例對象 參數2：要設置的值writeMethod.invoke(object, value);}list.add((E) object);}return list;} catch (Exception exception) {throw new RuntimeException(exception);}}/*** 1. 將#{}占位符替換成?* 2. 解析替換的過程中 將#{}里面保存的值保存下來** @param sql* @return*/private BoundSql getBoundSql(String sql) {// 1. 創建標記處理器：配合標記解析器完成標記的處理解析工作ParameterMappingTokenHandler parameterMappingTokenHandler = new ParameterMappingTokenHandler();// 2. 創建標記解析器GenericTokenParser genericTokenParser = new GenericTokenParser("#{", "}", parameterMappingTokenHandler);// #{}占位符替換成? 解析替換過程中 將#{}里面保存的值保存下來ParameterMapping集合中String finalSql = genericTokenParser.parse(sql);// #{}里面的值的一個集合List<ParameterMapping> parameterMappings = parameterMappingTokenHandler.getParameterMappings();BoundSql boundSql = new BoundSql(finalSql, parameterMappings);return boundSql;}/*** 釋放資源*/@Overridepublic void close() {if (resultSet != null) {try {resultSet.close();} catch (SQLException e) {throw new RuntimeException(e);}}if (preparedStatement != null) {try {preparedStatement.close();} catch (SQLException e) {throw new RuntimeException(e);}}if (connection != null) {try {connection.close();} catch (SQLException e) {throw new RuntimeException(e);}}}
}

解析配置文件邏輯：

XMLConfigBuilder

package com.mybatis.it.sdk.config;import com.alibaba.druid.pool.DruidDataSource;
import com.mybatis.it.sdk.io.Resources;
import com.mybatis.it.sdk.pojo.Configuration;
import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;import org.dom4j.io.SAXReader;import java.io.InputStream;
import java.util.List;
import java.util.Properties;public class XMLConfigBuilder {private Configuration configuration;public XMLConfigBuilder() {this.configuration = new Configuration();}/*** 使用dom4j+xpath解析配置文件，封裝Configuration對象** @param inputStream* @return*/public Configuration parse(InputStream inputStream) {try {Document document = new SAXReader().read(inputStream);Element rootElement = document.getRootElement();List<Element> list = rootElement.selectNodes("//property");Properties properties = new Properties();for (Element element : list) {String name = element.attributeValue("name");String value = element.attributeValue("value");properties.setProperty(name, value);}// 創建數據源對象DruidDataSource druidDataSource = new DruidDataSource();druidDataSource.setDriverClassName(properties.getProperty("driverClassName"));druidDataSource.setUrl(properties.getProperty("url"));druidDataSource.setUsername(properties.getProperty("username"));druidDataSource.setPassword(properties.getProperty("password"));// 創建好的數據源對象封裝到Configuration對象中configuration.setDataSource(druidDataSource);/*** 解析映射配置文件* 1.獲取映射配置文件的路徑* 2.根據路徑進行映射配置文件的加載解析* 3.封裝到MappedStatement對象中 --> Configuration里面Map<String, MappedStatement>中*/// 1.獲取映射配置文件的路徑List<Element> mapperList = rootElement.selectNodes("//mapper");for (Element element : mapperList) {String mapperPath = element.attributeValue("resource");InputStream resourceAsStream = Resources.getResourceAsStream(mapperPath);// 專門解析映射配置文件的對象XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(configuration);// 2.根據路徑進行映射配置文件的加載解析// 3.封裝到MappedStatement對象中 --> Configuration里面Map<String, MappedStatement>中xmlMapperBuilder.parse(resourceAsStream);}return configuration;} catch (DocumentException e) {throw new RuntimeException(e);}}
}

XMLMapperBuilder

package com.mybatis.it.sdk.config;import com.mybatis.it.sdk.pojo.Configuration;
import com.mybatis.it.sdk.pojo.MappedStatement;
import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;import java.io.InputStream;
import java.util.List;/*** parse：解析配置文件 --> mappedStatement --> Configuration里面Map<String, MappedStatement>中*/
public class XMLMapperBuilder {private Configuration configuration;public XMLMapperBuilder(Configuration configuration) {this.configuration = configuration;}public void parse(InputStream resourceAsStream) {try {Document document = new SAXReader().read(resourceAsStream);Element rootElement = document.getRootElement();String namespace = rootElement.attributeValue("namespace");List<Element> selectList = rootElement.selectNodes("//select");for (Element element : selectList) {String id = element.attributeValue("id");String resultType = element.attributeValue("resultType");String parameterType = element.attributeValue("parameterType");String sql = element.getTextTrim();String statementId = namespace + "." + id;// 封裝MappedStatement對象MappedStatement mappedStatement = new MappedStatement();mappedStatement.setStatementId(statementId);mappedStatement.setParameterType(parameterType);mappedStatement.setResultType(resultType);mappedStatement.setSql(sql);mappedStatement.setSqlCommandType("select");// 將封裝好的MappedStatement封裝到Configuration里面Map<String, MappedStatement>集合中this.configuration.getMappedStatementMap().put(statementId, mappedStatement);}} catch (DocumentException e) {throw new RuntimeException(e);}}
}

BoundSql

package com.mybatis.it.sdk.config;import com.mybatis.it.sdk.utils.ParameterMapping;import java.util.List;public class BoundSql {private String finalSql;private List<ParameterMapping> list;public BoundSql(String finalSql, List<ParameterMapping> list) {this.finalSql = finalSql;this.list = list;}public String getFinalSql() {return finalSql;}public void setFinalSql(String finalSql) {this.finalSql = finalSql;}public List<ParameterMapping> getList() {return list;}public void setList(List<ParameterMapping> list) {this.list = list;}
}

解析參數工具類：

GenericTokenParser：來自mybatis源碼

package com.mybatis.it.sdk.utils;public class GenericTokenParser {private final String openToken; //開始標記private final String closeToken; //結束標記private final TokenHandler handler; // 標記處理器public GenericTokenParser(String openToken, String closeToken, TokenHandler handler) {this.openToken = openToken;this.closeToken = closeToken;this.handler = handler;}/*** 解析${}和#{}* 該方法主要實現了配置文件、腳本等片段中占位符的解析、處理工作，并返回最終需要的數據。* 其中，解析工作由該方法完成，處理工作由處理器handler的handleToken()方法來實現** @param text* @return*/public String parse(String text) {// 驗證參數問題，如果是null，就返回空字符串if (text == null || text.isEmpty()) {return "";}// search open token// 下面繼續驗證是否包含開始標簽，如果不包含，默認不是占位符，直接原樣返回即可，否則繼續執行int start = text.indexOf(openToken, 0);if (start == -1) {return text;}// 把text轉成字符數組src，并且定義默認偏移量offset=0、存儲最終需要返回字符串的變量builder// text變量中占位符對應的變量名是expression。判斷start是否大于-1（即text中是否存在openToken），如果存在就執行char[] src = text.toCharArray();int offset = 0;final StringBuilder builder = new StringBuilder();StringBuilder expression = null;while (start > -1) {// 判斷如果開始標記前如果有轉義字符，就不作為openToken進行處理，否則繼續處理if (start > 0 && src[start - 1] == '\\') {// this open token is escaped. remove the backslash and continue.builder.append(src, offset, start - offset - 1).append(openToken);offset = start + openToken.length();} else {// 重置expression變量，避免空指針或者老數據干擾。// found open token. let's search close token.if (expression == null) {expression = new StringBuilder();} else {expression.setLength(0);}builder.append(src, offset, start - offset);offset = start + openToken.length();int end = text.indexOf(closeToken, offset);while (end > -1) { // 存在結束標記時if (end > offset && src[end - 1] == '\\') {// 如果結束標記前面有轉義字符時// this close token is escaped. remove the backslash and continue.expression.append(src, offset, end - offset - 1).append(closeToken);offset = end + closeToken.length();end = text.indexOf(closeToken, offset);} else {// 不存在轉義字符，即需要作為參數進行處理expression.append(src, offset, end - offset);offset = end + closeToken.length();break;}}if (end == -1) {// close token was not found.builder.append(src, start, src.length - start);offset = src.length;} else {// 首先根據參數的key（即expression）進行參數處理，返回?作為占位符builder.append(handler.handleToken(expression.toString()));offset = end + closeToken.length();}}start = text.indexOf(openToken, offset);}if (offset < src.length) {builder.append(src, offset, src.length - offset);}return builder.toString();}
}

TokenHandler：來自mybatis源碼

package com.mybatis.it.sdk.utils;public interface TokenHandler {String handleToken(String content);
}

ParameterMapping：

package com.mybatis.it.sdk.utils;public class ParameterMapping {// 值為#{}里面的內容：如：id、usernameprivate String content;public ParameterMapping(String content) {this.content = content;}public String getContent() {return content;}public void setContent(String content) {this.content = content;}
}

ParameterMappingTokenHandler：參考mybatis源碼

package com.mybatis.it.sdk.utils;import java.util.ArrayList;
import java.util.List;public class ParameterMappingTokenHandler implements TokenHandler {private List<ParameterMapping> parameterMappings = new ArrayList<ParameterMapping>();// content是參數名稱 #{id} #{username}@Overridepublic String handleToken(String content) {parameterMappings.add(buildParameterMapping(content));return "?";}private ParameterMapping buildParameterMapping(String content) {ParameterMapping parameterMapping = new ParameterMapping(content);return parameterMapping;}public List<ParameterMapping> getParameterMappings() {return parameterMappings;}public void setParameterMappings(List<ParameterMapping> parameterMappings) {this.parameterMappings = parameterMappings;}
}