文章目录

一、目标：XML语句构建器
二、设计：XML语句构建器
三、实现：XML语句构建器
- 3.0 引入依赖
- 3.1 工程结构
- 3.2 XML语句构建器关系图
- 3.3 I/O资源扫描
- 3.4 SQL源码
- - 3.4.1 SQL对象
  - 3.4.2 SQL源码接口
  - 3.4.3 原始SQL源码实现类
  - 3.4.4 静态SQL源码实现类
- 3.5 动态上下文
- 3.6 SQL节点
- - 3.6.1 SQL节点接口
  - 3.6.2 混合SQL节点实现类
  - 3.6.3 静态文本SQL节点
- 3.7 脚本语言驱动
- - 3.7.1 脚本语言驱动接口
  - 3.7.2 XML语言驱动器
  - 3.7.3 脚本语言注册器
- 3.8 类型处理器
- - 3.8.1 类型处理器接口
  - 3.8.2 类型处理器注册机
- 3.9 记号处理器
- - 3.9.1 记号处理器接口
  - 3.9.2 普通记号解析器
- 3.10 参数表达式
- 3.11 修改映射器语句和参数映射
- - 3.11.1 修改映射器语句
  - 3.11.2 修改参数映射
- 3.12 修改类型别名
- 3.13 修改配置文件
- 3.14 解析构建器
- - 3.14.1 修改构建器基类
  - 3.14.2 XML脚本构建器
  - 3.14.3 SQL源码构建器
  - 3.14.4 XML语言构建器
  - 3.14.5 XML映射构建器，解耦映射解析
  - 3.14.6 XML配置构建器
- 3.15 DefaultSqlSession 调用调整
四、测试：XML语句构建器
五、总结：XML语句构建器

一、目标：XML语句构建器

Mybatis ORM 框架的核心结构逐步体现出来，包括：解析、绑定、映射、事务、执行、数据源等。
着手处理 XML 解析问题。满足我们解析时一些参数的整合和处理

在这里插入图片描述

💡 这部分的解析，就是在 XMLConfigBuilder#mapperElement 方法中的操作。看上去实现了功能，但是会让人感觉不够规整。
怎么才能设计的易于扩展，又比较干净？

将这部分解析的处理，使用设计原则将流程和职责进行解耦，并结合我们的当前诉求，优先处理静态 SQL 内容，后面再处理动态 SQL 和更多的参数类型的处理。

二、设计：XML语句构建器

💡 怎么使用设计原则将流程和职责进行解耦，并处理静态SQL内容？

参照设计原则，对于 XML 信息的读取，各个功能模块的流程上应该符合单一职责，而每个具体的实现又得具备迪米特法则，这样实现出来的功能才能具备良好的扩展性。通常这类代码也会看着很干净。
在解析过程中，所属解析的不同内容，按照各自的职责类进行拆解和串联调用。

在这里插入图片描述

不把所有的解析都在一个循环中处理，而是在整个解析过程中，引入 映射构建器 和 语句构建器，按照不同的职责分别进行解析。
- XMLMapperBuilder: 映射构建器
- XMLStatementBuilder: 语句构建器
  - 同时在语句构建器中，引入脚本语言驱动器，默认实现的是 XMLLanguageDriver，这个类来具体操作静态和动态 SQL 语句节点的解析。
  - Mybatis 源码中使用 Ognl 的方式进行处理。对于的类是 DynamicContext。

三、实现：XML语句构建器

3.0 引入依赖

pom.xml

<!-- https://mvnrepository.com/artifact/ognl/ognl -->
<dependency>
    <groupId>ognl</groupId>
    <artifactId>ognl</artifactId>
    <version>3.3.2</version>
</dependency>

3.1 工程结构

mybatis-step-08
|-src
	|-main
	|	|-java
	|		|-com.lino.mybatis
    |			|-binding
    |			|	|-MapperMethod.java
	|			|	|-MapperProxy.java
	|			|	|-MapperProxyFactory.java
    |			|	|-MapperRegistry.java
    |			|-builder
    |			|	|-xml
    |			|	|	|-XMLConfigBuilder.java
    |			|	|	|-XMLMapperBuilder.java
    |			|	|	|-XMLStatementBuilder.java
    |			|	|-BaseBuilder.java
    |			|	|-ParameterExpression.java
    |			|	|-SqlSourceBuilder.java
    |			|	|-StaticSqlSource.java
	|			|-datasource
	|			|	|-druid
	|			|	|	|-DruidDataSourceFacroty.java
	|			|	|-pooled
	|			|	|	|-PooledConnection.java
	|			|	|	|-PooledDataSource.java
	|			|	|	|-PooledDataSourceFacroty.java
	|			|	|	|-PoolState.java
	|			|	|-unpooled
	|			|	|	|-UnpooledDataSource.java
	|			|	|	|-UnpooledDataSourceFacroty.java
	|			|	|-DataSourceFactory.java
	|			|-executor
	|			|	|-resultset
	|			|	|	|-DefaultResultSetHandler.java
	|			|	|	|-ResultSetHandler.java
	|			|	|-statement
	|			|	|	|-BaseStatementHandler.java
	|			|	|	|-PreparedStatementHandler.java
	|			|	|	|-SimpleStatementHandler.java
	|			|	|	|-StatementHandler.java
	|			|	|-BaseExecutor.java
	|			|	|-Executor.java
	|			|	|-SimpleExecutor.java
    |			|-io
    |			|	|-Resources.java
    |			|-mapping
    |			|	|-BoundSql.java
    |			|	|-Environment.java
    |			|	|-MappedStatement.java
    |			|	|-ParameterMapping.java
    |			|	|-SqlCommandType.java
    |			|	|-SqlSource.java
    |			|-parsing
    |			|	|-GenericTokenParser.java
    |			|	|-TokenHandler.java
	|			|-reflection
	|			|	|-factory
	|			|	|	|-DefaultObjectFactory.java
	|			|	|	|-ObjectFactory.java
	|			|	|-invoker
	|			|	|	|-GetFieldInvoker.java
	|			|	|	|-Invoker.java
	|			|	|	|-MethodInvoker.java
	|			|	|	|-SetFieldInvoker.java
	|			|	|-property
	|			|	|	|-PropertyNamer.java
	|			|	|	|-PropertyTokenizer.java
	|			|	|-wrapper
	|			|	|	|-BaseWrapper.java
	|			|	|	|-BeanWrapper.java
	|			|	|	|-CollectionWrapper.java
	|			|	|	|-DefaultObjectWrapperFactory.java
	|			|	|	|-MapWrapper.java
	|			|	|	|-ObjectWrapper.java
	|			|	|	|-ObjectWrapperFactory.java
	|			|	|-MetaClass.java
	|			|	|-MetaObject.java
	|			|	|-Reflector.java
	|			|	|-SystemMetaObject.java
	|			|-scripting
	|			|	|-defaults
	|			|	|	|-RawSqlSource.java
	|			|	|-xmltags
	|			|	|	|-DynamicContext.java
	|			|	|	|-MixedSqlNode.java
	|			|	|	|-SqlNode.java
	|			|	|	|-StaticTextSqlNode.java
	|			|	|	|-XMLLanguageDriver.java
	|			|	|	|-XMLScriptBuilder.java
	|			|	|-LanguageDriver.java
	|			|	|-LanguageDriverRegistry.java
    |			|-session
    |			|	|-defaults
    |			|	|	|-DefaultSqlSession.java
    |			|	|	|-DefaultSqlSessionFactory.java
    |			|	|-Configuration.java
    |			|	|-ResultHandler.java
    |			|	|-SqlSession.java
    |			|	|-SqlSessionFactory.java
    |			|	|-SqlSessionFactoryBuilder.java
    |			|	|-TransactionIsolationLevel.java
    |			|-transaction
    |			|	|-jdbc
    |			|	|	|-JdbcTransaction.java
    |			|	|	|-JdbcTransactionFactory.java
    |			|	|-Transaction.java
    |			|	|-TransactionFactory.java
    |			|-type
    |			|	|-JdbcType.java
    |			|	|-TypeAliasRegistry.java
    |			|	|-TypeHandler.java
    |			|	|-TypeHandlerRegistry.java
	|-test
		|-java
		|	|-com.lino.mybatis.test
		|	|-dao
		|	|	|-IUserDao.java
		|	|-po
		|	|	|-User.java
		|	|-ApiTest.java
        |-resources
        	|-mapper
        	|	|-User_Mapper.xml
        	|-mybatis-config-datasource.xml

3.2 XML语句构建器关系图

在这里插入图片描述

解耦原 XMLConfigBuilder 中对 XML 的解析，扩展映射构建器、语句构建器，处理 SQL 的提取和参数的包装，整个核心流程图以 XMLConfigBuilder#mapperElement 为入口串联调用。
在 XMLStatement#parseStatementNode 方法中解析配置语句，提取参数类型、结果类型
- <select id="queryUserInfoById" parameterType="java.lang.Long" resultType="com.lino.mybatis.test.po.User"> SELECT id, userId, userName, userHead FROM user WHERE id = #{id} </select>
- 这里使用到脚本语言驱动器，今昔解析处理，创建 SqlSource 语句信息。SqlSource 包含了 BoundSql。
- 同时这里扩展了 ParameterMapping 作为参数包装传递类，而不仅仅作为 Map 结构包装。因为通过这样的方式，可以封装解析后的 javaType/jdbcType 信息。

3.3 I/O资源扫描

Resources.java

package com.lino.mybatis.io;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;

/**
 * @description: 通过类加载器获得resource的辅助类
 */
public class Resources {

    public static Reader getResourceAsReader(String resource) throws IOException {
        return new InputStreamReader(getResourceAsStream(resource));
    }

    public static InputStream getResourceAsStream(String resource) throws IOException {
        ClassLoader[] classLoaders = getClassLoaders();
        for (ClassLoader classLoader : classLoaders) {
            InputStream inputStream = classLoader.getResourceAsStream(resource);
            if (null != inputStream) {
                return inputStream;
            }
        }
        throw new IOException("Could not find resource " + resource);
    }

    private static ClassLoader[] getClassLoaders() {
        return new ClassLoader[]{
                ClassLoader.getSystemClassLoader(),
                Thread.currentThread().getContextClassLoader()};
    }

    /**
     * 获取类示例
     * @param className 类名称
     * @return 实例类
     */
    public static Class<?> classForName(String className) throws ClassNotFoundException {
        return Class.forName(className);
    }
}

将 getResourceAsStream 从 private 改为 public 。

3.4 SQL源码

3.4.1 SQL对象

BoundSql.java

package com.lino.mybatis.mapping;

import com.lino.mybatis.reflection.MetaObject;
import com.lino.mybatis.session.Configuration;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * @description: 绑定的SQL，是从SqlSource而来，将动态内容都处理完成得到的SQL语句字符串，其中包括?，还有绑定的参数
 */
public class BoundSql {

    private String sql;
    private List<ParameterMapping> parameterMappings;
    private Object parameterObject;
    private Map<String, Object> additionalParameters;
    private MetaObject metaParameters;

    public BoundSql(Configuration configuration, String sql, List<ParameterMapping> parameterMappings, Object parameterObject) {
        this.sql = sql;
        this.parameterMappings = parameterMappings;
        this.parameterObject = parameterObject;
        this.additionalParameters = new HashMap<>();
        this.metaParameters = configuration.newMetaObject(additionalParameters);
    }

    public String getSql() {
        return sql;
    }

    public List<ParameterMapping> getParameterMappings() {
        return parameterMappings;
    }

    public Object getParameterObject() {
        return parameterObject;
    }

    public Object getAdditionalParameter(String name) {
        return metaParameters.getValue(name);
    }

    public void setAdditionalParameter(String name, Object value) {
        metaParameters.setValue(name, value);
    }

    public boolean hasAdditionalParameter(String name) {
        return metaParameters.hasGetter(name);
    }
}

3.4.2 SQL源码接口

SqlSource.java

package com.lino.mybatis.mapping;

/**
 * @description: SQL源码
 */
public interface SqlSource {
    /**
     * 获取SQL源
     *
     * @param parameterObject 参数对象
     * @return BoundSqlSQL源
     */
    BoundSql getBoundSql(Object parameterObject);
}

3.4.3 原始SQL源码实现类

RawSqlSource.java

package com.lino.mybatis.scripting.defaults;

import com.lino.mybatis.mapping.BoundSql;
import com.lino.mybatis.mapping.SqlSource;
import com.lino.mybatis.builder.SqlSourceBuilder;
import com.lino.mybatis.scripting.xmltags.DynamicContext;
import com.lino.mybatis.scripting.xmltags.SqlNode;
import com.lino.mybatis.session.Configuration;
import java.util.HashMap;

/**
 * @description: 原始SQL源码， 比 DynamicSqlSource 动态SQL处理快
 */
public class RawSqlSource implements SqlSource {

    private final SqlSource sqlSource;

    public RawSqlSource(Configuration configuration, SqlNode rootSqlNode, Class<?> parameterType) {
        this(configuration, getSql(configuration, rootSqlNode), parameterType);
    }

    public RawSqlSource(Configuration configuration, String sql, Class<?> parameterType) {
        SqlSourceBuilder sqlSourceParser = new SqlSourceBuilder(configuration);
        Class<?> clazz = parameterType == null ? Object.class : parameterType;
        sqlSource = sqlSourceParser.parse(sql, clazz, new HashMap<>());
    }

    @Override
    public BoundSql getBoundSql(Object parameterObject) {
        return sqlSource.getBoundSql(parameterObject);
    }

    private static String getSql(Configuration configuration, SqlNode rootSqlNode) {
        DynamicContext context = new DynamicContext(configuration, null);
        rootSqlNode.apply(context);
        return context.getSql();
    }
}

3.4.4 静态SQL源码实现类

StaticSqlSource.java

package com.lino.mybatis.builder;

import com.lino.mybatis.mapping.BoundSql;
import com.lino.mybatis.mapping.ParameterMapping;
import com.lino.mybatis.mapping.SqlSource;
import com.lino.mybatis.session.Configuration;
import java.util.List;

/**
 * @description: 静态sql源码
 */
public class StaticSqlSource implements SqlSource {

    private String sql;
    private List<ParameterMapping> parameterMappings;
    private Configuration configuration;

    public StaticSqlSource(Configuration configuration, String sql) {
        this(configuration, sql, null);
    }

    public StaticSqlSource(Configuration configuration, String sql, List<ParameterMapping> parameterMappings) {
        this.sql = sql;
        this.parameterMappings = parameterMappings;
        this.configuration = configuration;
    }

    @Override
    public BoundSql getBoundSql(Object parameterObject) {
        return new BoundSql(configuration, sql, parameterMappings, parameterObject);
    }
}

3.5 动态上下文

DynamicContext.java

package com.lino.mybatis.scripting.xmltags;

import com.lino.mybatis.reflection.MetaObject;
import com.lino.mybatis.session.Configuration;
import ognl.OgnlContext;
import ognl.OgnlException;
import ognl.OgnlRuntime;
import ognl.PropertyAccessor;
import java.util.HashMap;
import java.util.Map;

/**
 * @description: 动态上下文
 */
public class DynamicContext {

    public static final String PARAMETER_OBJECT_KEY = "_parameter";
    public static final String DATABASE_ID_KEY = "_databaseId";

    static {
        // 定义属性->getter方法映射，ContextMap到ContextAccessor的映射，注册到ognl运行时
        // 参考http://commons.apache.org/proper/commons-ognl/developer-guide.html
        OgnlRuntime.setPropertyAccessor(ContextMap.class, new ContextAccessor());
        // 将传入的参数对象统一封装为ContextMap对象（继承了HashMap对象），
        // 然后Ognl运行时环境在动态计算sql语句时，
        // 会按照ContextAccessor中描述的Map接口的方式来访问和读取ContextMap对象，获取计算过程中需要的参数。
        // ContextMap对象内部可能封装了一个普通的POJO对象，也可以是直接传递的Map对象，当然从外部是看不出来的，因为都是使用Map的接口来读取数据。
    }

    private final ContextMap bindings;
    private final StringBuilder sqlBuilder = new StringBuilder();
    private int uniqueNumber;

    /**
     * 在DynamicContext的构造函数中，根据传入的参数对象是否为Map类型，有两个不同构造ContextMap的方式。
     * 而ContextMap作为一个继承了HashMap的对象，作用就是用于统一参数的访问方式；用Map接口方法来访问数据。
     * 具体来说，当传入的参数对象不是Map类型时，Mybatis会将传入的POJO对象用MetaObject对象来封装。
     * 当动态计算sql过程需要获取数据时，用Map接口的get方法包装 MetaObject对象的取值过程。
     *
     * @param configuration   配置项
     * @param parameterObject 参数对象
     */
    public DynamicContext(Configuration configuration, Object parameterObject) {
        // 绝大多数调用的地方 parameterObject 为null
        if (parameterObject != null && !(parameterObject instanceof Map)) {
            // 如果是map型 ?? 这句是 如果不是map型
            MetaObject metaObject = configuration.newMetaObject(parameterObject);
            bindings = new ContextMap(metaObject);
        } else {
            bindings = new ContextMap(null);
        }
        bindings.put(PARAMETER_OBJECT_KEY, parameterObject);
        bindings.put(DATABASE_ID_KEY, configuration.getDatabaseId());
    }

    public Map<String, Object> getBindings() {
        return bindings;
    }

    public void bind(String name, Object value) {
        bindings.put(name, value);
    }

    public void appendSql(String sql) {
        sqlBuilder.append(sql);
        sqlBuilder.append(" ");
    }

    public String getSql() {
        return sqlBuilder.toString().trim();
    }

    public int getUniqueNumber() {
        return uniqueNumber++;
    }

    /**
     * 上下文map， 静态内部类
     */
    static class ContextMap extends HashMap<String, Object> {

        private static final long serialVersionUID = 2977601501966151582L;

        private MetaObject parameterMetaObject;

        public ContextMap(MetaObject parameterMetaObject) {
            this.parameterMetaObject = parameterMetaObject;
        }

        @Override
        public Object get(Object key) {
            String strKey = (String) key;
            // 先去map中找
            if (super.containsKey(strKey)) {
                return super.get(strKey);
            }
            // 如果没找到，再用ognl表达式去取值
            // 如person[0].birthdate.year
            if (parameterMetaObject != null) {
                return parameterMetaObject.getValue(strKey);
            }
            return null;
        }
    }

    static class ContextAccessor implements PropertyAccessor {

        @Override
        public Object getProperty(Map context, Object target, Object name) throws OgnlException {
            Map map = (Map) target;

            Object result = map.get(name);
            if (result != null) {
                return result;
            }

            Object parameterObject = map.get(PARAMETER_OBJECT_KEY);
            if (parameterObject instanceof Map) {
                return ((Map) parameterObject).get(name);
            }
            return null;
        }

        @Override
        public void setProperty(Map context, Object target, Object name, Object value) throws OgnlException {
            Map<Object, Object> map = (Map<Object, Object>) target;
            map.put(name, value);
        }

        @Override
        public String getSourceAccessor(OgnlContext ognlContext, Object o, Object o1) {
            return null;
        }

        @Override
        public String getSourceSetter(OgnlContext ognlContext, Object o, Object o1) {
            return null;
        }
    }
}

3.6 SQL节点

3.6.1 SQL节点接口

SqlNode.java

package com.lino.mybatis.scripting.xmltags;

/**
 * @description: SQL 节点
 */
public interface SqlNode {
    /**
     * 应用动态上下文
     *
     * @param context 动态上下文
     * @return boolean
     */
    boolean apply(DynamicContext context);
}

3.6.2 混合SQL节点实现类

MixedSqlNode.java

package com.lino.mybatis.scripting.xmltags;

import java.util.List;

/**
 * @description: 混合SQL节点
 */
public class MixedSqlNode implements SqlNode {

    /**
     * 组合模式，拥有一个SqlNode的List
     */
    private List<SqlNode> contexts;

    public MixedSqlNode(List<SqlNode> contexts) {
        this.contexts = contexts;
    }

    @Override
    public boolean apply(DynamicContext context) {
        // 依次调用list里每个元素的apply
        contexts.forEach(node -> node.apply(context));
        return true;
    }
}

3.6.3 静态文本SQL节点

StaticTestNode.java

package com.lino.mybatis.scripting.xmltags;

/**
 * @description: 静态文本SQL节点
 */
public class StaticTextSqlNode implements SqlNode {

    private String text;

    public StaticTextSqlNode(String text) {
        this.text = text;
    }

    @Override
    public boolean apply(DynamicContext context) {
        // 将文本加入context中
        context.appendSql(text);
        return true;
    }
}

3.7 脚本语言驱动

获取默认语言驱动器并解析 SQL 操作。在 XMLSriptBuilder 中处理静态 SQL 和动态 SQL

3.7.1 脚本语言驱动接口

LanguageDriver.java

package com.lino.mybatis.scripting;

import com.lino.mybatis.mapping.SqlSource;
import com.lino.mybatis.session.Configuration;
import org.dom4j.Element;

/**
 * @description: 脚本语言驱动
 */
public interface LanguageDriver {

    /**
     * 创建SQL源
     *
     * @param configuration 配置项
     * @param script        元素
     * @param parameterType 参数类型
     * @return SqlSource SQL源码
     */
    SqlSource createSqlSource(Configuration configuration, Element script, Class<?> parameterType);
}

定义脚本语言驱动接口，提供创建 SQL 信息的方法，入参包括：配置、元素、参数。
它有3个实现类：XMLLanguageDriver、RawLanguageDriver、VelocityLanguageDriver，这里只实现了第一种实现。

3.7.2 XML语言驱动器

XMLLanguageDriver.java

package com.lino.mybatis.scripting.xmltags;

import com.lino.mybatis.mapping.SqlSource;
import com.lino.mybatis.scripting.LanguageDriver;
import com.lino.mybatis.session.Configuration;
import org.dom4j.Element;

/**
 * @description: XML 语言驱动器
 */
public class XMLLanguageDriver implements LanguageDriver {

    @Override
    public SqlSource createSqlSource(Configuration configuration, Element script, Class<?> parameterType) {
        // 用XML脚本构建器解析
        XMLScriptBuilder builder = new XMLScriptBuilder(configuration, script, parameterType);
        return builder.parseScriptNode();
    }
}

关于 XML 语言驱动器的实现较简单，只是封装了对 XMLScriptBuilder 的调用处理。

3.7.3 脚本语言注册器

LanguageDriverRegistry.java

package com.lino.mybatis.scripting;

import java.util.HashMap;
import java.util.Map;

/**
 * @description: 脚本语言注册器
 */
public class LanguageDriverRegistry {
    /**
     * 脚本语言Map
     */
    private final Map<Class<?>, LanguageDriver> LANGUAGE_DRIVER_MAP = new HashMap<>(16);

    private Class<?> defaultDriverClass = null;

    public void register(Class<?> cls) {
        if (cls == null) {
            throw new IllegalArgumentException("null is not a valid Language Driver");
        }
        if (!LanguageDriver.class.isAssignableFrom(cls)) {
            throw new RuntimeException(cls.getName() + " does not implements" + LanguageDriver.class.getName());
        }
        // 如果没注册过，再去注册
        LanguageDriver driver = LANGUAGE_DRIVER_MAP.get(cls);
        if (driver == null) {
            try {
                // 单例模式，即一个Class只有一个对应的LanguageDriver
                driver = (LanguageDriver) cls.newInstance();
                LANGUAGE_DRIVER_MAP.put(cls, driver);
            } catch (Exception e) {
                throw new RuntimeException("Failed to load language driver for " + cls.getName(), e);
            }
        }
    }

    public LanguageDriver getDriver(Class<?> cls) {
        return LANGUAGE_DRIVER_MAP.get(cls);
    }

    public LanguageDriver getDefaultDriver() {
        return getDriver(getDefaultDriverClass());
    }

    public Class<?> getDefaultDriverClass() {
        return defaultDriverClass;
    }

    /**
     * Configuration()有调用， 默认为XMLLanguageDriver
     *
     * @param defaultDriverClass 默认驱动类型
     */
    public void setDefaultDriverClass(Class<?> defaultDriverClass) {
        register(defaultDriverClass);
        this.defaultDriverClass = defaultDriverClass;
    }
}

3.8 类型处理器

3.8.1 类型处理器接口

TypeHandler.java

package com.lino.mybatis.type;

import java.sql.PreparedStatement;
import java.sql.SQLException;

/**
 * @description: 类型处理器
 */
public interface TypeHandler<T> {

    /**
     * 设置参数
     *
     * @param ps        预处理语言
     * @param i         次数
     * @param parameter 参数对象
     * @param jdbcType  JDBC类型
     * @throws SQLException SQL异常
     */
    void setParameter(PreparedStatement ps, int i, T parameter, JdbcType jdbcType) throws SQLException;
}

3.8.2 类型处理器注册机

TypeHandlerRegistry.java

package com.lino.mybatis.type;

import java.lang.reflect.Type;
import java.util.EnumMap;
import java.util.HashMap;
import java.util.Map;

/**
 * @description: 类型处理器注册机
 */
public final class TypeHandlerRegistry {

    private final Map<JdbcType, TypeHandler<?>> JDBC_TYPE_HANDLER_MAP = new EnumMap<>(JdbcType.class);
    private final Map<Type, Map<JdbcType, TypeHandler<?>>> TYPE_HANDLER_MAP = new HashMap<>(16);
    private final Map<Class<?>, TypeHandler<?>> ALL_TYPE_HANDLER_MAP = new HashMap<>(16);

    public TypeHandlerRegistry() {
    }

    private void register(Type javaType, JdbcType jdbcType, TypeHandler<?> handler) {
        if (null != javaType) {
            Map<JdbcType, TypeHandler<?>> map = TYPE_HANDLER_MAP.computeIfAbsent(javaType, k -> new HashMap<>(16));
            map.put(jdbcType, handler);
        }
        ALL_TYPE_HANDLER_MAP.put(handler.getClass(), handler);
    }
}

3.9 记号处理器

3.9.1 记号处理器接口

TokenHandler.java

package com.lino.mybatis.parsing;

/**
 * @description: 记号处理器
 */
public interface TokenHandler {
    /**
     * 处理记号
     *
     * @param content 内容
     * @return String 处理结果
     */
    String handleToken(String content);
}

3.9.2 普通记号解析器

GenericTokenParser

package com.lino.mybatis.parsing;

/**
 * @description: 普通记号解析器，处理 #{} 和 ${} 参数
 */
public class GenericTokenParser {
    /**
     * 开始记号
     */
    private final String openToken;
    /**
     * 结束记号
     */
    private final String closeToken;
    /**
     * 记号处理器
     */
    private final TokenHandler handler;

    public GenericTokenParser(String openToken, String closeToken, TokenHandler handler) {
        this.openToken = openToken;
        this.closeToken = closeToken;
        this.handler = handler;
    }

    public String parse(String text) {
        StringBuilder builder = new StringBuilder();
        if (text != null && text.length() > 0) {
            char[] src = text.toCharArray();
            int offset = 0;
            int start = text.indexOf(openToken, offset);
            // #{favouriteSection,jdbcType=VARCHAR}
            // 这里循环解析参数，参考 GenericTokenParserTest， 如果解析 ${first_name} ${initial} ${last_name} reporting.这样的字符串,里面有3个${}
            while (start > -1) {
                // 判断一下 ${ 前面是否有反斜杠，这个逻辑在老版的mybatis(3.1.0)中是没有的
                if (start > 0 && src[start - 1] == '\\') {
                    // 新版已经没有调用substring了，改为调用offset方式，提高效率
                    builder.append(src, offset, start - offset - 1).append(openToken);
                    offset = start + openToken.length();
                } else {
                    int end = text.indexOf(closeToken, start);
                    if (end == -1) {
                        builder.append(src, offset,src.length - offset);
                        offset = src.length;
                    } else {
                        builder.append(src, offset, start - offset);
                        offset = start + openToken.length();
                        String context = new String(src, offset, end - offset);
                        // 得到一对大括号里的字符串后，调用handler.handleToken，比如替换变量
                        builder.append(handler.handleToken(context));
                        offset = end + closeToken.length();
                    }
                }
                start = text.indexOf(openToken, offset);
            }
            if (offset < src.length) {
                builder.append(src, offset, src.length - offset);
            }
        }
        return builder.toString();
    }
}

3.10 参数表达式

ParameterExpression.java

package com.lino.mybatis.builder;

import java.util.HashMap;

/**
 * @description: 参数表达式
 */
public class ParameterExpression extends HashMap<String, String> {

    private static final long serialVersionUID = -2417552199605158680L;

    public ParameterExpression(String expression) {
        parse(expression);
    }

    private void parse(String expression) {
        // #{property,javaType=int,jdbcType=NUMERIC}
        // 首先去除空白，返回的p是第一个不是空白的字符位置
        int p = skipWS(expression, 0);
        if (expression.charAt(p) == '(') {
            // 处理表达式
            expression(expression, p + 1);
        } else {
            // 处理属性
            property(expression, p);
        }
    }

    /**
     * 表达式可能是3.2的新功能
     *
     * @param expression 参数
     * @param left       索引
     */
    private void expression(String expression, int left) {
        int match = 1;
        int right = left + 1;
        while (match > 0) {
            if (expression.charAt(right) == ')') {
                match--;
            } else if (expression.charAt(right) == '(') {
                match++;
            }
            right++;
        }
        put("expression", expression.substring(left, right - 1));
        jdbcTypeOpt(expression, right);
    }

    private void property(String expression, int left) {
        // #{property,javaType=int,jdbcType=NUMERIC}
        // property:VARCHAR
        if (left < expression.length()) {
            // 首先，得到逗号或者冒号之前的字符串，加入到property
            int right = skipUntil(expression, left, ",:");
            put("property", trimmedStr(expression, left, right));
            // 第二，处理javaType，jdbcType
            jdbcTypeOpt(expression, right);
        }
    }

    private int skipWS(String expression, int p) {
        for (int i = p; i < expression.length(); i++) {
            if (expression.charAt(i) > 0x20) {
                return i;
            }
        }
        return expression.length();
    }

    private int skipUntil(String expression, int p, String endChars) {
        for (int i = p; i < expression.length(); i++) {
            char c = expression.charAt(i);
            if (endChars.indexOf(c) > -1) {
                return i;
            }
        }
        return expression.length();
    }

    private void jdbcTypeOpt(String expression, int p) {
        // #{property,javaType=int,jdbcType=NUMERIC}
        // property:VARCHAR
        // 首先去除空白，返回的p是第一个不是空白的字符位置
        p = skipWS(expression, p);
        if (p < expression.length()) {
            // 第一个property解析完有两种情况，逗号和冒号
            if (expression.charAt(p) == ':') {
                jdbcType(expression, p + 1);
            } else if (expression.charAt(p) == ',') {
                option(expression, p + 1);
            } else {
                throw new RuntimeException("Parsing error in {" + new String(expression) + "} in position " + p);
            }
        }
    }

    private void jdbcType(String expression, int p) {
        // property:VARCHAR
        int left = skipWS(expression, p);
        int right = skipUntil(expression, left, ",");
        if (right > left) {
            put("jdbcType", trimmedStr(expression, left, right));
        } else {
            throw new RuntimeException("Parsing error in {" + new String(expression) + "} in position " + p);
        }
        option(expression, right + 1);
    }

    private void option(String expression, int p) {
        // #{property,javaType=int,jdbcType=NUMERIC}
        int left = skipWS(expression, p);
        if (left < expression.length()) {
            int right = skipUntil(expression, left, "=");
            String name = trimmedStr(expression, left, right);
            left = right + 1;
            right = skipUntil(expression, left, ",");
            String value = trimmedStr(expression, left, right);
            put(name, value);
            // 递归调用option，进行逗号后面一个属性的解析
            option(expression, right + 1);
        }
    }

    private String trimmedStr(String str, int start, int end) {
        while (str.charAt(start) <= 0x20) {
            start++;
        }
        while (str.charAt(end - 1) <= 0x20) {
            end--;
        }
        return start >= end ? "" : str.substring(start, end);
    }
}

3.11 修改映射器语句和参数映射

3.11.1 修改映射器语句

MappedStatement.java

package com.lino.mybatis.mapping;

import com.lino.mybatis.session.Configuration;

/**
 * @description: 映射器语句类
 */
public class MappedStatement {

    private Configuration configuration;
    private String id;
    private SqlCommandType sqlCommandType;
    private SqlSource sqlSource;
    Class<?> resultType;

    public MappedStatement() {
    }

    public static class Builder {

        private MappedStatement mappedStatement = new MappedStatement();

        public Builder(Configuration configuration, String id, SqlCommandType sqlCommandType, SqlSource sqlSource, Class<?> resultType) {
            mappedStatement.configuration = configuration;
            mappedStatement.id = id;
            mappedStatement.sqlCommandType = sqlCommandType;
            mappedStatement.sqlSource = sqlSource;
            mappedStatement.resultType = resultType;
        }

        public MappedStatement build() {
            assert mappedStatement.configuration != null;
            assert mappedStatement.id != null;
            return mappedStatement;
        }
    }

    public Configuration getConfiguration() {
        return configuration;
    }

    public String getId() {
        return id;
    }

    public SqlCommandType getSqlCommandType() {
        return sqlCommandType;
    }

    public SqlSource getSqlSource() {
        return sqlSource;
    }

    public Class<?> getResultType() {
        return resultType;
    }
}

修改 BoundSql 为 SqlSource。

3.11.2 修改参数映射

ParameterMapping.java

package com.lino.mybatis.mapping;

import cn.hutool.db.meta.JdbcType;
import com.lino.mybatis.session.Configuration;

/**
 * @description: 参数映射 #{property,javaType=int,jdbcType=NUMERIC}
 */
public class ParameterMapping {

    private Configuration configuration;
    /**
     * property
     */
    private String property;
    /**
     * javaType = int
     */
    private Class<?> javaType = Object.class;
    /**
     * javaType = NUMERIC
     */
    private JdbcType jdbcType;

    private ParameterMapping() {
    }

    public static class Builder {

        private ParameterMapping parameterMapping = new ParameterMapping();

        public Builder(Configuration configuration, String property, Class<?> javaType) {
            parameterMapping.configuration = configuration;
            parameterMapping.property = property;
            parameterMapping.javaType = javaType;
        }

        public Builder javaType(Class<?> javaType) {
            parameterMapping.javaType = javaType;
            return this;
        }

        public Builder jdbcType(JdbcType jdbcType) {
            parameterMapping.jdbcType = jdbcType;
            return this;
        }

        public ParameterMapping build() {
            return parameterMapping;
        }
    }

    public Configuration getConfiguration() {
        return configuration;
    }

    public String getProperty() {
        return property;
    }

    public Class<?> getJavaType() {
        return javaType;
    }

    public JdbcType getJdbcType() {
        return jdbcType;
    }
}

3.12 修改类型别名

TypeAliasRegistry.java

package com.lino.mybatis.type;

import com.lino.mybatis.io.Resources;
import java.util.HashMap;
import java.util.Locale;
import java.util.Map;

/**
 * @description: 类型别名注册机
 */
public class TypeAliasRegistry {

    private final Map<String, Class<?>> TYPE_ALIASES = new HashMap<>();

    public TypeAliasRegistry() {
        // 构造函数里注册系统内置的类型别名
        registerAlias("string", String.class);

        // 基本包装类型
        registerAlias("byte", Byte.class);
        registerAlias("long", Long.class);
        registerAlias("short", Short.class);
        registerAlias("int", Integer.class);
        registerAlias("integer", Integer.class);
        registerAlias("double", Double.class);
        registerAlias("float", Float.class);
        registerAlias("boolean", Boolean.class);
    }

    public void registerAlias(String alias, Class<?> value) {
        String key = alias.toLowerCase(Locale.ENGLISH);
        TYPE_ALIASES.put(key, value);
    }

    public <T> Class<T> resolveAlias(String string) {
        try {
            if (string == null) {
                return null;
            }
            String key = string.toLowerCase(Locale.ENGLISH);
            Class<T> value;
            if (TYPE_ALIASES.containsKey(key)) {
                value = (Class<T>) TYPE_ALIASES.get(key);
            } else {
                value = (Class<T>) Resources.classForName(string);
            }
            return value;
        } catch (ClassNotFoundException e) {
            throw new RuntimeException("Could not resolve type alias '" + string + "'.  Cause: " + e, e);
        }
    }
}

修改 resolveAlias 方法，添加不同别名之间和异常信息的处理。

3.13 修改配置文件

Configuration.java

package com.lino.mybatis.session;

import com.lino.mybatis.binding.MapperRegistry;
import com.lino.mybatis.datasource.druid.DruidDataSourceFactory;
import com.lino.mybatis.datasource.pooled.PooledDataSourceFactory;
import com.lino.mybatis.datasource.unpooled.UnpooledDataSourceFactory;
import com.lino.mybatis.executor.Executor;
import com.lino.mybatis.executor.SimpleExecutor;
import com.lino.mybatis.executor.resultset.DefaultResultSetHandler;
import com.lino.mybatis.executor.resultset.ResultSetHandler;
import com.lino.mybatis.executor.statement.PreparedStatementHandler;
import com.lino.mybatis.executor.statement.StatementHandler;
import com.lino.mybatis.mapping.BoundSql;
import com.lino.mybatis.mapping.Environment;
import com.lino.mybatis.mapping.MappedStatement;
import com.lino.mybatis.reflection.MetaObject;
import com.lino.mybatis.reflection.factory.DefaultObjectFactory;
import com.lino.mybatis.reflection.factory.ObjectFactory;
import com.lino.mybatis.reflection.wrapper.DefaultObjectWrapperFactory;
import com.lino.mybatis.reflection.wrapper.ObjectWrapperFactory;
import com.lino.mybatis.scripting.LanguageDriverRegistry;
import com.lino.mybatis.scripting.xmltags.XMLLanguageDriver;
import com.lino.mybatis.transaction.Transaction;
import com.lino.mybatis.transaction.jdbc.JdbcTransactionFactory;
import com.lino.mybatis.type.TypeAliasRegistry;
import com.lino.mybatis.type.TypeHandlerRegistry;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;

/**
 * @description: 配置项
 */
public class Configuration {

    /**
     * 环境
     */
    protected Environment environment;
    /**
     * 映射注册机
     */
    protected MapperRegistry mapperRegistry = new MapperRegistry(this);
    /**
     * 映射的语句，存在Map里
     */
    protected final Map<String, MappedStatement> mappedStatements = new HashMap<>(16);
    /**
     * 类型别名注册机
     */
    protected final TypeAliasRegistry typeAliasRegistry = new TypeAliasRegistry();
    /**
     * 脚本语言注册器
     */
    protected final LanguageDriverRegistry languageRegistry = new LanguageDriverRegistry();
    /**
     * 类型处理器注册机
     */
    protected final TypeHandlerRegistry typeHandlerRegistry = new TypeHandlerRegistry();
    /**
     * 对象工厂
     */
    protected ObjectFactory objectFactory = new DefaultObjectFactory();
    /**
     * 对象包装工厂
     */
    protected ObjectWrapperFactory objectWrapperFactory = new DefaultObjectWrapperFactory();
    /**
     * 准备资源列表
     */
    protected final Set<String> loadedResources = new HashSet<>();
    /**
     * 数据库ID
     */
    protected String databaseId;

    public Configuration() {
        typeAliasRegistry.registerAlias("JDBC", JdbcTransactionFactory.class);

        typeAliasRegistry.registerAlias("DRUID", DruidDataSourceFactory.class);
        typeAliasRegistry.registerAlias("UNPOOLED", UnpooledDataSourceFactory.class);
        typeAliasRegistry.registerAlias("POOLED", PooledDataSourceFactory.class);

        languageRegistry.setDefaultDriverClass(XMLLanguageDriver.class);
    }

    public void addMappers(String packageName) {
        mapperRegistry.addMappers(packageName);
    }

    public <T> void addMapper(Class<T> type) {
        mapperRegistry.addMapper(type);
    }

    public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
        return mapperRegistry.getMapper(type, sqlSession);
    }

    public boolean hasMapper(Class<?> type) {
        return mapperRegistry.hasMapper(type);
    }

    public void addMappedStatement(MappedStatement ms) {
        mappedStatements.put(ms.getId(), ms);
    }

    public MappedStatement getMappedStatement(String id) {
        return mappedStatements.get(id);
    }

    public TypeAliasRegistry getTypeAliasRegistry() {
        return typeAliasRegistry;
    }

    public Environment getEnvironment() {
        return environment;
    }

    public void setEnvironment(Environment environment) {
        this.environment = environment;
    }

    public String getDatabaseId() {
        return databaseId;
    }

    /**
     * 生产执行器
     *
     * @param transaction 事务
     * @return 执行器
     */
    public Executor newExecutor(Transaction transaction) {
        return new SimpleExecutor(this, transaction);
    }

    /**
     * 创建语句处理器
     *
     * @param executor        执行器
     * @param mappedStatement 映射器语句类
     * @param parameter       参数
     * @param resultHandler   结果处理器
     * @param boundSql        SQL语句
     * @return StatementHandler 语句处理器
     */
    public StatementHandler newStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameter, ResultHandler resultHandler, BoundSql boundSql) {
        return new PreparedStatementHandler(executor, mappedStatement, parameter, resultHandler, boundSql);
    }

    /**
     * 创建结果集处理器
     *
     * @param executor        执行器
     * @param mappedStatement 映射器语句类
     * @param boundSql        SQL语句
     * @return ResultSetHandler 结果集处理器
     */
    public ResultSetHandler newResultSetHandler(Executor executor, MappedStatement mappedStatement, BoundSql boundSql) {
        return new DefaultResultSetHandler(executor, mappedStatement, boundSql);
    }

    /**
     * 创建元对象
     *
     * @param object 原对象
     * @return 元对象
     */
    public MetaObject newMetaObject(Object object) {
        return MetaObject.forObject(object, objectFactory, objectWrapperFactory);
    }

    /**
     * 创建类型处理器注册机
     *
     * @return TypeHandlerRegistry 类型处理器注册机
     */
    public TypeHandlerRegistry getTypeHandlerRegistry() {
        return typeHandlerRegistry;
    }

    /**
     * 是否包含资源
     *
     * @param resource 资源
     * @return 是否
     */
    public boolean isResourceLoaded(String resource) {
        return loadedResources.contains(resource);
    }

    /**
     * 添加资源
     *
     * @param resource 资源
     */
    public void addLoadedResource(String resource) {
        loadedResources.add(resource);
    }

    /**
     * 获取脚本语言注册机
     *
     * @return languageRegistry 脚本语言注册机
     */
    public LanguageDriverRegistry getLanguageRegistry() {
        return languageRegistry;
    }
}

3.14 解析构建器

3.14.1 修改构建器基类

BaseBuilder.java

package com.lino.mybatis.builder;

import com.lino.mybatis.session.Configuration;
import com.lino.mybatis.type.TypeAliasRegistry;
import com.lino.mybatis.type.TypeHandlerRegistry;

/**
 * @description: 构建器的基类，建造者模式
 */
public class BaseBuilder {

    protected final Configuration configuration;
    protected final TypeAliasRegistry typeAliasRegistry;
    protected final TypeHandlerRegistry typeHandlerRegistry;

    public BaseBuilder(Configuration configuration) {
        this.configuration = configuration;
        this.typeAliasRegistry = this.configuration.getTypeAliasRegistry();
        this.typeHandlerRegistry = this.configuration.getTypeHandlerRegistry();
    }

    public Configuration getConfiguration() {
        return configuration;
    }

    protected Class<?> resolveAlias(String alias) {
        return typeAliasRegistry.resolveAlias(alias);
    }
}

添加类型处理器注册机 TypeHandlerRegistry。

3.14.2 XML脚本构建器

XMLScriptBuilder.java

package com.lino.mybatis.scripting.xmltags;

import com.lino.mybatis.builder.BaseBuilder;
import com.lino.mybatis.mapping.SqlSource;
import com.lino.mybatis.scripting.defaults.RawSqlSource;
import com.lino.mybatis.session.Configuration;
import org.dom4j.Element;
import java.util.ArrayList;
import java.util.List;

/**
 * @description: XML脚本构建器
 */
public class XMLScriptBuilder extends BaseBuilder {

    private Element element;
    private boolean isDynamic;
    private Class<?> parameterType;

    public XMLScriptBuilder(Configuration configuration, Element element, Class<?> parameterType) {
        super(configuration);
        this.element = element;
        this.parameterType = parameterType;
    }

    public SqlSource parseScriptNode() {
        List<SqlNode> contents = parseDynamicTags(element);
        MixedSqlNode rootSqlNode = new MixedSqlNode(contents);
        return new RawSqlSource(configuration, rootSqlNode, parameterType);
    }

    private List<SqlNode> parseDynamicTags(Element element) {
        List<SqlNode> contents = new ArrayList<>();
        // element.getText 拿到 SQL
        String data = element.getText();
        contents.add(new StaticTextSqlNode(data));
        return contents;
    }
}

XMLScriptBuilder#parseScriptNode 解析 SQL 节点的处理方式，主要是对 RawSqlSource 的包装处理。

3.14.3 SQL源码构建器

SqlSourceBuilder.java

package com.lino.mybatis.builder;

import com.lino.mybatis.mapping.ParameterMapping;
import com.lino.mybatis.mapping.SqlSource;
import com.lino.mybatis.parsing.GenericTokenParser;
import com.lino.mybatis.parsing.TokenHandler;
import com.lino.mybatis.reflection.MetaObject;
import com.lino.mybatis.session.Configuration;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;

/**
 * @description: SQL源码构建器
 */
public class SqlSourceBuilder extends BaseBuilder {

    private static final String parameterProperties = "javaType,jdbcType,mode,numericScale,resultMap,typeHandler,jdbcTypeName";

    public SqlSourceBuilder(Configuration configuration) {
        super(configuration);
    }

    public SqlSource parse(String originalSql, Class<?> parameterType, Map<String, Object> additionalParameters) {
        ParameterMappingTokenHandler handler = new ParameterMappingTokenHandler(configuration, parameterType, additionalParameters);
        GenericTokenParser parser = new GenericTokenParser("#{", "}", handler);
        String sql = parser.parse(originalSql);
        // 返回静态SQL
        return new StaticSqlSource(configuration, sql, handler.getParameterMappings());
    }

    private static class ParameterMappingTokenHandler extends BaseBuilder implements TokenHandler {

        private List<ParameterMapping> parameterMappings = new ArrayList<>();
        private Class<?> parameterType;
        private MetaObject metaParameters;

        public ParameterMappingTokenHandler(Configuration configuration, Class<?> parameterType, Map<String, Object> additionalParameters) {
            super(configuration);
            this.parameterType = parameterType;
            this.metaParameters = configuration.newMetaObject(additionalParameters);
        }

        public List<ParameterMapping> getParameterMappings() {
            return parameterMappings;
        }

        @Override
        public String handleToken(String content) {
            parameterMappings.add(buildParameterMapping(content));
            return "?";
        }

        /**
         * 构建参数映射
         *
         * @param content 参数
         * @return 参数映射
         */
        private ParameterMapping buildParameterMapping(String content) {
            // 先解析参数映射，就是转化成一个 HashMap | #{favouriteSection,jdbcType=VARCHAR}
            Map<String, String> propertiesMap = new ParameterExpression(content);
            String property = propertiesMap.get("property");
            Class<?> propertyType = parameterType;
            ParameterMapping.Builder builder = new ParameterMapping.Builder(configuration, property, propertyType);
            return builder.build();
        }
    }
}

在上一章中，关于 BoundSql.parameterMappings 的参数就是来自于 ParameterMappingTokenHandler#buildParameterMapping 方法进行构建处理的。
具体的 javaType、jdbcType 会体现到 ParameterExpression 参数表达式中完成解析操作。

3.14.4 XML语言构建器

XMLStatementBuilder 语句构建器主要解析 XML 中 select|insert|update|delete 中的语句。

XMLStatementBuilder.java

package com.lino.mybatis.builder.xml;

import com.lino.mybatis.builder.BaseBuilder;
import com.lino.mybatis.mapping.MappedStatement;
import com.lino.mybatis.mapping.SqlCommandType;
import com.lino.mybatis.mapping.SqlSource;
import com.lino.mybatis.scripting.LanguageDriver;
import com.lino.mybatis.session.Configuration;
import org.dom4j.Element;
import java.util.Locale;

/**
 * @description: XML语言构建器
 */
public class XMLStatementBuilder extends BaseBuilder {

    private String currentNamespace;
    private Element element;

    public XMLStatementBuilder(Configuration configuration, Element element, String currentNamespace) {
        super(configuration);
        this.element = element;
        this.currentNamespace = currentNamespace;
    }

    /**
     * 解析语句(select|insert|update|delete)
     * <select
     * id="selectPerson"
     * parameterType="int"
     * parameterMap="deprecated"
     * resultType="hashmap"
     * resultMap="personResultMap"
     * flushCache="false"
     * useCache="true"
     * timeout="10000"
     * fetchSize="256"
     * statementType="PREPARED"
     * resultSetType="FORWARD_ONLY">
     * SELECT * FROM PERSON WHERE ID = #{id}
     * </select>
     */
    public void parseStatementNode() {
        String id = element.attributeValue("id");
        // 参数类型
        String parameterType = element.attributeValue("parameterType");
        Class<?> parameterTypeClass = resolveAlias(parameterType);
        // 结果类型
        String resultType = element.attributeValue("resultType");
        Class<?> resultTypeClass = resolveAlias(resultType);
        // 获取命令类型(select|insert|update|delete)
        String nodeName = element.getName();
        SqlCommandType sqlCommandType = SqlCommandType.valueOf(nodeName.toUpperCase(Locale.ENGLISH));

        // 获取默认语言驱动器
        Class<?> langClass = configuration.getLanguageRegistry().getDefaultDriverClass();
        LanguageDriver langDriver = configuration.getLanguageRegistry().getDriver(langClass);

        SqlSource sqlSource = langDriver.createSqlSource(configuration, element, parameterTypeClass);

        MappedStatement mappedStatement =
                new MappedStatement.Builder(configuration, currentNamespace + "." + id, sqlCommandType, sqlSource, resultTypeClass).build();

        // 添加解析 SQL
        configuration.addMappedStatement(mappedStatement);
    }
}

这部分内容的解析，就是从 XMLConfigBuilder 拆解出来关于 Mapper 语句解析的部分，通过这样的解耦设计，会让整个流程更加清晰。
XMLStatementBuilder#parseStatementNode 方法是解析 SQL 语句节点的过程，包括：语句的ID、参数类型、结果类型、命令(select|insert|update|delete)，以及使用语言驱动器处理和封装 SQL 信息。
当解析完成后写入到 Confiuration 配置文件中的 Map<String, MappedStatement> 映射语句存放中。

3.14.5 XML映射构建器，解耦映射解析

XMLMapperBuilder.java

package com.lino.mybatis.builder.xml;

import com.lino.mybatis.builder.BaseBuilder;
import com.lino.mybatis.io.Resources;
import com.lino.mybatis.session.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;

/**
 * @description: XML映射构建器
 */
public class XMLMapperBuilder extends BaseBuilder {

    private Element element;
    private String resource;
    private String currentNamespace;

    public XMLMapperBuilder(InputStream inputStream, Configuration configuration, String resource) throws DocumentException {
        this(new SAXReader().read(inputStream), configuration, resource);
    }

    public XMLMapperBuilder(Document document, Configuration configuration, String resource) {
        super(configuration);
        this.element = document.getRootElement();
        this.resource = resource;
    }

    /**
     * 解析
     *
     * @throws Exception 异常
     */
    public void parse() throws Exception {
        // 如果当前资源没有加载过再加载，防止重复加载
        if (!configuration.isResourceLoaded(resource)) {
            configurationElement(element);
            // 标记一下，已经加载过了
            configuration.addLoadedResource(resource);
            // 绑定映射器到namespace
            configuration.addMapper(Resources.classForName(currentNamespace));
        }
    }

    /**
     * 配置mapper元素
     * <mapper namespace="org.mybatis.example.BlogMapper">
     * <select id="selectBlog" parameterType="int" resultType="Blog">
     * select * from Blog where id = #{id}
     * </select>
     * </mapper>
     *
     * @param element 元素
     */
    private void configurationElement(Element element) {
        // 1.配置namespace
        currentNamespace = element.attributeValue("namespace");
        if ("".equals(currentNamespace)) {
            throw new RuntimeException("Mapper's namespace cannot be empty");
        }

        // 2.配置select|insert|update|delete
        buildStatementFromContext(element.elements("select"));
    }

    /**
     * 配置select|insert|update|delete
     *
     * @param list 元素列表
     */
    private void buildStatementFromContext(List<Element> list) {
        for (Element element : list) {
            final XMLStatementBuilder statementBuilder = new XMLStatementBuilder(configuration, element, currentNamespace);
            statementBuilder.parseStatementNode();
        }
    }
}

在 XMLMapperBuilder#parse 的解析中，主要体现在资源解析判断、Mapper 解析和绑定映射器。
- configuration.isResourceLoaded 资源判断避免重复解析，做了一个记录。
- configuration.addMapper 绑定映射器：主要是把 namespace com.lino.mybatis.test.dao.IUserDao 绑定到 Mapper 上。
  - 也就是注册到映射器注册机里。
- configurationElement 方法调用的 buildStatementFromContext，重在处理 XML 语句构建器。

3.14.6 XML配置构建器

XMLConfigBuilder.java

package com.lino.mybatis.builder.xml;

import com.lino.mybatis.builder.BaseBuilder;
import com.lino.mybatis.datasource.DataSourceFactory;
import com.lino.mybatis.io.Resources;
import com.lino.mybatis.mapping.Environment;
import com.lino.mybatis.session.Configuration;
import com.lino.mybatis.transaction.TransactionFactory;
import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;
import org.xml.sax.InputSource;
import javax.sql.DataSource;
import java.io.InputStream;
import java.io.Reader;
import java.util.List;
import java.util.Properties;
import java.util.regex.Pattern;

/**
 * @description: XML配置构建器，建造者模式，集成BaseBuilder
 */
public class XMLConfigBuilder extends BaseBuilder {

    private Element root;

    public XMLConfigBuilder(Reader reader) {
        // 1.调用父类初始化Configuration
        super(new Configuration());
        // 2.dom4j 处理xml
        SAXReader saxReader = new SAXReader();
        try {
            Document document = saxReader.read(new InputSource(reader));
            root = document.getRootElement();
        } catch (DocumentException e) {
            e.printStackTrace();
        }
    }

    /**
     * 解析配置：类型别名、插件、对象工厂、对象包装工厂、设置、环境、类型转换、映射器
     *
     * @return Configuration
     */
    public Configuration parse() {
        try {
            // 环境
            environmentsElement(root.element("environments"));
            // 解析映射器
            mapperElement(root.element("mappers"));
        } catch (Exception e) {
            throw new RuntimeException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
        }
        return configuration;
    }

    /**
     * <environments default="development">
     * <environment id="development">
     * <transactionManager type="JDBC">
     * <property name="..." value="..."/>
     * </transactionManager>
     * <dataSource type="POOLED">
     * <property name="driver" value="${driver}"/>
     * <property name="url" value="${url}"/>
     * <property name="username" value="${username}"/>
     * <property name="password" value="${password}"/>
     * </dataSource>
     * </environment>
     * </environments>
     */
    private void environmentsElement(Element context) throws Exception {
        String environment = context.attributeValue("default");

        List<Element> environmentList = context.elements("environment");
        for (Element e : environmentList) {
            String id = e.attributeValue("id");
            if (environment.equals(id)) {
                // 事务管理器
                TransactionFactory txFactory = (TransactionFactory) typeAliasRegistry.resolveAlias(e.element("transactionManager").attributeValue("type")).newInstance();

                // 数据源
                Element dataSourceElement = e.element("dataSource");
                DataSourceFactory dataSourceFactory = (DataSourceFactory) typeAliasRegistry.resolveAlias(dataSourceElement.attributeValue("type")).newInstance();
                List<Element> propertyList = dataSourceElement.elements("property");
                Properties props = new Properties();
                for (Element property : propertyList) {
                    props.setProperty(property.attributeValue("name"), property.attributeValue("value"));
                }
                dataSourceFactory.setProperties(props);
                DataSource dataSource = dataSourceFactory.getDataSource();

                // 构建环境
                Environment.Builder environmentBuilder = new Environment.Builder(id)
                        .transactionFactory(txFactory)
                        .dataSource(dataSource);

                configuration.setEnvironment(environmentBuilder.build());
            }

        }
    }

    /**
     * <mappers>
     * <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
     * <mapper resource="org/mybatis/builder/BlogMapper.xml"/>
     * <mapper resource="org/mybatis/builder/PostMapper.xml"/>
     * </mappers>
     */
    private void mapperElement(Element mappers) throws Exception {
        List<Element> mapperList = mappers.elements("mapper");
        for (Element e : mapperList) {
            String resource = e.attributeValue("resource");
            InputStream inputStream = Resources.getResourceAsStream(resource);

            // 在for循环里每个mapper都重新new一个XMLMapperBuilder，来解析
            XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource);
            mapperParser.parse();
        }

    }
}

在 XMLConfigBuilder#mapperElement 中，把原来的流程化的处理进行解耦，调用 XMLMapperBuilder#parse 方法进行解析处理。

3.15 DefaultSqlSession 调用调整

DefaultSqlSession.java

package com.lino.mybatis.session.defaults;

import com.lino.mybatis.executor.Executor;
import com.lino.mybatis.mapping.MappedStatement;
import com.lino.mybatis.session.Configuration;
import com.lino.mybatis.session.SqlSession;
import java.util.List;

/**
 * @description: 默认sqlSession实现类
 */
public class DefaultSqlSession implements SqlSession {

    private Configuration configuration;
    private Executor executor;

    public DefaultSqlSession(Configuration configuration, Executor executor) {
        this.configuration = configuration;
        this.executor = executor;
    }

    @Override
    public <T> T selectOne(String statement) {
        return this.selectOne(statement, null);
    }

    @Override
    public <T> T selectOne(String statement, Object parameter) {
        MappedStatement ms = configuration.getMappedStatement(statement);
        List<T> list = executor.query(ms, parameter, Executor.NO_RESULT_HANDLER, ms.getSqlSource().getBoundSql(parameter));
        return list.get(0);
    }

    @Override
    public <T> T getMapper(Class<T> type) {
        return configuration.getMapper(type, this);
    }

    @Override
    public Configuration getConfiguration() {
        return configuration;
    }
}

这里调整不大，主要体现在获取 SQL 的操作上。ms.getSqlSource().getBoundSql(parameter) 。

四、测试：XML语句构建器

ApiText.java

@Test
public void test_SqlSessionFactoryExecutor() throws IOException {
    // 1.从SqlSessionFactory中获取SqlSession
    SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsReader("mybatis-config-datasource.xml"));
    SqlSession sqlSession = sqlSessionFactory.openSession();

    // 2.获取映射器对象
    IUserDao userDao = sqlSession.getMapper(IUserDao.class);

    // 3.测试验证
    User user = userDao.queryUserInfoById(1L);
    logger.info("测试结果：{}", JSON.toJSONString(user));
}

测试结果

10:31:42.114 [main] INFO  c.l.m.d.pooled.PooledDataSource - PooledDataSource forcefully closed/removed all connections.
10:31:43.207 [main] INFO  c.l.m.d.pooled.PooledDataSource - Created connention 331418503.
10:31:43.333 [main] INFO  com.lino.mybatis.test.ApiTest - 测试结果：{"id":1,"userHead":"1_04","userId":"10001","userName":"小灵哥"}