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SimpleExecutor执行sql过程
BoundSql加载完成之后，下一步就可以执行select/update/insert/delete语句了。在SimpleExecutor中执行语句最终会由doQuery和doUpdate方法完成。
public int doUpdate(MappedStatement ms, Object parameter) throws SQLException {
Statement stmt = null;
try {
Configuration configuration = ms.getConfiguration();
//生成一个StatementHandler
StatementHandler handler = configuration.newStatementHandler(this, ms, parameter, RowBounds.DEFAULT, null, null);
//执行之前的准备
stmt = prepareStatement(handler, ms.getStatementLog());
//执行sql
return handler.update(stmt);
} finally {
closeStatement(stmt);
}
}
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();
//生成一个StatementHandler
StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);
//执行之前的准备
stmt = prepareStatement(handler, ms.getStatementLog());
//执行sql
return handler.<E>query(stmt, resultHandler);
} finally {
closeStatement(stmt);
}
}private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException {
Statement stmt;
//获取一个连接
Connection connection = getConnection(statementLog);
//由StatementHandler从connection获取一个StatementHandler
stmt = handler.prepare(connection);
//设置执行参数
handler.parameterize(stmt);
return stmt;
}从以上代码中可以到出Executor是怎么利用StatementHandler执行SQL的
- 获取一个数据库连接
- 调用StatementHandler.prepare()方法获取一个statement
- 调用StatementHandler.parameterize()方法设置sql执行时所需要的参数
- 调用StatementHandler.update或query方法执行sql
StatementHandler
这个接口定义了执行sql的基本操作
public interface StatementHandler {
//从连接中获取一个Statement
Statement prepare(Connection connection)
throws SQLException;
//设置statement执行里所需的参数
void parameterize(Statement statement)
throws SQLException;
//批量
void batch(Statement statement)
throws SQLException;
//更新：update/insert/delete语句
int update(Statement statement)
throws SQLException;
//执行查询
<E> List<E> query(Statement statement, ResultHandler resultHandler)
throws SQLException;
BoundSql getBoundSql();
ParameterHandler getParameterHandler();
}再来看他的类关系图
跟Executor的实现非常相似。
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RoutingStatementHandler
这个类只是根据MappedStatement的配置，生成一个对应的StatementHandler(delegate),然后所有的实现都由delegate完成。
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());
}
}BaseStatementHandler
这个类是一个模板类。其中有两个主要的属性和一个主要的方法。先来看两个属性。
//处理结果的Handler
protected final ResultSetHandler resultSetHandler;
//设置参数的Handler
protected final ParameterHandler parameterHandler;public interface ResultSetHandler {
//转换结果集
<E> List<E> handleResultSets(Statement stmt) throws SQLException;
void handleOutputParameters(CallableStatement cs) throws SQLException;
}public interface ParameterHandler {
Object getParameterObject();
//设置SQL执行的参数
void setParameters(PreparedStatement ps)
throws SQLException;
}这ParameterHandler和ResultSetHandler在Mybatis中都只有一个实现：DefaultParameterHandler和DefaultResultSetHandler。之后会有详细有分析。
Prepare方法
public Statement prepare(Connection connection) throws SQLException {
ErrorContext.instance().sql(boundSql.getSql());
Statement statement = null;
try {
//这个方法是抽象的，由子类实现
statement = instantiateStatement(connection);
//设置执行的超时时间
setStatementTimeout(statement);
//fetchSize，对大的结果集才有明显的效果
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);
}
}BaseStatementHandler子类
- PreparedStatementHandler,处理PreparedStatement对象，即带参数运行的SQL,这个类以后详细分析。
- CallableStatementHandler,处理CallableStatement对象，即执行过程的SQL,不做讨论。
- SimpleStatementHandler,处理Statement对象，即不带参数运行的SQL,不做讨论。