mybatis源码(四)SqlSession执行mapper的过程下篇

PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">


SELECT id, account, passwd, nickname, phone, email, create_time as createTime, update_time as updateTime
FROM user


public class TestUserMapper {
private static SqlSessionFactory sqlSessionFactory;
@BeforeClass
public static void init(){
try {
Reader reader = Resources.getResourceAsReader("mybatis.config.xml");
sqlSessiOnFactory= new SqlSessionFactoryBuilder().build(reader);
reader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
@Test
public void TestMybatis(){
SqlSession sqlSession = sqlSessionFactory.openSession();
List userList = sqlSession.selectList("selectUsers");
System.out.println(userList.size());
System.out.println(userList.get(0).getNickname());
System.out.println(userList.get(0).getCreateTime());
}
}

@Override
public List selectList(String statement, Object parameter, RowBounds rowBounds) {
try {
// 根据Mapper的Id，获取对应的MappedStatement对象
MappedStatement ms = configuration.getMappedStatement(statement);
// 以MappedStatement对象作为参数，调用Executor的query（）方法
return executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER);
} catch (Exception e) {
throw ExceptionFactory.wrapException("Error querying database. Cause: " + e, e);
} finally {
ErrorContext.instance().reset();
}
}

@Override
public List query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {
// 获取BoundSql对象，BoundSql是对动态SQL解析生成的SQL语句和参数映射信息的封装
BoundSql boundSql = ms.getBoundSql(parameter);
// 创建CacheKey，用于缓存Key
CacheKey key = createCacheKey(ms, parameter, rowBounds, boundSql);
// 调用重载的query（）方法
return query(ms, parameter, rowBounds, resultHandler, key, boundSql);
}
@SuppressWarnings("unchecked")
@Override
public List query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {
ErrorContext.instance().resource(ms.getResource()).activity("executing a query").object(ms.getId());
if (closed) {
throw new ExecutorException("Executor was closed.");
}
if (queryStack == 0 && ms.isFlushCacheRequired()) {
clearLocalCache();
}
List list;
try {
queryStack++;
// 从缓存中获取结果
list = resultHandler == null ? (List) localCache.getObject(key) : null;
if (list != null) {
handleLocallyCachedOutputParameters(ms, key, parameter, boundSql);
} else {
// 缓存中获取不到，则调用queryFromDatabase（）方法从数据库中查询
list = queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql);
}
} finally {
queryStack--;
}
if (queryStack == 0) {
for (DeferredLoad deferredLoad : deferredLoads) {
deferredLoad.load();
}
// issue #601
deferredLoads.clear();
if (configuration.getLocalCacheScope() == LocalCacheScope.STATEMENT) {
// issue #482
clearLocalCache();
}
}
return list;
}
private List queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {
List list;
localCache.putObject(key, EXECUTION_PLACEHOLDER);
try {
// 调用doQuery（）方法查询
list = doQuery(ms, parameter, rowBounds, resultHandler, boundSql);
} finally {
localCache.removeObject(key);
}
// 缓存查询结果
localCache.putObject(key, list);
if (ms.getStatementType() == StatementType.CALLABLE) {
localOutputParameterCache.putObject(key, parameter);
}
return list;
}
protected abstract List doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql)
throws SQLException;

@Override
public List doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {
Statement stmt = null;
try {
Configuration cOnfiguration= ms.getConfiguration();
// 获取StatementHandler对象
StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);
// 调用prepareStatement（）方法,创建Statement对象，并进行设置参数等操作
stmt = prepareStatement(handler, ms.getStatementLog());
// 调用StatementHandler对象的query（）方法执行查询操作
return handler.query(stmt, resultHandler);
} finally {
closeStatement(stmt);
}
}

@Override
public List doQuery(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql)
throws SQLException {
Statement stmt = null;
try {
flushStatements();
Configuration cOnfiguration= ms.getConfiguration();
StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameterObject, rowBounds, resultHandler, boundSql);
Connection cOnnection= getConnection(ms.getStatementLog());
stmt = handler.prepare(connection, transaction.getTimeout());
handler.parameterize(stmt);
return handler.query(stmt, resultHandler);
} finally {
closeStatement(stmt);
}
}

@Override
public List doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {
Configuration cOnfiguration= ms.getConfiguration();
StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);
Statement stmt = prepareStatement(handler, ms.getStatementLog());
return handler.query(stmt, resultHandler);
}
Statement 操作数据库就是JDBC提供的操作数据的实现