From be41228dffa9ed159ee4c4821d7229683aa47ff8 Mon Sep 17 00:00:00 2001 From: AmyliaY <471816751@qq.com> Date: Sat, 28 Dec 2019 21:43:47 +0800 Subject: [PATCH] =?UTF-8?q?StatementHandler=E7=B3=BB=E5=88=97=E7=BB=84?= =?UTF-8?q?=E4=BB=B6?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- .../核心处理层/4、StatementHandler.md | 238 ++++++++++++++++++ 1 file changed, 238 insertions(+) diff --git a/docs/Mybatis/核心处理层/4、StatementHandler.md b/docs/Mybatis/核心处理层/4、StatementHandler.md index e69de29..db187b5 100644 --- a/docs/Mybatis/核心处理层/4、StatementHandler.md +++ b/docs/Mybatis/核心处理层/4、StatementHandler.md @@ -0,0 +1,238 @@ +StatementHandler接口是MyBatis的核心接口之一，它完成了MyBatis中最核心的工作，也是Executor 接口实现的基础。 + +StatementHandler接口中的功能很多，例如创建Statement对象，为SQL语句绑定实参，执行select、insert、update、delete等多种类型的SQL语句，批量执行SQL语句，将结果集映射成结果对象。 +```java +public interface StatementHandler { + + // 从连接中获取一个Statement + Statement prepare(Connection connection, Integer transactionTimeout) + throws SQLException; + + // 绑定statement执行时所需的实参 + void parameterize(Statement statement) + throws SQLException; + + // 批量执行SQL语句 + void batch(Statement statement) + throws SQLException; + + // 执行update/insert/delete语句 + int update(Statement statement) + throws SQLException; + + // 执行select语句 + List query(Statement statement, ResultHandler resultHandler) + throws SQLException; + + Cursor queryCursor(Statement statement) + throws SQLException; + + BoundSql getBoundSql(); + + // 获取参数处理器 + ParameterHandler getParameterHandler(); + +} +``` +## RoutingStatementHandler +RoutingStatementHandler使用了策略模式，RoutingStatementHandler是策略类，而SimpleStatementHandler、PreparedStatementHandler、CallableStatementHandler则是实现了具体算法的实现类，RoutingStatementHandler对象会根据MappedStatement对象的StatementType属性值选择使用相应的策略去执行。 +```java +public class RoutingStatementHandler implements StatementHandler { + + // 持有的真正实现StatementHandler接口功能的对象 + private final StatementHandler delegate; + + public RoutingStatementHandler(Executor executor, MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) { + // RoutingStatementHandler的作用就是根据ms的配置，生成一个相对应的StatementHandler对象 + // 并设置到持有的delegate属性中，本对象的所有方法都是通过调用delegate的相应方法实现的 + 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()); + } + + } + + @Override + public Statement prepare(Connection connection, Integer transactionTimeout) throws SQLException { + return delegate.prepare(connection, transactionTimeout); + } + + @Override + public void parameterize(Statement statement) throws SQLException { + delegate.parameterize(statement); + } + + @Override + public void batch(Statement statement) throws SQLException { + delegate.batch(statement); + } + + @Override + public int update(Statement statement) throws SQLException { + return delegate.update(statement); + } + + @Override + public List query(Statement statement, ResultHandler resultHandler) throws SQLException { + return delegate.query(statement, resultHandler); + } + + @Override + public Cursor queryCursor(Statement statement) throws SQLException { + return delegate.queryCursor(statement); + } + + @Override + public BoundSql getBoundSql() { + return delegate.getBoundSql(); + } + + @Override + public ParameterHandler getParameterHandler() { + return delegate.getParameterHandler(); + } +} +``` +## BaseStatementHandler +看它以Base开头，就可以猜到 它是一个实现了StatementHandler接口的抽象类，这个类只提供了一些参数绑定相关的方法，并没有实现操作数据库的方法。 +```java +public abstract class BaseStatementHandler implements StatementHandler { + + // 持有的这些属性都是通过构造方法完成初始化的，typeHandlerRegistry、 + // objectFactory、parameterHandler等则是通过configuration属性获得的 + protected final Configuration configuration; + protected final ObjectFactory objectFactory; + protected final TypeHandlerRegistry typeHandlerRegistry; + protected final ResultSetHandler resultSetHandler; + // parameterHandler的功能主要是为SQL语句绑定实参，也就是使用传入的实参 + // 替换SQL语句中的占位符"?" + protected final ParameterHandler parameterHandler; + + // 用来执行SQL语句的执行器 + protected final Executor executor; + protected final MappedStatement mappedStatement; + // 记录了用户设置的offset和limit，用于在结果集中定位 + // 映射的起始位置和结束位置 + protected final RowBounds rowBounds; + + protected BoundSql boundSql; + + // BaseStatementHandler的构造方法主要用于属性的初始化 + 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 + // 其中调用了KeyGenerator的processBefore()方法 + // 用于初始化SQL语句的主键 + 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); + } + + protected void generateKeys(Object parameter) { + KeyGenerator keyGenerator = mappedStatement.getKeyGenerator(); + ErrorContext.instance().store(); + keyGenerator.processBefore(executor, mappedStatement, null, parameter); + ErrorContext.instance().recall(); + } + + @Override + public BoundSql getBoundSql() { + return boundSql; + } + + @Override + public ParameterHandler getParameterHandler() { + return parameterHandler; + } + + @Override + public Statement prepare(Connection connection, Integer transactionTimeout) throws SQLException { + ErrorContext.instance().sql(boundSql.getSql()); + Statement statement = null; + try { + // 这是一个抽象方法，用于初始化java.sql.Statement对象 + statement = instantiateStatement(connection); + // 为Statement对象设置超时时间及fetchSize + 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 + } + } + +} +``` +BaseStatementHandler主要实现了StatementHandler接口中的prepare()方法，BaseStatementHandler依赖两个重要的组件，ParameterHandler和ResultSetHandler。 +## ParameterHandler + + + +## SimpleStatementHandler + + + +## PreparedStatementHandler +