MyBatis 解析运行原理

摘要：提供一个接口查询接口如何生成对象采用的动态代理技术生成对象使用动态代理可以实现在不提供接口的时候生成对象构建过程在源代码中是通过出一个对象然后调用方法进入重写的方法通过这一句配置文件读入所有的都将会调用该方法这一段中这一句配置读入进入由

提供一个接口

package com.ming.MyBatis;


import com.ming.MyBatis.POJO.Role;
import com.ming.MyBatis.POJO.Student;
import com.ming.MyBatis.POJO.StudentCard;
import org.apache.ibatis.annotations.Param;
import java.util.List;
import java.util.Map;

public interface RoleMapper {
    /**
     * @param id
     * @return
     */
    public Role getRole(int id);

    /**
     * 查询Map
     * @param params
     * @return
     */
    public List findRoleByteMap(Map params);


    /**
     * @param roleName
     * @param note
     * @return
     */
    public List findRoleByteMap1(@Param("roleName") String roleName, @Param("note") String note);

    public List findStudentSelfCardByStudentId(@Param("studentId") int studentId);

    public List getStudent(@Param("uid")int uid);
}

接口如何生成对象,采用jdk的动态代理技术,生成对象

使用CGLB动态代理可以实现在不提供接口的时候,生成对象

在源代码中是

sqlSessionFactory = new SqlSessionFactoryBuilder().build(cfgReader, properties);

通过new 出一个 SqlSessionFactoryBuilder对象,然后调用build方法.

进入 SqlSessionFactoryBuilder

/**
 *    Copyright 2009-2019 the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.session;

import java.io.IOException;
import java.io.InputStream;
import java.io.Reader;
import java.util.Properties;

import org.apache.ibatis.builder.xml.XMLConfigBuilder;
import org.apache.ibatis.exceptions.ExceptionFactory;
import org.apache.ibatis.executor.ErrorContext;
import org.apache.ibatis.session.defaults.DefaultSqlSessionFactory;

/**
 * Builds {@link SqlSession} instances.
 *
 * @author Clinton Begin
 */
public class SqlSessionFactoryBuilder {

  public SqlSessionFactory build(Reader reader) {
    return build(reader, null, null);
  }

  public SqlSessionFactory build(Reader reader, String environment) {
    return build(reader, environment, null);
  }

  public SqlSessionFactory build(Reader reader, Properties properties) {
    return build(reader, null, properties);
  }

  public SqlSessionFactory build(Reader reader, String environment, Properties properties) {
    try {
      XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties);
      return build(parser.parse());
    } catch (Exception e) {
      throw ExceptionFactory.wrapException("Error building SqlSession.", e);
    } finally {
      ErrorContext.instance().reset();
      try {
        reader.close();
      } catch (IOException e) {
        // Intentionally ignore. Prefer previous error.
      }
    }
  }

  public SqlSessionFactory build(InputStream inputStream) {
    return build(inputStream, null, null);
  }

  public SqlSessionFactory build(InputStream inputStream, String environment) {
    return build(inputStream, environment, null);
  }

  public SqlSessionFactory build(InputStream inputStream, Properties properties) {
    return build(inputStream, null, properties);
  }

  public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
    try {
      XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
      return build(parser.parse());
    } catch (Exception e) {
      throw ExceptionFactory.wrapException("Error building SqlSession.", e);
    } finally {
      ErrorContext.instance().reset();
      try {
        inputStream.close();
      } catch (IOException e) {
        // Intentionally ignore. Prefer previous error.
      }
    }
  }

  public SqlSessionFactory build(Configuration config) {
    return new DefaultSqlSessionFactory(config);
  }

}

重写的方法
通过这一句配置文件读入

XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties);

所有的都将会调用该方法

public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
    try {
      XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
      return build(parser.parse());
    } catch (Exception e) {
      throw ExceptionFactory.wrapException("Error building SqlSession.", e);
    } finally {
      ErrorContext.instance().reset();
      try {
        inputStream.close();
      } catch (IOException e) {
        // Intentionally ignore. Prefer previous error.
      }
    }
  }

这一段中

XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);

这一句
XML配置读入进入

由于返回的是XMLConfigBuilder对象 所以是使用该对象去创建SqlSessionFactory对象

其中SqlSessionFactory为接口

/**
 *    Copyright 2009-2019 the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.session;

import java.sql.Connection;

/**
 * Creates an {@link SqlSession} out of a connection or a DataSource
 *
 * @author Clinton Begin
 */
public interface SqlSessionFactory {

  SqlSession openSession();

  SqlSession openSession(boolean autoCommit);

  SqlSession openSession(Connection connection);

  SqlSession openSession(TransactionIsolationLevel level);

  SqlSession openSession(ExecutorType execType);

  SqlSession openSession(ExecutorType execType, boolean autoCommit);

  SqlSession openSession(ExecutorType execType, TransactionIsolationLevel level);

  SqlSession openSession(ExecutorType execType, Connection connection);

  Configuration getConfiguration();

}

其中根据源码可以看到XMLConfigBuilder对象继承于BaseBuilder, BaseBuilder为抽象类 其中的BaseBuilder 继承 XMLConfigBuilder

所以,这两句成立

private volatile static SqlSessionFactory sqlSessionFactory = null;
sqlSessionFactory = new SqlSessionFactoryBuilder().build(cfgReader, properties);

最后就有了SqlSessionFactory实现类

这种创建为Builder创建

进入XMLConfigBuilder 可以看到第115行

      // read it after objectFactory and objectWrapperFactory issue #631
      environmentsElement(root.evalNode("environments"));

可以看到读入配置文件environments节点

其中还可以看到

  private XMLConfigBuilder(XPathParser parser, String environment, Properties props) {
    super(new Configuration());
    ErrorContext.instance().resource("SQL Mapper Configuration");
    this.configuration.setVariables(props);
    this.parsed = false;
    this.environment = environment;
    this.parser = parser;
  }

使用的是super 所以进入 Configuration()对象
可以看到这是所有的配置文件

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

    typeAliasRegistry.registerAlias("JNDI", JndiDataSourceFactory.class);
    typeAliasRegistry.registerAlias("POOLED", PooledDataSourceFactory.class);
    typeAliasRegistry.registerAlias("UNPOOLED", UnpooledDataSourceFactory.class);

    typeAliasRegistry.registerAlias("PERPETUAL", PerpetualCache.class);
    typeAliasRegistry.registerAlias("FIFO", FifoCache.class);
    typeAliasRegistry.registerAlias("LRU", LruCache.class);
    typeAliasRegistry.registerAlias("SOFT", SoftCache.class);
    typeAliasRegistry.registerAlias("WEAK", WeakCache.class);

    typeAliasRegistry.registerAlias("DB_VENDOR", VendorDatabaseIdProvider.class);

    typeAliasRegistry.registerAlias("XML", XMLLanguageDriver.class);
    typeAliasRegistry.registerAlias("RAW", RawLanguageDriver.class);

    typeAliasRegistry.registerAlias("SLF4J", Slf4jImpl.class);
    typeAliasRegistry.registerAlias("COMMONS_LOGGING", JakartaCommonsLoggingImpl.class);
    typeAliasRegistry.registerAlias("LOG4J", Log4jImpl.class);
    typeAliasRegistry.registerAlias("LOG4J2", Log4j2Impl.class);
    typeAliasRegistry.registerAlias("JDK_LOGGING", Jdk14LoggingImpl.class);
    typeAliasRegistry.registerAlias("STDOUT_LOGGING", StdOutImpl.class);
    typeAliasRegistry.registerAlias("NO_LOGGING", NoLoggingImpl.class);

    typeAliasRegistry.registerAlias("CGLIB", CglibProxyFactory.class);
    typeAliasRegistry.registerAlias("JAVASSIST", JavassistProxyFactory.class);

    languageRegistry.setDefaultDriverClass(XMLLanguageDriver.class);
    languageRegistry.register(RawLanguageDriver.class);
  }

配置文件信息将会在这个类中保存

该类中的方法MappedStatement 为获取映射器的节点

  public MappedStatement getMappedStatement(String id, boolean validateIncompleteStatements) {
    if (validateIncompleteStatements) {
      buildAllStatements();
    }
    return mappedStatements.get(id);
  }

public final class MappedStatement {

  private String resource;
  private Configuration configuration;
  private String id;
  private Integer fetchSize;
  private Integer timeout;
  private StatementType statementType;
  private ResultSetType resultSetType;
  private SqlSource sqlSource;
  private Cache cache;
  private ParameterMap parameterMap;
  private List resultMaps;
  private boolean flushCacheRequired;
  private boolean useCache;
  private boolean resultOrdered;
  private SqlCommandType sqlCommandType;
  private KeyGenerator keyGenerator;
  private String[] keyProperties;
  private String[] keyColumns;
  private boolean hasNestedResultMaps;
  private String databaseId;
  private Log statementLog;
  private LanguageDriver lang;
  private String[] resultSets;

这里进入的是映射器的节点信息

在插件中可以通过MappedStatement类,来获取到映射器的节点,即,获取到映射器的信息.在Tomcat编译成为class文件的时候,会写死在class文件中..

其中MappedStatement为final类型

在映射类的第43行有一个重要的属性

  private SqlSource sqlSource;

进入该接口

public interface SqlSource {

  BoundSql getBoundSql(Object parameterObject);

}

其接口有方法

  BoundSql getBoundSql(Object parameterObject);

进入该类的查看BoundSql

public class BoundSql {

  private final String sql;
  private final List parameterMappings;
  private final Object parameterObject;
  private final Map additionalParameters;
  private final MetaObject metaParameters;

  public BoundSql(Configuration configuration, String sql, List 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 getParameterMappings() {
    return parameterMappings;
  }

  public Object getParameterObject() {
    return parameterObject;
  }

  public boolean hasAdditionalParameter(String name) {
    String paramName = new PropertyTokenizer(name).getName();
    return additionalParameters.containsKey(paramName);
  }

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

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

BoundSql有三个属性,

    this.sql = sql;
    this.parameterMappings = parameterMappings;
    // 传递进入的参数 根据Param注解
    this.parameterObject = parameterObject;
    this.additionalParameters = new HashMap<>();
    this.metaParameters = configuration.newMetaObject(additionalParameters);

SqlSession通过动态代理的方式运行

首先 SqlSessionFactory sqlSessionFactory 是SqlSessionFactory接口
SqlSession类如下

/**
 *    Copyright 2009-2019 the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.session;

import java.sql.Connection;

/**
 * Creates an {@link SqlSession} out of a connection or a DataSource
 *
 * @author Clinton Begin
 */
public interface SqlSessionFactory {

  SqlSession openSession();

  SqlSession openSession(boolean autoCommit);

  SqlSession openSession(Connection connection);

  SqlSession openSession(TransactionIsolationLevel level);

  SqlSession openSession(ExecutorType execType);

  SqlSession openSession(ExecutorType execType, boolean autoCommit);

  SqlSession openSession(ExecutorType execType, TransactionIsolationLevel level);

  SqlSession openSession(ExecutorType execType, Connection connection);

  Configuration getConfiguration();

}

首先try里面的第四行

            sqlSession = SqlSessionFactoryUtil.openSqlSesion();
            roleMapper = sqlSession.getMapper(RoleMapper.class);
            students = roleMapper.getStudent(1);
            students1 = roleMapper.getStudent(1);
            sqlSession.commit();

进入getMapper

/**
 *    Copyright 2009-2019 the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.session;

import java.io.Closeable;
import java.sql.Connection;
import java.util.List;
import java.util.Map;

import org.apache.ibatis.cursor.Cursor;
import org.apache.ibatis.executor.BatchResult;

/**
 * The primary Java interface for working with MyBatis.
 * Through this interface you can execute commands, get mappers and manage transactions.
 *
 * @author Clinton Begin
 */
public interface SqlSession extends Closeable {

  /**
   * Retrieve a single row mapped from the statement key.
   * @param  the returned object type
   * @param statement
   * @return Mapped object
   */
   T selectOne(String statement);

  /**
   * Retrieve a single row mapped from the statement key and parameter.
   * @param  the returned object type
   * @param statement Unique identifier matching the statement to use.
   * @param parameter A parameter object to pass to the statement.
   * @return Mapped object
   */
   T selectOne(String statement, Object parameter);

  /**
   * Retrieve a list of mapped objects from the statement key and parameter.
   * @param  the returned list element type
   * @param statement Unique identifier matching the statement to use.
   * @return List of mapped object
   */
   List selectList(String statement);

  /**
   * Retrieve a list of mapped objects from the statement key and parameter.
   * @param  the returned list element type
   * @param statement Unique identifier matching the statement to use.
   * @param parameter A parameter object to pass to the statement.
   * @return List of mapped object
   */
   List selectList(String statement, Object parameter);

  /**
   * Retrieve a list of mapped objects from the statement key and parameter,
   * within the specified row bounds.
   * @param  the returned list element type
   * @param statement Unique identifier matching the statement to use.
   * @param parameter A parameter object to pass to the statement.
   * @param rowBounds  Bounds to limit object retrieval
   * @return List of mapped object
   */
   List selectList(String statement, Object parameter, RowBounds rowBounds);

  /**
   * The selectMap is a special case in that it is designed to convert a list
   * of results into a Map based on one of the properties in the resulting
   * objects.
   * Eg. Return a of Map[Integer,Author] for selectMap("selectAuthors","id")
   * @param  the returned Map keys type
   * @param  the returned Map values type
   * @param statement Unique identifier matching the statement to use.
   * @param mapKey The property to use as key for each value in the list.
   * @return Map containing key pair data.
   */
   Map selectMap(String statement, String mapKey);

  /**
   * The selectMap is a special case in that it is designed to convert a list
   * of results into a Map based on one of the properties in the resulting
   * objects.
   * @param  the returned Map keys type
   * @param  the returned Map values type
   * @param statement Unique identifier matching the statement to use.
   * @param parameter A parameter object to pass to the statement.
   * @param mapKey The property to use as key for each value in the list.
   * @return Map containing key pair data.
   */
   Map selectMap(String statement, Object parameter, String mapKey);

  /**
   * The selectMap is a special case in that it is designed to convert a list
   * of results into a Map based on one of the properties in the resulting
   * objects.
   * @param  the returned Map keys type
   * @param  the returned Map values type
   * @param statement Unique identifier matching the statement to use.
   * @param parameter A parameter object to pass to the statement.
   * @param mapKey The property to use as key for each value in the list.
   * @param rowBounds  Bounds to limit object retrieval
   * @return Map containing key pair data.
   */
   Map selectMap(String statement, Object parameter, String mapKey, RowBounds rowBounds);

  /**
   * A Cursor offers the same results as a List, except it fetches data lazily using an Iterator.
   * @param  the returned cursor element type.
   * @param statement Unique identifier matching the statement to use.
   * @return Cursor of mapped objects
   */
   Cursor selectCursor(String statement);

  /**
   * A Cursor offers the same results as a List, except it fetches data lazily using an Iterator.
   * @param  the returned cursor element type.
   * @param statement Unique identifier matching the statement to use.
   * @param parameter A parameter object to pass to the statement.
   * @return Cursor of mapped objects
   */
   Cursor selectCursor(String statement, Object parameter);

  /**
   * A Cursor offers the same results as a List, except it fetches data lazily using an Iterator.
   * @param  the returned cursor element type.
   * @param statement Unique identifier matching the statement to use.
   * @param parameter A parameter object to pass to the statement.
   * @param rowBounds  Bounds to limit object retrieval
   * @return Cursor of mapped objects
   */
   Cursor selectCursor(String statement, Object parameter, RowBounds rowBounds);

  /**
   * Retrieve a single row mapped from the statement key and parameter
   * using a {@code ResultHandler}.
   * @param statement Unique identifier matching the statement to use.
   * @param parameter A parameter object to pass to the statement.
   * @param handler ResultHandler that will handle each retrieved row
   */
  void select(String statement, Object parameter, ResultHandler handler);

  /**
   * Retrieve a single row mapped from the statement
   * using a {@code ResultHandler}.
   * @param statement Unique identifier matching the statement to use.
   * @param handler ResultHandler that will handle each retrieved row
   */
  void select(String statement, ResultHandler handler);

  /**
   * Retrieve a single row mapped from the statement key and parameter
   * using a {@code ResultHandler} and {@code RowBounds}.
   * @param statement Unique identifier matching the statement to use.
   * @param rowBounds RowBound instance to limit the query results
   * @param handler ResultHandler that will handle each retrieved row
   */
  void select(String statement, Object parameter, RowBounds rowBounds, ResultHandler handler);

  /**
   * Execute an insert statement.
   * @param statement Unique identifier matching the statement to execute.
   * @return int The number of rows affected by the insert.
   */
  int insert(String statement);

  /**
   * Execute an insert statement with the given parameter object. Any generated
   * autoincrement values or selectKey entries will modify the given parameter
   * object properties. Only the number of rows affected will be returned.
   * @param statement Unique identifier matching the statement to execute.
   * @param parameter A parameter object to pass to the statement.
   * @return int The number of rows affected by the insert.
   */
  int insert(String statement, Object parameter);

  /**
   * Execute an update statement. The number of rows affected will be returned.
   * @param statement Unique identifier matching the statement to execute.
   * @return int The number of rows affected by the update.
   */
  int update(String statement);

  /**
   * Execute an update statement. The number of rows affected will be returned.
   * @param statement Unique identifier matching the statement to execute.
   * @param parameter A parameter object to pass to the statement.
   * @return int The number of rows affected by the update.
   */
  int update(String statement, Object parameter);

  /**
   * Execute a delete statement. The number of rows affected will be returned.
   * @param statement Unique identifier matching the statement to execute.
   * @return int The number of rows affected by the delete.
   */
  int delete(String statement);

  /**
   * Execute a delete statement. The number of rows affected will be returned.
   * @param statement Unique identifier matching the statement to execute.
   * @param parameter A parameter object to pass to the statement.
   * @return int The number of rows affected by the delete.
   */
  int delete(String statement, Object parameter);

  /**
   * Flushes batch statements and commits database connection.
   * Note that database connection will not be committed if no updates/deletes/inserts were called.
   * To force the commit call {@link SqlSession#commit(boolean)}
   */
  void commit();

  /**
   * Flushes batch statements and commits database connection.
   * @param force forces connection commit
   */
  void commit(boolean force);

  /**
   * Discards pending batch statements and rolls database connection back.
   * Note that database connection will not be rolled back if no updates/deletes/inserts were called.
   * To force the rollback call {@link SqlSession#rollback(boolean)}
   */
  void rollback();

  /**
   * Discards pending batch statements and rolls database connection back.
   * Note that database connection will not be rolled back if no updates/deletes/inserts were called.
   * @param force forces connection rollback
   */
  void rollback(boolean force);

  /**
   * Flushes batch statements.
   * @return BatchResult list of updated records
   * @since 3.0.6
   */
  List flushStatements();

  /**
   * Closes the session.
   */
  @Override
  void close();

  /**
   * Clears local session cache.
   */
  void clearCache();

  /**
   * Retrieves current configuration.
   * @return Configuration
   */
  Configuration getConfiguration();

  /**
   * Retrieves a mapper.
   * @param  the mapper type
   * @param type Mapper interface class
   * @return a mapper bound to this SqlSession
   */
   T getMapper(Class type);

  /**
   * Retrieves inner database connection.
   * @return Connection
   */
  Connection getConnection();
}

这是一个接口
其中DefaultSqlSession为旧版本,新版本使用的是SqlSessionManager
进入SqlSessionManager

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

可以看到使用getConfiguration().getMapper(type, this);
getConfiguration()为获取配置信息,mapperRegistry为映射配置类的映射注册表,进入getMapper

  public  T getMapper(Class type, SqlSession sqlSession) {
    final MapperProxyFactory mapperProxyFactory = (MapperProxyFactory) knownMappers.get(type);
    if (mapperProxyFactory == null) {
      throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
    }
    try {
      return mapperProxyFactory.newInstance(sqlSession);
    } catch (Exception e) {
      throw new BindingException("Error getting mapper instance. Cause: " + e, e);
    }
  }

如下

 @SuppressWarnings("unchecked")
  public  T getMapper(Class type, SqlSession sqlSession) {
    final MapperProxyFactory mapperProxyFactory = (MapperProxyFactory) knownMappers.get(type);
    if (mapperProxyFactory == null) {
      throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
    }
    try {
      return mapperProxyFactory.newInstance(sqlSession);
    } catch (Exception e) {
      throw new BindingException("Error getting mapper instance. Cause: " + e, e);
    }
  }

然后进入代理工厂类

public class MapperProxyFactory {

  private final Class mapperInterface;
  private final Map methodCache = new ConcurrentHashMap<>();

  public MapperProxyFactory(Class mapperInterface) {
    this.mapperInterface = mapperInterface;
  }

  public Class getMapperInterface() {
    return mapperInterface;
  }

  public Map getMethodCache() {
    return methodCache;
  }

  @SuppressWarnings("unchecked")
  protected T newInstance(MapperProxy mapperProxy) {
    return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
  }

  public T newInstance(SqlSession sqlSession) {
    final MapperProxy mapperProxy = new MapperProxy<>(sqlSession, mapperInterface, methodCache);
    return newInstance(mapperProxy);
  }

}

有这么一句

  @SuppressWarnings("unchecked")
  protected T newInstance(MapperProxy mapperProxy) {
    return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
  }

调用的是这一句

  public T newInstance(SqlSession sqlSession) {
    final MapperProxy mapperProxy = new MapperProxy<>(sqlSession, mapperInterface, methodCache);
    return newInstance(mapperProxy);
  }

在MapperProxy中有如下几个

  @Override
  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    try {
      if (Object.class.equals(method.getDeclaringClass())) {
        return method.invoke(this, args);
      } else if (isDefaultMethod(method)) {
        return invokeDefaultMethod(proxy, method, args);
      }
    } catch (Throwable t) {
      throw ExceptionUtil.unwrapThrowable(t);
    }
    final MapperMethod mapperMethod = cachedMapperMethod(method);
    return mapperMethod.execute(sqlSession, args);
  }

通过动态代理生成该对象
然后接着查看execute源码

 public Object execute(SqlSession sqlSession, Object[] args) {
    Object result;
    switch (command.getType()) {
      case INSERT: {
        Object param = method.convertArgsToSqlCommandParam(args);
        result = rowCountResult(sqlSession.insert(command.getName(), param));
        break;
      }
      case UPDATE: {
        Object param = method.convertArgsToSqlCommandParam(args);
        result = rowCountResult(sqlSession.update(command.getName(), param));
        break;
      }
      case DELETE: {
        Object param = method.convertArgsToSqlCommandParam(args);
        result = rowCountResult(sqlSession.delete(command.getName(), param));
        break;
      }
      case SELECT:
        if (method.returnsVoid() && method.hasResultHandler()) {
          executeWithResultHandler(sqlSession, args);
          result = null;
        } else if (method.returnsMany()) {
          result = executeForMany(sqlSession, args);
        } else if (method.returnsMap()) {
          result = executeForMap(sqlSession, args);
        } else if (method.returnsCursor()) {
          result = executeForCursor(sqlSession, args);
        } else {
          Object param = method.convertArgsToSqlCommandParam(args);
          result = sqlSession.selectOne(command.getName(), param);
          if (method.returnsOptional()
              && (result == null || !method.getReturnType().equals(result.getClass()))) {
            result = Optional.ofNullable(result);
          }
        }
        break;
      case FLUSH:
        result = sqlSession.flushStatements();
        break;
      default:
        throw new BindingException("Unknown execution method for: " + command.getName());
    }
    if (result == null && method.getReturnType().isPrimitive() && !method.returnsVoid()) {
      throw new BindingException("Mapper method "" + command.getName()
          + " attempted to return null from a method with a primitive return type (" + method.getReturnType() + ").");
    }
    return result;
  }

这里就能看到sql啦

接着任意进入一个

private  Object executeForMany(SqlSession sqlSession, Object[] args) {
    List result;
    Object param = method.convertArgsToSqlCommandParam(args);
    if (method.hasRowBounds()) {
      RowBounds rowBounds = method.extractRowBounds(args);
      result = sqlSession.selectList(command.getName(), param, rowBounds);
    } else {
      result = sqlSession.selectList(command.getName(), param);
    }
    // issue #510 Collections & arrays support
    if (!method.getReturnType().isAssignableFrom(result.getClass())) {
      if (method.getReturnType().isArray()) {
        return convertToArray(result);
      } else {
        return convertToDeclaredCollection(sqlSession.getConfiguration(), result);
      }
    }
    return result;
  }

不想看了.....反正就是最后调用sqlsession的

/**
 * The primary Java interface for working with MyBatis.
 * Through this interface you can execute commands, get mappers and manage transactions.
 *
 * @author Clinton Begin
 */
public interface SqlSession extends Closeable {

  /**
   * Retrieve a single row mapped from the statement key.
   * @param  the returned object type
   * @param statement
   * @return Mapped object
   */
   T selectOne(String statement);

  /**
   * Retrieve a single row mapped from the statement key and parameter.
   * @param  the returned object type
   * @param statement Unique identifier matching the statement to use.
   * @param parameter A parameter object to pass to the statement.
   * @return Mapped object
   */
   T selectOne(String statement, Object parameter);

  /**
   * Retrieve a list of mapped objects from the statement key and parameter.
   * @param  the returned list element type
   * @param statement Unique identifier matching the statement to use.
   * @return List of mapped object
   */
   List selectList(String statement);

  /**
   * Retrieve a list of mapped objects from the statement key and parameter.
   * @param  the returned list element type
   * @param statement Unique identifier matching the statement to use.
   * @param parameter A parameter object to pass to the statement.
   * @return List of mapped object
   */
   List selectList(String statement, Object parameter);

  /**
   * Retrieve a list of mapped objects from the statement key and parameter,
   * within the specified row bounds.
   * @param  the returned list element type
   * @param statement Unique identifier matching the statement to use.
   * @param parameter A parameter object to pass to the statement.
   * @param rowBounds  Bounds to limit object retrieval
   * @return List of mapped object
   */
   List selectList(String statement, Object parameter, RowBounds rowBounds);

  /**
   * The selectMap is a special case in that it is designed to convert a list
   * of results into a Map based on one of the properties in the resulting
   * objects.
   * Eg. Return a of Map[Integer,Author] for selectMap("selectAuthors","id")
   * @param  the returned Map keys type
   * @param  the returned Map values type
   * @param statement Unique identifier matching the statement to use.
   * @param mapKey The property to use as key for each value in the list.
   * @return Map containing key pair data.
   */
   Map selectMap(String statement, String mapKey);

  /**
   * The selectMap is a special case in that it is designed to convert a list
   * of results into a Map based on one of the properties in the resulting
   * objects.
   * @param  the returned Map keys type
   * @param  the returned Map values type
   * @param statement Unique identifier matching the statement to use.
   * @param parameter A parameter object to pass to the statement.
   * @param mapKey The property to use as key for each value in the list.
   * @return Map containing key pair data.
   */
   Map selectMap(String statement, Object parameter, String mapKey);

  /**
   * The selectMap is a special case in that it is designed to convert a list
   * of results into a Map based on one of the properties in the resulting
   * objects.
   * @param  the returned Map keys type
   * @param  the returned Map values type
   * @param statement Unique identifier matching the statement to use.
   * @param parameter A parameter object to pass to the statement.
   * @param mapKey The property to use as key for each value in the list.
   * @param rowBounds  Bounds to limit object retrieval
   * @return Map containing key pair data.
   */
   Map selectMap(String statement, Object parameter, String mapKey, RowBounds rowBounds);

  /**
   * A Cursor offers the same results as a List, except it fetches data lazily using an Iterator.
   * @param  the returned cursor element type.
   * @param statement Unique identifier matching the statement to use.
   * @return Cursor of mapped objects
   */
   Cursor selectCursor(String statement);

  /**
   * A Cursor offers the same results as a List, except it fetches data lazily using an Iterator.
   * @param  the returned cursor element type.
   * @param statement Unique identifier matching the statement to use.
   * @param parameter A parameter object to pass to the statement.
   * @return Cursor of mapped objects
   */
   Cursor selectCursor(String statement, Object parameter);

  /**
   * A Cursor offers the same results as a List, except it fetches data lazily using an Iterator.
   * @param  the returned cursor element type.
   * @param statement Unique identifier matching the statement to use.
   * @param parameter A parameter object to pass to the statement.
   * @param rowBounds  Bounds to limit object retrieval
   * @return Cursor of mapped objects
   */
   Cursor selectCursor(String statement, Object parameter, RowBounds rowBounds);

  /**
   * Retrieve a single row mapped from the statement key and parameter
   * using a {@code ResultHandler}.
   * @param statement Unique identifier matching the statement to use.
   * @param parameter A parameter object to pass to the statement.
   * @param handler ResultHandler that will handle each retrieved row
   */
  void select(String statement, Object parameter, ResultHandler handler);

  /**
   * Retrieve a single row mapped from the statement
   * using a {@code ResultHandler}.
   * @param statement Unique identifier matching the statement to use.
   * @param handler ResultHandler that will handle each retrieved row
   */
  void select(String statement, ResultHandler handler);

  /**
   * Retrieve a single row mapped from the statement key and parameter
   * using a {@code ResultHandler} and {@code RowBounds}.
   * @param statement Unique identifier matching the statement to use.
   * @param rowBounds RowBound instance to limit the query results
   * @param handler ResultHandler that will handle each retrieved row
   */
  void select(String statement, Object parameter, RowBounds rowBounds, ResultHandler handler);

  /**
   * Execute an insert statement.
   * @param statement Unique identifier matching the statement to execute.
   * @return int The number of rows affected by the insert.
   */
  int insert(String statement);

  /**
   * Execute an insert statement with the given parameter object. Any generated
   * autoincrement values or selectKey entries will modify the given parameter
   * object properties. Only the number of rows affected will be returned.
   * @param statement Unique identifier matching the statement to execute.
   * @param parameter A parameter object to pass to the statement.
   * @return int The number of rows affected by the insert.
   */
  int insert(String statement, Object parameter);

  /**
   * Execute an update statement. The number of rows affected will be returned.
   * @param statement Unique identifier matching the statement to execute.
   * @return int The number of rows affected by the update.
   */
  int update(String statement);

  /**
   * Execute an update statement. The number of rows affected will be returned.
   * @param statement Unique identifier matching the statement to execute.
   * @param parameter A parameter object to pass to the statement.
   * @return int The number of rows affected by the update.
   */
  int update(String statement, Object parameter);

  /**
   * Execute a delete statement. The number of rows affected will be returned.
   * @param statement Unique identifier matching the statement to execute.
   * @return int The number of rows affected by the delete.
   */
  int delete(String statement);

  /**
   * Execute a delete statement. The number of rows affected will be returned.
   * @param statement Unique identifier matching the statement to execute.
   * @param parameter A parameter object to pass to the statement.
   * @return int The number of rows affected by the delete.
   */
  int delete(String statement, Object parameter);

  /**
   * Flushes batch statements and commits database connection.
   * Note that database connection will not be committed if no updates/deletes/inserts were called.
   * To force the commit call {@link SqlSession#commit(boolean)}
   */
  void commit();

  /**
   * Flushes batch statements and commits database connection.
   * @param force forces connection commit
   */
  void commit(boolean force);

  /**
   * Discards pending batch statements and rolls database connection back.
   * Note that database connection will not be rolled back if no updates/deletes/inserts were called.
   * To force the rollback call {@link SqlSession#rollback(boolean)}
   */
  void rollback();

  /**
   * Discards pending batch statements and rolls database connection back.
   * Note that database connection will not be rolled back if no updates/deletes/inserts were called.
   * @param force forces connection rollback
   */
  void rollback(boolean force);

  /**
   * Flushes batch statements.
   * @return BatchResult list of updated records
   * @since 3.0.6
   */
  List flushStatements();

  /**
   * Closes the session.
   */
  @Override
  void close();

  /**
   * Clears local session cache.
   */
  void clearCache();

  /**
   * Retrieves current configuration.
   * @return Configuration
   */
  Configuration getConfiguration();

  /**
   * Retrieves a mapper.
   * @param  the mapper type
   * @param type Mapper interface class
   * @return a mapper bound to this SqlSession
   */
   T getMapper(Class type);

  /**
   * Retrieves inner database connection.
   * @return Connection
   */
  Connection getConnection();
}

映射器的本质是动态代理对象

最后都是调用sqlsession接口的定义的方法完成和数据库的交互