原生mybatis与myBatis-spring

原生mybatis使用方法：
String resource = “mybatis-config.xml”;
InputStream inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
SqlSession session = sqlSessionFactory.openSession();
try {
Employee employee = new Employee(null, “doubi”, “1”, "[email protected]");
EmployeeMapper mapper = session.getMapper(EmployeeMapper.class);
mapper.addEmp(employee);
session.commit();
} finally {
session.close();
}
spring使用方法，直接注入即可
@Autowired
EmployeeMapper employeeMapper
那么spring为我们做了什么？下面研究一下mybatis-spring.jar这个jar包

首先来看一下如何使用spring整合mybatis，下面是使用spring-mybatis的四种方法：

方法一：（使用MapperFactoryBean）

这样做的缺点是每一个mapper接口都要在xml里配置一下

方法二：采用接口org.apache.ibatis.session.SqlSession的实现类 org.mybatis.spring.SqlSessionTemplate

mybatis中, sessionFactory可由SqlSessionFactoryBuilder.来创建。MyBatis-Spring 中，使用了SqlSessionFactoryBean来替代。SqlSessionFactoryBean有一个必须属性dataSource，另外其还有一个通用属性configLocation（用来指定mybatis的xml配置文件路径）。

SqlSessionFactoryBean即相当于原生mybatis中的SqlSessionFactoryBuilder

//使用方法： @Repositorypublic class UserDao{ @Resource private SqlSessionTemplate sqlSessionTemplate; public User getUser(int id) { return sqlSessionTemplate.selectOne(this.getClass().getName() + ".getUser", 1); } } 为什么可以这样写，来看一下SqlSessionTemplate public class SqlSessionTemplate implements SqlSession { private final SqlSessionFactory sqlSessionFactory; private final ExecutorType executorType; private final SqlSession sqlSessionProxy; private final PersistenceExceptionTranslator exceptionTranslator; /** * Constructs a Spring managed SqlSession with the {@code SqlSessionFactory} * provided as an argument. * * @param sqlSessionFactory */ public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory) { this(sqlSessionFactory, sqlSessionFactory.getConfiguration().getDefaultExecutorType()); } ........省略...... public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType, PersistenceExceptionTranslator exceptionTranslator) { notNull(sqlSessionFactory, "Property 'sqlSessionFactory' is required"); notNull(executorType, "Property 'executorType' is required"); this.sqlSessionFactory = sqlSessionFactory; this.executorType = executorType; this.exceptionTranslator = exceptionTranslator; this.sqlSessionProxy = (SqlSession) newProxyInstance( SqlSessionFactory.class.getClassLoader(), new Class[] { SqlSession.class }, new SqlSessionInterceptor()); } } 如上面代码所示，SqlSessionTemplate类实现了原生Mybatis中的SqlSession接口，实际上它就是原生mybatis中的SqlSession

方法三：采用抽象类 org.mybatis.spring.support.SqlSessionDaoSupport 提供SqlSession

public class BaseDao extends SqlSessionDaoSupport{ //使用sqlSessionFactory @Autowired private SqlSessionFactory sqlSessionFactory; @Autowired public void setSqlSessionFactory(SqlSessionFactory sqlSessionFactory) { super.setSqlSessionFactory(sqlSessionFactory); } /** * 执行insert操作 * @param statement * @return */ public int insert(String statement) { return getSqlSession().insert(statement); } /** * 执行insert操作 * @param statement * @param parameter * @return */ public int insert(String statement, Object parameter) { return getSqlSession().insert(statement, parameter); } public int update(String statement) { return getSqlSession().update(statement); } public int update(String statement, Object parameter) { return getSqlSession().update(statement, parameter); } public int delete(String statement) { return getSqlSession().delete(statement); } public int delete(String statement, Object parameter) { return getSqlSession().delete(statement, parameter); } /** * 获取一个list集合 * @param statement * @return */ public List selectList(String statement) { return getSqlSession().selectList(statement); } /** * 根据参数 获取一个list集合 * @param statement * @param parameter * @return */ public List selectList(String statement, Object parameter) { return getSqlSession().selectList(statement, parameter); } public Map selectMap(String statement, String mapKey) { return getSqlSession().selectMap(statement, mapKey); } public Map selectMap(String statement, Object parameter, String mapKey) { return getSqlSession().selectMap(statement, parameter, mapKey); } /** * 获取Object对象 * @param statement * @return */ public Object selectOne(String statement) { return getSqlSession().selectOne(statement); } /** * 获取connection, 以便执行较为复杂的用法 * @return */ public Connection getConnection() { return getSqlSession().getConnection(); } } 如上代码，一个Dao类继承了SqlSessionDaoSupport类后，就可以在类中注入SessionFact ory，进而通过getSqlSession()获取当前SqlSession

下面是 SqlSessionDaoSupport的源码 ，它是一个抽象类，并拥有sqlSession属性，在setSqlSessionFactory方法中实例化了该sqlSession：
public abstract class SqlSessionDaoSupport extends DaoSupport
{
private SqlSession sqlSession; private boolean externalSqlSession;
public void setSqlSessionFactory(SqlSessionFactory sqlSessionFactory)
{
if (!this.externalSqlSession) {
this.sqlSession = new SqlSessionTemplate(sqlSessionFactory);
}
}
public void setSqlSessionTemplate(SqlSessionTemplate sqlSessionTemplate)
{
this.sqlSession = sqlSessionTemplate; this.externalSqlSession = true;
}
public SqlSession getSqlSession()
{
return this.sqlSession;
}
protected void checkDaoConfig()
{
notNull(this.sqlSession, “Property ‘sqlSessionFactory’ or ‘sqlSessionTemplate’ are required”); }}
方法四：（也是 最常见的使用方法 ，使用MapperScannerConfigurer，它将会查找类路径下的映射器并自动将它们创建成MapperFactoryBean）

由于直接使用MapperFactoryBean会在配置文件中配置大量mapper，因此这里使用包扫描的方式通过注解获取该bean

//使用如下代码，即可完成注入 @Resource private UserDao userDao; 下面看一下MapperScannerConfigurer这个类：

public class MapperScannerConfigurer implements BeanDefinitionRegistryPostProcessor, InitializingBean, ApplicationContextAware, BeanNameAware { private String basePackage; private boolean addToConfig = true; private SqlSessionFactory sqlSessionFactory; private SqlSessionTemplate sqlSessionTemplate; private String sqlSessionFactoryBeanName; private String sqlSessionTemplateBeanName; private Class annotationClass; private Class markerInterface; private ApplicationContext applicationContext; private String beanName; private boolean processPropertyPlaceHolders; private BeanNameGenerator nameGenerator;
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException { if (this.processPropertyPlaceHolders) { processPropertyPlaceHolders(); } ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry); scanner.setAddToConfig(this.addToConfig); scanner.setAnnotationClass(this.annotationClass); scanner.setMarkerInterface(this.markerInterface); scanner.setSqlSessionFactory(this.sqlSessionFactory); scanner.setSqlSessionTemplate(this.sqlSessionTemplate); scanner.setSqlSessionFactoryBeanName(this.sqlSessionFactoryBeanName); scanner.setSqlSessionTemplateBeanName(this.sqlSessionTemplateBeanName); scanner.setResourceLoader(this.applicationContext); scanner.setBeanNameGenerator(this.nameGenerator); scanner.registerFilters(); scanner.scan(StringUtils.tokenizeToStringArray(this.basePackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS)); }
ClassPathMapperScanner ：
public Set doScan(String… basePackages) { Set beanDefinitions = super.doScan(basePackages); if (beanDefinitions.isEmpty()) { logger.warn(“No MyBatis mapper was found in '” + Arrays.toString(basePackages) + “’ package. Please check your configuration.”); } else { for (BeanDefinitionHolder holder : beanDefinitions) { GenericBeanDefinition definition = (GenericBeanDefinition) holder.getBeanDefinition(); if (logger.isDebugEnabled()) { logger.debug(“Creating MapperFactoryBean with name '” + holder.getBeanName() + “’ and '” + definition.getBeanClassName() + “’ mapperInterface”); } // the mapper interface is the original class of the bean // but, the actual class of the bean is MapperFactoryBean definition.getPropertyValues().add(“mapperInterface”, definition.getBeanClassName()); definition.setBeanClass(MapperFactoryBean.class); definition.getPropertyValues().add(“addToConfig”, this.addToConfig); boolean explicitFactoryUsed = false; if (StringUtils.hasText(this.sqlSessionFactoryBeanName)) { definition.getPropertyValues().add(“sqlSessionFactory”, new RuntimeBeanReference(this.sqlSessionFactoryBeanName)); explicitFactoryUsed = true; } else if (this.sqlSessionFactory != null) { definition.getPropertyValues().add(“sqlSessionFactory”, this.sqlSessionFactory); explicitFactoryUsed = true; } if (StringUtils.hasText(this.sqlSessionTemplateBeanName)) { if (explicitFactoryUsed) { logger.warn(“Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored.”); } definition.getPropertyValues().add(“sqlSessionTemplate”, new RuntimeBeanReference(this.sqlSessionTemplateBeanName)); explicitFactoryUsed = true; } else if (this.sqlSessionTemplate != null) { if (explicitFactoryUsed) { logger.warn(“Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored.”); } definition.getPropertyValues().add(“sqlSessionTemplate”, this.sqlSessionTemplate); explicitFactoryUsed = true; } if (!explicitFactoryUsed) { if (logger.isDebugEnabled()) { logger.debug(“Enabling autowire by type for MapperFactoryBean with name '” + holder.getBeanName() + “’.”); } definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE); } } } return beanDefinitions; }
总结：spring-mybatis与原生Mybatis相比，如下概念：

1）SqlSessionFactory类在两者中都存在

2）前者用SqlSessionFactoryBean生成SqlSessionFactory，后者则使用SqlSessionFactoryBuilder;

3）前者使用SqlSessionTemplate，后者使用SqlSession，实际上前者实现了后者

4）MapperFactoryBean中实现了原生mybatis中下面的步骤，因此通过该类可以直接获取到一个mapper接口的实现对象
EmployeeMapper mapper = session.getMapper(EmployeeMapper.class);