mybatis源码分析——SqlSession的作用
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sqlSession,顾名思义,是一次sql的回话,它起到了承上启下的作用,这个类既维护了Configuration对象,又包含Executor对象,可以
执行jdbc操作,在mybatis体系中非常重要,下面我们来看一下这个类的源码:
1:sqlSession类的源码
SqlSession接口类定义了增删改查的操作:
public interface SqlSession extends Closeable { /** * Retrieve a single row mapped from the statement key * @param <T> the returned object type * @param statement * @return Mapped object */ <T> T selectOne(String statement); /** * Retrieve a single row mapped from the statement key and parameter. * @param <T> the returned object type * @param statement Unique identifier matching the statement to use. * @param parameter A parameter object to pass to the statement. * @return Mapped object */ <T> T selectOne(String statement, Object parameter); /** * Retrieve a list of mapped objects from the statement key and parameter. * @param <E> the returned list element type * @param statement Unique identifier matching the statement to use. * @return List of mapped object */ <E> List<E> selectList(String statement); /** * Retrieve a list of mapped objects from the statement key and parameter. * @param <E> the returned list element type * @param statement Unique identifier matching the statement to use. * @param parameter A parameter object to pass to the statement. * @return List of mapped object */ <E> List<E> selectList(String statement, Object parameter); /** * Retrieve a list of mapped objects from the statement key and parameter, * within the specified row bounds. * @param <E> the returned list element type * @param statement Unique identifier matching the statement to use. * @param parameter A parameter object to pass to the statement. * @param rowBounds Bounds to limit object retrieval * @return List of mapped object */ <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds); /** * The selectMap is a special case in that it is designed to convert a list * of results into a Map based on one of the properties in the resulting * objects. * Eg. Return a of Map[Integer,Author] for selectMap("selectAuthors","id") * @param <K> the returned Map keys type * @param <V> the returned Map values type * @param statement Unique identifier matching the statement to use. * @param mapKey The property to use as key for each value in the list. * @return Map containing key pair data. */ <K, V> Map<K, V> selectMap(String statement, String mapKey); /** * The selectMap is a special case in that it is designed to convert a list * of results into a Map based on one of the properties in the resulting * objects. * @param <K> the returned Map keys type * @param <V> the returned Map values type * @param statement Unique identifier matching the statement to use. * @param parameter A parameter object to pass to the statement. * @param mapKey The property to use as key for each value in the list. * @return Map containing key pair data. */ <K, V> Map<K, V> selectMap(String statement, Object parameter, String mapKey); /** * The selectMap is a special case in that it is designed to convert a list * of results into a Map based on one of the properties in the resulting * objects. * @param <K> the returned Map keys type * @param <V> the returned Map values type * @param statement Unique identifier matching the statement to use. * @param parameter A parameter object to pass to the statement. * @param mapKey The property to use as key for each value in the list. * @param rowBounds Bounds to limit object retrieval * @return Map containing key pair data. */ <K, V> Map<K, V> selectMap(String statement, Object parameter, String mapKey, RowBounds rowBounds); /** * Retrieve a single row mapped from the statement key and parameter * using a {@code ResultHandler}. * @param statement Unique identifier matching the statement to use. * @param parameter A parameter object to pass to the statement. * @param handler ResultHandler that will handle each retrieved row * @return Mapped object */ void select(String statement, Object parameter, ResultHandler handler); /** * Retrieve a single row mapped from the statement * using a {@code ResultHandler}. * @param statement Unique identifier matching the statement to use. * @param handler ResultHandler that will handle each retrieved row * @return Mapped object */ void select(String statement, ResultHandler handler); /** * Retrieve a single row mapped from the statement key and parameter * using a {@code ResultHandler} and {@code RowBounds} * @param statement Unique identifier matching the statement to use. * @param rowBounds RowBound instance to limit the query results * @param handler ResultHandler that will handle each retrieved row * @return Mapped object */ void select(String statement, Object parameter, RowBounds rowBounds, ResultHandler handler); /** * Execute an insert statement. * @param statement Unique identifier matching the statement to execute. * @return int The number of rows affected by the insert. */ int insert(String statement); /** * Execute an insert statement with the given parameter object. Any generated * autoincrement values or selectKey entries will modify the given parameter * object properties. Only the number of rows affected will be returned. * @param statement Unique identifier matching the statement to execute. * @param parameter A parameter object to pass to the statement. * @return int The number of rows affected by the insert. */ int insert(String statement, Object parameter); /** * Execute an update statement. The number of rows affected will be returned. * @param statement Unique identifier matching the statement to execute. * @return int The number of rows affected by the update. */ int update(String statement); /** * Execute an update statement. The number of rows affected will be returned. * @param statement Unique identifier matching the statement to execute. * @param parameter A parameter object to pass to the statement. * @return int The number of rows affected by the update. */ int update(String statement, Object parameter); /** * Execute a delete statement. The number of rows affected will be returned. * @param statement Unique identifier matching the statement to execute. * @return int The number of rows affected by the delete. */ int delete(String statement); /** * Execute a delete statement. The number of rows affected will be returned. * @param statement Unique identifier matching the statement to execute. * @param parameter A parameter object to pass to the statement. * @return int The number of rows affected by the delete. */ int delete(String statement, Object parameter); /** * Flushes batch statements and commits database connection. * Note that database connection will not be committed if no updates/deletes/inserts were called. * To force the commit call {@link SqlSession#commit(boolean)} */ void commit(); /** * Flushes batch statements and commits database connection. * @param force forces connection commit */ void commit(boolean force); /** * Discards pending batch statements and rolls database connection back. * Note that database connection will not be rolled back if no updates/deletes/inserts were called. * To force the rollback call {@link SqlSession#rollback(boolean)} */ void rollback(); /** * Discards pending batch statements and rolls database connection back. * Note that database connection will not be rolled back if no updates/deletes/inserts were called. * @param force forces connection rollback */ void rollback(boolean force); /** * Flushes batch statements. * @return BatchResult list of updated records * @since 3.0.6 */ List<BatchResult> flushStatements(); /** * Closes the session */ @Override void close(); /** * Clears local session cache */ void clearCache(); /** * Retrieves current configuration * @return Configuration */ Configuration getConfiguration(); /** * Retrieves a mapper. * @param <T> the mapper type * @param type Mapper interface class * @return a mapper bound to this SqlSession */ <T> T getMapper(Class<T> type); /** * Retrieves inner database connection * @return Connection */ Connection getConnection(); }
实现类DefaultSqlSession维护了Configuration对象,可以直接从Configuration对象中拿到代理对象,也可以直接从Configuration对象中拿到MapperStatement对象
然后就是对SqlSession接口类的具体实现
public class DefaultSqlSession implements SqlSession { private Configuration configuration; private Executor executor; private boolean autoCommit; private boolean dirty; public DefaultSqlSession(Configuration configuration, Executor executor, boolean autoCommit) { this.configuration = configuration; this.executor = executor; this.dirty = false; this.autoCommit = autoCommit; } public DefaultSqlSession(Configuration configuration, Executor executor) { this(configuration, executor, false); } @Override public <T> T selectOne(String statement) { return this.<T>selectOne(statement, null); } @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.<T>selectList(statement, parameter); if (list.size() == 1) { return list.get(0); } else 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 <K, V> Map<K, V> selectMap(String statement, String mapKey) { return this.selectMap(statement, null, mapKey, RowBounds.DEFAULT); } @Override public <K, V> Map<K, V> selectMap(String statement, Object parameter, String mapKey) { return this.selectMap(statement, parameter, mapKey, RowBounds.DEFAULT); } @Override public <K, V> Map<K, V> selectMap(String statement, Object parameter, String mapKey, RowBounds rowBounds) { final List<? extends V> list = selectList(statement, parameter, rowBounds); final DefaultMapResultHandler<K, V> mapResultHandler = new DefaultMapResultHandler<K, V>(mapKey, configuration.getObjectFactory(), configuration.getObjectWrapperFactory(), configuration.getReflectorFactory()); final DefaultResultContext<V> context = new DefaultResultContext<V>(); for (V o : list) { context.nextResultObject(o); mapResultHandler.handleResult(context); } return mapResultHandler.getMappedResults(); } @Override public <E> List<E> selectList(String statement) { return this.selectList(statement, 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) { try { MappedStatement ms = configuration.getMappedStatement(statement); 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(); } } @Override public void select(String statement, Object parameter, ResultHandler handler) { select(statement, parameter, RowBounds.DEFAULT, handler); } @Override public void select(String statement, ResultHandler handler) { select(statement, null, RowBounds.DEFAULT, handler); } @Override public void select(String statement, Object parameter, RowBounds rowBounds, ResultHandler handler) { try { MappedStatement ms = configuration.getMappedStatement(statement); executor.query(ms, wrapCollection(parameter), rowBounds, handler); } catch (Exception e) { throw ExceptionFactory.wrapException("Error querying database. Cause: " + e, e); } finally { ErrorContext.instance().reset(); } } @Override public int insert(String statement) { return insert(statement, null); } @Override public int insert(String statement, Object parameter) { return update(statement, parameter); } @Override public int update(String statement) { return update(statement, null); } @Override public int update(String statement, Object parameter) { try { dirty = true; MappedStatement ms = configuration.getMappedStatement(statement); return executor.update(ms, wrapCollection(parameter)); } catch (Exception e) { throw ExceptionFactory.wrapException("Error updating database. Cause: " + e, e); } finally { ErrorContext.instance().reset(); } } @Override public int delete(String statement) { return update(statement, null); } @Override public int delete(String statement, Object parameter) { return update(statement, parameter); } @Override public void commit() { commit(false); } @Override public void commit(boolean force) { try { executor.commit(isCommitOrRollbackRequired(force)); dirty = false; } catch (Exception e) { throw ExceptionFactory.wrapException("Error committing transaction. Cause: " + e, e); } finally { ErrorContext.instance().reset(); } } @Override public void rollback() { rollback(false); } @Override public void rollback(boolean force) { try { executor.rollback(isCommitOrRollbackRequired(force)); dirty = false; } catch (Exception e) { throw ExceptionFactory.wrapException("Error rolling back transaction. Cause: " + e, e); } finally { ErrorContext.instance().reset(); } } @Override public List<BatchResult> flushStatements() { try { return executor.flushStatements(); } catch (Exception e) { throw ExceptionFactory.wrapException("Error flushing statements. Cause: " + e, e); } finally { ErrorContext.instance().reset(); } } @Override public void close() { try { executor.close(isCommitOrRollbackRequired(false)); dirty = false; } finally { ErrorContext.instance().reset(); } } @Override public Configuration getConfiguration() { return configuration; } @Override public <T> T getMapper(Class<T> type) { return configuration.<T>getMapper(type, this); } @Override public Connection getConnection() { try { return executor.getTransaction().getConnection(); } catch (SQLException e) { throw ExceptionFactory.wrapException("Error getting a new connection. Cause: " + e, e); } } @Override public void clearCache() { executor.clearLocalCache(); } private boolean isCommitOrRollbackRequired(boolean force) { return (!autoCommit && dirty) || force; } private Object wrapCollection(final Object object) { if (object instanceof Collection) { StrictMap<Object> map = new StrictMap<Object>(); map.put("collection", object); if (object instanceof List) { map.put("list", object); } return map; } else if (object != null && object.getClass().isArray()) { StrictMap<Object> map = new StrictMap<Object>(); map.put("array", object); return map; } return object; } public static class StrictMap<V> extends HashMap<String, V> { private static final long serialVersionUID = -5741767162221585340L; @Override public V get(Object key) { if (!super.containsKey(key)) { throw new BindingException("Parameter \'" + key + "\' not found. Available parameters are " + this.keySet()); } return super.get(key); } } }
类中经常用到的方法:
从configuration对象中获取代理对象
从configuration对象中获取MappedStatement对象,执行jdbc操作
2:sqlSession的创建以及使用
如果要使用sqlSession,首先要从sqlSessionFactory中获取,sqlSessionFactory中维护了configuration对象
SqlSession sqlSession = sqlSessionFactory.openSession();
public SqlSession openSession() { return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, false); }
从下面构造的方法中,可以看到构建defaultSqlSession的入参有3个,configuration对象,executor对象,是否自动提交标志
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); 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(); } }
下面是newExecutor方法创建Executor的过程,因为executorType为null,所以使用的是SimpleExecutor
public Executor newExecutor(Transaction transaction, ExecutorType executorType) { executorType = executorType == null ? defaultExecutorType : executorType; executorType = executorType == null ? ExecutorType.SIMPLE : executorType; Executor executor; 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); } if (cacheEnabled) { executor = new CachingExecutor(executor); } executor = (Executor) interceptorChain.pluginAll(executor); return executor; }
到这里,sqlSession对象完成初始化configuration和executor。
如何使用sqlSession呢,上面已经提到类中比较重要的方法,下面我们再来串一遍
a:调用sqlSessionFactory的openSession方法
b:在openSessionFromDataSource中完成DefaultSqlSession对象的构建,主要是Executor的创建
c:创建Executor
从configuration中获取environment,这个对象封装了数据源,然后根据数据源创建Transaction对象,封装到Executor对象中
最后创建DefaultSqlSession对象,返回。
sqlSession的使用:
a:获取代理对象
从第一节解析命名空间,然后注册到mapperRegistry中,现在根据类型获取这个代理工厂对象,然后根据代理工厂创建代理
调用代理工厂mapperProxyFactory的newInstance创建代理对象,然后返回,这里在数据绑定那一节提到过
使用代理对象userMapper调用方法listUsers,实例会调用到切面MapperProxy的invoke方法
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { if (Object.class.equals(method.getDeclaringClass())) { try { return method.invoke(this, args); } catch (Throwable t) { throw ExceptionUtil.unwrapThrowable(t); } } final MapperMethod mapperMethod = cachedMapperMethod(method); return mapperMethod.execute(sqlSession, args); }
先抛开缓存,这里会调用MapperMethod的execute的方法
mapperMethod.execute(sqlSession, args);
public Object execute(SqlSession sqlSession, Object[] args) { Object result; if (SqlCommandType.INSERT == command.getType()) { Object param = method.convertArgsToSqlCommandParam(args); result = rowCountResult(sqlSession.insert(command.getName(), param)); } else if (SqlCommandType.UPDATE == command.getType()) { Object param = method.convertArgsToSqlCommandParam(args); result = rowCountResult(sqlSession.update(command.getName(), param)); } else if (SqlCommandType.DELETE == command.getType()) { Object param = method.convertArgsToSqlCommandParam(args); result = rowCountResult(sqlSession.delete(command.getName(), param)); } else if (SqlCommandType.SELECT == command.getType()) { 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 { Object param = method.convertArgsToSqlCommandParam(args); result = sqlSession.selectOne(command.getName(), param); } } else if (SqlCommandType.FLUSH == command.getType()) { result = sqlSession.flushStatements(); } else { 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; }
会调到select分支,多个返回值的方法
executeForMany方法最终还是会调用到sqlSession的selectList方法
private <E> Object executeForMany(SqlSession sqlSession, Object[] args) { List<E> result; Object param = method.convertArgsToSqlCommandParam(args); if (method.hasRowBounds()) { RowBounds rowBounds = method.extractRowBounds(args); result = sqlSession.<E>selectList(command.getName(), param, rowBounds); } else { result = sqlSession.<E>selectList(command.getName(), param); } // issue #510 Collections & arrays support if (!method.getReturnType().isAssignableFrom(result.getClass())) { if (method.getReturnType().isArray()) { return convertToArray(result); } else { return convertToDeclaredCollection(sqlSession.getConfiguration(), result); } } return result; }
到这里我们知道具体的查询还是调用sqlSession的selectList,这里的逻辑就类似ibatis了,ibatis是直接把sqlId传入,更加sqlId找到MappedStatement,没有数据绑定的环节,
下面的逻辑就是executor执行jdbc的逻辑,下一节我们再来分析
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