1 基本知识
MyBatis中如果每次配置类名都要写全称也太不友好了，我们可以通过在主配置文件中配置别名，就不再需要指定完整的包名了。
别名的基本用法：
&configuration&
&typeAliases&
&typeAlias type="com.domain.Student" alias="Student"/&
&/typeAliases&
&/configuration&
&但是如果每一个实体类都这样配置还是有点麻烦这时我们可以直接指定package的名字， mybatis会自动扫描指定包下面的javabean，并且默认设置一个别名，默认的名字为： javabean 的首字母小写的非限定类名来作为它的别名（其实别名是不去分大小写的）。也可在javabean 加上注解@Alias 来自定义别名， 例如： @Alias(student)
&typeAliases&
&package name="com.domain"/&
&/typeAliases&
这样，在Mapper中我们就不用每次配置都写类的全名了，但是有一个例外，那就是namespace。
namespace属性
在MyBatis中，Mapper中的namespace用于绑定Dao接口的，即面向接口编程。
它的好处在于当使用了namespace之后就可以不用写接口实现类，业务逻辑会直接通过这个绑定寻找到相对应的SQL语句进行对应的数据处理
student = (Student) session.selectOne("com.domain.Student.selectById", new Integer(10));
&mapper namespace="com.domain.Student"&
&select id="selectById" parameterType="int" resultType="student"&
select * from student where id=#{id}
2 Mybitis配置
这里新建一个spring boot程序
2.1 目录结构
2.2 xml文件配置
mybatis-config.xml配置：
&?xml version="1.0" encoding="UTF-8" ?&
&!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd"&
&configuration&
&typeAliases&
&package name="sample.mybatis.domain"/&
&/typeAliases&
&mapper resource="mapper/CityMapper.xml"/&
&mapper resource="mapper/HotelMapper.xml"/&
&/mappers&
&/configuration&
这里要注意别名namespace和mappers的配置。
CityMapper.xml配置：
&?xml version="1.0" encoding="UTF-8" ?&
&!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd"&
&mapper namespace="sample.mybatis.mapper.CityMapper"&
&select id="selectCityById" resultType="City"&
select * from city where id = #{id}
HotelMapper.xml配置：
&?xml version="1.0" encoding="UTF-8" ?&
&!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd"&
&mapper namespace="sample.mybatis.mapper.HotelMapper"&
&select id="selectByCityId" resultType="Hotel"&
select * from hotel where city = #{id}
2.3 &Mapper接口、dao实现
HotelMapper.java:
package sample.mybatis.
import org.apache.ibatis.annotations.M
import sample.mybatis.domain.H
* @author Eduardo Macarron
public interface HotelMapper {
Hotel selectByCityId(int city_id);
CityDao.java:
package sample.mybatis.
import org.apache.ibatis.session.SqlS
import org.springframework.beans.factory.annotation.A
import org.
import sample.mybatis.domain.C
* @author Edd& Mel&ndez
@Component
public class CityDao {
@Autowired
private SqlSession sqlS
public City selectCityById(long id) {
return this.sqlSession.selectOne("selectCityById", id);
City.java:
package sample.mybatis.
import java.io.S
* @author Edd& Mel&ndez
public class City implements Serializable {
private static final long serialVersionUID = 1L;
public Long getId() {
return this.
public void setId(Long id) {
public String getName() {
return this.
public void setName(String name) {
this.name =
public String getState() {
return this.
public void setState(String state) {
this.state =
public String getCountry() {
return this.
public void setCountry(String country) {
this.country =
public String toString() {
return getId() + "," + getName() + "," + getState() + "," + getCountry();
Hotel.java:
package sample.mybatis.
import java.io.S
public class Hotel implements Serializable {
private static final long serialVersionUID = 1L;
public Long getCity() {
public void setCity(Long city) {
this.city =
public String getName() {
public void setName(String name) {
this.name =
public String getAddress() {
public void setAddress(String address) {
this.address =
public String getZip() {
public void setZip(String zip) {
this.zip =
public String toString() {
return getCity() + "," + getName() + "," + getAddress() + "," + getZip();
执行结果：
阅读(...) 评论()mybatis如何根据mapper接口生成其实现类 - 推酷
mybatis如何根据mapper接口生成其实现类
mybatis里头给sqlSession指定执行哪条sql的时候，有两种方式，一种是写mapper的xml的namespace+statementId，如下：
public Student findStudentById(Integer studId) {
logger.debug(&Select Student By ID :{}&, studId);
SqlSession sqlSession = MyBatisSqlSessionFactory.getSqlSession();
return sqlSession.selectOne(&com.mybatis3.StudentMapper.findStudentById&, studId);
} finally {
sqlSession.close();
另外一种方法是指定mapper的接口：
public Student findStudentById(Integer studId) {
logger.debug(&Select Student By ID :{}&, studId);
SqlSession sqlSession = MyBatisSqlSessionFactory.getSqlSession();
StudentMapper studentMapper = sqlSession.getMapper(StudentMapper.class);
return studentMapper.findStudentById(studId);
} finally {
sqlSession.close();
一般的话，比较推荐第二种方法，因为手工写namespace和statementId极大增加了犯错误的概率，而且也降低了开发的效率。
mapper的实现类如何生成
如果使用mapper接口的方式，问题来了，这个是个接口，通过sqlSession对象get出来的一定是个实现类，问题是，我们并没有手工去写实现类，那么谁去干了这件事情呢？答案是mybatis通过JDK的动态代理方式，在启动加载配置文件时，根据配置mapper的xml去生成。
mybatis-spring帮忙做了什么
自动open和close session
一、mapper代理类是如何生成的
启动时加载解析mapper的xml
如果不是集成spring的，会去读取&mappers&节点，去加载mapper的xml配置
&?xml version=&1.0& encoding=&UTF-8& ?&
&!DOCTYPE configuration PUBLIC &-//mybatis.org//DTD Config 3.0//EN& &http://mybatis.org/dtd/mybatis-3-config.dtd&&
&configuration&
&settings&
&setting name=&cacheEnabled& value=&true&/&
&setting name=&lazyLoadingEnabled& value=&true&/&
&setting name=&multipleResultSetsEnabled& value=&true&/&
&setting name=&useColumnLabel& value=&true&/&
&setting name=&useGeneratedKeys& value=&false&/&
&setting name=&defaultExecutorType& value=&SIMPLE&/&
&setting name=&defaultStatementTimeout& value=&2&/&
&/settings&
&typeAliases&
&typeAlias alias=&CommentInfo& type=&com.mentInfo&/&
&/typeAliases&
&environments default=&development&&
&environment id=&development&&
&transactionManager type=&JDBC&/&
&dataSource type=&POOLED&&
&property name=&driver& value=&com.mysql.jdbc.Driver&/&
&property name=&url& value=&jdbc:mysql://localhost:3306/demo&/&
&property name=&username& value=&root&/&
&property name=&password& value=&&/&
&/dataSource&
&/environment&
&/environments&
&mapper resource=&com/xixicat/dao/CommentMapper.xml&/&
&/mappers&
&/configuration&
如果是集成spring的，会去读spring的sqlSessionFactory的xml配置中的mapperLocations，然后去解析mapper的xml
&bean id=&sqlSessionFactory& class=&org.mybatis.spring.SqlSessionFactoryBean&&
&property name=&dataSource& ref=&dataSource&/&
&!-- 配置mybatis配置文件的位置 --&
&property name=&configLocation& value=&classpath:mybatis-config.xml&/&
&property name=&typeAliasesPackage& value=&com.xixicat.domain&/&
&!-- 配置扫描Mapper XML的位置 --&
&property name=&mapperLocations& value=&classpath:com/xixicat/dao/*.xml&/&
然后绑定namespace(
XMLMapperBuilder
private void bindMapperForNamespace() {
String namespace = builderAssistant.getCurrentNamespace();
if (namespace != null) {
Class&?& boundType =
boundType = Resources.classForName(namespace);
} catch (ClassNotFoundException e) {
//ignore, bound type is not required
if (boundType != null) {
if (!configuration.hasMapper(boundType)) {
// Spring may not know the real resource name so we set a flag
// to prevent loading again this resource from the mapper interface
// look at MapperAnnotationBuilder#loadXmlResource
configuration.addLoadedResource(&namespace:& + namespace);
configuration.addMapper(boundType);
这里先去判断该namespace能不能找到对应的class，若可以则调用
configuration.addMapper(boundType);
configuration委托给MapperRegistry:
public &T& void addMapper(Class&T& type) {
mapperRegistry.addMapper(type);
生成该mapper的代理工厂(
MapperRegistry
public &T& void addMapper(Class&T& type) {
if (type.isInterface()) {
if (hasMapper(type)) {
throw new BindingException(&Type & + type + & is already known to the MapperRegistry.&);
boolean loadCompleted =
knownMappers.put(type, new MapperProxyFactory&T&(type));
// It's important that the type is added before the parser is run
// otherwise the binding may automatically be attempted by the
// mapper parser. If the type is already known, it won't try.
MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);
parser.parse();
loadCompleted =
} finally {
if (!loadCompleted) {
knownMappers.remove(type);
这里的重点就是MapperProxyFactory类：
public class MapperProxyFactory&T& {
private final Class&T& mapperI
private final Map&Method, MapperMethod& methodCache = new ConcurrentHashMap&Method, MapperMethod&();
public MapperProxyFactory(Class&T& mapperInterface) {
this.mapperInterface = mapperI
public Class&T& getMapperInterface() {
return mapperI
public Map&Method, MapperMethod& getMethodCache() {
return methodC
@SuppressWarnings(&unchecked&)
protected T newInstance(MapperProxy&T& mapperProxy) {
return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
public T newInstance(SqlSession sqlSession) {
final MapperProxy&T& mapperProxy = new MapperProxy&T&(sqlSession, mapperInterface, methodCache);
return newInstance(mapperProxy);
getMapper的时候生成mapper代理类
@SuppressWarnings(&unchecked&)
public &T& T getMapper(Class&T& type, SqlSession sqlSession) {
final MapperProxyFactory&T& mapperProxyFactory = (MapperProxyFactory&T&) knownMappers.get(type);
if (mapperProxyFactory == null) {
throw new BindingException(&Type & + type + & is not known to the MapperRegistry.&);
return mapperProxyFactory.newInstance(sqlSession);
} catch (Exception e) {
throw new BindingException(&Error getting mapper instance. Cause: & + e, e);
new出来MapperProxy
public T newInstance(SqlSession sqlSession) {
final MapperProxy&T& mapperProxy = new MapperProxy&T&(sqlSession, mapperInterface, methodCache);
return newInstance(mapperProxy);
@SuppressWarnings(&unchecked&)
protected T newInstance(MapperProxy&T& mapperProxy) {
return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
这里给代理类注入了sqlSession
MapperProxy实现InvocationHandler接口进行拦截代理
public class MapperProxy&T& implements InvocationHandler, Serializable {
private static final long serialVersionUID = -9729838L;
private final SqlSession sqlS
private final Class&T& mapperI
private final Map&Method, MapperMethod& methodC
public MapperProxy(SqlSession sqlSession, Class&T& mapperInterface, Map&Method, MapperMethod& methodCache) {
this.sqlSession = sqlS
this.mapperInterface = mapperI
this.methodCache = methodC
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
if (Object.class.equals(method.getDeclaringClass())) {
return method.invoke(this, args);
} catch (Throwable t) {
throw ExceptionUtil.unwrapThrowable(t);
final MapperMethod mapperMethod = cachedMapperMethod(method);
return mapperMethod.execute(sqlSession, args);
private MapperMethod cachedMapperMethod(Method method) {
MapperMethod mapperMethod = methodCache.get(method);
if (mapperMethod == null) {
mapperMethod = new MapperMethod(mapperInterface, method, sqlSession.getConfiguration());
methodCache.put(method, mapperMethod);
return mapperM
这里的代理拦截，主要是寻找到MapperMethod，通过它去执行SQL。
MapperMethod委托给SqlSession去执行sql
public Object execute(SqlSession sqlSession, Object[] args) {
if (SqlCommandType.INSERT == command.getType()) {
Object param = method.convertArgsToSqlCommandParam(args);
result = rowCountResult(sqlSession.insert(command.getName(), param));
} else if (SqlCommandType.UPDATE == command.getType()) {
Object param = method.convertArgsToSqlCommandParam(args);
result = rowCountResult(sqlSession.update(command.getName(), param));
} else if (SqlCommandType.DELETE == command.getType()) {
Object param = method.convertArgsToSqlCommandParam(args);
result = rowCountResult(sqlSession.delete(command.getName(), param));
} else if (SqlCommandType.SELECT == command.getType()) {
if (method.returnsVoid() && method.hasResultHandler()) {
executeWithResultHandler(sqlSession, args);
} else if (method.returnsMany()) {
result = executeForMany(sqlSession, args);
} else if (method.returnsMap()) {
result = executeForMap(sqlSession, args);
Object param = method.convertArgsToSqlCommandParam(args);
result = sqlSession.selectOne(command.getName(), param);
} else if (SqlCommandType.FLUSH == command.getType()) {
result = sqlSession.flushStatements();
throw new BindingException(&Unknown execution method for: & + command.getName());
if (result == null && method.getReturnType().isPrimitive() && !method.returnsVoid()) {
throw new BindingException(&Mapper method '& + command.getName()
+ & attempted to return null from a method with a primitive return type (& + method.getReturnType() + &).&);
其实这里就回到了第一种模式，该模式是直接指定了statement的Id（这里是command.getName()），而通过mapper的接口方式，则多了这么步骤，最后通过MapperMethod，给sqlSession传入statement的id。
sqlSession其实自己也不执行sql，它只是mybatis对外公布的一个api入口，具体它委托给了executor去执行sql。
什么时候去getMapper
手工get，比如
public void createStudent(Student student) {
SqlSession sqlSession = MyBatisSqlSessionFactory.getSqlSession();
StudentMapper studentMapper = sqlSession.getMapper(StudentMapper.class);
studentMapper.insertStudent(student);
} finally {
sqlSession.close();
集成spring的话
在spring容器给指定的bean注入mapper的时候get出来(
见MapperFactoryBean的getObject方法
二、mybatis-spring帮忙做了什么
通过MapperScannerConfigurer将mapper适配成spring bean
&!-- 配置扫描Mapper接口的包路径 --&
&bean class=&org.mybatis.spring.mapper.MapperScannerConfigurer&&
&property name=&sqlSessionFactoryBeanName& value=&sqlSessionFactory&/&
&property name=&basePackage& value=&com.xixicat.dao&/&
这里使用 MapperFactoryBean将Mapper接口配置成 Spring bean 实体同时注入sqlSessionFactory。
MapperScannerConfigurer给每个mapper生成对应的MapperFactoryBean
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));
委托给ClassPathMapperScanner去scan
public Set&BeanDefinitionHolder& doScan(String... basePackages) {
Set&BeanDefinitionHolder& beanDefinitions = super.doScan(basePackages);
if (beanDefinitions.isEmpty()) {
logger.warn(&No MyBatis mapper was found in '& + Arrays.toString(basePackages) + &' package. Please check your configuration.&);
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 =
if (StringUtils.hasText(this.sqlSessionFactoryBeanName)) {
definition.getPropertyValues().add(&sqlSessionFactory&, new RuntimeBeanReference(this.sqlSessionFactoryBeanName));
explicitFactoryUsed =
} else if (this.sqlSessionFactory != null) {
definition.getPropertyValues().add(&sqlSessionFactory&, this.sqlSessionFactory);
explicitFactoryUsed =
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 =
} 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 =
if (!explicitFactoryUsed) {
if (logger.isDebugEnabled()) {
logger.debug(&Enabling autowire by type for MapperFactoryBean with name '& + holder.getBeanName() + &'.&);
definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);
return beanD
这里出现了MapperFactoryBean的身影，然后判断配置文件是指定注入sqlSessionFactory，还是sqlTemplate(二者不能同时指定，这里是指定了sqlSessionFactory)。这里通过sqlSessionFactoryBeanName暂时先注入引用，因为此时还在给spring托管的bean进行create，不确定sqlSessionFactory是否已经被创建。
关于MapperFactoryBean
public class MapperFactoryBean&T& extends SqlSessionDaoSupport implements FactoryBean&T& {
private Class&T& mapperI
private boolean addToConfig =
* Sets the mapper interface of the MyBatis mapper
* @param mapperInterface class of the interface
public void setMapperInterface(Class&T& mapperInterface) {
this.mapperInterface = mapperI
* If addToConfig is false the mapper will not be added to MyBatis. This means
* it must have been included in mybatis-config.xml.
* If it is true, the mapper will be added to MyBatis in the case it is not already
* registered.
* By default addToCofig is true.
* @param addToConfig
public void setAddToConfig(boolean addToConfig) {
this.addToConfig = addToC
* {@inheritDoc}
protected void checkDaoConfig() {
super.checkDaoConfig();
notNull(this.mapperInterface, &Property 'mapperInterface' is required&);
Configuration configuration = getSqlSession().getConfiguration();
if (this.addToConfig && !configuration.hasMapper(this.mapperInterface)) {
configuration.addMapper(this.mapperInterface);
} catch (Throwable t) {
logger.error(&Error while adding the mapper '& + this.mapperInterface + &' to configuration.&, t);
throw new IllegalArgumentException(t);
} finally {
ErrorContext.instance().reset();
* {@inheritDoc}
public T getObject() throws Exception {
return getSqlSession().getMapper(this.mapperInterface);
* {@inheritDoc}
public Class&T& getObjectType() {
return this.mapperI
* {@inheritDoc}
public boolean isSingleton() {
注意这里继承了SqlSessionDaoSupport，在spring把sqlSessionFactory创建出来后，会去把之前注入的引用改为真的实例，调用SqlSessionDaoSupport的setSqlSessionFactory方法。
public abstract class SqlSessionDaoSupport extends DaoSupport {
private SqlSession sqlS
private boolean externalSqlS
public void setSqlSessionFactory(SqlSessionFactory sqlSessionFactory) {
if (!this.externalSqlSession) {
this.sqlSession = new SqlSessionTemplate(sqlSessionFactory);
public void setSqlSessionTemplate(SqlSessionTemplate sqlSessionTemplate) {
this.sqlSession = sqlSessionT
this.externalSqlSession =
* Users should use this method to get a SqlSession to call its statement methods
* This is SqlSession is managed by spring. Users should not commit/rollback/close it
* because it will be automatically done.
* @return Spring managed thread safe SqlSession
public SqlSession getSqlSession() {
return this.sqlS
* {@inheritDoc}
protected void checkDaoConfig() {
notNull(this.sqlSession, &Property 'sqlSessionFactory' or 'sqlSessionTemplate' are required&);
这里值得注意的是setSqlSessionFactory方法new了一个SqlSessionTemplate。
SqlSessionTemplate
它的一个重要的构造器为
public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType,
PersistenceExceptionTranslator exceptionTranslator) {
notNull(sqlSessionFactory, &Property 'sqlSessionFactory' is required&);
notNull(executorType, &Property 'executorType' is required&);
this.sqlSessionFactory = sqlSessionF
this.executorType = executorT
this.exceptionTranslator = exceptionT
this.sqlSessionProxy = (SqlSession) newProxyInstance(
SqlSessionFactory.class.getClassLoader(),
new Class[] { SqlSession.class },
new SqlSessionInterceptor());
mybatis-srping比传统mybatis方法多做的事情就在于此，生成了一个sqlSessionProxy。这里static import了java.lang.reflect.Proxy.newProxyI也就是使用使用jdk代理进行了SqlSessionInterceptor拦截。
SqlSessionInterceptor
private class SqlSessionInterceptor implements InvocationHandler {
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
SqlSession sqlSession = getSqlSession(
SqlSessionTemplate.this.sqlSessionFactory,
SqlSessionTemplate.this.executorType,
SqlSessionTemplate.this.exceptionTranslator);
Object result = method.invoke(sqlSession, args);
if (!isSqlSessionTransactional(sqlSession, SqlSessionTemplate.this.sqlSessionFactory)) {
// force commit even on non-dirty sessions because some databases require
// a commit/rollback before calling close()
mit(true);
} catch (Throwable t) {
Throwable unwrapped = unwrapThrowable(t);
if (SqlSessionTemplate.this.exceptionTranslator != null && unwrapped instanceof PersistenceException) {
// release the connection to avoid a deadlock if the translator is no loaded. See issue #22
closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
sqlSession =
Throwable translated = SqlSessionTemplate.this.exceptionTranslator.translateExceptionIfPossible((PersistenceException) unwrapped);
if (translated != null) {
unwrapped =
} finally {
if (sqlSession != null) {
closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
到了这里就明白了mybatis-spring帮忙做了session的open和close。
关于一级缓存
最后留个问题给大家，如果是使用mybatis-spring，那么mybatis的一级缓存默认开启的话，那么有达到一级缓存的设计初衷的效果么？
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