@Override
 public <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {
 Statement stmt = null;
 try {
 Configuration configuration = ms.getConfiguration();
 // 這里也就是采用了策略模式(個(gè)人感覺有點(diǎn)像)，實(shí)際的statementHandler為routingStatementHandler
 StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);
 stmt = prepareStatement(handler, ms.getStatementLog());
 // 雖然是執(zhí)行的routingStatementHandler.query，但返回結(jié)果的還是PreparedStatementHandler處理
 return handler.query(stmt, resultHandler);
 } finally {
 closeStatement(stmt);
 }
 }

private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException {
 Statement stmt;
 // 使用了代理模式，也可以理解為對(duì)connection進(jìn)行了一層包裝，這里的作用就是加了log處理
 Connection connection = getConnection(statementLog);
 //進(jìn)行預(yù)編譯,即類似jdbc的 sql,如 select * from user where id=?
 stmt = handler.prepare(connection, transaction.getTimeout());
 // 對(duì)執(zhí)行查詢的sql進(jìn)行參數(shù)設(shè)置
 handler.parameterize(stmt);
 return stmt;
 }

@Override
 public void setParameters(PreparedStatement ps) {
 ErrorContext.instance().activity("setting parameters").object(mappedStatement.getParameterMap().getId());
 // 獲取配置文件里面的sql參數(shù)信息，如sql為select * from user where id=#{userId,jdbcType=INTEGER}
 // ParameterMapping 記錄了參數(shù)名也就是userId,還有記錄了對(duì)應(yīng)的jdbc類型，還有對(duì)應(yīng)的javaType等等，具體可以debug看下
 List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
 if (parameterMappings != null) {
 for (int i = 0; i < parameterMappings.size(); i++) {
 ParameterMapping parameterMapping = parameterMappings.get(i);
 if (parameterMapping.getMode() != ParameterMode.OUT) {
  Object value;
  String propertyName = parameterMapping.getProperty();
  // 如果為true，那么sql參數(shù)中有類似 user.name 格式
  if (boundSql.hasAdditionalParameter(propertyName)) { // issue #448 ask first for additional params
  value = boundSql.getAdditionalParameter(propertyName);
  } else if (parameterObject == null) {
  value = null;
  } else if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass())) {
  value = parameterObject;
  } else {
  // metaObject 類似一個(gè)工具類，它里面有一個(gè)反射工廠，可以專門解析一個(gè)類的信息，如字段的setter/getter/屬性信息，這里不做多余介紹
  // 1、下面詳細(xì)介紹 
  MetaObject metaObject = configuration.newMetaObject(parameterObject);
  value = metaObject.getValue(propertyName);// 取值
  }
  // 獲取對(duì)應(yīng)的typeHandler，一般情況不設(shè)置的話，基本都是ObjectTypeHandler
  TypeHandler typeHandler = parameterMapping.getTypeHandler();
  JdbcType jdbcType = parameterMapping.getJdbcType();
  if (value == null && jdbcType == null) {
  jdbcType = configuration.getJdbcTypeForNull();
  }
  try {
  // 進(jìn)行設(shè)值
  typeHandler.setParameter(ps, i + 1, value, jdbcType);
  } catch (TypeException e) {
  throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + e, e);
  } catch (SQLException e) {
  throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + e, e);
  }
 }
 }
 }
 }

/**
 * mybatis數(shù)據(jù)處理有單結(jié)果集和多結(jié)果集處理，一般多結(jié)果集出現(xiàn)存儲(chǔ)過程中，如果存儲(chǔ)過程中寫了兩條select語句，如
 * select * from user , select * from classes 這種情況這里不做介紹，因?yàn)楸救擞玫牟欢?，理解的也不是很透徹?
 * 這里不多做介紹，這里只針對(duì)簡單映射做一個(gè)大概介紹
 *
 */
public List<Object> handleResultSets(Statement stmt) throws SQLException {
 ErrorContext.instance().activity("handling results").object(mappedStatement.getId());
 // 保存查詢結(jié)果
 final List<Object> multipleResults = new ArrayList<>();

 int resultSetCount = 0;
 // 獲取第一條數(shù)據(jù)
 ResultSetWrapper rsw = getFirstResultSet(stmt);
 // 如果不是多結(jié)果集映射，一般resultMaps的大小為1
 // resultMap中存儲(chǔ)的有類的字段屬性，數(shù)據(jù)庫字段名稱等信息
 List<ResultMap> resultMaps = mappedStatement.getResultMaps();
 int resultMapCount = resultMaps.size();
 // 校驗(yàn)數(shù)據(jù)的正確性
 validateResultMapsCount(rsw, resultMapCount);
 while (rsw != null && resultMapCount > resultSetCount) {
 ResultMap resultMap = resultMaps.get(resultSetCount);
 // 處理結(jié)果集映射
 handleResultSet(rsw, resultMap, multipleResults, null);
 rsw = getNextResultSet(stmt);
 cleanUpAfterHandlingResultSet();
 resultSetCount++;
 }
 // 處理slect 標(biāo)簽的resultSets屬性，多個(gè)用逗號(hào)隔開，個(gè)人幾乎沒用過，略過
 String[] resultSets = mappedStatement.getResultSets();
 if (resultSets != null) {
 while (rsw != null && resultSetCount < resultSets.length) {
 ResultMapping parentMapping = nextResultMaps.get(resultSets[resultSetCount]);
 if (parentMapping != null) {
  String nestedResultMapId = parentMapping.getNestedResultMapId();
  ResultMap resultMap = configuration.getResultMap(nestedResultMapId);
  handleResultSet(rsw, resultMap, null, parentMapping);
 }
 rsw = getNextResultSet(stmt);
 cleanUpAfterHandlingResultSet();
 resultSetCount++;
 }
 }

 return collapseSingleResultList(multipleResults);
 }

private void handleResultSet(ResultSetWrapper rsw, ResultMap resultMap, List<Object> multipleResults, ResultMapping parentMapping) throws SQLException {
 try {// 針對(duì)簡單映射，parentMapping是為Null的
 if (parentMapping != null) {
 handleRowValues(rsw, resultMap, null, RowBounds.DEFAULT, parentMapping);
 } else {
 // 默認(rèn)使用defaultResultHandler，如需使用自定義的，則可在傳參加入resultHandler接口實(shí)現(xiàn)類
 if (resultHandler == null) {
  DefaultResultHandler defaultResultHandler = new DefaultResultHandler(objectFactory);
  // 處理結(jié)果，結(jié)果存在resultHandler里
  handleRowValues(rsw, resultMap, defaultResultHandler, rowBounds, null);
  multipleResults.add(defaultResultHandler.getResultList());
 } else {
  handleRowValues(rsw, resultMap, resultHandler, rowBounds, null);
 }
 }
 } finally {
 // issue #228 (close resultsets)
 closeResultSet(rsw.getResultSet());
 }
 }

public void handleRowValues(ResultSetWrapper rsw, ResultMap resultMap, ResultHandler<?> resultHandler, RowBounds rowBounds, ResultMapping parentMapping) throws SQLException {
 // 處理有嵌套映射的情況
 if (resultMap.hasNestedResultMaps()) {
 ensureNoRowBounds();
 checkResultHandler();
 handleRowValuesForNestedResultMap(rsw, resultMap, resultHandler, rowBounds, parentMapping);
 } else {//沒有嵌套映射
 handleRowValuesForSimpleResultMap(rsw, resultMap, resultHandler, rowBounds, parentMapping);
 }
 }

private void handleRowValuesForSimpleResultMap(ResultSetWrapper rsw, ResultMap resultMap, ResultHandler<?> resultHandler, RowBounds rowBounds, ResultMapping parentMapping)
 throws SQLException {
 DefaultResultContext<Object> resultContext = new DefaultResultContext<>();
 ResultSet resultSet = rsw.getResultSet();
 // 跳過多少行，到達(dá)指定記錄位置，如在傳參的時(shí)候傳入了rowBounds，則會(huì)根據(jù)該類的offset值跳到指定記錄位置
 skipRows(resultSet, rowBounds);
 // shouldProcessMoreRows 用來檢測(cè)是否能繼續(xù)對(duì)后續(xù)的結(jié)果進(jìn)行映射
 while (shouldProcessMoreRows(resultContext, rowBounds) && !resultSet.isClosed() && resultSet.next()) {
 //用來處理resultMap節(jié)點(diǎn)中配置了discriminator節(jié)點(diǎn)，這里忽略掉
 ResultMap discriminatedResultMap = resolveDiscriminatedResultMap(resultSet, resultMap, null);
 // 得到的結(jié)果就是sql執(zhí)行后的一行記錄，如返回User對(duì)象信息，則rowValue就代表一個(gè)user實(shí)例，里面已經(jīng)有值了
 Object rowValue = getRowValue(rsw, discriminatedResultMap, null);
 //保存數(shù)據(jù)
 storeObject(resultHandler, resultContext, rowValue, parentMapping, resultSet);
 }
 }

private Object getRowValue(ResultSetWrapper rsw, ResultMap resultMap, String columnPrefix) throws SQLException {
 final ResultLoaderMap lazyLoader = new ResultLoaderMap();
 // 創(chuàng)建對(duì)象，可以理解為對(duì)resultMap節(jié)點(diǎn)的type屬性值，進(jìn)行了反射處理，得到了一個(gè)對(duì)象，但屬性值都是默認(rèn)值。
 Object rowValue = createResultObject(rsw, resultMap, lazyLoader, columnPrefix);
 if (rowValue != null && !hasTypeHandlerForResultObject(rsw, resultMap.getType())) {
 final MetaObject metaObject = configuration.newMetaObject(rowValue);
 boolean foundValues = this.useConstructorMappings;
 //是否需要自動(dòng)映射，有三種映射，分別為None,partial,full，默認(rèn)第二種，處理非嵌套映射，可通過autoMappingBehavior 配置
 if (shouldApplyAutomaticMappings(resultMap, false)) {
 // 映射resultMap中未明確指定的列，如類中含有username屬性，但是resultMap中沒配置，則通過這個(gè)進(jìn)行數(shù)據(jù)映射，還是可以查詢到結(jié)果
 foundValues = applyAutomaticMappings(rsw, resultMap, metaObject, columnPrefix) || foundValues;
 }
 // 處理resultMap中指定的列
 foundValues = applyPropertyMappings(rsw, resultMap, metaObject, lazyLoader, columnPrefix) || foundValues;
 foundValues = lazyLoader.size() > 0 || foundValues;
 // 如果沒查詢到結(jié)果，但配置可返回空對(duì)象(指的是沒有設(shè)置屬性值得對(duì)象)，則返回空對(duì)象，否則返回null
 rowValue = foundValues || configuration.isReturnInstanceForEmptyRow() ? rowValue : null;
 }
 return rowValue;
 }

private boolean applyPropertyMappings(ResultSetWrapper rsw, ResultMap resultMap, MetaObject metaObject, ResultLoaderMap lazyLoader, String columnPrefix)
 throws SQLException {
 // 獲取數(shù)據(jù)字段名
 final List<String> mappedColumnNames = rsw.getMappedColumnNames(resultMap, columnPrefix);
 boolean foundValues = false;
 // 獲取的數(shù)據(jù)就是resultMap節(jié)點(diǎn)中配置的result節(jié)點(diǎn)，有多個(gè)result節(jié)點(diǎn)，這個(gè)集合大小就是多少
 // 里面存儲(chǔ)的是屬性名/字段名等信息
 final List<ResultMapping> propertyMappings = resultMap.getPropertyResultMappings();
 for (ResultMapping propertyMapping : propertyMappings) {
 String column = prependPrefix(propertyMapping.getColumn(), columnPrefix);
 // 是否有嵌套映射
 if (propertyMapping.getNestedResultMapId() != null) {
 // the user added a column attribute to a nested result map, ignore it
 column = null;
 }
 // 針對(duì)1來說一般常與嵌套查詢配合使用
 // 2 判斷屬性基本映射
 // 3 多結(jié)果集的一個(gè)處理
 if (propertyMapping.isCompositeResult()// 1
  || (column != null && mappedColumnNames.contains(column.toUpperCase(Locale.ENGLISH)))// 2
  || propertyMapping.getResultSet() != null) {// 3
 // 獲取當(dāng)前column字段對(duì)于的值，有用到typeHandler來進(jìn)行參數(shù)的一個(gè)轉(zhuǎn)換
 Object value = getPropertyMappingValue(rsw.getResultSet(), metaObject, propertyMapping, lazyLoader, columnPrefix);
 
 //獲取類的屬性字段名
 final String property = propertyMapping.getProperty();
 if (property == null) {
  continue;
 } else if (value == DEFERRED) {// 類似占位符。處理懶加載數(shù)據(jù)
  foundValues = true;
  continue;
 }
 if (value != null) {
  foundValues = true;
 }
 if (value != null || (configuration.isCallSettersOnNulls() && !metaObject.getSetterType(property).isPrimitive())) {
  // 進(jìn)行設(shè)置屬性值
  metaObject.setValue(property, value);
 }
 }
 }
 return foundValues;
 }