MyBatis源码解析

首先是mybatis简单的使用Demo（源码基于3.5.1版本）:

String resource = "mybatis-config.xml";
InputStream inputStream = null;
try {
    inputStream = Resources.getResourceAsStream(resource);
} catch (IOException e) {
    e.printStackTrace();
}
//构建 SqlSessionFactory
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
//从 SqlSessionFactory 中获取 SqlSession
SqlSession sqlSession = sqlSessionFactory.openSession();
//获取接口代理对象
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
//执行查询方法
User user = mapper.selectOne(1L);
System.out.println(user);
sqlSession.close();

 

一、构建 SqlSessionFactory

SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

SqlSessionFactoryBuilder.build()方法：

public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
  try {
    //xml配置文件的解析器
    XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
    //返回一个SqlSessionFactory的实现类DefaultSqlSessionFactory
    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.
    }
  }
}

主要的方法parser.parse()：解析全局配置文件

 //解析全局配置文件 将配置信息封装成一个Configuration
public Configuration parse() {
  if (parsed) {
    throw new BuilderException("Each XMLConfigBuilder can only be used once.");
  }
  parsed = true;
  //解析配置文件的configuration标签节点，并将配置信息保存到Configuration对象
  parseConfiguration(parser.evalNode("/configuration"));
  //返回一个Configuration对象，包含了所有的全局配置信息和映射文件信息
  return configuration;
}

parseConfiguration(parser.evalNode("/configuration"))：

//解析全局配置文件configuration标签的各子标签，并将配置信息保存到Configuration对象
private void parseConfiguration(XNode root) {
  try {
    //解析properties标签
    propertiesElement(root.evalNode("properties"));
    //解析settings标签，并封装成一个Properties
    Properties settings = settingsAsProperties(root.evalNode("settings"));
    loadCustomVfs(settings);
    loadCustomLogImpl(settings);
    //解析typeAliases标签
    typeAliasesElement(root.evalNode("typeAliases"));
    //解析plugins标签
    pluginElement(root.evalNode("plugins"));
    objectFactoryElement(root.evalNode("objectFactory"));
    objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
    reflectorFactoryElement(root.evalNode("reflectorFactory"));
    settingsElement(settings);
    environmentsElement(root.evalNode("environments"));
    databaseIdProviderElement(root.evalNode("databaseIdProvider"));
    typeHandlerElement(root.evalNode("typeHandlers"));
    //解析mappers标签
    mapperElement(root.evalNode("mappers"));
  } catch (Exception e) {
    throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
  }
}

重点：解析配置文件的mappers标签（sql映射文件位置） mapperElement(root.evalNode("mappers"))：

private void mapperElement(XNode parent) throws Exception {
  if (parent != null) {
    //遍历<mappers>子标签：
    for (XNode child : parent.getChildren()) {
      //使用<package name="org.mybatis.builder"/>子标签
      if ("package".equals(child.getName())) {
        String mapperPackage = child.getStringAttribute("name");
        //保存包名
        configuration.addMappers(mapperPackage);
      } else {
        //<mapper>
        String resource = child.getStringAttribute("resource");
        String url = child.getStringAttribute("url");
        String mapperClass = child.getStringAttribute("class");
        // <mapper resource="org/mybatis/builder/AuthorMapper.xml"/>
        if (resource != null && url == null && mapperClass == null) {
          ErrorContext.instance().resource(resource);
          //获取映射文件流
          InputStream inputStream = Resources.getResourceAsStream(resource);
          //映射文件解析器
          XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());
          //解析映射文件
          mapperParser.parse();
        } else if (resource == null && url != null && mapperClass == null) {
          ErrorContext.instance().resource(url);
          InputStream inputStream = Resources.getUrlAsStream(url);
          XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, url, configuration.getSqlFragments());
          mapperParser.parse();
        } else if (resource == null && url == null && mapperClass != null) {
          Class<?> mapperInterface = Resources.classForName(mapperClass);
          configuration.addMapper(mapperInterface);
        } else {
          throw new BuilderException("A mapper element may only specify a url, resource or class, but not more than one.");
        }
      }
    }
  }
}

解析sql映射文件mapperParser.parse()：

public void parse() {
  //该映射文件是否已经加载过
  if (!configuration.isResourceLoaded(resource)) {
    //解析映射文件的mapper标签
    configurationElement(parser.evalNode("/mapper"));
    configuration.addLoadedResource(resource);
    bindMapperForNamespace();
  }
  parsePendingResultMaps();
  parsePendingCacheRefs();
  parsePendingStatements();
}

解析sql映射文件的mapper标签，configurationElement(parser.evalNode("/mapper"))：

//解析mapper的各个子标签信息并保存在Configuration中
private void configurationElement(XNode context) {
  try {
    String namespace = context.getStringAttribute("namespace");
    if (namespace == null || namespace.equals("")) {
      throw new BuilderException("Mapper's namespace cannot be empty");
    }
    builderAssistant.setCurrentNamespace(namespace);
    cacheRefElement(context.evalNode("cache-ref"));
    cacheElement(context.evalNode("cache"));
    parameterMapElement(context.evalNodes("/mapper/parameterMap"));
    resultMapElements(context.evalNodes("/mapper/resultMap"));
    sqlElement(context.evalNodes("/mapper/sql"));
    //解析所有的增删改查四大标签
    buildStatementFromContext(context.evalNodes("select|insert|update|delete"));
  } catch (Exception e) {
    throw new BuilderException("Error parsing Mapper XML. The XML location is '" + resource + "'. Cause: " + e, e);
  }
}

解析增删改查标签buildStatementFromContext(context.evalNodes("select|insert|update|delete"))：

private void buildStatementFromContext(List<XNode> list) {
  //如果标签有指定databaseId
  if (configuration.getDatabaseId() != null) {
    buildStatementFromContext(list, configuration.getDatabaseId());
  }
  buildStatementFromContext(list, null);
}

接下来buildStatementFromContext(list, null):

private void buildStatementFromContext(List<XNode> list, String requiredDatabaseId) {
  //遍历所有select|insert|update|delete标签
  for (XNode context : list) {
    //Statement（代表一个增删改查标签）解析器
    final XMLStatementBuilder statementParser = new XMLStatementBuilder(configuration, builderAssistant, context, requiredDatabaseId);
    try {
      //解析标签
      statementParser.parseStatementNode();
    } catch (IncompleteElementException e) {
      configuration.addIncompleteStatement(statementParser);
    }
  }
}

解析每增删改查标签 statementParser.parseStatementNode()：

public void parseStatementNode() {
  String id = context.getStringAttribute("id");
  String databaseId = context.getStringAttribute("databaseId");

  if (!databaseIdMatchesCurrent(id, databaseId, this.requiredDatabaseId)) {
    return;
  }
  
  String nodeName = context.getNode().getNodeName();
  SqlCommandType sqlCommandType = SqlCommandType.valueOf(nodeName.toUpperCase(Locale.ENGLISH));
  boolean isSelect = sqlCommandType == SqlCommandType.SELECT;
  //是否清空缓存，不设置的话 select标签默认为false，其他三个都为为true
  boolean flushCache = context.getBooleanAttribute("flushCache", !isSelect);
  //是否使用二级缓存，不设置的话 select标签默认为true，其他三个都为为false
  boolean useCache = context.getBooleanAttribute("useCache", isSelect);
  boolean resultOrdered = context.getBooleanAttribute("resultOrdered", false);
  //解析include标签，将sql片段包含进来
  XMLIncludeTransformer includeParser = new XMLIncludeTransformer(configuration, builderAssistant);
  includeParser.applyIncludes(context.getNode());

  //参数类型
  String parameterType = context.getStringAttribute("parameterType");
  Class<?> parameterTypeClass = resolveClass(parameterType);
  
  String lang = context.getStringAttribute("lang");
  LanguageDriver langDriver = getLanguageDriver(lang);

  // Parse selectKey after includes and remove them.
  processSelectKeyNodes(id, parameterTypeClass, langDriver);

  // Parse the SQL (pre: <selectKey> and <include> were parsed and removed)
  KeyGenerator keyGenerator;
  String keyStatementId = id + SelectKeyGenerator.SELECT_KEY_SUFFIX;
  keyStatementId = builderAssistant.applyCurrentNamespace(keyStatementId, true);
  if (configuration.hasKeyGenerator(keyStatementId)) {
    keyGenerator = configuration.getKeyGenerator(keyStatementId);
  } else {
    keyGenerator = context.getBooleanAttribute("useGeneratedKeys",
        configuration.isUseGeneratedKeys() && SqlCommandType.INSERT.equals(sqlCommandType))
        ? Jdbc3KeyGenerator.INSTANCE : NoKeyGenerator.INSTANCE;
  }
  SqlSource sqlSource = langDriver.createSqlSource(configuration, context, parameterTypeClass);
  //Statement类型，STATEMENT：普通的字符串拼接, PREPARED（默认）：sql预处理, CALLABLE：可以使用存储过程
  StatementType statementType = StatementType.valueOf(context.getStringAttribute("statementType", StatementType.PREPARED.toString()));
  //下面都是些获取相应的标签属性值
  Integer fetchSize = context.getIntAttribute("fetchSize");
  Integer timeout = context.getIntAttribute("timeout");
  String parameterMap = context.getStringAttribute("parameterMap");
  String resultType = context.getStringAttribute("resultType");
  Class<?> resultTypeClass = resolveClass(resultType);
  String resultMap = context.getStringAttribute("resultMap");
  String resultSetType = context.getStringAttribute("resultSetType");
  ResultSetType resultSetTypeEnum = resolveResultSetType(resultSetType);
  String keyProperty = context.getStringAttribute("keyProperty");
  String keyColumn = context.getStringAttribute("keyColumn");
  String resultSets = context.getStringAttribute("resultSets");
  //每一个增删改查标签信息最终都会被封装成一个MappedStatement并保存在configuration中
  builderAssistant.addMappedStatement(id, sqlSource, statementType, sqlCommandType,
      fetchSize, timeout, parameterMap, parameterTypeClass, resultMap, resultTypeClass,
      resultSetTypeEnum, flushCache, useCache, resultOrdered,
      keyGenerator, keyProperty, keyColumn, databaseId, langDriver, resultSets);
}

 

 

二、从 SqlSessionFactory 中获取 SqlSession

SqlSession sqlSession = sqlSessionFactory.openSession();

openSession()-->openSessionFromDataSource:

private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
  Transaction tx = null;
  try {
    final Environment environment = configuration.getEnvironment();
    final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
    //创建事务对象
    tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
    //创建执行器Executor
    final Executor executor = configuration.newExecutor(tx, execType);
    //创建DefaultSqlSession，包含configuration，executor
    return new DefaultSqlSession(configuration, executor, autoCommit);
  } catch (Exception e) {
    closeTransaction(tx); // may have fetched a connection so lets call close()
    throw ExceptionFactory.wrapException("Error opening session.  Cause: " + e, e);
  } finally {
    ErrorContext.instance().reset();
  }
}

创建执行器Executor，configuration.newExecutor(tx, execType)：

public Executor newExecutor(Transaction transaction, ExecutorType executorType) {
  executorType = executorType == null ? defaultExecutorType : executorType;
  executorType = executorType == null ? ExecutorType.SIMPLE : executorType;
  Executor executor;
  //根据Executor在全局配置文件中的类型，创建SimpleExecutor（默认）/BatchExecutor/ReuseExecutor
  if (ExecutorType.BATCH == executorType) {
    executor = new BatchExecutor(this, transaction);
  } else if (ExecutorType.REUSE == executorType) {
    executor = new ReuseExecutor(this, transaction);
  } else {
    executor = new SimpleExecutor(this, transaction);
  }
  //如果开启了二级缓存，则创建CachingExecutor来包装executor
  if (cacheEnabled) {
    executor = new CachingExecutor(executor);
  }
  //使用每一个拦截器包装executor
  executor = (Executor) interceptorChain.pluginAll(executor);
  return executor;
}

 

 

三、SqlSession.getMapper():返回接口的代理对象

UserMapper mapper = sqlSession.getMapper(UserMapper.class);

getMapper:

public <T> T getMapper(Class<T> type) {
  //从configuration对象中获取
  return configuration.getMapper(type, this);
}

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

public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
  //根据接口类型在knownMappers中获取对应得MapperProxyFactory
  final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type);
  if (mapperProxyFactory == null) {
    throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
  }
  try {
    //创建代理对象
    return mapperProxyFactory.newInstance(sqlSession);
  } catch (Exception e) {
    throw new BindingException("Error getting mapper instance. Cause: " + e, e);
  }
}

public T newInstance(SqlSession sqlSession) {
  //MapperProxy实现了InvocationHandler接口,包含sqlSession（包含configuration，executor）
  final MapperProxy<T> mapperProxy = new MapperProxy<>(sqlSession, mapperInterface, methodCache);
  return newInstance(mapperProxy);
}

protected T newInstance(MapperProxy<T> mapperProxy) {
  //利用jdk动态代理创建代理对象
  return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
}

 

 

四、执行查询方法：

User user = mapper.selectOne(1L);

mapper是一个代理对象，实际是执行MapperProxy（implements InvocationHandler)的invoke方法：

@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
  try {
    if (Object.class.equals(method.getDeclaringClass())) {
      //直接执行Object对象中定义的方法
      return method.invoke(this, args);
      //是否是接口的默认方法（jdk1.8）
    } else if (isDefaultMethod(method)) {
      return invokeDefaultMethod(proxy, method, args);
    }
  } catch (Throwable t) {
    throw ExceptionUtil.unwrapThrowable(t);
  }
  //MapperMethod代表当前执行的方法，包含了configuration对象
  final MapperMethod mapperMethod = cachedMapperMethod(method);
  //执行增删改查方法
  return mapperMethod.execute(sqlSession, args);
}

cachedMapperMethod（method）:

private MapperMethod cachedMapperMethod(Method method) {
  //先从methodCache中获取，如果不存在就new一个MapperMethod添加到methodCache并返回
  return methodCache.computeIfAbsent(method, k -> new MapperMethod(mapperInterface, method, sqlSession.getConfiguration()));
}

mapperMethod.execute(sqlSession, args)：执行具体的增删改方法

public Object execute(SqlSession sqlSession, Object[] args) {
  Object result;
  //判断执行sql语言的类型，这里是select类型
  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:
      //方法无返回值
      if (method.returnsVoid() && method.hasResultHandler()) {
        executeWithResultHandler(sqlSession, args);
        result = null;
        //返回值为集合时
      } else if (method.returnsMany()) {
        result = executeForMany(sqlSession, args);
       //返回值为Map时
      } else if (method.returnsMap()) {
        result = executeForMap(sqlSession, args);
        //返回值为游标
      } else if (method.returnsCursor()) {
        result = executeForCursor(sqlSession, args);
      } else {
        //返回值为单个
        //将方法参数转换成sql语言可以使用的形式
        Object param = method.convertArgsToSqlCommandParam(args);
        //查询单条记录command.getName()为方法的全限定名
        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() + ").");
  }
  //返回结果
  return result;
}

method.convertArgsToSqlCommandParam(args)：参数解析

public Object convertArgsToSqlCommandParam(Object[] args) {
  return paramNameResolver.getNamedParams(args);
}

public Object getNamedParams(Object[] args) {
  //参数的数量
  final int paramCount = names.size();
  if (args == null || paramCount == 0) {
    return null;
    //如果方法参数没有使用@Param注解命名，且方法只有一个参数，直接返回该参数值
  } else if (!hasParamAnnotation && paramCount == 1) {
    return args[names.firstKey()];
  } else {
    //如果是多个参数则封装成一个Map
    final Map<String, Object> param = new ParamMap<>();
    int i = 0;
    for (Map.Entry<Integer, String> entry : names.entrySet()) {
      param.put(entry.getValue(), args[entry.getKey()]);
      // add generic param names (param1, param2, ...)
      final String genericParamName = GENERIC_NAME_PREFIX + String.valueOf(i + 1);
      // ensure not to overwrite parameter named with @Param
      if (!names.containsValue(genericParamName)) {
        param.put(genericParamName, args[entry.getKey()]);
      }
      i++;
    }
    return param;
  }
}

sqlSession.selectOne(command.getName(), param):查询单条记录

@Override
public <T> T selectOne(String statement, Object parameter) {
  // 查询单条其实也是和查询多条记录一样返回List,再取第一条
  List<T> list = this.selectList(statement, parameter);
  if (list.size() == 1) {
    return list.get(0);
  } else if (list.size() > 1) {
    //如果查到多条记录就报错
    throw new TooManyResultsException("Expected one result (or null) to be returned by selectOne(), but found: " + list.size());
  } else {
    return null;
  }
}

selectList(statement, parameter)：

@Override
public <E> List<E> selectList(String statement, Object parameter) {
  return this.selectList(statement, parameter, RowBounds.DEFAULT);
}

@Override
public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {
  try {
    //configuration中获取到MappedStatement（代表一个增删改查标签的所有信息）
    MappedStatement ms = configuration.getMappedStatement(statement);
    //执行器执行查询操作，wrapCollection(parameter)处理参数是集合的情况
    return executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER);
  } catch (Exception e) {
    throw ExceptionFactory.wrapException("Error querying database.  Cause: " + e, e);
  } finally {
    ErrorContext.instance().reset();
  }
}

executor.query（）：

//CachingExecutor:
@Override
public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {
  //BoundSql 代表sql的详细信息，包括sql语言，参数值以及参数在sql语句中的映射关系
  BoundSql boundSql = ms.getBoundSql(parameterObject);
  //使用了二级缓存，所有需要生成缓存的key
  CacheKey key = createCacheKey(ms, parameterObject, rowBounds, boundSql);
  return query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
}

query(ms, parameterObject, rowBounds, resultHandler, key, boundSql):

@Override
public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql)
    throws SQLException {
  //如果映射文件使用了 </cache>标签 ,就能获取到缓存对象
  Cache cache = ms.getCache();
  if (cache != null) {
    flushCacheIfRequired(ms);
    if (ms.isUseCache() && resultHandler == null) {
      ensureNoOutParams(ms, boundSql);
      @SuppressWarnings("unchecked")
      //先从缓存中获取，存在就直接返回，不存在再查询
      List<E> list = (List<E>) tcm.getObject(cache, key);
      if (list == null) {
        //delegate，就是真正执行sql的Executor（当前为）,CachingExecutor只是对其的一层包装
        list = delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
        tcm.putObject(cache, key, list); // issue #578 and #116
      }
      return list;
    }
  }
  return delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
}

delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql)：

//BaseExecutor：
public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {
  ErrorContext.instance().resource(ms.getResource()).activity("executing a query").object(ms.getId());
  if (closed) {
    throw new ExecutorException("Executor was closed.");
  }
  //是否需要清本地缓存
  if (queryStack == 0 && ms.isFlushCacheRequired()) {
    clearLocalCache();
  }
  List<E> list;
  try {
    queryStack++;
    //先从本地缓存中获取
    list = resultHandler == null ? (List<E>) localCache.getObject(key) : null;
    if (list != null) {
      handleLocallyCachedOutputParameters(ms, key, parameter, boundSql);
    } else {
      //缓存不存在，再从数据库中查
      list = queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql);
    }
  } finally {
    queryStack--;
  }
  if (queryStack == 0) {
    for (DeferredLoad deferredLoad : deferredLoads) {
      deferredLoad.load();
    }
    // issue #601
    deferredLoads.clear();
    if (configuration.getLocalCacheScope() == LocalCacheScope.STATEMENT) {
      // issue #482
      clearLocalCache();
    }
  }
  return list;
}

queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql)：

private <E> List<E> queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {
  List<E> list;
  localCache.putObject(key, EXECUTION_PLACEHOLDER);
  try {
    //从数据库中查
    list = doQuery(ms, parameter, rowBounds, resultHandler, boundSql);
  } finally {
    localCache.removeObject(key);
  }
  //将查到的结果放入本地缓存
  localCache.putObject(key, list);
  if (ms.getStatementType() == StatementType.CALLABLE) {
    localOutputParameterCache.putObject(key, parameter);
  }
  return list;
}

doQuery(ms, parameter, rowBounds, resultHandler, boundSql)：

@Override
public <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {
  //原生jdbc的Statement
  Statement stmt = null;
  try {
    Configuration configuration = ms.getConfiguration();
    //StatementHandler(用于获取Statement)
    StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);
    //获取PreparedStatement
    stmt = prepareStatement(handler, ms.getStatementLog());
    //执行sql,返回结果集
    return handler.query(stmt, resultHandler);
  } finally {
    closeStatement(stmt);
  }
}

configuration.newStatementHandler(...):获取StatementHandler对象

public StatementHandler newStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
  //RoutingStatementHandler是一个包装对象
  StatementHandler statementHandler = new RoutingStatementHandler(executor, mappedStatement, parameterObject, rowBounds, resultHandler, boundSql);
  //使用每一个拦截器包装statementHandler
  statementHandler = (StatementHandler) interceptorChain.pluginAll(statementHandler);
  return statementHandler;
}

public RoutingStatementHandler(Executor executor, MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
  //根据MappedStatement的类型创建一个实际使用的StatementHandler，默认为PREPARED
  switch (ms.getStatementType()) {
    case STATEMENT:
      delegate = new SimpleStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);
      break;
    case PREPARED:
      //chuan'jPreparedStatementHandler
      delegate = new PreparedStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);
      break;
    case CALLABLE:
      delegate = new CallableStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);
      break;
    default:
      throw new ExecutorException("Unknown statement type: " + ms.getStatementType());
  }

}

public PreparedStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
  //父类为BaseStatementHandler
  super(executor, mappedStatement, parameter, rowBounds, resultHandler, boundSql);
}

protected BaseStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
  this.configuration = mappedStatement.getConfiguration();
  this.executor = executor;
  this.mappedStatement = mappedStatement;
  this.rowBounds = rowBounds;

  this.typeHandlerRegistry = configuration.getTypeHandlerRegistry();
  this.objectFactory = configuration.getObjectFactory();

  if (boundSql == null) { // issue #435, get the key before calculating the statement
    generateKeys(parameterObject);
    boundSql = mappedStatement.getBoundSql(parameterObject);
  }

  this.boundSql = boundSql;
  //创建参数处理器，会经过拦截器链的包装
  this.parameterHandler = configuration.newParameterHandler(mappedStatement, parameterObject, boundSql);
  //创建结果集处理器，会经过拦截器链的包装
  this.resultSetHandler = configuration.newResultSetHandler(executor, mappedStatement, rowBounds, parameterHandler, resultHandler, boundSql);
}

stmt = prepareStatement(handler, ms.getStatementLog())：获取Statement（PreparedStatement）

private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException {
  Statement stmt;
  //获取连接（Transaction.getConnection -> DataSource.getConnection）
  Connection connection = getConnection(statementLog);
  //预编译sql,获取Statement（Connection.prepareStatement）
  stmt = handler.prepare(connection, transaction.getTimeout());
  //使用parameterHandler给预编译的sql设置参数
  handler.parameterize(stmt);
  return stmt;
}

handler.query(stmt, resultHandler):执行sql语言

@Override
public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {
  PreparedStatement ps = (PreparedStatement) statement;
  //执行查询
  ps.execute();
  //使用resultSetHandler处理结果集，并返回
  return resultSetHandler.handleResultSets(ps);
}