1、StatementHandler

StatementHandler接口定义包含创建Statement, 绑定参数，批量执行，更新，查询，获取参数处理器

类结构图为

PreparedStatementHandler用于处理带有占位符的语句

SimpleStatementHandler处理不带占位符的

CallableStatementHandler处理存储过程调用语句

1.1、RoutingStatementHandler

起代理作用，根据不同的语句类型创建不同BaseStatementHandler子类。

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());}}

1.2、BaseStatementHandler

是其它子类的基类，会创建ParameterHandler,ResultSetHandler。BaseStatementHandler依赖两个组件ParameterHandler和ResultSetHandler。

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 statementgenerateKeys(parameterObject);boundSql = mappedStatement.getBoundSql(parameterObject);}this.boundSql = boundSql;this.parameterHandler = configuration.newParameterHandler(mappedStatement, parameterObject, boundSql);this.resultSetHandler = configuration.newResultSetHandler(executor, mappedStatement, rowBounds, parameterHandler, resultHandler, boundSql);}

实现StatementHandlere接口中的prepare，首先调用instantiateStatement抽象方法初始化java.sql.Statement对象，配置超时时间和fetchSize。

public Statement prepare(Connection connection, Integer transactionTimeout) throws SQLException {ErrorContext.instance().sql(boundSql.getSql());Statement statement = null;try {statement = instantiateStatement(connection);setStatementTimeout(statement, transactionTimeout);setFetchSize(statement);return statement;} catch (SQLException e) {closeStatement(statement);throw e;} catch (Exception e) {closeStatement(statement);throw new ExecutorException("Error preparing statement.  Cause: " + e, e);}}

1.3、SimpleStatementHandler

继承BaseStatementHandler抽象类，sql语句中没有占位符，相应的parameterize方法为空实现。

instantiateStatement直接通过JDBC Connection创建Statemtn对象。

protected Statement instantiateStatement(Connection connection) throws SQLException {if (mappedStatement.getResultSetType() == ResultSetType.DEFAULT) {return connection.createStatement();} else {return connection.createStatement(mappedStatement.getResultSetType().getValue(), ResultSet.CONCUR_READ_ONLY);}}

查询query 通过创建的Statement对象来完成数据库查询操作，结果通过ResultSetHandler将结果集映射成结果对象。

public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {String sql = boundSql.getSql();statement.execute(sql);return resultSetHandler.handleResultSets(statement);}

queryCursor，batch方法与query方法类似。也是直接调用Statement对象的对应方法。

update方法执行insert、update或delete等sql语句，并且会根据配置的KeyGenerator获取数据库的主键。

public int update(Statement statement) throws SQLException {String sql = boundSql.getSql();Object parameterObject = boundSql.getParameterObject();KeyGenerator keyGenerator = mappedStatement.getKeyGenerator();int rows;if (keyGenerator instanceof Jdbc3KeyGenerator) {statement.execute(sql, Statement.RETURN_GENERATED_KEYS);rows = statement.getUpdateCount();keyGenerator.processAfter(executor, mappedStatement, statement, parameterObject);} else if (keyGenerator instanceof SelectKeyGenerator) {statement.execute(sql);rows = statement.getUpdateCount();keyGenerator.processAfter(executor, mappedStatement, statement, parameterObject);} else {statement.execute(sql);rows = statement.getUpdateCount();}return rows;}

1.4、PreparedStatementHandler

依赖java.sql.PreparedStatement对象来完成数据库的相关操作。

parameterize方法会调用ParameterHandler.setParameters完成sql语句的参数绑定。

instantiateStatement方法会直接调用JDBC Connection的prepareStatement方法创建PreparedStatement对象。

protected Statement instantiateStatement(Connection connection) throws SQLException {String sql = boundSql.getSql();if (mappedStatement.getKeyGenerator() instanceof Jdbc3KeyGenerator) {String[] keyColumnNames = mappedStatement.getKeyColumns();if (keyColumnNames == null) {return connection.prepareStatement(sql, PreparedStatement.RETURN_GENERATED_KEYS);} else {return connection.prepareStatement(sql, keyColumnNames);}} else if (mappedStatement.getResultSetType() == ResultSetType.DEFAULT) {return connection.prepareStatement(sql);} else {return connection.prepareStatement(sql, mappedStatement.getResultSetType().getValue(), ResultSet.CONCUR_READ_ONLY);}}

1.5、CallableStatementHandler

依赖于java.sql.CallableStatement调用指定的存储过程，其parameterize方法会调用ParameterHandler.setParameter方法完成sql语句的参数绑定，并指定输出参数的索引位置和JDBC类型。

public void parameterize(Statement statement) throws SQLException {registerOutputParameters((CallableStatement) statement);parameterHandler.setParameters((CallableStatement) statement);}private void registerOutputParameters(CallableStatement cs) throws SQLException {List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();for (int i = 0, n = parameterMappings.size(); i < n; i++) {ParameterMapping parameterMapping = parameterMappings.get(i);if (parameterMapping.getMode() == ParameterMode.OUT || parameterMapping.getMode() == ParameterMode.INOUT) {if (null == parameterMapping.getJdbcType()) {throw new ExecutorException("The JDBC Type must be specified for output parameter.  Parameter: " + parameterMapping.getProperty());} else {if (parameterMapping.getNumericScale() != null && (parameterMapping.getJdbcType() == JdbcType.NUMERIC || parameterMapping.getJdbcType() == JdbcType.DECIMAL)) {cs.registerOutParameter(i + 1, parameterMapping.getJdbcType().TYPE_CODE, parameterMapping.getNumericScale());} else {if (parameterMapping.getJdbcTypeName() == null) {cs.registerOutParameter(i + 1, parameterMapping.getJdbcType().TYPE_CODE);} else {cs.registerOutParameter(i + 1, parameterMapping.getJdbcType().TYPE_CODE, parameterMapping.getJdbcTypeName());}}}}}}

instantiateStatement直接调用JDBC Connection的prepareCall创建CallableStatement对象。

protected Statement instantiateStatement(Connection connection) throws SQLException {String sql = boundSql.getSql();if (mappedStatement.getResultSetType() == ResultSetType.DEFAULT) {return connection.prepareCall(sql);} else {return connection.prepareCall(sql, mappedStatement.getResultSetType().getValue(), ResultSet.CONCUR_READ_ONLY);}}

其它方法与以上有一些差异，就是会调用ResultSetHandler的handleOutputParameters处理输出参数

public int update(Statement statement) throws SQLException {CallableStatement cs = (CallableStatement) statement;cs.execute();int rows = cs.getUpdateCount();Object parameterObject = boundSql.getParameterObject();KeyGenerator keyGenerator = mappedStatement.getKeyGenerator();keyGenerator.processAfter(executor, mappedStatement, cs, parameterObject);resultSetHandler.handleOutputParameters(cs);return rows;}public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {CallableStatement cs = (CallableStatement) statement;cs.execute();List<E> resultList = resultSetHandler.handleResultSets(cs);resultSetHandler.handleOutputParameters(cs);return resultList;}public <E> Cursor<E> queryCursor(Statement statement) throws SQLException {CallableStatement cs = (CallableStatement) statement;cs.execute();Cursor<E> resultList = resultSetHandler.handleCursorResultSets(cs);resultSetHandler.handleOutputParameters(cs);return resultList;}

2、ParameterHandler

主要包含绑定参数，及获取参数对象。

DefaultParameterHandler是唯一实现。

绑定参数时，遍历boundSql中的参数映射，忽略输出类型参数。提取值基于以下规则

属性名是否在boundSql中的附加参数中，如果有，则直接从map中取值。
参数对象为空时，值设置为null
TypeHandlerRegistry中是否参参数对象所必类型的处理器，有则直接取参数对象(说明是基础类型)
基于MetaObject获取属性值。

使用TypeHandler来设置PreparementStatement对应的值。

public void setParameters(PreparedStatement ps) {ErrorContext.instance().activity("setting parameters").object(mappedStatement.getParameterMap().getId());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();if (boundSql.hasAdditionalParameter(propertyName)) { // issue #448 ask first for additional paramsvalue = 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);}TypeHandler typeHandler = parameterMapping.getTypeHandler();JdbcType jdbcType = parameterMapping.getJdbcType();if (value == null && jdbcType == null) {jdbcType = configuration.getJdbcTypeForNull();}try {typeHandler.setParameter(ps, i + 1, value, jdbcType);} catch (TypeException | SQLException e) {throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + e, e);}}}}}

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