ResultSetHandler 参数映射核心逻辑 -1
一、ResultSetHandler
public interface ResultSetHandler {
//处理ResultSet
<E> List<E> handleResultSets(Statement stmt) throws SQLException;
//处理游标ResultSet
<E> Cursor<E> handleCursorResultSets(Statement stmt) throws SQLException;
//处理输出参数
void handleOutputParameters(CallableStatement cs) throws SQLException;
}
二、实现类 DefaultResultSetHandler
- 包含的属性：
private final Executor executor;
//mybatis配置类
private final Configuration configuration;
//
private final MappedStatement mappedStatement;
//limit offset
private final RowBounds rowBounds;
//参数处理器
private final ParameterHandler parameterHandler;
//结果处理器
private final ResultHandler<?> resultHandler;
//sql 对象
private final BoundSql boundSql;
//类型处理器注册中心
private final TypeHandlerRegistry typeHandlerRegistry;
//对象工厂
private final ObjectFactory objectFactory;
//反射工厂
private final ReflectorFactory reflectorFactory;
// nested resultmaps
private final Map<CacheKey, Object> nestedResultObjects = new HashMap<>();
private final Map<String, Object> ancestorObjects = new HashMap<>();
private Object previousRowValue;
// multiple resultsets
private final Map<String, ResultMapping> nextResultMaps = new HashMap<>();
private final Map<CacheKey, List<PendingRelation>> pendingRelations = new HashMap<>();
// Cached Automappings
private final Map<String, List<UnMappedColumnAutoMapping>> autoMappingsCache = new HashMap<>();
// temporary marking flag that indicate using constructor mapping (use field to reduce memory usage)
private boolean useConstructorMappings;
1.处理结果 handleResultSets
public List<Object> handleResultSets(Statement stmt) throws SQLException {
//
ErrorContext.instance().activity("handling results").object(mappedStatement.getId());
//结果列表
final List<Object> multipleResults = new ArrayList<>();
int resultSetCount = 0;
//获取第一个结果集对象
ResultSetWrapper rsw = getFirstResultSet(stmt);
//MappedStatement 在初始化的时候 resultMap对象被解析为 ResultMap对象，保存在resultMaps的集合中
List<ResultMap> resultMaps = mappedStatement.getResultMaps();
int resultMapCount = resultMaps.size();
//验证结果集不为空，否则抛出异常
validateResultMapsCount(rsw, resultMapCount);
while (rsw != null && resultMapCount > resultSetCount) {
//获取ResultMap对象
ResultMap resultMap = resultMaps.get(resultSetCount);
//解析result内容
handleResultSet(rsw, resultMap, multipleResults, null);
//获取下一个集合
rsw = getNextResultSet(stmt);
//清空nestedResultObjects
cleanUpAfterHandlingResultSet();
//递增resultSetCount
resultSetCount++;
}
//MappedStatement resultSets 针对于多结果集的情况
String[] resultSets = mappedStatement.getResultSets();
if (resultSets != null) {
while (rsw != null && resultSetCount < resultSets.length) {
//根据resultSet的名称，获取未处理的ResultMapping
ResultMapping parentMapping = nextResultMaps.get(resultSets[resultSetCount]);
if (parentMapping != null) {
String nestedResultMapId = parentMapping.getNestedResultMapId();
ResultMap resultMap = configuration.getResultMap(nestedResultMapId);
//根据ResultMap对象映射结果集
handleResultSet(rsw, resultMap, null, parentMapping);
}
//获取下一个结果集
rsw = getNextResultSet(stmt);
//清空nestedResultObjects集合
cleanUpAfterHandlingResultSet();
resultSetCount++;
}
}
return collapseSingleResultList(multipleResults);
}
private ResultSetWrapper getFirstResultSet(Statement stmt) throws SQLException {
ResultSet rs = stmt.getResultSet();
while (rs == null) {
// move forward to get the first resultset in case the driver
// doesn't return the resultset as the first result (HSQLDB 2.1)
if (stmt.getMoreResults()) {
rs = stmt.getResultSet();
} else {
if (stmt.getUpdateCount() == -1) {
// no more results. Must be no resultset
break;
}
}
}
return rs != null ? new ResultSetWrapper(rs, configuration) : null;
}
//主要应对SQL片段内部还有嵌套的未解析的SQL片段的场景
private ResultSetWrapper getNextResultSet(Statement stmt) {
// Making this method tolerant of bad JDBC drivers
try {
if (stmt.getConnection().getMetaData().supportsMultipleResultSets()) {
// Crazy Standard JDBC way of determining if there are more results
if (!(!stmt.getMoreResults() && stmt.getUpdateCount() == -1)) {
ResultSet rs = stmt.getResultSet();
if (rs == null) {
return getNextResultSet(stmt);
} else {
return new ResultSetWrapper(rs, configuration);
}
}
}
} catch (Exception e) {
// Intentionally ignored.
}
return null;
}
ResultSetWrapper 封装ResultSet的一些属性
//resultSet对象
private final ResultSet resultSet;
//处理器注册中心
private final TypeHandlerRegistry typeHandlerRegistry;
//记录ResultSet 中每列列名
private final List<String> columnNames = new ArrayList<>();
//记录ResultSet 中每列对应的Java类型
private final List<String> classNames = new ArrayList<>();
//记录ResultSet 中每列对应的JdbcType类型
private final List<JdbcType> jdbcTypes = new ArrayList<>();
// 记录每列TypeHandler对象，key是列名，value是TypeHandler集合
private final Map<String, Map<Class<?>, TypeHandler<?>>> typeHandlerMap = new HashMap<>();
//记录被映射的列名，其中key是ResultMap对象的id，value是该ResultMap对象映射的类名集合
private final Map<String, List<String>> mappedColumnNamesMap = new HashMap<>();
//记录了未映射的列名，其中key是ResultMap对象的id，value是ResultMap对象未映射的列名集合
private final Map<String, List<String>> unMappedColumnNamesMap = new HashMap<>();
- 初始化java类型 jdbc类型
final ResultSetMetaData metaData = rs.getMetaData();
final int columnCount = metaData.getColumnCount();
for (int i = 1; i <= columnCount; i++) {
columnNames.add(configuration.isUseColumnLabel() ? metaData.getColumnLabel(i) : metaData.getColumnName(i));
jdbcTypes.add(JdbcType.forCode(metaData.getColumnType(i)));
classNames.add(metaData.getColumnClassName(i));
}
- 获取映射与未映射的列名
public List<String> getMappedColumnNames(ResultMap resultMap, String columnPrefix) throws SQLException {
List<String> mappedColumnNames = mappedColumnNamesMap.get(getMapKey(resultMap, columnPrefix));
if (mappedColumnNames == null) {
loadMappedAndUnmappedColumnNames(resultMap, columnPrefix);
mappedColumnNames = mappedColumnNamesMap.get(getMapKey(resultMap, columnPrefix));
}
return mappedColumnNames;
}
private void loadMappedAndUnmappedColumnNames(ResultMap resultMap, String columnPrefix) throws SQLException {
List<String> mappedColumnNames = new ArrayList<>();
List<String> unmappedColumnNames = new ArrayList<>();
final String upperColumnPrefix = columnPrefix == null ? null : columnPrefix.toUpperCase(Locale.ENGLISH);
final Set<String> mappedColumns = prependPrefixes(resultMap.getMappedColumns(), upperColumnPrefix);
for (String columnName : columnNames) {
final String upperColumnName = columnName.toUpperCase(Locale.ENGLISH);
if (mappedColumns.contains(upperColumnName)) {
mappedColumnNames.add(upperColumnName);
} else {
unmappedColumnNames.add(columnName);
}
}
mappedColumnNamesMap.put(getMapKey(resultMap, columnPrefix), mappedColumnNames);
unMappedColumnNamesMap.put(getMapKey(resultMap, columnPrefix), unmappedColumnNames);
}
