获取 SqlSession 后,下一步就是执行 sql.
User user=sqlSession.selectOne("last.soul.mapper.UserMapper.selectById",map);
DefaultSqlSession 的次要性能就是实现增删改查性能,以及它们的重载办法。就查问来说,最初都会调用 select 办法,而后改装成 selectOne,selectMap 等,代码如下:
/**
*
* @param statement sql 语句 ID=xxxMapper.xml 文件中的 namespace+sql 标签的 id.
* 如:last.soul.mapper.UserMapper.selectById
* @param parameter sql 的参数
* @param rowBounds 分页信息
* @param <E>
* @return
*/
@Override
public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {
try {
//sql 相干音讯的包装对象,比方:sql 语句,返回类型,是否应用缓存等
MappedStatement ms = configuration.getMappedStatement(statement);
// 执行 sql
return executor.query(ms, wrapCollection(parameter)/* 包装汇合类型参数 */, rowBounds, Executor.NO_RESULT_HANDLER);
} catch (Exception e) {throw ExceptionFactory.wrapException("Error querying database. Cause:" + e, e);
} finally {ErrorContext.instance().reset();}
}
由上文得悉 executor 是 CachingExecutor, 执行的是 CachingExecutor 的 query 办法。
public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql)
throws SQLException {Cache cache = ms.getCache();
if (cache != null) {flushCacheIfRequired(ms);
if (ms.isUseCache() && resultHandler == null) {ensureNoOutParams(ms, boundSql);
@SuppressWarnings("unchecked")
List<E> list = (List<E>) tcm.getObject(cache, key);
if (list == null) {list = delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
tcm.putObject(cache, key, list); // issue #578 and #116
}
return list;
}
}
//delegate 是 SimpleExecutor 对象
return delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
}
query 办法中次要逻辑是判断是否有缓存,有缓存返回缓存值,否则执行 delegate 对象的 query 办法,即 SimpleExecutor 对象的 query 办法,然而你会发现该类中没有些办法,那它执行的就是他的父类 BaseExecutor 的 query 办法。query 办法又会调用它的公有办法 queryFromDatabase。
queryFromDatabase 源代码如下:
private <E> List<E> queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {
List<E> list;
localCache.putObject(key, EXECUTION_PLACEHOLDER);
try {
// 调用子类的实现
list = doQuery(ms, parameter, rowBounds, resultHandler, boundSql);
} finally {localCache.removeObject(key);
}
localCache.putObject(key, list);
if (ms.getStatementType() == StatementType.CALLABLE) {localOutputParameterCache.putObject(key, parameter);
}
return list;
}
其中最要害的代码就是调用了子类 (SimpleExecutor 类,CachingExecutor 类没有实现该办法) 的 doQuery 办法。源代码如下:
@Override
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();
StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);
stmt = prepareStatement(handler, ms.getStatementLog());
return handler.query(stmt, resultHandler);
} finally {closeStatement(stmt);
}
}
这个办法的次要逻辑是创立 StatementHandler,而后调用它的 query 办法。关上 configuration.newStatementHandler, 咱们发现生成的是 RoutingStatementHandler 对象。源代码如下:
public StatementHandler newStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {StatementHandler statementHandler = new RoutingStatementHandler(executor, mappedStatement, parameterObject, rowBounds, resultHandler, boundSql);
statementHandler = (StatementHandler) interceptorChain.pluginAll(statementHandler);
return statementHandler;
}
所以 SimpleExecutor 类 doQuery()办法最初一行执行的 query 办法是执行的咱们发现生成的是 RoutingStatementHandler 看的 query 办法。它的源代码如下:
public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {return delegate.query(statement, resultHandler);
}
delegate 代理的是哪个 StatementHandler 对象呢? 这个对象在 RoutingStatementHandler 构造方法中赋值的。
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());
}
}
ms.getStatementType()在本例中应用的是默认值。MappedStatement 的外部类 Builder 源代码中。
mappedStatement.statementType = StatementType.PREPARED;
所以 delegate 为 PreparedStatementHandler 对象,最终调用的也是 PreparedStatementHandler 下的 query 办法,源代码如下:
public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {PreparedStatement ps = (PreparedStatement) statement;
ps.execute();
return resultSetHandler.handleResultSets(ps);
}
逻辑比拟清晰,1、执行 sql。2、解决返回后果。