在使用MyBatis時,使用XML文件來構建SqlSessionFactory類。
SqlSessionFactory 是由SqlSessionFactoryBuilder類來創建。
SqlSessionFactoryBuilder.build(Configuration)
SqlSessionFactoryBuilder.build(InputStream, String, Properties)
SqlSessionFactoryBuilder.build(InputStream)
public SqlSessionFactory build(Configuration config) {
return new DefaultSqlSessionFactory(config);
}
在SqlSessionFactoryBuilder.build()一個DefaultSqlSessionFactory類後,SqlSessionFactoryBuilder類就可以被丟棄了。
正確使用SqlSessionFactory的模式：
使用 SqlSessionFactory 的最佳實踐是在應用運行期間不要重複創建多次，多次重建 SqlSessionFactory 被視爲一種代碼“壞味道（bad smell）”。因此 SqlSessionFactory 的最佳範圍是應用範圍。有很多方法可以做到，最簡單的就是使用單例模式或者靜態單例模式。
在SqlSessionFactory被創建完成後,就一直存在於整個應用的生命週期。可以通過SqlSessionFactory來創建SqlSession. 而SqlSession是Mybatis暴露給開發者使用的接口。
正確使用SqlSession的模式：
每個線程都應該有它自己的 SqlSession 實例。SqlSession 的實例不是線程安全的，因此是不能被共享的，所以它的最佳的範圍是請求或方法範圍。
public class SqlSessionUtil {
private static SqlSessionFactory instance = null;
static {
try {
String resource = "org/mybatis/example/mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
instance = new SqlSessionFactoryBuilder().build(inputStream);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public static SqlSession getSqlSession() {
return instance.openSession();
}
}SqlSession:The primary Java interface for working with MyBatis.Through this interface you can execute commands, get mappers and manage transactions.
SqlSession是MyBatis暴露給開發者最主要的接口。通過這個接口可以執行CRUD命令,獲取映射器和管理事務。
/**
* The primary Java interface for working with MyBatis.
* Through this interface you can execute commands, get mappers and manage transactions.
*
* @author Clinton Begin
*/
public interface SqlSession extends Closeable {
/**
* Retrieve a single row mapped from the statement key
通過sql語句獲取一行數據記錄
*/
<T> T selectOne(String statement);
/**
* Retrieve a single row mapped from the statement key and parameter.
*/
<T> T selectOne(String statement, Object parameter);
/**
* Retrieve a list of mapped objects from the statement key and parameter.
通過sql語句可以獲取多條數據庫記錄
*/
<E> List<E> selectList(String statement);
/**
* Retrieve a list of mapped objects from the statement key and parameter.
*/
<E> List<E> selectList(String statement, Object parameter);
/**
* Retrieve a list of mapped objects from the statement key and parameter,
* within the specified row bounds.
*/
<E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds);
/**
* The selectMap is a special case in that it is designed to convert a list
* of results into a Map based on one of the properties in the resulting
* objects.
* Eg. Return a of Map[Integer,Author] for selectMap("selectAuthors","id")
* 把一個隊列的數據庫記錄映射到map中。 key 爲唯一鍵，value爲一行數據庫記錄
*/
<K, V> Map<K, V> selectMap(String statement, String mapKey);
/**
* The selectMap is a special case in that it is designed to convert a list
* of results into a Map based on one of the properties in the resulting
* objects.
*/
<K, V> Map<K, V> selectMap(String statement, Object parameter, String mapKey);
/**
* The selectMap is a special case in that it is designed to convert a list
* of results into a Map based on one of the properties in the resulting
* objects.
*/
<K, V> Map<K, V> selectMap(String statement, Object parameter, String mapKey, RowBounds rowBounds);
/**
* A Cursor offers the same results as a List, except it fetches data lazily using an Iterator.
*/
<T> Cursor<T> selectCursor(String statement);
/**
* A Cursor offers the same results as a List, except it fetches data lazily using an Iterator.
*/
<T> Cursor<T> selectCursor(String statement, Object parameter);
/**
* A Cursor offers the same results as a List, except it fetches data lazily using an Iterator.
*/
<T> Cursor<T> selectCursor(String statement, Object parameter, RowBounds rowBounds);
/**
* Retrieve a single row mapped from the statement key and parameter
* using a {@code ResultHandler}.
*/
void select(String statement, Object parameter, ResultHandler handler);
/**
* Retrieve a single row mapped from the statement
* using a {@code ResultHandler}.
*/
void select(String statement, ResultHandler handler);
/**
* Retrieve a single row mapped from the statement key and parameter
* using a {@code ResultHandler} and {@code RowBounds}
*/
void select(String statement, Object parameter, RowBounds rowBounds, ResultHandler handler);
/**
* Execute an insert statement.
*/
int insert(String statement);
/**
* Execute an insert statement with the given parameter object. Any generated
* autoincrement values or selectKey entries will modify the given parameter
* object properties. Only the number of rows affected will be returned.
* @param statement Unique identifier matching the statement to execute.
* @param parameter A parameter object to pass to the statement.
* @return int The number of rows affected by the insert.
*/
int insert(String statement, Object parameter);
/**
* Execute an update statement. The number of rows affected will be returned.
* @param statement Unique identifier matching the statement to execute.
* @return int The number of rows affected by the update.
*/
int update(String statement);
/**
* Execute an update statement. The number of rows affected will be returned.
* @param statement Unique identifier matching the statement to execute.
* @param parameter A parameter object to pass to the statement.
* @return int The number of rows affected by the update.
*/
int update(String statement, Object parameter);
/**
* Execute a delete statement. The number of rows affected will be returned.
* @param statement Unique identifier matching the statement to execute.
* @return int The number of rows affected by the delete.
*/
int delete(String statement);
/**
* Execute a delete statement. The number of rows affected will be returned.
* @param statement Unique identifier matching the statement to execute.
* @param parameter A parameter object to pass to the statement.
* @return int The number of rows affected by the delete.
*/
int delete(String statement, Object parameter);
/**
* Flushes batch statements and commits database connection.
* Note that database connection will not be committed if no updates/deletes/inserts were called.
* To force the commit call {@link SqlSession#commit(boolean)}
*/
void commit();
/**
* Flushes batch statements and commits database connection.
* @param force forces connection commit
*/
void commit(boolean force);
/**
* Discards pending batch statements and rolls database connection back.
* Note that database connection will not be rolled back if no updates/deletes/inserts were called.
* To force the rollback call {@link SqlSession#rollback(boolean)}
*/
void rollback();
/**
* Discards pending batch statements and rolls database connection back.
* Note that database connection will not be rolled back if no updates/deletes/inserts were called.
* @param force forces connection rollback
*/
void rollback(boolean force);
/**
* Flushes batch statements.
* @return BatchResult list of updated records
* @since 3.0.6
*/
List<BatchResult> flushStatements();
/**
* Closes the session
*/
@Override
void close();
/**
* Clears local session cache
*/
void clearCache();
/**
* Retrieves current configuration
* @return Configuration
*/
Configuration getConfiguration();
/**
* Retrieves a mapper.
* @param <T> the mapper type
* @param type Mapper interface class
* @return a mapper bound to this SqlSession
*/
<T> T getMapper(Class<T> type);
/**
* Retrieves inner database connection
* @return Connection
*/
Connection getConnection();
}
在MyBatis官網中，提供的文檔也很簡潔。
主要包括：
1、Configuration XML 例如： mybatis-config.xml 主配置文件
2、Mapper XML 數據庫，Pojo類映射關係的配置
3、Dynamic SQL 動態sql語句的說明
4、 Java Api MyBatis 暴露給開發者使用的java開發api 接口
5、在java代碼中構建SQL 語句
6、MyBatis 日誌配置
總結：總體來說，MyBatis使用簡單，暴露給開發者的接口只有SqlSession,但是功能極其強大。