mybatis系列-第一条sql的细节
先补充两个点，
第一是前面我们说了
使用org.apache.ibatis.builder.xml.XMLConfigBuilder 创建了parser解析器，那么解析的结果是什么
看这个方法的返回值
public Configuration parse() {
if (parsed) {
throw new BuilderException("Each XMLConfigBuilder can only be used once.");
}
parsed = true;
parseConfiguration(parser.evalNode("/configuration"));
return configuration;
}返回的是 org.apache.ibatis.session.Configuration , 而这个 Configuration 也是 mybatis 中特别重要的配置核心类，贴一下里面的成员变量，
public class Configuration {
protected Environment environment;
protected boolean safeRowBoundsEnabled;
protected boolean safeResultHandlerEnabled = true;
protected boolean mapUnderscoreToCamelCase;
protected boolean aggressiveLazyLoading;
protected boolean multipleResultSetsEnabled = true;
protected boolean useGeneratedKeys;
protected boolean useColumnLabel = true;
protected boolean cacheEnabled = true;
protected boolean callSettersOnNulls;
protected boolean useActualParamName = true;
protected boolean returnInstanceForEmptyRow;
protected boolean shrinkWhitespacesInSql;
protected boolean nullableOnForEach;
protected boolean argNameBasedConstructorAutoMapping;
protected String logPrefix;
protected Class<? extends Log> logImpl;
protected Class<? extends VFS> vfsImpl;
protected Class<?> defaultSqlProviderType;
protected LocalCacheScope localCacheScope = LocalCacheScope.SESSION;
protected JdbcType jdbcTypeForNull = JdbcType.OTHER;
protected Set<String> lazyLoadTriggerMethods = new HashSet<>(Arrays.asList("equals", "clone", "hashCode", "toString"));
protected Integer defaultStatementTimeout;
protected Integer defaultFetchSize;
protected ResultSetType defaultResultSetType;
protected ExecutorType defaultExecutorType = ExecutorType.SIMPLE;
protected AutoMappingBehavior autoMappingBehavior = AutoMappingBehavior.PARTIAL;
protected AutoMappingUnknownColumnBehavior autoMappingUnknownColumnBehavior = AutoMappingUnknownColumnBehavior.NONE;
protected Properties variables = new Properties();
protected ReflectorFactory reflectorFactory = new DefaultReflectorFactory();
protected ObjectFactory objectFactory = new DefaultObjectFactory();
protected ObjectWrapperFactory objectWrapperFactory = new DefaultObjectWrapperFactory();
protected boolean lazyLoadingEnabled = false;
protected ProxyFactory proxyFactory = new JavassistProxyFactory(); // #224 Using internal Javassist instead of OGNL
protected String databaseId;
/**
* Configuration factory class.
* Used to create Configuration for loading deserialized unread properties.
*
* @see <a href='https://github.com/mybatis/old-google-code-issues/issues/300'>Issue 300 (google code)</a>
*/
protected Class<?> configurationFactory;
protected final MapperRegistry mapperRegistry = new MapperRegistry(this);
protected final InterceptorChain interceptorChain = new InterceptorChain();
protected final TypeHandlerRegistry typeHandlerRegistry = new TypeHandlerRegistry(this);
protected final TypeAliasRegistry typeAliasRegistry = new TypeAliasRegistry();
protected final LanguageDriverRegistry languageRegistry = new LanguageDriverRegistry();
protected final Map<String, MappedStatement> mappedStatements = new StrictMap<MappedStatement>("Mapped Statements collection")
.conflictMessageProducer((savedValue, targetValue) ->
". please check " + savedValue.getResource() + " and " + targetValue.getResource());
protected final Map<String, Cache> caches = new StrictMap<>("Caches collection");
protected final Map<String, ResultMap> resultMaps = new StrictMap<>("Result Maps collection");
protected final Map<String, ParameterMap> parameterMaps = new StrictMap<>("Parameter Maps collection");
protected final Map<String, KeyGenerator> keyGenerators = new StrictMap<>("Key Generators collection");
protected final Set<String> loadedResources = new HashSet<>();
protected final Map<String, XNode> sqlFragments = new StrictMap<>("XML fragments parsed from previous mappers");
protected final Collection<XMLStatementBuilder> incompleteStatements = new LinkedList<>();
protected final Collection<CacheRefResolver> incompleteCacheRefs = new LinkedList<>();
protected final Collection<ResultMapResolver> incompleteResultMaps = new LinkedList<>();
protected final Collection<MethodResolver> incompleteMethods = new LinkedList<>();这么多成员变量，先不一一解释作用，但是其中的几个参数我们应该是已经知道了的，第一个就是 mappedStatements ，上一篇我们知道被解析的mapper就是放在这里，后面的 resultMaps ，parameterMaps 也比较常用的就是我们参数和结果的映射map，这里跟我之前有一篇解释为啥我们一些变量的使用会比较特殊，比如list，可以参考这篇，keyGenerators是在我们需要定义主键生成器的时候使用。
然后第二点是我们创建的 org.apache.ibatis.session.SqlSessionFactory 是哪个，
public SqlSessionFactory build(Configuration config) {
return new DefaultSqlSessionFactory(config);
}是这个 DefaultSqlSessionFactory ，这是其中一个 SqlSessionFactory 的实现
接下来我们看看 openSession 里干了啥
public SqlSession openSession() {
return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, false);
}这边有几个参数，第一个是默认的执行器类型，往上找找上面贴着的 Configuration 的成员变量里可以看到默认是protected ExecutorType defaultExecutorType = ExecutorType.SIMPLE;
因为没有指明特殊的执行逻辑，所以默认我们也就用简单类型的，第二个参数是是事务级别，第三个是是否自动提交
private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
Transaction tx = null;
try {
final Environment environment = configuration.getEnvironment();
final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
// --------> 先关注这里
final Executor executor = configuration.newExecutor(tx, execType);
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();
}
}具体是调用了 Configuration 的这个方法
public Executor newExecutor(Transaction transaction, ExecutorType executorType) {
executorType = executorType == null ? defaultExecutorType : executorType;
Executor executor;
if (ExecutorType.BATCH == executorType) {
executor = new BatchExecutor(this, transaction);
} else if (ExecutorType.REUSE == executorType) {
executor = new ReuseExecutor(this, transaction);
} else {
// ---------> 会走到这个分支
executor = new SimpleExecutor(this, transaction);
}
if (cacheEnabled) {
executor = new CachingExecutor(executor);
}
executor = (Executor) interceptorChain.pluginAll(executor);
return executor;
}上面传入的 executorType 是 Configuration 的默认类型，也就是 simple 类型，并且 cacheEnabled 在 Configuration 默认为 true，所以会包装成CachingExecutor ,然后后面就是插件了，这块我们先不展开
然后我们的openSession返回的就是创建了DefaultSqlSession
public DefaultSqlSession(Configuration configuration, Executor executor, boolean autoCommit) {
this.configuration = configuration;
this.executor = executor;
this.dirty = false;
this.autoCommit = autoCommit;
}然后就是调用 selectOne, 因为前面已经把这部分代码说过了，就直接跳转过来org.apache.ibatis.session.defaults.DefaultSqlSession#selectList(java.lang.String, java.lang.Object, org.apache.ibatis.session.RowBounds, org.apache.ibatis.session.ResultHandler)
private <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds, ResultHandler handler) {
try {
MappedStatement ms = configuration.getMappedStatement(statement);
return executor.query(ms, wrapCollection(parameter), rowBounds, handler);
} catch (Exception e) {
throw ExceptionFactory.wrapException("Error querying database. Cause: " + e, e);
} finally {
ErrorContext.instance().reset();
}
}因为前面说了 executor 包装了 CachingExecutor ，所以会先调用
@Override
public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {
BoundSql boundSql = ms.getBoundSql(parameterObject);
CacheKey key = createCacheKey(ms, parameterObject, rowBounds, boundSql);
return query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
}然后是调用的真实的query方法
@Override
public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql)
throws SQLException {
Cache cache = ms.getCache();
if (cache != null) {
flushCacheIfRequired(ms);
if (ms.isUseCache() && resultHandler == null) {
ensureNoOutParams(ms, boundSql);
@SuppressWarnings("unchecked")
List<E> list = (List<E>) tcm.getObject(cache, key);
if (list == null) {
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);
}这里是第一次查询，没有缓存就先到最后一行，继续是调用到 org.apache.ibatis.executor.BaseExecutor#queryFromDatabase
@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++;
list = resultHandler == null ? (List<E>) localCache.getObject(key) : null;
if (list != null) {
handleLocallyCachedOutputParameters(ms, key, parameter, boundSql);
} else {
// ----------->会走到这里
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;
}然后是
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;
}然后就是 simpleExecutor 的执行过程
@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();
StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);
stmt = prepareStatement(handler, ms.getStatementLog());
return handler.query(stmt, resultHandler);
} finally {
closeStatement(stmt);
}
}接下去其实就是跟jdbc交互了
@Override
public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {
PreparedStatement ps = (PreparedStatement) statement;
ps.execute();
return resultSetHandler.handleResultSets(ps);
}com.mysql.cj.jdbc.ClientPreparedStatement#execute
public boolean execute() throws SQLException {
try {
synchronized(this.checkClosed().getConnectionMutex()) {
JdbcConnection locallyScopedConn = this.connection;
if (!this.doPingInstead && !this.checkReadOnlySafeStatement()) {
throw SQLError.createSQLException(Messages.getString("PreparedStatement.20") + Messages.getString("PreparedStatement.21"), "S1009", this.exceptionInterceptor);
} else {
ResultSetInternalMethods rs = null;
this.lastQueryIsOnDupKeyUpdate = false;
if (this.retrieveGeneratedKeys) {
this.lastQueryIsOnDupKeyUpdate = this.containsOnDuplicateKeyUpdate();
}
this.batchedGeneratedKeys = null;
this.resetCancelledState();
this.implicitlyCloseAllOpenResults();
this.clearWarnings();
if (this.doPingInstead) {
this.doPingInstead();
return true;
} else {
this.setupStreamingTimeout(locallyScopedConn);
Message sendPacket = ((PreparedQuery)this.query).fillSendPacket(((PreparedQuery)this.query).getQueryBindings());
String oldDb = null;
if (!locallyScopedConn.getDatabase().equals(this.getCurrentDatabase())) {
oldDb = locallyScopedConn.getDatabase();
locallyScopedConn.setDatabase(this.getCurrentDatabase());
}
CachedResultSetMetaData cachedMetadata = null;
boolean cacheResultSetMetadata = (Boolean)locallyScopedConn.getPropertySet().getBooleanProperty(PropertyKey.cacheResultSetMetadata).getValue();
if (cacheResultSetMetadata) {
cachedMetadata = locallyScopedConn.getCachedMetaData(((PreparedQuery)this.query).getOriginalSql());
}
locallyScopedConn.setSessionMaxRows(this.getQueryInfo().getFirstStmtChar() == 'S' ? this.maxRows : -1);
rs = this.executeInternal(this.maxRows, sendPacket, this.createStreamingResultSet(), this.getQueryInfo().getFirstStmtChar() == 'S', cachedMetadata, false);
if (cachedMetadata != null) {
locallyScopedConn.initializeResultsMetadataFromCache(((PreparedQuery)this.query).getOriginalSql(), cachedMetadata, rs);
} else if (rs.hasRows() && cacheResultSetMetadata) {
locallyScopedConn.initializeResultsMetadataFromCache(((PreparedQuery)this.query).getOriginalSql(), (CachedResultSetMetaData)null, rs);
}
if (this.retrieveGeneratedKeys) {
rs.setFirstCharOfQuery(this.getQueryInfo().getFirstStmtChar());
}
if (oldDb != null) {
locallyScopedConn.setDatabase(oldDb);
}
if (rs != null) {
this.lastInsertId = rs.getUpdateID();
this.results = rs;
}
return rs != null && rs.hasRows();
}
}
}
} catch (CJException var11) {
throw SQLExceptionsMapping.translateException(var11, this.getExceptionInterceptor());
}
}
