MyBatis源码学习三之查询主逻辑

于 2023-05-25 15:23:24 发布
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MyBatis源码学习三之查询主逻辑

继续上一章节。

MyBatis的一个主要流程图。从图中可以看出，核心的东西主要集中在3个Handler中。分别是入参处理，执行sql语句处理，以及返回结果处理。

在这里插入图片描述

一 实例

Test

public static void main(String[] args) {
    InputStream inputStream = null;
    try {
        inputStream = Resources.getResourceAsStream("mybatis-config.xml");
        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession session = factory.openSession();
        UserMapper mapper = session.getMapper(UserMapper.class);
        User user = mapper.getUserById("20");
        System.err.println(user.getId() + " : " + user.getUserName());
    } catch (IOException e) {
        throw new RuntimeException(e);
    }
}

UserMapper

public interface UserMapper {

    @Select("select name from user where id=#{id}")
    User getUserById(@Param String id);
}

上一节，我们看到MapperProxy.invoke和MapperMethod.execute那我们就接着进入这里来看。

MapperMethod.execute

这里的command.getType是select。而且是一个单结果集的返回，就会进入到case select中最后一个else中。

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;
}

二 参数处理

MethodSignature.convertArgsToSqlCommandParam

public MethodSignature(Configuration configuration, Class<?> mapperInterface, Method method) {
    Type resolvedReturnType = TypeParameterResolver.resolveReturnType(method, mapperInterface);
    if (resolvedReturnType instanceof Class<?>) {
        this.returnType = (Class<?>) resolvedReturnType;
    } else if (resolvedReturnType instanceof ParameterizedType) {
        this.returnType = (Class<?>) ((ParameterizedType) resolvedReturnType).getRawType();
    } else {
        this.returnType = method.getReturnType();
    }
    this.returnsVoid = void.class.equals(this.returnType);
    this.returnsMany = configuration.getObjectFactory().isCollection(this.returnType) || this.returnType.isArray();
    this.returnsCursor = Cursor.class.equals(this.returnType);
    this.returnsOptional = Optional.class.equals(this.returnType);
    this.mapKey = getMapKey(method);
    this.returnsMap = this.mapKey != null;
    this.rowBoundsIndex = getUniqueParamIndex(method, RowBounds.class);
    this.resultHandlerIndex = getUniqueParamIndex(method, ResultHandler.class);
    this.paramNameResolver = new ParamNameResolver(configuration, method);
}

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

ParamNameResolver.getNamedParams

public Object getNamedParams(Object[] args) {
    final int paramCount = names.size();
    if (args == null || paramCount == 0) {
        return null;
    }
    // 没有@Param注解，并且参数只有一个，符合这个条件
    if (!hasParamAnnotation && paramCount == 1) {
		// 把实际传入的value值赋值给参数
        Object value = args[names.firstKey()];
        // 进行了类型包装，只有当类型是Collection和Array才生效。
        return wrapToMapIfCollection(value, useActualParamName ? names.get(names.firstKey()) : null);
    } else {
        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 + (i + 1);
            // ensure not to overwrite parameter named with @Param
            if (!names.containsValue(genericParamName)) {
                param.put(genericParamName, args[entry.getKey()]);
            }
            i++;
        }
        return param;
    }
}
public static Object wrapToMapIfCollection(Object object, String actualParamName) {
    if (object instanceof Collection) {
        ParamMap<Object> map = new ParamMap<>();
        map.put("collection", object);
        if (object instanceof List) {
            map.put("list", object);
        }
        Optional.ofNullable(actualParamName).ifPresent(name -> map.put(name, object));
        return map;
    }
    if (object != null && object.getClass().isArray()) {
        ParamMap<Object> map = new ParamMap<>();
        map.put("array", object);
        Optional.ofNullable(actualParamName).ifPresent(name -> map.put(name, object));
        return map;
    }
    return object;
}

这里完了后，再次回到MapperMethod.execute中，继续往下走到sqlSession.selectOne

DefaultSqlSession.selectOne

多次重载后，进入到private的selectList方法中。从configuration中拿取了 MapperStatement，然后调用executor.query。

而这个executor有2个实现类，分别是BaseExecutor和CacheExecutor。而CacheExecutor是做二级缓存的，我们不开启二级缓存，那么就进入到BaseExecutor中。

@Override
public <T> T selectOne(String statement, Object parameter) {
    // Popular vote was to return null on 0 results and throw exception on too many.
    List<T> list = this.selectList(statement, parameter);
    if (list.size() == 1) {
        return list.get(0);
    }
    if (list.size() > 1) {
        throw new TooManyResultsException(
            "Expected one result (or null) to be returned by selectOne(), but found: " + list.size());
    } else {
        return null;
    }
}
@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) {
    return selectList(statement, parameter, rowBounds, Executor.NO_RESULT_HANDLER);
}

private <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds, ResultHandler handler) {
    try {
        MappedStatement ms = configuration.getMappedStatement(statement);
        dirty |= ms.isDirtySelect();
        return executor.query(ms, wrapCollection(parameter), rowBounds, handler);
    } catch (Exception e) {
        throw ExceptionFactory.wrapException("Error querying database.  Cause: " + e, e);
    } finally {
        ErrorContext.instance().reset();
    }
}

BaseExecutor.query

获取到原生的sql语句以及参数的映射，然后再创建一个用作缓存的key值，这个值的创建考虑的因素比较多。这里就不介绍了。

然后再继续调用query方法。

@Override
public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler)
    throws SQLException {
    // 获取到原生的sql语句以及参数的映射
    BoundSql boundSql = ms.getBoundSql(parameter);
    // 创建一个缓存的key
    CacheKey key = createCacheKey(ms, parameter, rowBounds, boundSql);
    return query(ms, parameter, rowBounds, resultHandler, key, boundSql);
}

@Override
public CacheKey createCacheKey(MappedStatement ms, Object parameterObject, RowBounds rowBounds, BoundSql boundSql) {
    if (closed) {
        throw new ExecutorException("Executor was closed.");
    }
    CacheKey cacheKey = new CacheKey();
    cacheKey.update(ms.getId());
    cacheKey.update(rowBounds.getOffset());
    cacheKey.update(rowBounds.getLimit());
    cacheKey.update(boundSql.getSql());
    List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
    TypeHandlerRegistry typeHandlerRegistry = ms.getConfiguration().getTypeHandlerRegistry();
    // mimic DefaultParameterHandler logic
    for (ParameterMapping parameterMapping : parameterMappings) {
        if (parameterMapping.getMode() != ParameterMode.OUT) {
            Object value;
            String propertyName = parameterMapping.getProperty();
            if (boundSql.hasAdditionalParameter(propertyName)) {
                value = boundSql.getAdditionalParameter(propertyName);
            } else if (parameterObject == null) {
                value = null;
            } else if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass())) {
                value = parameterObject;
            } else {
                MetaObject metaObject = configuration.newMetaObject(parameterObject);
                value = metaObject.getValue(propertyName);
            }
            cacheKey.update(value);
        }
    }
    if (configuration.getEnvironment() != null) {
        // issue #176
        cacheKey.update(configuration.getEnvironment().getId());
    }
    return cacheKey;
}

@Override
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.");
    }
    if (queryStack == 0 && ms.isFlushCacheRequired()) {
        clearLocalCache();
    }
    List<E> list;
    try {
        queryStack++;
        // localCache中没有存放任何东西，所以这里的list也是null，进入查询数据库的语句中
        list = resultHandler == null ? (List<E>) localCache.getObject(key) : null;
        if (list != null) {
            handleLocallyCachedOutputParameters(ms, key, parameter, boundSql);
        } else {
            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;
}

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 {
        list = doQuery(ms, parameter, rowBounds, resultHandler, boundSql);
    } finally {
        localCache.removeObject(key);
    }
    localCache.putObject(key, list);
    if (ms.getStatementType() == StatementType.CALLABLE) {
        localOutputParameterCache.putObject(key, parameter);
    }
    return list;
}
protected abstract <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds,
                                       ResultHandler resultHandler, BoundSql boundSql) throws SQLException;

再进入到doQuery方法。而这个doQuery是一个抽象的方法。那么只能看看实现类了。

在这里插入图片描述

而在初始化的时候，我们没有指定Executor的类型，那么这个类型就是默认的SimpleExecutor。

SimpleExecutor.doQuery

现获取到configuration对象，再去创建StatementHandler对象。

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();
        StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler,
                                                                     boundSql);
        stmt = prepareStatement(handler, ms.getStatementLog());
        return handler.query(stmt, resultHandler);
    } finally {
        closeStatement(stmt);
    }
}
Configuration.newStatementHandler
public StatementHandler newStatementHandler(Executor executor, MappedStatement mappedStatement,
                                            Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
    // 实例化statementHandler
    StatementHandler statementHandler = new RoutingStatementHandler(executor, mappedStatement, parameterObject,
                                                                    rowBounds, resultHandler, boundSql);
    // 用插件进行装饰
    return (StatementHandler) interceptorChain.pluginAll(statementHandler);
}
RoutingStatementHandler

ms的statementType默认是PREPARED。

public RoutingStatementHandler(Executor executor, MappedStatement ms, Object parameter, RowBounds rowBounds,
                               ResultHandler resultHandler, BoundSql boundSql) {
    switch (ms.getStatementType()) {
        case STATEMENT:
            delegate = new SimpleStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);
            break;
        case PREPARED:
            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());
    }

}
PreparedStatementHandler
public PreparedStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameter,
                                RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
    super(executor, mappedStatement, parameter, rowBounds, resultHandler, boundSql);
}
BaseStatementHandler
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;
	// 实例化另外2个插件修饰的对象
    this.parameterHandler = configuration.newParameterHandler(mappedStatement, parameterObject, boundSql);
    this.resultSetHandler = configuration.newResultSetHandler(executor, mappedStatement, rowBounds, parameterHandler,
                                                              resultHandler, boundSql);
}
Configuration
public ParameterHandler newParameterHandler(MappedStatement mappedStatement, Object parameterObject,
                                            BoundSql boundSql) {
    ParameterHandler parameterHandler = mappedStatement.getLang().createParameterHandler(mappedStatement,
                                                                                         parameterObject, boundSql);
    return (ParameterHandler) interceptorChain.pluginAll(parameterHandler);
}

public ResultSetHandler newResultSetHandler(Executor executor, MappedStatement mappedStatement, RowBounds rowBounds,
                                            ParameterHandler parameterHandler, ResultHandler resultHandler, BoundSql boundSql) {
    ResultSetHandler resultSetHandler = new DefaultResultSetHandler(executor, mappedStatement, parameterHandler,
                                                                    resultHandler, boundSql, rowBounds);
    return (ResultSetHandler) interceptorChain.pluginAll(resultSetHandler);
}

这里初始化就完成了，开始调用真正的query。

PreparedStatementHandler.query

调用jdbc中ps的execute方法。resultSetHandler刚才已经实例过，直接调用

@Override
public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {
    PreparedStatement ps = (PreparedStatement) statement;
    ps.execute();
    return resultSetHandler.handleResultSets(ps);
}

DefaultResultHandler.handleResultSets

public List<Object> handleResultSets(Statement stmt) throws SQLException {
    ErrorContext.instance().activity("handling results").object(mappedStatement.getId());
    final List<Object> multipleResults = new ArrayList<>();
    int resultSetCount = 0;
    // 获取ResutlSet的包装类
    ResultSetWrapper rsw = getFirstResultSet(stmt);
    List<ResultMap> resultMaps = mappedStatement.getResultMaps();
    int resultMapCount = resultMaps.size();
    validateResultMapsCount(rsw, resultMapCount);
    while (rsw != null && resultMapCount > resultSetCount) {
        ResultMap resultMap = resultMaps.get(resultSetCount);
        // 处理结果
        handleResultSet(rsw, resultMap, multipleResults, null);
        rsw = getNextResultSet(stmt);
        cleanUpAfterHandlingResultSet();
        resultSetCount++;
    }

    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 {
        // 这里是处理多返回结果的
        if (parentMapping != null) {
            handleRowValues(rsw, resultMap, null, RowBounds.DEFAULT, parentMapping);
        } else if (resultHandler == null) {
            // resultHandler还未实例化，进入到这里
            DefaultResultHandler defaultResultHandler = new DefaultResultHandler(objectFactory);
            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 {
    if (resultMap.hasNestedResultMaps()) {
        ensureNoRowBounds();
        checkResultHandler();
        handleRowValuesForNestedResultMap(rsw, resultMap, resultHandler, rowBounds, parentMapping);
    } else {
        // 单返回结果处理
        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();
    // 跳过逻辑分页
    skipRows(resultSet, rowBounds);
    while (shouldProcessMoreRows(resultContext, rowBounds) && !resultSet.isClosed() && resultSet.next()) {
        ResultMap discriminatedResultMap = resolveDiscriminatedResultMap(resultSet, resultMap, null);
        //  对对象进行赋值
        Object rowValue = getRowValue(rsw, discriminatedResultMap, null);
        storeObject(resultHandler, resultContext, rowValue, parentMapping, resultSet);
    }
}

private void skipRows(ResultSet rs, RowBounds rowBounds) throws SQLException {
    if (rs.getType() != ResultSet.TYPE_FORWARD_ONLY) {
        if (rowBounds.getOffset() != RowBounds.NO_ROW_OFFSET) {
            rs.absolute(rowBounds.getOffset());
        }
    } else {
        for (int i = 0; i < rowBounds.getOffset(); i++) {
            if (!rs.next()) {
                break;
            }
        }
    }
}

private Object getRowValue(ResultSetWrapper rsw, ResultMap resultMap, String columnPrefix) throws SQLException {
    final ResultLoaderMap lazyLoader = new ResultLoaderMap();
    // 实例化返回的对象，也就是User类 
    Object rowValue = createResultObject(rsw, resultMap, lazyLoader, columnPrefix);
    if (rowValue != null && !hasTypeHandlerForResultObject(rsw, resultMap.getType())) {
        final MetaObject metaObject = configuration.newMetaObject(rowValue);
        boolean foundValues = this.useConstructorMappings;
        // 需要自动映射对象，也就是id对应字段User中的id
        if (shouldApplyAutomaticMappings(resultMap, false)) {
            foundValues = applyAutomaticMappings(rsw, resultMap, metaObject, columnPrefix) || foundValues;
        }
        foundValues = applyPropertyMappings(rsw, resultMap, metaObject, lazyLoader, columnPrefix) || foundValues;
        foundValues = lazyLoader.size() > 0 || foundValues;
        rowValue = foundValues || configuration.isReturnInstanceForEmptyRow() ? rowValue : null;
    }
    return rowValue;
}

// 实例化返回的对象，也就是User类，这里一定用的是反射
private Object createResultObject(ResultSetWrapper rsw, ResultMap resultMap, ResultLoaderMap lazyLoader,
                                  String columnPrefix) throws SQLException {
    this.useConstructorMappings = false; // reset previous mapping result
    final List<Class<?>> constructorArgTypes = new ArrayList<>();
    final List<Object> constructorArgs = new ArrayList<>();
    Object resultObject = createResultObject(rsw, resultMap, constructorArgTypes, constructorArgs, columnPrefix);
    if (resultObject != null && !hasTypeHandlerForResultObject(rsw, resultMap.getType())) {
        final List<ResultMapping> propertyMappings = resultMap.getPropertyResultMappings();
        for (ResultMapping propertyMapping : propertyMappings) {
            // issue gcode #109 && issue #149
            if (propertyMapping.getNestedQueryId() != null && propertyMapping.isLazy()) {
                resultObject = configuration.getProxyFactory().createProxy(resultObject, lazyLoader, configuration,
                                                                           objectFactory, constructorArgTypes, constructorArgs);
                break;
            }
        }
    }
    this.useConstructorMappings = resultObject != null && !constructorArgTypes.isEmpty(); // set current mapping result
    return resultObject;
}
private Object createResultObject(ResultSetWrapper rsw, ResultMap resultMap, List<Class<?>> constructorArgTypes,
                                  List<Object> constructorArgs, String columnPrefix) throws SQLException {
    final Class<?> resultType = resultMap.getType();
    // 反射类
    final MetaClass metaType = MetaClass.forClass(resultType, reflectorFactory);
    final List<ResultMapping> constructorMappings = resultMap.getConstructorResultMappings();
    if (hasTypeHandlerForResultObject(rsw, resultType)) {
        return createPrimitiveResultObject(rsw, resultMap, columnPrefix);
    }
    if (!constructorMappings.isEmpty()) {
        return createParameterizedResultObject(rsw, resultType, constructorMappings, constructorArgTypes, constructorArgs,
                                               columnPrefix);
    } else if (resultType.isInterface() || metaType.hasDefaultConstructor()) {
        // 最终使用objectFactory.create了User对象出来了 
        return objectFactory.create(resultType);
    } else if (shouldApplyAutomaticMappings(resultMap, false)) {
        return createByConstructorSignature(rsw, resultMap, columnPrefix, resultType, constructorArgTypes,
                                            constructorArgs);
    }
    throw new ExecutorException("Do not know how to create an instance of " + resultType);
}

private boolean applyAutomaticMappings(ResultSetWrapper rsw, ResultMap resultMap, MetaObject metaObject,
                                       String columnPrefix) throws SQLException {
    List<UnMappedColumnAutoMapping> autoMapping = createAutomaticMappings(rsw, resultMap, metaObject, columnPrefix);
    boolean foundValues = false;
    if (!autoMapping.isEmpty()) {
        for (UnMappedColumnAutoMapping mapping : autoMapping) {
            final Object value = mapping.typeHandler.getResult(rsw.getResultSet(), mapping.column);
            if (value != null) {
                foundValues = true;
            }
            if (value != null || configuration.isCallSettersOnNulls() && !mapping.primitive) {
                // gcode issue #377, call setter on nulls (value is not 'found')
                // 通过反射一步步的把数据set进去
                metaObject.setValue(mapping.property, value);
            }
        }
    }
    return foundValues;
}

到这里再把结果封装一下，然后再返回给List对象，就完成了。

Monkey KevinWu
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