Mybatis源码之Statement处理器SimpleStatementHandler（四）

SimpleStatementHandler就是使用基本的Statement来执行query、batch、update等操作，其实现还是比较简单的，当然在执行过程中会涉及keyGenerator和ResultHandler操作，这些我们会在接下来的博客中进行详解。SimpleStatementHandler用于执行简单的sql语句，这里简单的sql语句是指sql语句中没有变量，不会通过外部进行参数传入的sql语句。

源码如下：

/**
* @author Clinton Begin
*/
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);
}

@Override
public int update(Statement statement) throws SQLException {
//获得sql语句
String sql = boundSql.getSql();
//获得参数
Object parameterObject = boundSql.getParameterObject();
KeyGenerator keyGenerator = mappedStatement.getKeyGenerator();
int rows;
//statement执行sql语句返回更新数目
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 {
//如果没有keyGenerator，直接调用Statement.execute和Statement.getUpdateCount
statement.execute(sql);
rows = statement.getUpdateCount();
}
return rows;
}

@Override
public void batch(Statement statement) throws SQLException {
//批处理
String sql = boundSql.getSql();
statement.addBatch(sql);
}

//ResultHandler resultHandler这个参数好像没用啊
@Override
public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {
String sql = boundSql.getSql();
//statement执行sql语句
statement.execute(sql);
return resultSetHandler.<E>handleResultSets(statement);
}

//实例化Statement
@Override
protected Statement instantiateStatement(Connection connection) throws SQLException {
if (mappedStatement.getResultSetType() != null) {
return connection.createStatement(mappedStatement.getResultSetType().getValue(), ResultSet.CONCUR_READ_ONLY);
} else {
return connection.createStatement();
}
}

@Override
public void parameterize(Statement statement) throws SQLException {
// N/A
}

}