轉載自??mybatis源碼閱讀(六) ---StatementHandler了解一下

StatementHandler類結構圖與接口設計

BaseStatementHandler：一個抽象類，只是實現了一些不涉及具體操作的方法

RoutingStatementHandler：類似路由器，根據配置文件來路由選擇具體實現類SimpleStatementHandler、CallableStatementHandler和PreparedStatementHandler

SimpleStatementHandler：就是直接使用普通的Statement對象，這樣每次執行SQL語句都需要數據庫對SQL進行預編譯

PrepareStatementHandler：使用PrepareStatement執行，雖然初次創建PrepareStatement時開銷比較大，但在多次處理SQL時只需要初始化一次，可以有效提高性能

CallableStatementHandler：使用CallableStatement執行，CallableStatement是用來執行存儲過程的。

在每個mapper節點可以設置statementType決定是否使用誰 ，如下

<!-- statementType （可選配置，默認配置為PREPARED）STATEMENT，PREPARED 或 CALLABLE 的一個。這會讓 MyBatis 分別使用 Statement，PreparedStatement 或 CallableStatement，默認值：PREPARED。 --> <select id="findUserById" resultType="com.lpf.entity.User" statementType="PREPARED">select * from m_user where id = #{id} </select>

1. StatementHandler

public interface StatementHandler {// 從連接中獲取一個Statement對象Statement prepare(Connection connection, Integer transactionTimeout)throws SQLException;// 綁定Statement執行是所需要的參數void parameterize(Statement statement)throws SQLException;// 批量執行SQLvoid batch(Statement statement)throws SQLException;// 執行update，delete，insert語句int update(Statement statement)throws SQLException;// 執行select語句<E> List<E> query(Statement statement, ResultHandler resultHandler)throws SQLException;<E> Cursor<E> queryCursor(Statement statement)throws SQLException;BoundSql getBoundSql();// 獲取封裝的ParameterterHandler對象ParameterHandler getParameterHandler();}

2. BaseStatementHandler

BaseStatementHandler是一個抽象類，和Executor一樣使用了模板設計方法。代碼如下：

public abstract class BaseStatementHandler implements StatementHandler {protected final Configuration configuration;protected final ObjectFactory objectFactory;protected final TypeHandlerRegistry typeHandlerRegistry;//將結果映射成結果對象protected final ResultSetHandler resultSetHandler;// 使用傳入的實參替換SQL語句中的？protected final ParameterHandler parameterHandler;// 記錄執行sql的executorprotected final Executor executor;protected final MappedStatement mappedStatement;// 分頁用到protected final RowBounds rowBounds;protected BoundSql boundSql;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// 獲取主鍵generateKeys(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);}@Overridepublic BoundSql getBoundSql() {return boundSql;}@Overridepublic ParameterHandler getParameterHandler() {return parameterHandler;}@Overridepublic Statement prepare(Connection connection, Integer transactionTimeout) throws SQLException {ErrorContext.instance().sql(boundSql.getSql());Statement statement = null;try {// 初始化Statement對象 instantiateStatement由具體的子類對象實現statement = instantiateStatement(connection);// 設置超時時間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);}}protected abstract Statement instantiateStatement(Connection connection) throws SQLException;protected void setStatementTimeout(Statement stmt, Integer transactionTimeout) throws SQLException {Integer queryTimeout = null;if (mappedStatement.getTimeout() != null) {queryTimeout = mappedStatement.getTimeout();} else if (configuration.getDefaultStatementTimeout() != null) {queryTimeout = configuration.getDefaultStatementTimeout();}if (queryTimeout != null) {stmt.setQueryTimeout(queryTimeout);}StatementUtil.applyTransactionTimeout(stmt, queryTimeout, transactionTimeout);}protected void setFetchSize(Statement stmt) throws SQLException {Integer fetchSize = mappedStatement.getFetchSize();if (fetchSize != null) {stmt.setFetchSize(fetchSize);return;}Integer defaultFetchSize = configuration.getDefaultFetchSize();if (defaultFetchSize != null) {stmt.setFetchSize(defaultFetchSize);}}protected void closeStatement(Statement statement) {try {if (statement != null) {statement.close();}} catch (SQLException e) {//ignore}}protected void generateKeys(Object parameter) {KeyGenerator keyGenerator = mappedStatement.getKeyGenerator();ErrorContext.instance().store();keyGenerator.processBefore(executor, mappedStatement, null, parameter);ErrorContext.instance().recall();}}

2.1 ParameterHandler

在BaseStatementHandler中有一個對象叫ParameterHandler是用來設置參數規則的，當StatementHandler調用prepare方法之后，接下來就是調用它來進行設置參數。

public interface ParameterHandler {Object getParameterObject();void setParameters(PreparedStatement ps)throws SQLException;}

getParameterObject是用來獲取參數的，setParameters(PreparedStatement ps)是用來設置參數的，相當于對sql中所有的參數都執行ps.setXXX(value);

ParameterHandler的默認實現類是DefaultParameterHandler，其實現了接口中定義的兩個方法。

getParameterObject是獲取參數，這個參數值就是你傳遞進來的值，可能是個實體、map或單個基本類型數據。

@Override public void setParameters(PreparedStatement ps) {ErrorContext.instance().activity("setting parameters").object(mappedStatement.getParameterMap().getId());// 去除SQL中的參數映射列表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) {//過濾掉存儲過程中的輸出參數Object value;//記錄綁定的實參值// 獲取參數名稱String propertyName = parameterMapping.getProperty();if (boundSql.hasAdditionalParameter(propertyName)) { // issue #448 ask first for additional params//獲取參數值value = boundSql.getAdditionalParameter(propertyName);} else if (parameterObject == null) {value = null;} else if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass())) {//如果是單個值則直接賦值value = parameterObject;} else {// 獲取對象中相應的屬性值或查找map對象中的值MetaObject metaObject = configuration.newMetaObject(parameterObject);value = metaObject.getValue(propertyName);}//獲取參數值對應的jdbc類型TypeHandler typeHandler = parameterMapping.getTypeHandler();JdbcType jdbcType = parameterMapping.getJdbcType();if (value == null && jdbcType == null) {jdbcType = configuration.getJdbcTypeForNull();}try {//設置參數值和jdbc類型的對應關系typeHandler.setParameter(ps, i + 1, value, jdbcType);} catch (TypeException e) {throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + e, e);} catch (SQLException e) {throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + e, e);}}}} }

3. RoutingStatementHandler

/*** RoutingStatementHandler的主要功能就是根據mapper文件中的Statement的配置，生成一個對應的StatementHandler* 可以是 SimpleStatementHandler，PreparedStatementHandler，CallableStatementHandler* 此類中的所有方法都是通過調用delegate對象的對應方法實現的*/ public class RoutingStatementHandler implements StatementHandler {private final StatementHandler delegate;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());}} }

4. SimpleStatementHandler

SimpleStatementHandler就是使用基本的Statement來執行query、batch、update等操作，其實現還是比較簡單的，SQL語句中是沒有占位符的，所以相應 的paramterize()方法是空實現。

public class SimpleStatementHandler extends BaseStatementHandler {public SimpleStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {super(executor, mappedStatement, parameter, rowBounds, resultHandler, boundSql);}@Overridepublic int update(Statement statement) throws SQLException {String sql = boundSql.getSql();Object parameterObject = boundSql.getParameterObject();KeyGenerator keyGenerator = mappedStatement.getKeyGenerator();int rows;if (keyGenerator instanceof Jdbc3KeyGenerator) {// 生成主鍵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();// 生成主鍵 keyGenerator.processAfter(executor, mappedStatement, statement, parameterObject);} else {statement.execute(sql);rows = statement.getUpdateCount();}return rows;}@Overridepublic void batch(Statement statement) throws SQLException {String sql = boundSql.getSql();statement.addBatch(sql);}@Overridepublic <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {String sql = boundSql.getSql();statement.execute(sql);return resultSetHandler.<E>handleResultSets(statement);}@Overridepublic <E> Cursor<E> queryCursor(Statement statement) throws SQLException {String sql = boundSql.getSql();statement.execute(sql);return resultSetHandler.<E>handleCursorResultSets(statement);}@Overrideprotected Statement instantiateStatement(Connection connection) throws SQLException {if (mappedStatement.getResultSetType() != null) {return connection.createStatement(mappedStatement.getResultSetType().getValue(), ResultSet.CONCUR_READ_ONLY);} else {return connection.createStatement();}}@Overridepublic void parameterize(Statement statement) throws SQLException {// N/A}}

5. PreparedStatementHandler

PreparedStatementHandler底層依賴PreparedStatement對象來完成數據庫的相關操作，在調用parameterize()方法完成SQL語句的參數綁定，代碼也比較簡單。

public class PreparedStatementHandler extends BaseStatementHandler {public PreparedStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {super(executor, mappedStatement, parameter, rowBounds, resultHandler, boundSql);}@Overridepublic int update(Statement statement) throws SQLException {PreparedStatement ps = (PreparedStatement) statement;ps.execute();int rows = ps.getUpdateCount();Object parameterObject = boundSql.getParameterObject();KeyGenerator keyGenerator = mappedStatement.getKeyGenerator();keyGenerator.processAfter(executor, mappedStatement, ps, parameterObject);return rows;}@Overridepublic void batch(Statement statement) throws SQLException {PreparedStatement ps = (PreparedStatement) statement;ps.addBatch();}@Overridepublic <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {PreparedStatement ps = (PreparedStatement) statement;ps.execute();return resultSetHandler.<E> handleResultSets(ps);}@Overridepublic <E> Cursor<E> queryCursor(Statement statement) throws SQLException {PreparedStatement ps = (PreparedStatement) statement;ps.execute();return resultSetHandler.<E> handleCursorResultSets(ps);}@Overrideprotected 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() != null) {return connection.prepareStatement(sql, mappedStatement.getResultSetType().getValue(), ResultSet.CONCUR_READ_ONLY);} else {return connection.prepareStatement(sql);}}@Overridepublic void parameterize(Statement statement) throws SQLException {parameterHandler.setParameters((PreparedStatement) statement);}}

6. CallableStatementHandler

CallableStatementHandler實際就是使用CallableStatement來執行SQL語句，當然它執行的是存儲過程。

public class CallableStatementHandler extends BaseStatementHandler {public CallableStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {super(executor, mappedStatement, parameter, rowBounds, resultHandler, boundSql);}@Overridepublic int update(Statement statement) throws SQLException {//用來調用存儲過程,它提供了對輸出和輸入/輸出參數的支持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;}@Overridepublic void batch(Statement statement) throws SQLException {CallableStatement cs = (CallableStatement) statement;cs.addBatch();}@Overridepublic <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {CallableStatement cs = (CallableStatement) statement;cs.execute();List<E> resultList = resultSetHandler.<E>handleResultSets(cs);resultSetHandler.handleOutputParameters(cs);return resultList;}@Overridepublic <E> Cursor<E> queryCursor(Statement statement) throws SQLException {CallableStatement cs = (CallableStatement) statement;cs.execute();Cursor<E> resultList = resultSetHandler.<E>handleCursorResultSets(cs);resultSetHandler.handleOutputParameters(cs);return resultList;}@Overrideprotected Statement instantiateStatement(Connection connection) throws SQLException {String sql = boundSql.getSql();if (mappedStatement.getResultSetType() != null) {return connection.prepareCall(sql, mappedStatement.getResultSetType().getValue(), ResultSet.CONCUR_READ_ONLY);} else {return connection.prepareCall(sql);}}@Overridepublic void parameterize(Statement statement) throws SQLException {//注冊out參數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);//處理存儲過程的INOUT和OUT 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());}}}}}}}

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